JP2016173958A - Manufacturing method of spark plug and manufacturing apparatus of spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress manufacturing cost of the whole manufacturing equipment of a spark plug and improve the safety of equipment by facilitating installation of such a testing container while improving evaluation precision of voltage resistance of an insulator used for a spark plug.SOLUTION: The manufacturing method of spark plug includes: (a) a process for forming a material including ceramics into a predetermined shape to obtain a molded body; (b) a process for obtaining an insulator by burning the molded body; and (c) a process for applying a predetermined voltage between two electrodes disposed with the insulator sandwiched in a container and evaluating voltage resistance of the insulator against the predetermined voltage. The process (c) includes a process for adjusting a pressure in the container to less than the atmospheric pressure.SELECTED DRAWING: Figure 5

Description

  The present invention relates to the manufacture of spark plugs.

  Conventionally, as a spark plug used for an internal combustion engine, an insulator is disposed between a central member including a center electrode and a terminal electrode and a metal shell, and an end of a ground electrode provided on the metal shell and the center electrode A spark plug that performs spark discharge in a gap (spark discharge gap) between the ends is used. If a defect such as a pinhole occurs in the insulator, a discharge may occur through the defect and a through hole in the thickness direction may be formed in the insulator. When such a through hole is generated, there is a possibility that normal spark discharge is not performed. Therefore, in the spark plug manufacturing process, a high voltage is applied between the central member and the metal shell, and the presence or absence of a defect in the insulator is specified based on the voltage waveform measured at this time and the imaged image. (Hereinafter referred to as “withstand voltage test process”). In this withstand voltage test, when a discharge (so-called flashover) occurs between the center member and the metal shell, the measured voltage waveform is measured when the insulator is defective. Therefore, even if the insulator has no defect, it may be erroneously identified as having a defect. In the withstand voltage test process of Patent Document 1, an assembly in which a center electrode, a metal shell, and an insulator are assembled is disposed in a pressure vessel, and the pressure in the pressure vessel is increased to atmospheric pressure or higher, for example, about 5 MPa. By doing so, the occurrence of flashover is suppressed and the accuracy of identifying the presence or absence of defects is improved.

JP 2012-185963 PR

  However, in the withstand voltage test process of Patent Document 1, since the pressure in the pressure vessel is increased to atmospheric pressure or higher, the pressure vessel is required to be strong enough to withstand such pressure. Therefore, when a highly rigid material is used as the material of the container, there arises a problem that the weight of the pressure vessel becomes very large and it becomes difficult to install the pressure vessel, and a problem that the manufacturing cost of the whole production equipment increases. In addition, since the pressure in the pressure vessel becomes very high, there is a problem that the safety of the manufacturing facility cannot be improved.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms or application examples.

  (1) According to one form of this invention, the manufacturing method of a spark plug is provided. The spark plug manufacturing method is a method of manufacturing a spark plug having an insulator, and (a) a step of obtaining a molded body by molding a material containing ceramics into a predetermined shape; and (b) the molded body. A step of obtaining the insulator by firing; and (c) a withstand voltage of the insulator with respect to the predetermined voltage by applying a predetermined voltage between two electrodes disposed between the insulators in the container. And the step (c) includes a step of adjusting the pressure in the container to less than atmospheric pressure. According to the method for manufacturing a spark plug of this embodiment, the withstand voltage resistance of the insulator is evaluated by adjusting the pressure in the container to less than atmospheric pressure. The robustness of the container can be reduced as compared with the configuration for evaluating the above. For this reason, the installation of the container can be easily realized. Moreover, the manufacturing cost of the spark plug manufacturing facility can be reduced. Moreover, since the withstand voltage of the insulator is evaluated by adjusting the pressure in the container to less than atmospheric pressure, the safety of the spark plug manufacturing facility can be improved.

  (2) In the manufacturing method of the spark plug of the said form, the said process (c) may include the process of adjusting the pressure in the said container to 5 Pa or less. According to the spark plug manufacturing method of this embodiment, the pressure in the container is adjusted to 5 Pa or less, so that the occurrence of corona discharge that is a precursor of flashover can be suppressed. Therefore, it is possible to accurately evaluate the voltage resistance of the insulator while applying a very high voltage as the predetermined voltage between the two electrodes.

  (3) In the method of manufacturing a spark plug according to the above aspect, the spark plug includes: the insulator having an axial hole extending along its own axis; and at least a part of the insulator being inserted into the axial hole; A central member exposed from the shaft hole; a cylindrical metal shell disposed on the outer periphery of the insulator; and a ground electrode joined to an end of the metal shell; In the step (c), the central member and the metallic shell may be used as the two electrodes. According to the spark plug manufacturing method of this aspect, the voltage resistance is evaluated by applying a predetermined voltage using the central member and the metal shell of the spark plug as two electrodes, so that the insulation is performed in a manner close to the actual usage. The withstand voltage of the body can be evaluated, that is, the withstand voltage of the insulator in the finished spark plug can be accurately evaluated.

  (4) The spark plug manufacturing method according to the above aspect may further include (d) a step that is performed after the step (c) and that bends the ground electrode toward the tip of the central member. According to the spark plug manufacturing method of this embodiment, since the step of bending the ground electrode is performed after step (c), the distance between the ground electrode and the center electrode can be made relatively long in step (c). . For this reason, the voltage applied between two electrodes in the step (c) can be further increased.

  The present invention can also be realized in various forms other than the spark plug manufacturing method. For example, it can be realized in the form of a spark plug manufacturing apparatus, a spark plug test method, a spark plug test apparatus, a spark plug insulator manufacturing apparatus, a spark plug insulator test apparatus, a spark plug, and the like. .

It is explanatory drawing which shows the structure of the manufacturing apparatus of the spark plug as one Embodiment of this invention. It is explanatory drawing which shows the detailed structure of the voltage application part 500 shown in FIG. It is a fragmentary sectional view which shows the detailed structure of the assembly | attachment body 100 shown in FIG. It is explanatory drawing which shows an example of the highest voltage which can be applied to the assembly | attachment body 100 in the pressure in the container 300, and the pressure. It is a flowchart which shows the manufacturing procedure of the spark plug as one Embodiment of this invention. It is explanatory drawing which shows an example of the waveform of the applied voltage measured in step S130.

A. Embodiment:
A1. Device configuration:
FIG. 1 is an explanatory diagram showing a configuration of a spark plug manufacturing apparatus according to an embodiment of the present invention. The spark plug manufacturing apparatus 200 is an apparatus that manufactures a spark plug, and is used to execute a part of a spark plug manufacturing process (withstand voltage test) described later.

  The spark plug manufacturing apparatus 200 includes a container 300, a current-carrying metal fitting 350, a pressure adjustment unit 400, a voltage application unit 500, a voltage measurement unit 510, and a test control unit 600.

  The container 300 accommodates the assembly 100 when performing a withstand voltage test described later. The container 300 has a substantially cubic external shape, and has an opening / closing portion (not shown) for taking the assembled body 100 in and out. Such an opening / closing part has a locking mechanism, and when the opening / closing part is locked by the locking mechanism, the inside of the container 300 becomes airtight. FIG. 1 shows a state where the assembly 100 is accommodated in the container 300. In FIG. 1, at least the container 300, the current-carrying metal fitting 350, and the assembly body 100 correspond to the vertically upward direction and the downward direction corresponds to the vertically downward direction. The above-mentioned “assembled body 100” is a member manufactured in the process of manufacturing the spark plug, and becomes a finished product of the spark plug through predetermined processes (a ground electrode bending process and a gasket mounting process described later). . As shown in FIG. 1, the assembly 100 is housed in the container 300 such that the distal end side of the assembly 100 is positioned on the vertically lower side and the proximal end side of the assembly 100 is positioned on the upper vertical side. “The front end side of the assembly 100” means the side on which the later-described ground electrode 30 is disposed in the assembly 100, and “the base end side of the assembly 100” means “the base end side of the assembly 100”. It means the side on which a later-described terminal fitting 40 is disposed.

  The container 300 includes a first support plate 311, a second support plate 312, and a conductive support part 320. The first support plate 311 is disposed in parallel with the horizontal plane at a predetermined distance above the inner bottom surface of the container 300 in a state where the container 300 is placed, and its peripheral edge is the inner surface of the casing of the container 300 It is joined to. A through hole is provided in the center of the first support plate 311 in the thickness direction, and the first support plate 311 supports the assembly 100 inserted into the through hole. The second support plate 312 is disposed in parallel with the first support plate 311 at a position above the first support plate 311 by a predetermined distance, and its peripheral edge is joined to the inner side surface of the casing of the container 300. A through hole is provided in the center of the second support plate 312 in the thickness direction, and the second support plate 312 supports the current-carrying metal fitting 350 inserted into the through hole. The conductive support 320 supports the assembly 100 together with the first support plate 311. The conductive support 320 is formed of a conductive member, is in contact with a later-described metal shell included in the assembly 100 at the upper end, and is joined to the inner bottom surface of the casing of the container 300 at the lower end. The conductive support 320 may be configured by a coil spring made of steel (for example, stainless steel or S45C-H). The casing of the container 300 is configured by bonding a conductive plate-like member, for example, a stainless steel plate, and is grounded. Therefore, the metal shell included in the assembly 100 is grounded via the conductive support 320 and the casing of the container 300. Two observation windows 331 and 332 made of a transparent material such as resin and glass are provided on one side surface of the casing of the container 300. The observation window 331 is disposed at a position where the tip of the assembly 100 can be observed in a state where the assembly 100 is accommodated inside the container 300. The observation window 332 is disposed at a position where the contact portion between the assembly 100 and the current-carrying metal fitting 350 can be visually recognized in a state where the assembly 100 is accommodated inside the container 300. The casing of the container 300 is provided with an air supply / exhaust port 340 in addition to the above-described two observation windows 331 and 332, and the pressure supply unit 400 is connected to the air supply / exhaust port 340.

  The current-carrying metal fitting 350 is a bar-like member having conductivity, the tip is in contact with a later-described terminal fitting included in the assembly 100, and the base end is electrically connected to the voltage application unit 500 via the connection wiring 550. Yes. The current-carrying metal fitting 350 transmits the voltage applied by the voltage application unit 500 to the assembly 100. Note that a spark plug may be used as the current-carrying metal fitting 350.

  The pressure adjustment unit 400 is connected to the container 300 and adjusts the pressure inside the container 300. The pressure adjustment unit 400 includes a piping unit 410, a rotary pump 421, and a turbo pump 422. The piping unit 410 communicates with the inside of the container 300 through the air supply / exhaust port 340. Further, the piping part 410 is connected to the rotary pump 421 and the turbo pump 422, respectively. The rotary pump 421 and the turbo pump 422 discharge the gas (air) in the container 300 through the piping unit 410 and reduce the pressure in the container 300. Note that the piping unit 410 is provided with an air release valve (not shown), and when the valve is opened, the pressure inside the decompressed container 300 is increased to atmospheric pressure.

  The voltage application unit 500 applies a voltage to the assembly 100 through the connection wiring 550 and the energization fitting 350. For example, in the withstand voltage test described later, a very high voltage of 32 kV or higher is applied. The voltage application unit 500 is electrically connected to the test control unit 600 and applies a voltage to the assembly 100 in accordance with a control signal output from the test control unit 600.

  FIG. 2 is an explanatory diagram showing a detailed configuration of the voltage application unit 500 shown in FIG. The voltage application unit 500 includes a primary coil 511, a secondary coil 512, a core 513, an igniter 514, and a battery 520. The primary coil 511 is composed of a winding with the core 513 as the center, and one end is connected to the battery 520 and the other end is connected to the igniter 514. The secondary coil 512 is composed of a winding centered on the core 513, and one end is connected to the primary coil 511 and the battery 520, and the other end is connected to the current-carrying metal fitting 350 via the connection wiring 550. In this embodiment, the igniter 514 is configured by a transistor. The igniter 514 switches between a state in which power is supplied from the battery 520 to the primary coil 511 and a state in which the supply of such power is stopped in accordance with a control signal output from the test control unit 600. When a high voltage is applied to the assembly 100 via the connection wiring 550 and the current-carrying metal fitting 350, a current is passed from the battery 520 to the primary coil 511 to form a magnetic field around the core 513, and the test control unit 600 By switching the control signal output from ON to OFF, the magnetic field of the core 513 is changed to generate a high voltage in the secondary coil 512. The voltage measurement unit 510 is connected to the connection wiring 550 and measures the voltage when the voltage application unit 500 applies a voltage. The voltage measurement unit 510 is electrically connected to the test control unit 600 and transmits a signal indicating the measured voltage value to the test control unit 600.

  A test control unit 600 shown in FIG. 1 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown), and controls each step of a withstand voltage test described later. The test control unit 600 is electrically connected to the voltage application unit 500, the rotary pump 421, and the turbo pump 422, and controls these functional units. For example, the test control unit 600 controls the magnitude of the voltage applied to the assembly 100 by outputting the control signal described above to the voltage application unit 500. Further, the test control unit 600 controls driving and stopping of the rotary pump 421 and the turbo pump 422. The test control unit 600 includes an evaluation unit 610. The evaluation unit 610 is a functional unit that functions when the CPU executes a program stored in the ROM. Evaluation unit 610 records the voltage measurement value received from voltage measurement unit 510 and evaluates the voltage resistance of assembly 100 (insulator 10) based on the voltage measurement value.

A2. Configuration of assembly 100:
FIG. 3 is a partial cross-sectional view showing a detailed configuration of the assembly 100 shown in FIG. The assembly 100 has an elongated columnar external shape along the axis AX indicated by a one-dot chain line in FIG. The right side of the axis AX shows an external front view, and the left side of the axis AX shows a cross-sectional view of the assembly 100 cut along a cross section passing through the axis AX. In the following description, the lower side in FIG. 3 (the side on which a later-described ground electrode 30 is disposed) is referred to as the distal end side, and the upper side in FIG. Call the side.

  The assembly 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The center electrode 20 has a rod-like appearance and is disposed inside the shaft hole 12 of the insulator 10 so that the tip protrudes from the insulator 10. Inside the shaft hole 12 of the insulator 10, the center electrode 20, the ceramic resistor 3 and the seal body 4a are arranged so that the seal body 4a is sandwiched between the base end portion of the center electrode 20 and the ceramic resistor 3, A seal body 4 b is disposed in contact with the base end of the ceramic resistor 3. Further, the distal end side of the terminal fitting 40 is disposed in contact with the seal body 4b inside the shaft hole 12 of the insulator 10. The base end side of the terminal fitting 40 is exposed from the end of the base end side of the insulator 10. The center electrode 20 is electrically connected to the terminal fitting 40 via the ceramic resistor 3 and the seal bodies 4a and 4b. The outer periphery of the insulator 10 is held by the metallic shell 50 at a position away from the terminal fitting 40 toward the distal end side. The ground electrode 30 has a rod-like appearance, is joined to the front end surface 57 of the metal shell 50 and is disposed in parallel with the axis AX. The ground electrode 30 is bent toward the center electrode 20 in the process of manufacturing the spark plug, and forms a spark discharge gap, which is a gap for generating a spark, with the tip of the center electrode 20. The member including the center electrode 20, the sealing bodies 4a and 4b, the ceramic resistor 3, and the terminal fitting 40 and extending along the axis AX corresponds to a subordinate concept of the center member in the claims. To do.

  The insulator 10 is an insulating member formed by firing a ceramic material such as alumina. The insulator 10 has a cylindrical external shape in which the shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 40 is formed at the center. A central body portion 19 having an outer diameter larger than that of other portions is formed at the center in the axial direction of the insulator 10. A proximal end body 18 that insulates between the terminal fitting 40 and the metal shell 50 is formed closer to the terminal fitting 40 than the central barrel 19. A distal end body portion 17 having an outer diameter smaller than that of the proximal end body portion 18 is formed on the center electrode 20 side with respect to the central body portion 19. A leg length portion 13 having a smaller outer diameter and a smaller outer diameter toward the center electrode 20 side is formed. The insulator 10 corresponds to a subordinate concept of an insulator in claims.

  The metal shell 50 is a cylindrical metal fitting that surrounds and holds a portion extending from a part on the distal end side of the base end side body portion 18 of the insulator 10 to the leg long portion 13. In the present embodiment, the metal shell 50 is made of low carbon steel, and is subjected to a plating process such as nickel plating or zinc plating. The metal shell 50 includes a tool engaging portion 51, a mounting screw portion 52, and a seal portion 54. The tool engaging portion 51 of the metal shell 50 is fitted with a tool for attaching the spark plug to the engine head. The mounting screw portion 52 of the metal shell 50 has a thread that is screwed into the mounting screw hole of the engine head. The seal portion 54 of the metal shell 50 is located at the base of the mounting screw portion 52 and has a bowl-like appearance. A gasket is attached to the front end surface 55 of the seal portion 54 in the process of manufacturing the spark plug, and the gasket is pressed against the engine head by the seal portion 54 to ensure airtightness in the engine compartment. The front end surface 57 of the metal shell 50 has an annular plane shape. The long leg portion 13 of the insulator 10 protrudes from the center of the distal end surface 57, and the center electrode 20 protrudes from the distal end surface of the long leg portion 13. A gap 31 having a predetermined size is formed between the inner peripheral surface of the shaft hole of the metal shell 50 and the outer peripheral surface of the leg long portion 13 of the insulator 10.

  A thin caulking portion 53 is provided on the base end side from the tool engaging portion 51 of the metal shell 50. In addition, a thin compression deformation portion 58 is provided between the seal portion 54 and the tool engagement portion 51 as in the caulking portion 53. Between the inner peripheral surface of the metal shell 50 and the outer peripheral surface of the base end side body portion 18 from the tool engaging portion 51 to the caulking portion 53, annular ring members 6 and 7 are interposed. Talc (talc) 9 powder is filled between the ring members 6 and 7. In the process of manufacturing the spark plug, the compression deformation portion 58 is compressed and deformed by pressing the caulking portion 53 inward so as to be bent inward, and the compression deformation of the compression deformation portion 58 causes the ring members 6, 7 and The insulator 10 is pressed toward the front end side in the metal shell 50 through the talc 9. By this pressing, the talc 9 is compressed in the direction of the axis AX, and the airtightness in the metal shell 50 is enhanced.

  Further, on the inner periphery of the metal shell 50, an insulator positioned at the base end of the leg long portion 13 of the insulator 10 via the annular plate packing 8 is attached to the metal inner step portion 56 formed at the position of the mounting screw portion 52. The step portion 15 is pressed. The plate packing 8 is a member that maintains airtightness between the metal shell 50 and the insulator 10 and prevents the combustion gas from flowing out. The metal shell 50 and the central member described above correspond to the subordinate concept of the two electrodes in the claims.

  In the present embodiment, the withstand voltage of the insulator 10 is evaluated using the spark plug manufacturing apparatus 200 in the manufacture of the spark plug described later. At this time, the pressure in the container 300 is reduced to less than atmospheric pressure, and a high voltage is applied to the assembly 100. In this way, a higher voltage can be applied to the assembly 100 without causing a flashover.

  FIG. 4 is an explanatory diagram showing an example of the pressure in the container 300 and the maximum voltage that can be applied to the assembly 100 at that pressure. In the example of FIG. 4, the assembly 100 is disposed in the container 300, the pressure in the container 300 is reduced to a predetermined pressure, and the voltage applied to the assembly is gradually increased, and the assembly 100 is actually increased. The voltage applied to is measured by the voltage measuring unit 510 and the maximum value of the voltage that can be applied is specified. The maximum voltage that can be applied to the assembly 100 was specified by reducing the pressure in the container 300 to 6.5 Pa, 6 Pa, and 5.0 Pa that are sufficiently lower than the standard atmospheric pressure (approximately 101 kPa). As shown in FIG. 4, the maximum voltage that can be applied to the assembly 100 increases as the pressure in the container 300 decreases. This is because, under a pressure environment close to a vacuum of 5.0 to 6.5 Pa, the number of free electrons existing in the container 300 is reduced, so that the occurrence of corona discharge, which is a precursor to flashover, is suppressed. It is estimated that the occurrence is suppressed. For this reason, it is estimated that a very high voltage of 32 kV can be applied as shown in FIG.

A3. Spark plug manufacturing:
FIG. 5 is a flowchart showing a manufacturing procedure of a spark plug as one embodiment of the present invention. When manufacturing the spark plug, first, each member constituting the spark plug is prepared (step S105). This step S105 includes two steps to be described later for preparing the insulator 10. That is, mud mixed with a ceramic raw material such as alumina or silica (silicon oxide) and a binder is granulated by spray drying, the granulated powder is pressed to form a pressed body, and a grindstone is used. A step of obtaining a molded body by cutting into a predetermined shape (step S205) and a step of obtaining the insulator 10 by firing the molded body obtained in step S205 (step S210) are included. In step S105, in addition to the insulator 10, other constituent elements (the center electrode 20, the terminal fitting 40, the metallic shell 50, etc.) constituting the assembly 100 are also prepared.

  The center electrode 20 and the terminal fitting 40 are inserted into the shaft hole 12 of the insulator 10, and the center electrode 20 and the terminal fitting 40 are assembled to the insulator 10 (step S110). In the shaft hole 12, the seal bodies 4 a and 4 b and the ceramic resistor 3 are enclosed between the shaft hole 12 and the terminal fitting 40. The ground electrode 30 is joined to the front end surface 57 of the metal shell 50 (step S115). After step S115, the metal shell 50 and the ground electrode 30 may be plated. The insulator 10 to which the center electrode 20 and the terminal metal fitting 40 are assembled in step S110 and the metal shell 50 are assembled to obtain the assembly 100 shown in FIG. 3 (step S120).

  After the assembly 100 is set in the container 300, the test control unit 600 controls the pressure adjusting unit 400 to reduce the pressure in the container 300 to a predetermined pressure less than atmospheric pressure (step S125). This predetermined pressure is determined in advance according to the maximum voltage applied to the assembly 100 in a later step. For example, when 32 kV is set as the maximum applied voltage to the assembly 100, a pressure of 5.0 Pa or less can be set as the predetermined pressure in step S125 based on the example of FIG. In step S125, the test control unit 600 first drives the rotary pump 421 to perform roughing exhaust, and then drives the turbo pump 422 to exhaust to a pressure range close to vacuum.

  The evaluation unit 610 controls the voltage application unit 500 to apply a predetermined voltage between the terminal fitting 40 and the metallic shell 50 of the assembly 100, and to determine the voltage value actually applied to the assembly 100. Recording is performed based on the measurement result of the voltage measuring unit 510 (step S130). As described above, since the pressure in the container 300 is reduced to a pressure close to a vacuum, a very high voltage can be set as the predetermined voltage in step S130. For example, if the pressure in the container 300 is reduced to 5.0 Pa or less in step S125, a voltage of 32 kV or more can be set as the predetermined voltage in step S130, and the assembly 100 (insulator 10) is defective. If not, the predetermined voltage can be actually applied to the assembly 100.

  When the measurement and recording of the applied voltage are completed in step S130, the test control unit 600 controls the pressure adjustment unit 400 to increase the pressure in the container 300 to atmospheric pressure (step S135). The evaluation unit 610 evaluates the voltage resistance of the insulator 10 based on the waveform of the applied voltage measured and recorded in step S130 (step S140). Steps S125 to S140 described above correspond to a withstand voltage test of the insulator 10. In addition, you may perform above-mentioned step S135 and step S140 in the reverse order to the order mentioned above. Further, these two steps S135 and S140 may be executed simultaneously.

  FIG. 6 is an explanatory diagram showing an example of the waveform of the applied voltage measured in step S130. FIG. 6A shows the voltage waveform S1 measured when the insulator 10 is not defective (normal), and FIG. 6B is measured when the insulator 10 is defective (abnormal). Shows the voltage waveform S2. As shown in FIG. 6A, during normal operation, a voltage V1 that is substantially equal to the predetermined voltage applied in step S130 is measured. On the other hand, as shown in FIG. 6B, at the time of abnormality, a high voltage is instantaneously applied because discharge occurs through the defective portion, but the highest voltage that can be applied continuously for a predetermined period. As V2, a voltage lower than the predetermined voltage applied in step S130 is measured. Thus, since the waveform of the applied voltage measured by the time of normality and an abnormality is different, the presence or absence of a defect can be estimated based on this waveform. If the waveform of the applied voltage is as shown in FIG. 6A, it is evaluated that the withstand voltage is high, and if it is as shown in FIG. 6B, it is evaluated that the withstand voltage is low. When a flashover and a corona discharge that is a precursor thereof occur during the execution of step S130, the waveform of the applied voltage approximates the waveform shown in FIG. However, since the pressure in the container 300 is reduced to less than atmospheric pressure in step S125, the occurrence of flashover and corona discharge is suppressed. Therefore, when the waveform of the applied voltage obtained in step S130 approximates the waveform shown in FIG. 6B, a defect in the insulator 10 occurs compared to the possibility that flashover and corona discharge have occurred. Very likely.

  As a result of the evaluation in step S140, the ground electrode 30 is bent in the assembly 100 that satisfies a predetermined standard (step S145). Specifically, the ground electrode 30 is bent so that the tip of the ground electrode 30 faces the center electrode 20. In the present embodiment, the ground electrode 30 is bent so that the front end surface of the center electrode 20 faces the inner surface of the front end portion of the ground electrode 30. At this time, bending is performed so that a gap between the tip surface of the center electrode 20 and the ground electrode 30, that is, a spark discharge gap, has a predetermined dimension. Instead of the bending as described above, the ground electrode 30 may be bent so that the tip surface of the ground electrode 30 faces the outer peripheral surface of the tip portion of the center electrode 20.

  A gasket (not shown) is attached so as to be in contact with the front end surface 55 of the seal portion 54 (step S150). As the gasket, for example, an annular gasket formed by bending a metal plate may be used. The gasket can be attached by inserting the mounting screw portion 52 of the metal shell 50 into the central hole of the gasket. As described above, since the gasket is attached after the withstand voltage test, when the assembly 100 comes into close contact with the container 300 in the withstand voltage test, the gasket is damaged or the repulsive force in the direction along the axis AX of the gasket is weakened. It can suppress that property falls. When step S165 is completed, the spark plug is completed. The spark plug manufactured in this way is attached to an internal combustion engine, for example, and used to ignite an air-fuel mixture in a combustion chamber.

  According to the spark plug manufacturing apparatus 200 and the spark plug manufacturing procedure of the embodiment described above, the pressure resistance of the insulator 10 is evaluated by adjusting the pressure in the container 300 to less than atmospheric pressure. The robustness of the container 300 can be reduced as compared with a configuration in which the withstand voltage is evaluated by increasing the pressure of the container to the atmospheric pressure or higher. For this reason, the installation of the container 300 can be easily realized. Moreover, the manufacturing cost of the spark plug manufacturing facility can be reduced. Moreover, since the withstand voltage property of the insulator 10 is evaluated by adjusting the pressure in the container 300 to less than atmospheric pressure, the safety of the spark plug manufacturing facility can be improved.

  Moreover, since the voltage resistance of the insulator 10 is evaluated by adjusting the pressure in the container 300 to less than atmospheric pressure, the voltage resistance can be evaluated in a state in which the occurrence of flashover and corona discharge is suppressed. For this reason, it is possible to accurately evaluate the voltage resistance of the insulator 10 while applying a very high voltage to the assembly 100.

  Moreover, since the withstand voltage of the insulator 10 is evaluated using the assembly 100 in the state where the center member and the metal shell 50 are assembled to the insulator 10, the withstand voltage is evaluated in a manner close to the actual usage. it can. That is, the voltage resistance of the insulator 10 in the finished spark plug can be evaluated with high accuracy.

  In addition, since the withstand voltage test can be performed before the ground electrode 30 is bent, the distance between the ground electrode 30 and the center electrode 20 when performing the withstand voltage test can be made relatively large. it can. For this reason, in a withstand voltage test, since the discharge between the ground electrode 30 and the center electrode 20 can be suppressed, a very high voltage can be applied.

B. Variations:
B1. Modification 1:
In the said embodiment, although the front-end | tip part of the assembly 100 was exposed in the internal space of the container 300 during execution of a withstand voltage test, this invention is not limited to this. For example, an insulating oil tank filled with insulating oil may be prepared in the container 300, and the tip of the assembly 100 may be immersed in the oil tank. Further, for example, the assembly 100 is disposed upside down from the state shown in FIG. 1, and the distal end portion (the portion on the distal end side from the mounting screw portion 52) of the metal shell 50 is inserted into the cylindrical tube. And you may fill this tube with insulating oil. According to these configurations, since the insulation resistance value between the tip of the center electrode 20 and the ground electrode 30 can be increased, the occurrence of flashover is further suppressed when a high voltage is applied to the assembly 100 thereafter. it can.

B2. Modification 2:
In the said embodiment, although 5.0 Pa or less was illustrated as a pressure in the container 300 at the time of depressurizing the inside of the container 300 in step S125, this invention is not limited to this. The lower the value is, the better. It is because generation | occurrence | production of a corona discharge can be suppressed more because the number of free electrons in the container 300 reduces more so that the pressure in the container 300 is lower. Further, the pressure in the container 300 may be reduced to an arbitrary pressure higher than 5.0 Pa and not higher than 6.5 Pa. Even in such a configuration, the number of free electrons in the container 300 can be reduced as compared with the case where the number of free electrons is equal to or higher than the atmospheric pressure. As described in the embodiment, it is preferable to reduce the pressure to 5.0 Pa or less.

B3. Modification 3:
In the above embodiment, the withstand voltage of the insulator 10 is determined based on the waveform of the applied voltage measured by the voltage measuring unit 510, but the present invention is not limited to this. For example, in step S130, in addition to the measurement of the applied voltage by the voltage measurement unit 510, the tip of the assembly 100 is photographed, and the resistance of the insulator 10 is determined based on the obtained captured image and the waveform of the applied voltage. You may evaluate voltage property. Specifically, for example, when the waveform of the applied voltage approximates the waveform shown in FIG. 6B, it is determined whether or not a spark is reflected in the captured image obtained at the timing when the voltage is measured. . And if a spark is reflected, it is evaluated that the withstand voltage of the insulator 10 is high because flashover or corona discharge has occurred. On the other hand, when the waveform of the applied voltage approximates the waveform shown in FIG. 6B and no spark is captured in the captured image, it is estimated that the current is supplied through the defect of the insulator 10. Therefore, in this case, it is evaluated that the dielectric strength of the insulator 10 is low. With such a configuration, the presence or absence of a defect in the insulator 10 can be determined with higher accuracy. In this configuration, the tip of the assembly 100 may be photographed through the observation window 331. Instead of photographing, the presence or absence of a spark may be visually observed through the observation window 331. Further, if the applied voltage (for example, maximum voltage or average voltage) measured by the voltage measuring unit 510 is equal to or higher than a predetermined threshold voltage, it is determined that the withstand voltage is high, and if it is less than the threshold voltage, the withstand voltage is You may determine with low. With such a configuration, the voltage resistance can be evaluated easily and in a short time.

B4. Modification 4:
In the said embodiment, although the withstand voltage test evaluated the withstand voltage property of the insulator 10 of a spark plug, this invention is not limited to this. For example, in the process of manufacturing an arbitrary device (ceramic-containing device) using an insulator containing ceramic, such as a glow plug, a gas sensor, and a vacuum switch, the present invention is used when evaluating the withstand voltage of the insulator. May be applied.

B5. Modification 5:
In the above embodiment, the bending process of the ground electrode 30 (step S145) and the gasket mounting process (step S150) are both performed after the withstand voltage test (steps S125 to S140). May be executed.

B6. Modification 6:
In the above embodiment, the withstand voltage test (steps S125 to S140) is performed on the assembly 100, but the withstand voltage test may be performed on the insulator 10. In this configuration, for example, a withstand voltage test is performed on the assembly 100 obtained in step S105, and the center electrode 20, the terminal fitting 40, and the metallic shell 50 are placed on the insulator 10 that satisfies a predetermined standard. After that, the bending step of the ground electrode 30 and the gasket may be attached. Further, in the withstand voltage test of this configuration, two electrodes for voltage application are prepared in the container 300, one electrode is disposed inside the shaft hole 12 of the insulator 10 set in the container 300, and the other These electrodes may be arranged outside the insulator 10 and a predetermined voltage may be applied between these two electrodes. In this configuration, the two electrodes for voltage application prepared in the container 300 correspond to the subordinate concept of the two electrodes in the claims. Therefore, in this configuration, the metal shell 50 and the central member do not correspond to the subordinate concept of the two electrodes in the claims.

B7. Modification 7:
The configuration of the spark plug manufacturing apparatus 200 in the above embodiment is merely an example, and various changes can be made. For example, the housing of the container 300 includes the two observation windows 331 and 332, but the two observation windows 331 and 332 may be omitted. The container 300 is made of stainless steel except for the two observation windows 331 and 332. However, almost all of the container 300 is made of the same material (transparent resin or glass material) as the two observation windows 331 and 332. May be. In addition, although the air supply / exhaust port 340 is provided in the side surface portion of the casing of the container 300, it may be provided in the bottom surface portion or the top surface portion instead of the side surface portion. In the above embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit of the present invention. For example, the technical features in the present embodiment and the modified examples corresponding to the technical features in the embodiments described in the column of the summary of the invention are to solve part or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be appropriately performed. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4a ... Seal body 4b ... Seal body 6, 7 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 15 ... Insulator step part 17 ... Tip side trunk | drum 18 ... Base end side body part 19 ... Central body part 20 ... Center electrode 30 ... Ground electrode 31 ... Air gap 40 ... Terminal metal fitting 50 ... Main metal fitting 51 ... Tool engagement part 52 ... Mounting screw part 53 ... Clamping part 54 ... Seal part 55 ... tip end face 56 ... bracket inner step part 57 ... tip end face 58 ... compression deformation part 100 ... assembly 200 ... spark plug manufacturing apparatus 300 ... container 311 ... first support plate 312 ... second support plate 320 ... conductive support part 331 ... Observation window 332 ... Observation window 340 ... Air supply / exhaust port 350 ... Current-carrying metal fitting 400 ... Pressure adjustment part 410 ... Piping part 421 ... Rotary pump 422 ... Turbo pump 500 ... Voltage application part 510 ... Electricity Measuring unit 511 ... primary coil 512 ... secondary coil 513 ... core 514 ... igniter 520 ... battery 550 ... connection wiring 600 ... test control section 610 ... evaluation unit AX ... axis S1 ... voltage waveform S2 ... voltage waveform

Claims (5)

A method of manufacturing a spark plug having an insulator,
(A) forming a material containing ceramics into a predetermined shape to obtain a molded body;
(B) firing the molded body to obtain the insulator;
(C) applying a predetermined voltage between two electrodes disposed in the container with the insulator interposed therebetween, and evaluating the withstand voltage of the insulator with respect to the predetermined voltage;
With
The method of manufacturing a spark plug, wherein the step (c) includes a step of adjusting the pressure in the container to less than atmospheric pressure. In the spark plug manufacturing method according to claim 1,
The method of manufacturing a spark plug, wherein the step (c) includes a step of adjusting the pressure in the container to 5 Pa or less. In the manufacturing method of the spark plug of Claim 1 or Claim 2,
The spark plug is
The insulator having an axial hole extending along its own axis;
A central member in which at least a portion is inserted into the shaft hole, and a tip portion of the center member is exposed from the shaft hole;
A cylindrical metal shell disposed on the outer periphery of the insulator;
A ground electrode joined to an end of the metal shell,
Have
In the step (c), the center member and the metal shell are used as the two electrodes, and the method of manufacturing a spark plug. The spark plug manufacturing method according to claim 3, further comprising:
(D) A method for manufacturing a spark plug, which is performed after the step (c) and includes a step of bending the ground electrode toward the tip portion of the central member. An apparatus for producing a spark plug having an insulator,
A container capable of containing the insulator;
A pressure adjusting unit for adjusting the pressure in the container;
An evaluation unit that applies a predetermined voltage between two electrodes disposed between the insulators in the container, and evaluates a voltage resistance of the insulator with respect to the predetermined voltage;
With
The said pressure adjustment part adjusts the pressure in the said container to less than atmospheric pressure, when the application of the said predetermined voltage by the said evaluation part is performed, The manufacturing apparatus of the spark plug characterized by the above-mentioned.

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