METHOD AND APPARATUS FOR MAKING SPARK PLUG

Description

[0001] The invention relates to a method and an apparatus for making a spark plug for igniting a fuel gas in an internal combustion engine and more specifically relates to a method and apparatus for precisely making a spark gap between a center electrode and a ground electrode in the spark plug.

[0002] In recent years, an allowable deviation of the spark gap between a firing end of the spark plug and a metal strip of the ground electrode has been narrowing due to recent requirements for a high performance spark plug usable e.g. in a maintenance-free internal combustion engine. Therefore, contrivances are required to provide a reliable way for making such an accurate distance for the spark gap by precisely bending the ground electrode strip.

[0003] In a conventional gap-forming process, the ground electrode strip is bent in a single step by applying a punch to the metal strip that is welded upright to an end face of a metal shell of the spark plug with a spacer inserted between the center electrode and the ground electrode. However, a statistical uniformity of the narrowly-deviated gap distance is not easily attained from one spark plug gap to the other, probably due to various factors such as buckling of the metal strip per se, a welding condition for the strip, deviations of the strip diameter and length, and an extent of projection of the firing end of the center electrode from the metal shell.

[0004] Specifically, a high performance spark plug which uses a high-corrosion resistant hard metal tip made from precious metal such as Platinum and/or Iridium having a small diameter of 0.3-1 mm formed on the center electrode will only tolerate a very small deviation of the spark gap from the optimum spark gap. Due to the metal tip additionally welded to the center electrode, e.g. by laser-welding, the extent of projection of the firing end may differ from one spark plug to another. Such a high performance spark plug is described, for instance, in EP 0 872 928, USP 5,793,793 and USP 5,977,695.

[0005] If the spacer is made to abut against such a small- diameter metal tip of the center electrode so as to minimize the deviation, a high compressive force is applied to the metal strip through the spacer as a result of bending the metal strip, which may lead to a possible risk that the small diameter tip welded to the center electrode may crack, be damaged or come off.

[0006] It is therefore an object of the invention to provide a method and apparatus for making a spark plug with a precisely formed spark gap between a ground electrode and a center electrode. It is another preferred object of the invention to provide a method and apparatus for making a precisely formed spark gap between a ground electrode and a firing end of a precious metal tip of a center electrode in a spark plug.

[0007] DD-A-278,449 discloses a method and apparatus for bending the earth electrode of spark plugs according to the precharacterizing portions of independent claims 1 and 16.

[0008] According to the invention, there is provided a method for making a spark plug comprising a center electrode disposed in a bore formed in a ceramic insulator, a metallic shell fitting outside the ceramic insulator, and a ground electrode forming a spark gap with the center electrode, the method comprising steps of:

providing a metal strip which extends from an end of the metal shell, said metal strip being for forming said ground electrode;

positioning a spacer above a firing end of the center electrode;

preliminary bending the metal strip toward the spacer so as to form an arc portion in the metal strip;

and then precisely forming a gap-distance between the metal strip and the firing end of the center electrode by applying a force to the metal strip,

   characterized in that, during said preliminary bending step, a clearance is maintained between the spacer and the center electrode such that the spacer is only contacted by the metal strip for forming the ground electrode.

[0009] In this specification, the phrase "metal strip" refers to any elongate metal member, not limited to any specific cross-sectional shape or aspect ratio.

[0010] In one aspect of the invention, it is important that there is provided a spacer above the firing end so that the firing end is protected from being damaged during the step of preliminarily bending the metal strip. In another aspect of the invention, the position of the spacer is determined by referring to the position of the firing end of the center electrode so that the firing end of the center electrode does not touch the firing end of the center electrode and can form the arc portion in the metal strip. In other words, it is preferable that a clearance is provided between the spacer and the firing end of the center electrode so as to protect the firing end.

[0011] The arc portion formed in the metal strip assures leveling of a lateral side of the metal strip with the firing end face of the center electrode in the step of precisely forming the gap-distance between the metal strip and the firing end of the center electrode. The spacer has a rounded portion so that the arc portion in the metal strip is made between the ends of the strip by bending the metal strip toward or rather along the rounded portion by e.g. a punch. Instead of the rounded portion of the spacer, a comer-chamfered portion may accomplish the same purpose. It is best to make the arc portion at about the same level as the firing end face of the center electrode.

[0012] In a preferred aspect of the invention, the above method may further comprise a step of:

measuring the position of the firing end of the center electrode so as to determine a position for the spacer.

[0013] The measurement of the position of the firing end of the center electrode is importantly conducted before positioning the spacer so that the clearance between the spacer and the firing end of the center electrode is formed and maintained before and during bending the metal strip toward the spacer which is protecting the firing end of the center electrode.

[0014] In the same way as above, the firing end of the center electrode that has a firing tip having a small diameter, such as in the range of from 0.3 to 1.0 mm, is protected. The tip is preferably formed from metal selected from a group consisting of Pt, Ir, Rh, Pd, Re, Os, Ru or alloy thereof and is welded on the center electrode to form the firing end of the center electrode.

[0015] In a further preferred aspect of the invention, either of the above defined methods may further comprise a step of:

retrieving the spacer after bending the metal strip so that the gap-distance between the metal strip and the center electrode is adjusted to a required value by referring to a position of the preliminary bent metal strip and the position of the end of the firing metal.

[0016] In this preferred embodiment above, it is advantageous to retrieve the spacer after preliminarily bending the metal strip, because the gap distance between the metal strip (namely the ground electrode) and the firing end of the center electrode is easily measured or determined, for example, by a computer-controlled visual image processor that outputs to a metal-strip bending machine how much the gap distance between the ground electrode and the center electrode should be further narrowed or adjusted based on a side-view measurement of the gap distance.

[0017] In a preferred aspect of the invention, it is useful that information relating to the position of the firing end of the center electrode is stored in a computer memory so that the information is used for positioning the spacer. This information can be advantageously used also for the step that follows, in which step a gap-distance between the metal strip and the firing end of the center electrode is precisely formed or adjusted.

[0018] In yet another aspect of the invention, positional information is determined with reference to a position of a part constituting the spark plug. If a reference position is taken from an end of the metal shell by e.g. a position-detecting sensor using laser, the position of the firing end means how much the firing end of the center electrode is projected from the end of metal shell to which the metal strip is extendedly welded, thereby giving the positional information that directs how much above the spacer should be placed from the firing end of the center electrode and/or whereat the arc portion is formed in the metal strip.

[0019] In still another aspect of the invention, the positional information of the firing end of the center electrode can be used not only for positioning the spacer above the firing end as described above but also for precisely forming a gap-distance between the metal strip and the firing end of the center electrode. In this case, positional information is only required for the bent metal strip (of the ground electrode).

[0020] In a further aspect of the invention, the force applied to the metal strip for precisely forming the gap distance is caused by a punch or die moving in parallel with a center electrode axis of the spark plug. Alternatively, the preliminary bending of the metal strip may be done by a punch or die moving in perpendicular to the center electrode axis, or in a combined direction having both of these directions.

[0021] The present invention further provides an apparatus for making a spark plug comprising a center electrode disposed in a bore formed in a ceramic insulator, a metallic shell fitting outside the ceramic insulator, and a ground electrode forming a spark gap with the center electrode, the apparatus comprising:

means for positioning a spacer above a finng end of the center electrode;

means for preliminary bending a metal strip toward the spacer so as to form an arc portion in the metal strip, said metal strip being provided extending from an end of the metal shell and being for forming said ground electrode; and

means for precisely forming a gap-distance between the metal strip and the firing end of the center electrode by applying a force to the metal strip,

   characterized in that said means for positioning a spacer and said means for preliminary bending a metal strip maintain a clearance between the spacer and the center electrode and contact the spacer only with the metal strip for forming the ground electrode.

[0022] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Fig.1 is an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, showing a schematic view of a spark plug (W) having a straight metal strip (W₂) for forming a ground electrode which is welded uprightly to an end of a metal shell (W₃), wherein a position of a firing end of a precious metal tip (W₁) formed on the center electrode is determined by a position-detecting sensor 1 using a laser.

Fig.2 is an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, showing a schematic partial view of a spark plug in the same process as shown in Fig.1, but different in a position of the firing end and having a metal plate tip (W₁a) welded on the metal strip (W₂).

Fig.3 is an explanatory drawing in use for partly explaining a method and/or apparatus for making a spark plug according to the invention, showing a schematic partial view of the spark plug in process wherein a rounded portion of a spacer 3 abuts against a lateral portion of the metal strip (W₂) and the spacer 3 has a clearance (d) formed between the spacer 3 and the firing end of the precious metal tip (W₁).

Fig.4 is an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, showing a schematic partial view of the spark plug in process wherein a punch 4 has bent the metal strip (W₂) in a middle of the metal strip (W₂) by pushing the metal strip (W₂) along the rounded portion of the spacer 3.

Fig.5 is an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, showing a schematic partial view of the spark plug in process wherein a die 6 pushes a preliminary-bent metal strip (W₂) to form precisely a spark gap (g) between the metal strip (W₂) and the metal tip (W₁) with assistance of a visual-image processor 7.

Fig.6 shows a block diagram of a gap-forming controller 8, wherein a position-detecting sensor 1 sends a positional information of the firing end to be digitally stored in a computer memory (ROM or RAM) for use in preliminarily bending the metal strip and/or precisely forming the gap distance.

Fig.7 is an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, similar to Fig.4 but different in a shape of the die 75 and a shape of the spacer 73 that is capable of forming an arc portion in the metal strip (W₂) at about the same level with the firing end of the center electrode.

Fig.8 shows an explanatory drawing for partly explaining a method and/or apparatus for making a spark plug according to the invention, wherein a position of the preliminarily-bent metal strip (W₁) is measured by the position-detecting sensor 1.

Fig.9 shows an explanatory drawing in use for partly explaining a method and/or apparatus for making a spark plug according to the invention, wherein a position of the end of metal shell (W₃) is measured by the position-detecting sensor 1.

[0023] A spark plug used for igniting a fuel gas in a combustion engine comprises a center electrode penetratingly disposed through a bore formed in an alumina ceramic insulator that electrically insulates the center electrode from a metallic shell fitted outside the ceramic insulator. The metal shell has a threaded portion to be screwed into a bore of the engine and an end face from which a ground electrode is extended as a ground electrode. A gap is made between a firing end of the center electrode and the metal strip (namely the ground electrode) so as to make a spark between the electrodes when a high voltage is applied across the electrodes.

[0024] The firing end of the center electrode is desirably pointed from a view point that the spark occurs easily. However, such a pointed firing end tends to erode or wear very quickly under a continuous spark condition inside the engine. For this reason, a spark-erosion resistant metal such as platinum and Ir-Rh(5-30%) alloy has come to be used as an firing end tip having a small diameter of about 0.3-1 mm. This spark-erosion resistant metal tip having a length of about 0.2-1 mm is preferably welded at a conical end of the center electrode by applying a laser. The center electrode disposed firmly inside the ceramic bore has a comparatively large diameter of 1 5 - 3 mm. The material of the center electrode to which the metal tip is welded is normally a nickel-based alloy.

Example

[0025] A method and apparatus for making a spark plug, embodied according to the invention, will now be explained and described in detail by referring to the accompanying drawings.

[0026] Referring to Fig.1, an end of a straight metal strip (W₂) for a ground electrode of the spark plug (W) is connected to a circular end of a metal shell (W₃) by a resistance-welding method. A material of the metal shell (W₃) is preferably made of carbon steel. Nickel containing iron is used for a material of the metal strip (W₂).

[0027] The center electrode 2 has a conical end made of a high temperature resistant metal such as Inconel 600 (trade name). A metal tip (W₁) made of a spark-erosion resistant metal such as Ir-20%Rh, Ir-5%Pt, Ir-1.5%Y₂O₃ and Pt-20%Ir is welded to the conical end of the center electrode. The metal tip (W₁) having a diameter of about 0.3-1 mm and a length of about 0.2-0.9 mm is welded to the conical end of the center electrode 2 by applying a laser beam to an interface between the tip (W₁) and the conical end.

[0028] When the metal tip (W₁) is required at the conical end of the center electrode 2 so as to have a spark-erosion resistance firing end, a small plate tip (W₁a) of spark-erosion resistance material such as Pt-20%Ni is optionally welded on an lateral side of the metal strip (W₂) as shown in Fig.2 so as to also enhance the spark-erosion of the ground electrode. Since the metal strip for the ground electrode is uprightly and/or straightly formed during this step, a best position of the erosion resistance plate tip (W₁a) to be welded to the metal strip (W₂) is advantageously determined by referring to the position of the firing end of the metal tip (W₁). In other words, if the position of the firing end of the center electrode is detected as at a higher position, the position of the plate tip (W₁a) is elevated accordingly so as to face the plate tip (W₁a) with the metal tip (W₁) just in place by bending the metal strip (W₂) in a gap-forming step as will be described later.

[0029] The metal plate tip (W₁a) is normally in thickness of 0.2-0.5 mm and is made of a spark-erosion resistant metal which can be made of Pt, Ir, Rh, Pd, Re, Os, Ru, Ni or alloy thereof.

[0030] After the step wherein the metal strip (W₂) is uprightly or straightly formed on the end of the metal shell (W₃), as shown in Fig.1 or Fig.2, a position-detecting sensor 1 measures a position of an end of the metal tip (W₁) formed on the conical end of the center electrode 2 by emitting a laser light to an end face of the metal tip (W₁) and gathering a reflected laser light therefrom. The position of the metal tip (W₁) means , in this case, a distance between the metal tip end face and the position-detecting sensor 1. The distance measured by the sensor 1 is longer in the case of Fig.1 than that measured in the case of Fig.2, because the insulator (W₄) holding the center electrode in Fig.2 is projecting more than the insulator of Fig.1. In other words, the position of the metal tip (W₁) in Fig.1 indicates that a height (h₁) of the center electrode measured from the end of the metal shell (W₃) in Fig. 1 is less than the height (h₂) of the center electrode in Fig.2.

[0031] After the position of the metal tip (W₁) is determined as explained in the above step, a step of preliminarily bending the metal strip (W₂) is provided, as will be explained hereafter with reference to Fig.3 and Fig.4.

[0032] A spacer 3 is placed at the position spaced away from the end of the metal tip with a clearance (d) between the spacer 3 and the metal tip (W₁) as shown in Fig.3. This clearance has a relation with the position of the metal tip end measured in the previous step. In other words, the spacer 3 can be placed above the metal tip (W₁), without touching the tip, by referring to positional information of the metal tip. When a statistical data is gathered on the heights or positions of many metal tips formed on the center electrodes of the spark plugs, the clearance (d) should be determined as more than the maximum height computed based on such statistical data. In such a statistical case in mass production, it may be unnecessary to measure the position of the metal tip (W₁) every time before the spacer 3 is placed above the metal tip.

[0033] The spacer 3 has a rounded nose portion (3a) at its end and a back face (3b) slanting up from the rounded portion. The rounded nose portion (3a) abuts against a lateral side of the metal strip (W₂) as shown in Fig.3. Then as shown in Fig.4, a punch 4 having a slanting end face (4a) moves downward from the above position of the metal strip (W₁) to apply a force to the metal strip (W₂) and to bend the metal strip along the rounded nose portion (3a). The punch 4 may move horizontally to bend the strip along the rounded portion (3a). It is preferable that the punch 4 has the same slanting angle as that of the spacer back (3b).

[0034] As a result of the force thus applied, an arc portion is formed in the metal strip (W₂), maintaining a straight free end portion (W₃f). A bending angle for the metal strip (W₂) is preferably about 110-135 degrees at this preliminary bending step.

[0035] It is important that the spacer 3 protects the metal tip (W₁) forming a pointed firing end of the center electrode during the preliminary bending step, since such a small diameter of 0.3-0.7 mm is mostly selected for the pointed firing end of a high performance spark plug. In addition, the spacer should be rigid and tough so that the spacer does not deform or break during the preliminary bending step in mass production of spark plugs, eliminating any chance of causing any damage to the metal tip (W₁) or not touching the metal tip in any event. One of the recommended materials for the spacer is an alloy tool steel of SKD11 (shown in JIS G 4404) which is also wear-resistant.

[0036] The spacer can have a different shape. For instance, the spacer 73 as shown in Fig.7 has a rounded nose portion (73a) extending downward more than the one (3a) in Figs.3 or 4, assuring that the position of the arc portion (73c) is formed at about the same level of the firing end and maintaining a protection clearance between the firing end of the metal tip (W₁) and the spacer 73. When the position of the arc portion made in the metal strip (W₂) is at about the same horizontal level with the metal tip end face, it is easy to bend the metal strip and to make the lateral side of the metal strip in parallel with the end face of the metal tip (W₁) in the following step.

[0037] After the spacer 3 is retrieved or moved away from the position as explained above with Fig.4, instead of the punch 4, a die 6 having a horizontally flat face as seen in Fig.5 comes downward in an axial direction of the center electrode to push an outer lateral side of the metal strip (W₂) so as to make an inner side of the metal strip to be almost in parallel with the end face of the metal tip (W₁). In this step, the gap-distance (g) between the metal strip (W₂) and the metal tip (W₁) can be precisely formed by referring to the positional information data of the metal tip (W₁) memorized in the computer memory. A visual-image processor 7 using e.g. a CCD (charge coupled device) for detecting the gap-distance may check whether the gap-distance (g) is formed within a required value as seen in the Fig.5 or may assist to precisely form the gap distance (g) by referring to the gap distance measured by the processor 7. The required value for the high performance spark plug in actual use is for instance 1.1 mm with a tolerance of +0 and -0.1 mm.

[0038] As shown in Fig.8 or Fig.9, the position-detecting sensor 1 using a laser can also determine the position of the preliminary bent metal strip (W₂) or of the end face of the metal shell (W₃). In the case that the position of the preliminary bent metal strip is determined as shown in Fig.8, how much the preliminary bent metal strip should be further bent can be computably determined by comparing with the positional data of the spark -erosion metal tip (W₁). In the case that the position of the end face of the metal shell (W₃) is determined as shown in Fig.9, not only the height (h) of the metal tip, namely the distance from the end face of the metal shell (W₃) to the firing end of the metal tip (W₁) can be computably determined by comparing the positional information data of the metal tip (W₁), but also the spark-erosion resistant metal plate tip (W₁a) can be welded onto a best place of the metal stri (W₂) as described previously by referring to the data of the height (h) thus computably determined. These positional information and data in part or whole or in modification can be usable in accomplishing the invention.

[0039] Referring now to Fig.6 showing a gap-forming controller 8 for a gap-forming apparatus, the positional information analogously measured by the position-detection sensor 1 may be electrically converted into a digital information form through an analog/digital converter 9 so as to be stored in a memory of a computer 10 having CPU 11, ROM 12 and RAM 12 through a I/O port and a gap-forming program and/or may be computed directly or indirectly by the computer 10, so as to send or receive signals (S₁, S₂, S₂, S₄...S_n) to or from the gap-forming apparatus.

[0040] For instance, when a signal (S₁) informing that the metal strip (W₁) is welded to the metal shell (W₃) is received by the computer 10, the computer 10 sends out a signal (S₃) to the dimension-detecting sensor 1 to measure the positions of the metal tip (W₁) and/or the end face of the metal shell as seen in Fig.1 or Fig.9. Then, based on positional information data gathered in the computer 10 and computation, the computer 10 sends a signal (S₄) to a preliminary bending machine ordering to place the spacer 3 above the metal tip (W₁) with such a clearance between the spacer 3, 73 and the metal tip (W₁) for forming the arc portion in the metal strip (W₂).

[0041] When a signal (S₂) informing that the spacer is placed at the required position is received, the computer 10 sends a signal (S_n) to a punch-machine to come down and preliminarily bend the metal strip to form the arc portion. In a similar way, when the computer 10 receives a signal that the preliminary bending is over, the processor orders the punch-machine to retrieve the spacer 3, 73 and after the retrieval is confirmed the processor orders a die-machine and a visual-image processor to cooperate in further bending the metal strip (W₁) so as to make or adjust the gap-distance to be within a required value for the high performance spark plugs based on the positional information data.

Claims

1. A method for making a spark plug (W) comprising a center electrode (2) disposed in a bore formed in a ceramic insulator (W₄), a metallic shell (W₃) fitting outside the ceramic insulator (W₄), and a ground electrode forming a spark gap (g) with the center electrode (2), the method comprising steps of:

providing a metal strip (W₂) which extends from an end of the metal shell (W₃), said metal strip (W₂) being for forming said ground electrode;

positioning a spacer (3; 73) above a firing end of the center electrode (2);

preliminary bending the metal strip (W₂) toward the spacer (3; 73) so as to form an arc portion in the metal strip (W₂);

and then precisely forming a gap-distance (g) between the metal strip (W₂) and the firing end of the center electrode (2) by applying a force to the metal strip (W₂),

   characterized in that, during said preliminary bending step, a clearance (d) is maintained between the spacer (3; 73) and the center electrode (2) such that the spacer (3; 73) is only contacted by the metal strip (W₂) for forming the ground electrode.

2. A method according to claim 1, further comprising a step of:

measuring the position of the firing end of the center electrode (2) so as to determine a position for the spacer (3; 73).

3. A method according to claim 2, wherein,
   a clearance (d) between the spacer and the firing end of the center electrode (2) is determined based on the measured position of the center electrode (2).

4. A method according to claim 1 or 2, further comprising a step of:

retrieving the spacer (3) after bending the metal strip (W₂) so that the gap-distance between the metal strip (W₂) and the center electrode (2) is able to be adjusted to a required value (g) by referring to a position of the preliminary bent metal strip (W₂) and the position of the firing end of the center electrode (2).

5. A method according to claim 1, 2, 3 or 4, further comprising a step of:

welding a metal plate tip (W₁a) to a lateral side of the metal strip (W₂) for a ground electrode after providing the metal strip (W₂) extending from the end of the metal shell (W₃) and before positioning the spacer (3; 73) above the firing end of the center electrode (2), the metal plate tip (W₁a) being a spark-erosion resistant metal which includes Pt, Ir, Rh, Pd, Re, Os, Ru, Ni or alloy thereof.

6. A method according to any one of the preceding claims, wherein,
   a clearance (d) between the spacer (3) and the firing end is maintained during the step of bending the metal strip (W₂) so as to protect the firing end of the center electrode (2).

7. A method according to any one of the preceding claims, wherein,
   the firing end of the center electrode (2) is made of a tip (W₁) having a diameter in the range of from 0.3 to 1 mm.

8. A method according to claim 7, wherein,
   the tip (W₁) comprises a metal selected from the group consisting of Pt, Ir, Rh, Pd, Re, Os, Ru or an alloy thereof.

9. A method according to any one of the preceding claims, wherein the spacer (3; 73) has a rounded portion (3a; 73a) toward which the metal strip (W₂) is bent by a punch (4;75) in said preliminary bending step.

10. A method according to any one of the preceding claims, further comprising the steps of:

storing information relating to the position of the firing end of the center electrode (2) in a computer memory (13); and

using said information for positioning the spacer (3; 73).

11. A method according to any one of the preceding claims, further comprising the steps of:

storing information relating to the position of the firing end of the center electrode (2) in a computer memory (13); and

using said information for precisely forming a gap-distance (g) between the metal strip (W₂) and the firing end of the center electrode (2).

12. A method according to any one of the preceding claims, wherein the position for the spacer (3; 73) is determined by positional information of the firing end of the center electrode (2), the positional information being determined with reference to a position of a part constituting the spark plug (W).

13. A method according to any one of the preceding claims, wherein positional information of the firing end of the center electrode (2) is measured by use of a position-detecting sensor (1) using a laser.

14. A method according to any one of the preceding claims, wherein the force applied to the metal strip (W₂) for precisely forming the gap distance (g) is caused by a die (6) moving in parallel with a center electrode axis.

15. A method according to any one of the preceding claims, wherein the arc portion to be formed in the metal strip (W₂) by positioning the spacer (3; 73) is located at substantially the same level as the firing end of the center electrode (2).

16. An apparatus for making a spark plug (W) comprising a center electrode (2) disposed in a bore formed in a ceramic insulator (W₄), a metallic shell (W₃) fitting outside the ceramic insulator (W₄), and a ground electrode forming a spark gap (g) with the center electrode (2), the apparatus comprising:

means (1, 8) for positioning a spacer (3; 73) above a firing end of the center electrode (2);

means (4; 75) for preliminary bending a metal strip (W₂) toward the spacer (3; 73) so as to form an arc portion in the metal strip (W₄), said metal strip (W₂) being provided extending from an end of the metal shell (W₃) and being for forming said ground electrode; and

means (6, 7, 8) for precisely forming a gap-distance (g) between the metal strip (W₂) and the firing end of the center electrode (2) by applying a force to the metal strip (W₂),

   characterized in that said means (1, 8) for positioning a spacer (3; 73) and said means (7, 8) for preliminary bending a metal strip (W₂) maintain a clearance (d) between the spacer (3; 73) and the center electrode (2) and contact the spacer (3; 73) only with the metal strip (W₂) for forming the ground electrode.

17. An apparatus according to claim 16, further comprising a position-detecting sensor (1) incorporating a laser, for measuring positional information of the firing end of the center electrode (2).

18. An apparatus according to claim 16 or 17, further comprising a visual-image processor (7) for detecting information on said gap-distance.

19. An apparatus according to claim 17 or 18, further comprising a memory (13) for storing said measured positional information and/or said detected gap-distance information.

20. An apparatus according to claim 17, 18 or 19, further comprising a CPU (11) for controlling said means for positioning said spacer, said means for preliminary bending said metal strip and said means for precisely forming said gap-distance, based on said measured and/or stored information.

Ansprüche

1. Verfahren zur Herstellung einer Zündkerze (W), welche umfasst: eine Mittelelektrode (2), welche in einer Bohrung angeordnet ist, die in einem Keramikisolator (W₄) gebildet ist, einen Metallmantel (W₃), welcher außerhalb des Keramikisolators (W₄) angebracht ist, und eine Masseelektrode, welche einen Zündspalt (g) mit der Mittelelektrode (2) bildet, wobei das Verfahren die Schritte umfasst:

Schaffen eines Metallstreifens (W₂), welcher sich von einem Ende des Metallmantels (W₃) erstreckt, wobei der Metallstreifen (W₂) vorgesehen ist, die Masseelektrode zu bilden;

Positionieren eines Abstandshalters (3, 73) oberhalb eines Zündendes der Mittelelektrode (2);

vorbereitendes Biegen des Metallstreifens (W₂) in Richtung zum Abstandshalter (3, 73), um einen Bogenabschnitt im Metallstreifen (W₂) zu bilden;

und dann genaues Bilden eines Spaltabstandes (g) zwischen dem Metallstreifen (W₂) und dem Zündende der Mittelelektrode (2), indem eine Kraft auf den Metallstreifen (W₂) aufgebracht wird,

   dadurch gekennzeichnet, dass während des vorbereitenden Biegeschrittes ein Abstand (d) zwischen dem Abstandshalter (3, 73) und der Mittelelektrode (2) so beibehalten wird, dass der Abstandshalter (3, 73) nur von dem Metallstreifen (W₂) berührt wird, um die Masseelektrode zu bilden.

2. Verfahren nach Anspruch 1, welches ferner einen Schritt umfasst:

Messen der Position des Zündendes der Mittelelektrode (2), um eine Position für den Abstandshalter (3, 73) zu bestimmen.

3. Verfahren nach Anspruch 2, wobei
   ein Abstand (d) zwischen dem Abstandshalter und dem Zündende der Mittelelektrode (2) basierend auf der gemessenen Position der Mittelelektrode (2) bestimmt wird.

4. Verfahren gemäß Anspruch 1 oder 2, welches ferner einen Schritt umfasst:

Zurücksetzen des Abstandshalters (3) nach dem Biegen des Metallstreifens (W₂), so dass der Spaltabstand zwischen dem Metallstreifen (W₂) und der Mittelelektrode (2) auf einen geforderten Wert (g) eingestellt werden kann, indem auf eine Position des vorbereitend gebogenen Metallstreifens (W₂) und der Position des Zündendes der Mittelelektrode (2) Bezug genommen wird.

5. Verfahren nach Anspruch 1, 2, 3 oder 4, welches ferner einen Schritt umfasst:

Schweißen eines Metallplättchens (W₁a) auf eine Lateralseite des Metallstreifens (W₂) für eine Masseelektrode, nachdem der sich vom Ende des Metallmantels (W₂) erstreckende Metallstreifen (W₂) geschaffen ist und bevor der Abstandshalter (3, 73) oberhalb des Zündendes der Mittelelektrode (2) positioniert ist, wobei das Metallplättchen (W₁a) ein funkenerosionsfestes Metall ist, welches Pt, Ir, Rh, Pd, Re, Os, Ru, Ni oder eine Legierung daraus aufweist.

6. Verfahren nach einem der vorhergehenden Ansprüche, wobei
   ein Abstand (d) zwischen dem Abstandshalter (3) und dem Zündende während des Schrittes des Biegens des Metallstreifens (W₂) beibehalten wird, so dass das Zündende der Mittelelektrode (2) geschutzt wird.

7. Verfahren nach einem der vorhergehenden Ansprüche, wobei
   das Zündende der Mittelelektrode (2) aus einer Spitze (W₁) hergestellt ist, welche einen Durchmesser im Bereich von 0,3 bis 1 mm besitzt.

8. Verfahren nach Anspruch 7, wobei
   die Spitze ein Metall aufweist, welches aus der Gruppe ausgewählt ist, welche Pt, Ir, Rh, Pd, Re, Os, Ru oder eine Legierung daraus aufweist.

9. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Abstandhalter (3, 73) einen abgerundeten Abschnitt (3a, 73a) besitzt, zu welchem der Metallstreifen (W₂) von einem Formwerkzeug (4, 75) in dem vorbereitendem Biegeschritt gebogen wird.

10. Verfahren nach einem der vorhergehenden Ansprüche, welches ferner die Schritte umfasst:

Speichern von sich auf die Position des Zündendes der Mittelelektrode (2) beziehenden Information in einem Computerspeicher (13); und

Verwenden der Information, um den Abstandshalter (3, 73) zu positionieren.

11. Verfahren nach einem der vorhergehenden Ansprüche, welches weiter die Schritte umfasst:

Speichern von sich auf die Position des Zündendes der Mittelelektrode (2) beziehenden Information in einem Computerspeicher (13); und

Verwenden der Information, um einen Spaltabstand (g) zwischen dem Metallstreifen (W₂) und dem Zündende der Mittelelektrode (2) genau zu bilden.

12. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Position für den Abstandshalter (3, 73) durch eine Positionsinformation des Zündendes der Mittelelektrode (2) bestimmt wird, wobei die Positionsinformation mit Bezug auf eine Position eines Teiles bestimmt wird, welches die Zündkerze (W) bildet.

13. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Positionsinformation des Zündendes der Mittelelektrode (2) durch Einsatz eines Positionserfassungssensors (1) gemessen wird, welcher einen Laser verwendet.

14. Verfahren nach einem der vorhergehenden Ansprüche, wobei die auf den Metallstreifen (W₂) aufgebrachte Kraft zum genauen Bilden des Spaltabstandes (g) durch einen Stempel (6) bewirkt wird, welcher sich parallel zu einer Mittelelektrodenachse bewegt.

15. Verfahren nach einem der vorhergehenden Ansprüche, wobei die Bogenposition, welche in den Metallstreifen (W₂) durch Positionieren des Abstandshalters (3, 73) geformt wird, auf der im Wesentlichen gleichen Höhe angeordnet ist wie das Zündende der Mittelelektrode (2).

16. Vorrichtung zur Herstellung einer Zündkerze (W), welche umfasst: eine Mittelelektrode (2), welche in einer Bohrung angeordnet ist, die in einem Keramikisolator (W₄) gebildet ist, einen Metallmantel (W₃), welcher außerhalb des Keramikisolators (W₄) angebracht ist, und eine Masseelektrode, welche einen Zündspalt (g) mit der Mittelelektrode (2) bildet, wobei die Vorrichtung umfasst:

Mittel (1, 8) zum Positionieren eines Abstandshalters (3, 73) oberhalb eines Zündendes der Mittelelektrode (2);

Mittel (4, 75) zum vorbereitenden Biegen eines Metallstreifens (W₂) in Richtung zum Abstandshalter (3, 73), um einen Bogenabschnitt im Metallstreifen (W₂) zu bilden, wobei der Metallstreifen (W₂) vorgesehen ist, sich von einem Ende des Metallmantels (W₃) zu erstrecken und die Masseelektrode zu bilden; und

Mittel (6, 7, 8) zum genauen Bilden eines Spaltabstandes (g) zwischen dem Metallstreifen (W₂) und dem Zündende der Mittelelektrode (2), indem eine Kraft auf den Metallstreifen (W₂) aufgebracht wird,

   dadurch gekennzeichnet, dass die Mittel (1, 8) zum Positionieren eines Abstandshalters (3, 73) und die Mittel (7, 8) zum vorbereitenden Biegen eines Metallstreifens (W₂) einen Abstand (d) zwischen dem Abstandshalter (3, 73) und der Mittelelektrode (2) beibehalten und den Abstandshalter (3, 73) nur mit dem Metallstreifen (W₂) berühren, um die Masseelektrode zu bilden.

17. Vorrichtung gemäß Anspruch 16, welche ferner einen Positionserfassungssensor (1) umfasst, welcher einen Laser aufweist, um eine Positionsinformation des Zündendes der Mittelelektrode (2) zu messen.

18. Vorrichtung nach Anspruch 16 oder 17, welche ferner einen Bilderfassungssensor (7) umfasst, um eine Information über den Spaltabstand zu erfassen.

19. Vorrichtung nach Anspruch 17 oder 18, welche ferner einen Speicher (13) umfasst, um die gemessene Positionsinformation und/oder die erfasste Spaltabstandsinformation zu speichern.

20. Vorrichtung nach Anspruch 17, 18 oder 19, welche ferner eine CPU (11) umfasst zum Steuern des Mittels zum Positionieren des Abstandshalters, des Mittels zum vorbereitenden Biegen des Metallstreifens und des Mittels zum genauen Bilden des Spaltabstandes, basierend auf der gemessenen und/oder gespeicherten Information.

Revendications

1. Procédé de fabrication d'une bougie d'allumage (W), laquelle comprend une électrode centrale (2) disposée dans un alésage formé dans un isolant (W₄) en céramique, une enveloppe métallique (W₃) disposée à l'extérieur de l'isolant (W₄) en céramique, et une électrode de masse formant un intervalle de décharge (g) avec l'électrode centrale (2), le procédé comprenant les étapes consistant à :

fournir une bande métallique (W₂) qui s'étend depuis une extrémité de l'enveloppe métallique (W₃), ladite bande métallique (W₂) servant à former ladite électrode de masse ;

placer un élément d'espacement (3 ; 73) au-dessus d'une extrémité d'allumage de l'électrode centrale (2) ;

réaliser un cintrage préalable de la bande métallique (W₂) vers le moyen d'espacement (3 ; 73) de manière à former une partie arquée dans la bande métallique (W₂) ;

former ensuite avec précision une distance d'intervalle de décharge (g) entre la bande métallique (W₂) et l'extrémité d'allumage de l'électrode centrale (2) en exerçant une force sur la bande métallique (W₂),

   caractérisé en ce que, pendant ladite étape de cintrage préalable, un intervalle (d) est maintenu entre le moyen d'espacement (3 ; 73) et l'électrode centrale (2) de façon que le moyen d'espacement (3 ; 73) ne soit touché par la bande métallique (W₂) que pour former l'électrode de masse.

2. Procédé selon la revendication 1, comprenant en outre une étape consistant à :

mesurer la position de l'extrémité d'allumage de l'électrode centrale (2) afin de déterminer une position pour le moyen d'espacement (3 ; 73).

3. Procédé selon la revendication 2, dans lequel
   un intervalle (d) entre le moyen d'espacement et l'extrémité d'allumage de l'électrode centrale (2) est déterminé d'après la position mesurée de l'électrode centrale (2).

4. Procédé selon la revendication 1 ou 2, comprenant en outre une étape consistant à :

récupérer le moyen d'espacement (3) après le cintrage de la bande métallique (W₂) de façon que la distance d'intervalle de décharge entre la bande métallique (W₂) et l'électrode centrale (2) puisse être réglée à une valeur requise (g) par rapport à une position de la bande métallique (W₂) à cintrage préalable et à la position de l'extrémité d'allumage de l'électrode centrale (2).

5. Procédé selon la revendication 1, 2, 3 ou 4, comprenant en outre une étape consistant à :

souder un bout (W₁a) de plaque métallique à une face latérale de la bande métallique (W₂) pour une électrode de masse après la réalisation de la bande métallique (W₂) s'étendant depuis l'extrémité de l'enveloppe métallique (W₃) et avant la mise en place du moyen d'espacement (3 ; 73) au-dessus de l'extrémité d'allumage de l'électrode centrale (2), le bout (W₁a) de plaque métallique étant en métal résistant à l'électroérosion, qui contient Pt, Ir, Rh, Pd, Re, Os, Ru, Ni ou un alliage de ceux-ci.

6. Procédé selon l'une quelconque des revendications précédentes, dans lequel
   un intervalle (d) entre le moyen d'espacement (3) et l'extrémité d'allumage est maintenu pendant l'étape de cintrage de la bande métallique (W₂) afin de protéger l'extrémité d'allumage de l'électrode centrale (2).

7. Procédé selon l'une quelconque des revendications précédentes, dans lequel
   l'extrémité d'allumage de l'électrode centrale (2) est constituée par un bout (W₁) dont le diamètre est de 0,3 à 1 mm.

8. Procédé selon la revendication 7, dans lequel
   le bout (W₁) est constitué par un métal choisi dans le groupe comprenant Pt, Ir, Rh, Pd, Re, Os, Ru ou un alliage de ceux-ci.

9. Procédé selon l'une quelconque des revendications précédentes, dans lequel le moyen d'espacement (3 ; 73) a une partie arrondie (3a ; 73a) vers laquelle la bande métallique (W₂) est cintrée par un poinçon (4 ; 75) lors de ladite étape de cintrage préliminaire.

10. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre les étapes consistant à :

stocker dans une mémoire (13) d'ordinateur des informations relatives à la position de l'extrémité d'allumage de l'électrode centrale (2) ; et

utiliser lesdites informations pour mettre en place le moyen d'espacement (3 ; 73).

11. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre les étapes consistant à :

stocker dans une mémoire (13) d'ordinateur des informations relatives à la position de l'extrémité d'allumage de l'électrode centrale (2) ; et

utiliser lesdites informations pour former avec précision une distance d'intervalle de décharge (g) entre la bande métallique (W₂) et l'extrémité d'allumage de l'électrode centrale (2).

12. Procédé selon l'une quelconque des revendications précédentes, dans lequel la position pour le moyen d'espacement (3 ; 73) est déterminée par des informations de position de l'extrémité d'allumage de l'électrode centrale (2), les informations de position étant déterminées par rapport à une position d'une partie constituant la bougie d'allumage (W).

13. Procédé selon l'une quelconque des revendications précédentes, dans lequel les informations de position de l'extrémité d'allumage de l'électrode centrale (2) sont mesurées à l'aide d'un détecteur (1) de position utilisant un laser.

14. Procédé selon l'une quelconque des revendications précédentes, dans lequel la force appliquée à la bande métallique (72) pour former avec précision la distance d'intervalle de décharge (g) est créée par un poinçon (6) se déplaçant parallèlement à un axe de l'électrode centrale.

15. Procédé selon l'une quelconque des revendications précédentes, dans lequel la partie arquée à former dans la bande métallique (W₂) du fait de la mise en place du moyen d'espacement (3 ; 73) est située sensiblement au même niveau que l'extrémité d'allumage de l'électrode centrale (2).

16. Dispositif de fabrication d'une bougie d'allumage (W), laquelle comprend une électrode centrale (2) disposée dans un alésage formé dans un isolant (W₄) en céramique, une enveloppe métallique (W₃) disposée à l'extérieur de l'isolant (W₄) en céramique et une électrode de masse formant un intervalle de décharge (g) avec l'électrode centrale (2), le dispositif comprenant :

un moyen (1, 8) pour placer un moyen d'espacement (3 ; 73) au-dessus d'une extrémité d'allumage de l'électrode centrale (2) ;

un moyen (4 ; 75) de cintrage préliminaire d'une bande métallique (W₂) vers le moyen d'espacement (3 ; 73) de manière à former une partie arquée dans la bande métallique (W₄), ladite bande métallique (W₂) étant disposée de manière à s'étendre depuis une extrémité de l'enveloppe métallique (W₃) et servant à former ladite électrode de masse ; et

un moyen (6, 7, 8) pour former avec précision une distance d'intervalle de décharge (g) entre la bande métallique (W₂) et l'extrémité d'allumage de l'électrode centrale (2) en appliquant une force à la bande métallique (W₂),

   caractérisé en ce que ledit moyen (1, 8) pour mettre en place un moyen d'espacement (3 ; 73) et ledit moyen (7, 8) de cintrage préliminaire d'une bande métallique (W₂) maintient un intervalle (d) entre le moyen d'espacement (3 ; 73) et l'électrode centrale (2) et ne met le moyen d'espacement (3 ; 73) au contact de la bande métallique (W₂) que pour former l'électrode de masse.

17. Dispositif selon la revendication 16, comprenant en outre un détecteur (1) de position comprenant un laser, pour mesurer des informations de position de l'extrémité d'allumage de l'électrode centrale (2).

18. Dispositif selon la revendication 16 ou 17, comprenant en outre un processeur (7) d'image visuelle pour détecter des informations sur ladite distance d'intervalle de décharge.

19. Dispositif selon la revendication 17 ou 18, comprenant en outre une mémoire (13) pour stocker lesdites informations de position mesurées et/ou lesdites informations de distance d'intervalle de décharge détectées.

20. Dispositif selon la revendication 17, 18 ou 19, comprenant en outre une unité centrale (11) pour commander ledit moyen de mise en place dudit moyen d'espacement, ledit moyen de cintrage préliminaire de ladite bande métallique et ledit moyen de formation précise de ladite distance d'intervalle de décharge, d'après lesdites informations mesurées et/ou stockées.

Drawing