EP1850432B1 - Ignition plug - Google Patents

Description

The invention relates to a method of making a spark plug having a body, a center electrode and at least one body electrode defining therebetween a spark discharge gap.

It is known, in a spark plug having a body, a center electrode and at least one body electrode forming a discharge gap for the spark therebetween, to provide the center electrode and the body electrode with noble metal reinforcements, respectively.

Here, the aim is to achieve a high mileage through the noble metal reinforcements, which may consist of platinum alloys or iridium alloys.

The object underlying the invention is in contrast to increase the life and mileage of such a spark plug.

This object is achieved according to the invention by the combination of features of claims 1 and 2. A particularly preferred Embodiment of the method according to the invention is the subject of claim 3.

Here, noble metal reinforcements of the body electrode and the center electrode have an overlap, i. a measure of opposing arrangement of the noble metal surfaces, which is optionally at least 90%, preferably at least 92% based on the smaller noble metal surface.

Experiments have shown that at a noble metal coverage that does not meet this level, an early failure of the spark plug can occur and the required life is not met. Only through the inventively provided level of overlap the precious metal reinforcement of the electrode is optimally used and results in a long life and service life of the spark plug.

In the case of the spark plug produced according to the invention, the noble metal reinforcements on the center electrode and the body electrode are thus arranged relative to one another such that they form the discharge gap for the spark, which is designed such that an electrical spark can form. In this case, it is ensured that the two noble metal armatures of the center and body electrodes face each other such that the spark exit surface of the center electrode and the spark surface of the body electrode precisely oppose in the direction of the spark discharge such that the two noble metal surfaces of the center and body electrodes are at least 90% preferably at least 92% overlap

US 2002/0038992 A1 describes a spark plug whose discharge gap is reduced so far, until even a reasonable spark discharge is possible. The reduction of the discharge gap minimizes the overall size of the spark plug. Furthermore, in US 2005/0029915 A1 described a variety of differently shaped spark plugs, in which the center electrode and the body electrode are provided with a precious metal reinforcement. In a spark plug referred to in this document as the prior art, the center line of the center electrode is aligned with the center line of the body electrode. Otherwise, all differently configured spark plugs have an offset between the centerlines of the body and center electrodes.

In the case of spark plugs having a body, a center electrode and at least one body electrode, after screwing the spark plug over the thread provided on the body electrode, the position of the spark plug thread portion is not assigned to the position of the body electrode, i. the position of the body electrode after screwing each different, so that, for example, in the use of the spark plug in spray-guided direct injection systems, the access of the spark gap can be hidden from the injection jet. Furthermore, there is no association of the threaded portion of the spark plug body, i. the bolt thread to the cylinder head bore, i. of the nut thread. There is no targeted position of the body electrode can be reached at the spark plug, so that the position of the body electrode in the combustion chamber is random.

The attachment of the body electrode on the spark plug body is carried out after making the screw thread, wherein for the positionally accurate welding of the body electrode, the shape and the position of the thread profile is used as a reference.

In this case, the body is struck loose at the outer sealing seat and is brought with a rotational movement, the thread profile of the body in a defined measuring window in the desired position. The alignment, adjustment and positioning of the body is monitored by means of an optical measuring system, thereby ensuring a defined distance of the outer sealing seat from the thread profile.

After the positioning of the body, the body electrode is welded onto the front of the body, with subsequent further processing Deburred, embossed, nickel-plated and possibly precious metal-reinforced. The body electrode is then bent and the insulator is mounted.

Due to the positionally accurate production of the cylinder head thread with defined thread an exact positioning of the body electrode in the combustion chamber of the engine is ensured.

By changing the position of the threaded portion of the cylinder head nut thread beyond a best possible individual position of the body electrode in the combustion chamber is possible.

In the case of spark plugs having a body, a center electrode and at least one body electrode forming a discharge gap for the spark therebetween, the overall tolerance of the distance from the body-exterior sealing seat to the spark gap, i.e. the Vorstehmaßes large, so that a targeted installation, which is mainly required for use in spray-guided direct injection systems, is not guaranteed.

It should also be achieved that the installation tolerance of the Elektrodenmaßes is as small as possible.

The tolerance of the spark position is narrowed, so that an exact position of the spark gap is ensured in the combustion chamber. In this case, the spark plug is formed so that the dimensional and tolerance accuracy between the outer sealing seat and the center electrode tip is minimal.

When using spray-guided combustion methods in direct injection gasoline engines, a reliable ignition in the occupied area of the fuel spray is thus possible. The spark gap of the spark plug must be placed in this narrow zone of the fuel spray. For a stable ignition there are high demands on the jet stability as well as the spark gap positioning. Since in commercial spark plugs, the manufacturing tolerance of the Elektrodenvorstehmaßes is large and can be in the range of 1.5 mm, these commercially available spark plugs are hardly suitable for this use. By the large manufacturing tolerances of such spark plugs, the electrodes may be positioned so that the fuel cloud outside, especially formed below the spark gap, which consequently leads to misfiring. Furthermore, an exact positioning of the body electrode is advantageous so that the body electrode does not obstruct the so-called entrainment flow. This is to be understood as the intake of air from the environment of the injected spray jet as a result of the negative pressure arising in the spray due to the velocity distribution of the droplets and the Sprühstrahlabkühlung by removing the enthalpy of vaporization.

In an internal combustion engine with a combustion method such as the jet-guided gasoline direct injection thus a spark plug with a position-oriented spark gap is required. The Vorstehmaß the electrodes must also be assigned so that in the defined location of the fuel injection cone takes place a safe ignition. Conditions are an exact position, i. an exact protrusion of the spark gap into the combustion chamber and a best possible position of the body electrode in the combustion chamber or in the injection jet such that the body electrode does not hinder the ignition process, for example by shading the fuel particles in the direction of the discharge path or an unfavorable position of the body electrode leads to quenching.

In the spark plug according to the invention, the requirement for minimum allocation tolerance of the spark gap and accurate positioning of the body electrode is met. The spark plugs are inventively made so that the natural tolerances of the items in the Maßbetrachtung the distance between the outer sealing seat and center electrode tip do not add in the assembled state. Prior to assembly of the insulator and the body, an optical measuring method between the insulator seat and the Center electrode tip this length measured. The Vorstehmaß is matched with different inner gaskets.

In the following, particularly preferred embodiments of the invention will be described in more detail with reference to the accompanying drawings.

• Fig. 1 den Fertigungsablauf eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens zur Herstellung des Kerzenkörpers in drei Phasen und
• Fig. 2 den Fertigungsablauf bei einem Ausführungsbeispiels des erfindungsgemäßen Verfahrens zur Herstellung einer Zündkerze.

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• Fig. 1 the manufacturing process of an embodiment of the inventive method for producing the plug body in three phases and
• Fig. 2 the production process in an embodiment of the inventive method for producing a spark plug.

First, two embodiments of the method according to the invention for forming the Edelmetallarmierungen on a spark plug with welded non-bent body electrode and a fully assembled spark plug are described in which a Edelmetalloberflächenüberdeckung the Edelmetallarmierungen of at least 90%, preferably at least 92% is provided.

In the first method of Edelmetallarmierung in a spark plug with welded unbent body electrode, the body 1 is taken in calibrated height D1, the body electrode 3 is aligned, a noble metal piece 5 the ignited surface facing the body electrode 3, the precious metal piece in the middle of Width of the body electrode 3 is positioned, the noble metal piece 5 is resistance welded to the length dimension Z, the noble metal piece 5 is formed flat, the precious metal piece 5 is laser welded to the length dimension Z, the body electrode 3 is cut to the length dimension of the optimal stretched length, optionally contour cutting takes place the body electrode 3, the body electrode 3 is bent to the dimension A, the insulator and the body are mounted by that the dimension B of the insulator is determined by measuring that insulator 7 and body 1 after computation and targeted allocation unte are assigned in pairs so that an inner sealing ring 8 and the insulator 7 are inserted into the body 1 and a crimping and shrinking takes place, the body electrode 3 is calibrated in the X-axis, ie in the width direction of the body electrode 3, the Body electrode 3 in the Y-axis, that calibrated with respect to the front edge of the body electrode 3 and the body electrode 3 is calibrated in the Z-axis, ie in the direction of the electrode spacing or in the longitudinal axis of the spark plug.

In the second method of precious metal embellishment on a fully assembled spark plug, the assembled spark plug is picked up, the body electrode 3 is aligned in the X-axis direction, the body electrode 3 is aligned in the Y-axis direction, the jig dimension is measured, the positioning becomes When the precious metal piece 5 is resistance-welded to the length dimension Z, the noble metal piece 5 is embossed flat, laser welding is performed, the body electrode 3 is cut after calculation of the protruding amount When the body electrode 3 is bent, the body electrode 3 is calibrated in the X-axis direction, the body electrode 3 is calibrated in the Y-axis direction, and the body electrode 3 is calibrated in the Z-axis direction.

For example, if the noble metal piece 5 on the body electrode 3 is circular and has a diameter of 1 mm and the noble metal piece of the center electrode is circular and has a diameter of 0.8 mm, the desired coverage may be more than 90% of the area of the noble metal piece of the center electrode be achieved by the noble metal piece 5 on the body electrode 3 in that the center deviation, ie the deviation of the centers of the circular precious metal surfaces is less than 0.18 mm. With a center deviation of less than 0.15 mm, an overlap of 95% is already achieved.

The desired coverage can thus be achieved by keeping the center deviation within appropriate limits.

In order to continue to achieve the most accurate position of the spark gap, ie an accurate Vorstehmaß and a precise body electrode position in the combustion chamber, the dimension X of the outer sealing seat of the cold-extruded body is in the manufacture of the spark plug to the inner Sealing seat, ie turned to the calibrated height D1, the body is positioned to hit the collar of the outer sealing seat, wherein the thread profile is positioned as reference in the measuring window, the body electrode 3 is welded and then nickel-plated, a noble metal piece 5 on the body electrode 3 in Dimension Z is applied, the body electrode 3 is cut to length C, the body electrode 3 is bent to the dimension A, and the insulator 7 and body are assembled by measuring the distance of the sealing seat of the insulator 7 from the firing tip of the center electrode, ie, the dimension B. is that the calibrated height to the outer sealing seat, ie the measure X is measured, that an inner sealing ring 8 is chosen to dimension C after calculation of the dimension B, that a crimping and shrinking takes place and that a solid outer sealing ring 6 is mounted and caulked to it becomes captive.

In the Fig. 1 and 2 is a particularly preferred embodiment of the method according to the invention in a total of four phases shown in detail.

In phase 1 in Fig. 1 the production of a spark plug is such that the natural tolerances of the individual parts with respect to the measure of the spark position do not add up. In this case, the inner sealing seat D1 of the body 1 is the constructive reference point to which all further construction and manufacturing operations refer. From the inner sealing seat D1, the accuracy of the outer sealing seat 4 is made by revolving the sealing shoulder. The constructively determined distance X is maintained in the range of +/- 0.05 mm. By contrast, the previous tolerance accuracy was +/- 0.28 mm (calibrated height +/- 0.08 mm, body length +/- 0.2 mm).

In phase 2, thread rolling takes place prior to welding of the body electrode 3. The welding of the body electrode 3 then takes place in such a way that the position of the body electrode 3 to the threaded portion exactly is determined. In this case, the body 1 is placed with the sealing shoulder on the outer sealing seat 4 on a stop 2 and the thread profile is visualized using an image processing system. By means of a rotary movement, it can be adjusted to the exact position Y in a given measuring window.

In phase 3, a noble metal piece 5 can additionally be welded to the body electrode 3. The length reference is the inner sealing seat D1, wherein the exact position of the noble metal piece 5 is defined by the dimension Z.

After welding the noble metal chip 5, for example, by resistance welding or laser welding, the length C of the body electrode 3 is cut by cutting, e.g. produced by mechanical cutting. As a result, an optimal bending length of the body electrode 3 is ensured.

The body electrode 3 is then bent to the dimension A. Reference is the inner sealing seat D1 of the body. With this precise pre-bend adjustment of the electrode gap is ensured without much bending of the body electrode 3. As a result, a secure overlap of the precious metal parts at the center electrode and body electrode 3 is ensured in the axial direction.

In phase 4 in Fig. 2 is determined before the introduction of the insulator 7 in the body 1, the length B of the insulator sealing shoulder to the firing tip of the center electrode, which can be done for example by means of a camera measuring system. Reference is the sealing shoulder D2 of the insulator 7, which corresponds to the inner sealing seat D1 of the body 1 with the same test dimension.

Depending on the length B, the installation of the insulator 7 in the body 1 with the thickness s of the inner sealing ring 8 is made. The tolerance for dimension B is +/- 0.17 mm (sealing seat +/- 0.09 mm, center electrode +/- 0.08 mm).

An assortment of different sealing ring thicknesses s in increments of 0.1 mm is available to match an exact projection dimension. Preferred thicknesses s of the inner sealing rings 8 are 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm and 0.8 mm.

The assembly by crimping and shrinking is carried out according to the rule of a size dimension of difference insulator to body with a minimum of inner seal and vice versa. The outer sealing ring 6 consists of a solid good heat-conducting metal. The thickness K of the outer sealing ring 6 is matched to the engine requirements and is within the standard specifications. For example, by internal caulking of the outer sealing ring 6, the captivity is ensured. Compared to standard outer gaskets made of sheet metal parts, solid sealing rings offer the advantage that they only deform slightly when tightened. A tolerance of the sealing ring thickness of +/- 0.02 mm is certainly achievable.

With the method described above, a spark plug can be produced reliably with an accuracy of Vorstehmaßes V of +/- 0.1 mm.

The following is a specific example: Requested Vorstehmass V: 31.5 mm Thread length: 26.5 mm Spark position E: 5.0 mm nominal size: Respiratory / Outer Seal Body (X): 17.1 mm Insulator base / center electrode (B): 15 mm Inner sealing ring thickness s: 0.6 mm Vorstehmaß V: 31.5 mm Maximum dimension: Respiratory / Outer Seal Body (X): 17.15 mm Insulator base / center electrode (B): 14.83 mm Inner sealing ring thickness s: 0.8 mm Vorstehmaß V: 31.52 mm Lower limit: Respiratory / Outer Seal Body (X): 17.05 mm Insulator base / center electrode (B): 15.17 mm Inner sealing ring thickness s: 0.4 mm Vorstehmaß V: 31,48 mm Largest mating difference: Respiratory / Outer Seal Body (X): 17.10 mm Insulator base / center electrode (B): 15.05 mm Inner sealing ring thickness s: 0.5 mm Vorstehmaß V: 31.45 mm or Inner sealing ring thickness s: 0.6 mm Vorstehmaß V: 31.55 mm

The tolerances of the inner sealing ring with +/- 0.02 mm and the thickness dispersion after pressing the inner sealing ring during assembly are not taken into account and the tolerances of the outer sealing ring with +/- 0.02 mm are not taken into account. If these tolerances are taken into account in the evaluation of the Vorstehmaßes V, then an accuracy of the Vorstehmaßes V process reliable in the order +/- 0.1 mm can be achieved.

The invention thus provides a spark plug in which the body electrode is accurately positioned to the threaded portion, the Elektrodenvorstehmaß by minimizing the tolerances small variations in the range of 0.2 mm, mounting with standard assembly tool is possible, standard high voltage connections can be used and a long term is achieved by optimal use of precious metal reinforcement.

Claims (3)

1. Method for manufacturing a spark plug having a body (1), a centre electrode and at least one ground electrode (3) which define in between a discharge gap for the spark, wherein the centre electrode and the ground electrode (3) each comprise a noble metal reinforcement (5) which are provided and subsequently mounted on the components of the spark plug, and wherein the body (1) is received in a calibrated height, the ground electrode (3) is aligned, a noble metal piece (5) is supplied to the surface of the ground electrode (3) facing the spark, the noble metal piece (5) is positioned in the middle of the width of the ground electrode (3), a particular length of the noble metal piece (5) is resistance-welded, the noble metal piece (5) is embossed flat, the particular length of the noble metal piece (5) is laser-welded, the ground electrode (3) is cut to its length, the length of the sealing shoulder of the insulator to the tip of the centre electrode is measured, the insulator (7) is allocated to the body (1) upon calculation and selective allocation of different thicknesses of the interior sealing ring, an interior sealing ring (8) and the insulator (7) are incorporated into the body (1) upon which beading and shrinking is conducted, the ground electrode (3) is calibrated in the direction of its width, the ground electrode (3) is calibrated in the direction towards its front edge and the ground electrode (3) is calibrated in the direction of the electrode gap such that the noble metal reinforcements (5) of the ground electrode (3) and the centre electrode comprise an overlap of the noble metal areas of at least 90% relative to the smaller noble metal area, if applicable.
2. Method for manufacturing a spark plug having a body (1), a centre electrode and at least one ground electrode (3) which form in between a discharge gap for the spark, wherein the centre electrode and the ground electrode (3) each comprise a noble metal reinforcement (5), wherein the spark plug is pre-assembled from its components and is subsequently provided with the noble metal reinforcements (5), and wherein the pre-assembled spark plug is received, the ground electrode (3) is aligned with respect to its width, the ground electrode (3) is aligned in the direction of its front edge, the amount of overhang is measured, the position of a noble metal piece (5) is calculated, the noble metal piece (5) is supplied to the surface of the ground electrode (3) facing the spark, a particular length of the noble metal piece (5) is resistance-welded, the noble metal piece (5) is embossed flat, the noble metal piece (5) is laser-welded, the ground electrode (3) is cut upon measurement of its amount of overhang, the ground electrode (3) is bent, the ground electrode (3) is calibrated in the direction of the width, the ground electrode (3) is calibrated in the direction of the front edge, and the ground electrode (3) is calibrated in the direction of the electrode gap such that the noble metal reinforcements (5) of the ground electrode (3) and the centre electrode comprise an overlap of the noble metal areas of at least 90% relative to the smaller noble metal area, if applicable.
3. Method according to claim 1 or 2, wherein the overlap of the noble metal areas is at least 92%.

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