Patent Publication Number: US-10320156-B2

Title: Spark plug and method for manufacturing same

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of German Application No. 10 2016 115195.5, filed on Aug. 16, 2016, and German Application No. 10 2017 117452.4, filed on Aug. 2, 2017, the contents of which are hereby incorporated by reference in their entirety. 
     FIELD 
     The present invention is generally related to spark plugs, and more particularly, to spark plugs designed for internal combustion engines. 
     SUMMARY 
     The disclosure relates to a spark plug and a method for manufacturing a spark plug. 
     Disclosed in DE 10 2012 101,168 A1 is a spark plug that contains a body having a passage in which an insulator is inserted in a gas-tight manner. At the back end of the body, the edge of the body is flanged inward after insertion of the insulator as a retaining mechanism for the insulator, and engages an insulator shoulder. The body has a shrinkage zone, in which the cross-section of the body is reduced, and which is heated by a current pulse and is upset with the simultaneous application of axial force. During the subsequent cooling, shrinkage of the body takes place in the region of the shrinkage zone so that the insulator is clamped in the body with an axial preloading force. This known method, which is frequently used in practice, is also called “electro-upsetting.” The passage in the body, in particular the intermediate space between the insulator and the body, is sealed in this way against passage through it of combustion gases that act on the front end of the spark plug, which is in contact with the combustion chamber during operation of the internal combustion engine. 
     If the preloading force acting in the longitudinal direction decreases during a relatively long operating time of the spark plug, for example, due to fatigue of the body&#39;s material and/or an occasional overheating of the body, combustion gases may enter the intermediate space between insulator and body, or may even flow through the passage and escape from the combustion chamber of the internal combustion engine to the outside. This is undesirable. The flow of hot combustion gases through the passage leads to overheating of the spark plug and can even cause the strength of the flanged edge at the back end of the body to be reduced to such a degree that the insulator is pushed out of the body to the rear. The insulator can be driven out in projectile fashion by the highly pressurized combustion gases and cause considerable damage. 
     A spark plug and a manufacturing method of the initially mentioned type are known from 
     DE 10 2006 043,593 B3. The known spark plug contains a body having a passage in which an insulator is located and is retained in the passage under preloading force by means of a positive-acting retaining mechanism. Attached to the body is a securing mechanism acting in a positive manner that overlaps, at a very great distance, the side of the retaining mechanism facing away from the front end. The securing mechanism contains a tubular housing and a hexagon welded onto the back end that is intended to prevent spark plug parts, in particular the insulator, from being ejected from the tubular housing in the event of a failure of the retaining mechanism when dangerously high peak pressures occur. The tubular housing contains at least one vent opening in its lateral surface through which an overpressure can be relieved in the radial direction. Located in the back part of the tubular housing is a Teflon seal ring that prevents the entry of leakage gases into a back region where a center conductor exits the back end of the insulator. The tubular housing has a smooth inner wall that is continuous up to the hexagon, so if ejection of the insulator were to occur in the event of a failure, the insulator is first accelerated over a very long distance and then collides at high speed with the narrowing formed by the hexagon. 
     Disclosed in DE 10 2008 040,285 A1 is a special form of a spark plug optimized for installation space, which requires a special design of the cylinder head. Here, the body has no external thread for screwing into the cylinder head. Instead, a clamping nut is provided in the region of the back end of the body, and has an external thread that is screwed into a corresponding internal thread of the cylinder head, pressing the body of the spark plug in the direction of the combustion chamber against a seal seat. Due to a suitable design of the insulator, the clamping nut prevents it from being driven backward out of the body in the event of a failure. 
     DE 102 27 371 A1 discloses a spark plug with a piezoelectric sensor, wherein the sensor is arranged, with no gap, between a retaining mechanism of the insulator and a sleeve overlapping the back end of the insulator in order to measure changing deformation of the retaining mechanism with varying combustion pressures. Facing the front end of the body, the sleeve has an end section with sharply reduced cross-section that is welded onto a cylindrical section of the body. This thin-walled end section of the sleeve is not strong enough to stop an insulator that is accelerated backward out of the body in the event of failure of the retaining mechanism. Known from U.S. Pat. No. 2,300,646 A is a spark plug that has a body and a retaining mechanism for the insulator, wherein a rubber cap that overlaps the retaining mechanism is placed on the back end of the body. Such a rubber cap is likewise unsuitable for preventing ejection of the insulator in the event of failure of the retaining mechanism. EP 1,265,328 A1 discloses a spark plug containing a body assembled from multiple parts between which the insulator is held. The housing parts are preloaded against one another in their contact region by a welding process to achieve sealing of the insulator in the body. 
     An object of the present disclosure is to improve a spark plug and a method of the initially mentioned type. 
     The object can be attained by a spark plug with one or more of the features as described herein, and/or a manufacturing a method as described herein. Advantageous improvements to the spark plug and the methods described herein are the subject matter of the dependent claims. 
     The spark plug has a metal body with a front end and a back end, a longitudinal direction and a passage extending in the longitudinal direction. At least one ground electrode connected in an electrically conductive manner to the body can be located at the front end. An insulator containing a center electrode is located in the passage. The center electrode projects out of the insulator in the region of the front end, and, together with the at least one ground electrode, can form a spark gap or a spark air gap. In the region of its front end, the body has, located in the passage, a seal seat for the insulator. In the region of its back end, the body has a retaining mechanism holding the insulator in the body in a positive manner, by means of which the insulator is pressed against the seal seat in the longitudinal direction with a preloading force in order to seal the passage against the flow of combustion gases through it. The retaining mechanism can be designed to be ring-shaped, in particular as a continuous ring shape around the insulator.
     The retaining mechanism can be formed by a narrowing of the passage in the body. The retaining mechanism can in particular be formed by an edge of the body that is flanged after insertion of the insulator. The insulator can have an insulator shoulder, pointing toward the back end, that the retaining mechanism of the body engages. The body can be designed as a single continuous piece at least in its section extending from the seal seat to the retaining mechanism, in particular including the seal seat and retaining mechanism.   

     The insulator can have a shoulder that faces the front end of the body and rests against the seal seat of the body, in particular with a seal ring interposed. The insulator can likewise contain a passage extending in the longitudinal direction, in which the center electrode is located. An igniter that projects from the back end of the insulator and can be used to connect a supply line can be located in the passage of the insulator. The igniter and the center electrode are connected to one another inside the passage of the insulator by an electrically conductive fused glass element that simultaneously seals the passage in the insulator against the flow of combustion gases through it. 
     A positive-acting securing mechanism that at least partially overlaps the side of the retaining mechanism facing away from the front end is attached to the body. According to one embodiment, the insulator projects past the side of the securing mechanism facing away from the front end. The securing mechanism overlaps the retaining mechanism, forming a gap to the retaining mechanism as well as forming a gap to the insulator. Both gaps are small. The gap between the securing mechanism and the retaining mechanism and/or the gap between the securing mechanism and the insulator can be a maximum of 2 mm, in particular a maximum of 1 mm. The body can have, facing toward the back end, an external shoulder to which the securing mechanism is attached. The securing mechanism can include a ring-shaped section that surrounds the insulator while forming a gap, and overlaps the retaining mechanism while forming a gap. The inner contour of the ring-shaped section of the securing mechanism can, in particular, be matched to the outer contour of the retaining mechanism and/or of the insulator projecting from the back end of the body. 
     In the method for manufacturing a spark plug, first an insulator is placed in a body having a passage and is fixed in place therein by a positive-acting retaining mechanism. A forming of the retaining mechanism and the fixing in place of the insulator can be carried out in a manner known per se, for example in that an edge at the back end of the body is flanged after insertion of the insulator. Next, a positive-acting securing mechanism is placed on the body in a manner that at least partially overlaps the retaining mechanism, and is joined to the body. During placement, the securing mechanism is slipped onto the body in the longitudinal direction in such a manner that the insulator projects beyond the side of the securing mechanism facing away from the front end. Moreover, the securing mechanism is slipped on in such a manner that it contacts the external shoulder of the body, in particular with no gap, while a section of the securing mechanism that overlaps the retaining mechanism forms a gap in each case with the retaining mechanism as well as with the insulator. The securing mechanism can be joined to the body, in particular to its external shoulder, by welding. The securing mechanism and the body can be welded to one another continuously in the circumferential direction of the body, in particular by mechanism of a weld seam extending around the entire circumference of the body. In particular, provision can be made that the body is upset in the longitudinal direction between the external shoulder and the retaining mechanism after insertion of the insulator, and that the securing mechanism is not placed and attached until after the upsetting. 
     One or more embodiments may have important advantages:
         The securing mechanism reliably secures the insulator in the body if the retaining mechanism should fail. A failure of the retaining mechanism can be caused by, for example, material fatigue or overheating of the spark plug, and can—as described above—represent a high safety risk.   If the retaining mechanism should fail, the securing mechanism immediately captures the insulator due to the small gap and prevents the insulator from being accelerated to a high speed over a long distance and expelled from the body. The insulator is prevented from flying about.   The well-proven method, which is known per se, for installing the insulator in the body, in which an edge at the back end of the body is flanged and then a preloading force acting on the insulator in the longitudinal direction of the spark plug is created by electro-upsetting of a shrinkage zone, can continue to be used, namely, before the securing mechanism is put in place, in particular.   The securing mechanism, for example in the form of a securing sleeve, can be attached to the back end of the body without great effort.   The securing mechanism functions reliably even in a high temperature region, in particular up to 700° C.   The gap, in particular annular gap, between the securing mechanism and the insulator ensures an escape of hot gases in the axial direction in the event of a failure, such as also previously occurred in the spark plugs without securing mechanism that are known from DE 10 2012 101,168 A1. There is no need for any additional openings in the securing mechanism, which would weaken its cross-section as in DE 10 2006 043,593 B3. Furthermore, this narrow gap causes a degree of centering of the insulator in the event of a failure. During normal operation, in contrast, it ensures that the securing mechanism does not exert any undesirable forces on the insulator. Safety can be improved overall by this mechanism.   If the inner contour of the securing mechanism is matched to the outer contour of the retaining mechanism, then the retaining mechanism, which expands rearward in the event of a failure, can rest against the securing mechanism immediately after crossing the negligible gap and is reliably supported there without the possibility of strong acceleration of the insulator.   The gap between the securing mechanism and the retaining mechanism ensures that the securing mechanism can be slid onto the body until it contacts the external shoulder and that a reliable joint, in particular a weld seam, can be produced there. In particular, the gap between the securing mechanism and the retaining mechanism is chosen to be chosen to be just large enough to ensure that that the securing mechanism can contact the external shoulder of the body in a defined manner without the section of the securing mechanism that overlaps the retaining mechanism touching the retaining mechanism, even when manufacturing tolerances of the individual components occur. In this way, reliable manufacturing of the spark plug can be ensured.       

     In an embodiment, the securing mechanism can have a securing sleeve that is placed on the back end of the body. The securing sleeve can, in particular, be pushed or screwed onto the back end of the body. For attachment of the securing sleeve, it can be welded to the body. The body can be made in the shape of a circular cylinder at its back end for the securing sleeve to be pushed on. The ring-shaped section of the securing mechanism can be composed of a narrowing, particularly extending continuously in a ring shape, of the inner contour of the securing sleeve. The end of the securing sleeve opposite the narrowing can be welded to the external shoulder of the body. By means of the combination of the external shoulder and the securing sleeve attached thereto, it is possible to maintain an outer contour of the spark plug corresponding to established standards that can continue to be used in standardized cylinder heads. 
     In another embodiment, provision can be made such that the spark plug contains a screw-in mechanism and an external thread located at the front end of the body for screwing the spark plug into an internal combustion engine. The screw-in mechanism is arranged on the securing sleeve and can be formed, in particular, by wrench engagement surfaces, as, for example, a hexagon. The outer contour of the body at the back end and the matching inner contour of the securing sleeve can have a cross-section differing from the circular shape, in particular, grooves extending in the longitudinal direction or longitudinal teeth. In this way, the torque transmission from the screw-in mechanism located on the securing sleeve to the body can be improved. The body can have a shrinkage zone for electro-upsetting located between the external thread and the retaining mechanism. The shrinkage zone can in particular be located between the retaining mechanism and the backward-facing external shoulder for attachment of the securing device. The securing sleeve can cover the shrinkage zone and can be joined, in particular welded, to the body between the shrinkage zone and the external thread. As a result of this design, the securing sleeve can also protect the shrinkage zone, where the cross-section of the body is reduced, along with the retaining mechanism. Protection from a material failure of the body and ejection of the insulator can be increased in this way. As a result, the shrinkage zone is no longer stressed by the tightening torque when the spark plug is screwed in. This can avoid undesirable damage to the shrinkage zone that can cause leakage. 
     The body can have, between the external thread and the attachment region of the securing mechanism, an external shoulder pointing towards the front end of the body that limits the process of screwing the spark plug into the internal combustion engine and seals the spark plug with respect to the internal combustion engine. The spark plug can include a seal ring resting against the shoulder. A heat removal from the spark plug to the internal combustion engine and a cooling circuit located therein is accomplished through the external thread and the external shoulder of the body. 
     The securing mechanism can be designed as a single continuous piece, at least from its section overlapping the retaining mechanism, in particular its ring-shaped section, to its point of attachment to the body. In particular, the securing mechanism can be designed completely as a single piece. The securing mechanism, particularly the securing sleeve, can be made of a material with high heat resistance, particularly a nickel-based alloy. The nickel-based alloys with material No. 2.4816 (also known by the brand name INCONEL 600) and with material No. 2.4851 (also known by the brand name INCONEL 601) are especially suitable. Such a design of the securing mechanism can improve its stability and safety. 
    
    
     
       DRAWINGS 
       Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
         FIG. 1  a longitudinal half-section of a spark plug according to one embodiment. 
     
    
    
     DESCRIPTION 
     Partially shown in  FIG. 1  is a spark plug  1  that contains a metal body  2 . The body  2  has a front end  3  and a back end  4 , as well as a longitudinal direction  5  and a passage  6  extending in the longitudinal direction  5 . Welded to the face of the body  2  at the front end  3  is a ground electrode  7 . Located in the passage  6  is an insulator  8  which contains a center electrode  9 , an igniter  10  and a fused glass element  11 . The center electrode  9  projects out of the insulator  8  in the region of the front end  3  and, together with the ground electrode  7 , forms a spark gap  13 . The insulator  8  has a passage  12 , in which the center electrode  9 , igniter  10  and fused glass element  11  are located. At its front end  3 , the body  2  has an external thread  14  for screwing the spark plug  1  into an internal combustion engine, which thread is adjacent to an external shoulder  15 , facing the front end  3 , that a seal ring  16  rests against. 
     In the region of its front end  3 , the body  2  has a seal seat  17  that is in the form of an internal shoulder and is located in the passage  6 ; the insulator  8  rests against this shoulder with a seal ring  18  interposed. In the region of its back end  4 , the body  2  has a retaining mechanism  20  that is formed by the inwardly flanged back edge of the body  2  and rests against a shoulder  19  of the insulator  8 . The body  2  additionally has a shrinkage zone  25 , which represents a zone of reduced cross-section. The body  2  is designed as a single piece in a section that includes at least the seal seat  17 , the retaining mechanism  20  and the shrinkage zone  25 . 
     Fastened to the back end  4  is a securing mechanism  30  in the form of a securing sleeve  31  which secures the retaining mechanism  20  in a positive manner, and, for this purpose, overlaps the side of the retaining mechanism  20  facing away from the front end  3 . The insulator  8  projects beyond the side of the securing mechanism  30  facing away from the front end  3 . The securing mechanism  30  contains a ring-shaped section  32  that is formed by a continuous ring-shaped narrowing of the inner contour of the securing sleeve  31  and that surrounds the insulator  8  in its region projecting from the back end  4 , forming a gap  40 . In the depiction in  FIG. 1 , the cylindrical gap  41  is so small that it is not continuously visible. The section  32  overlaps the retaining mechanism  20 , forming a gap  41 , and captures the insulator  8  at its shoulder  19  in the event that the retaining mechanism  20  can no longer retain the insulator  8  due to material failure. The securing mechanism  30  thus prevents the possibility that the insulator  8  can be driven out of the back end  4  of the body  2  by the high combustion pressure arising in the combustion chamber of the internal combustion engine in the event that the retaining mechanism  20  fails. 
     The securing sleeve  31  is pushed onto the back end  4  and is welded to the body  2  in the region between the external thread  14  and the shrinkage zone  25 . The weld seam is indicated by the reference symbol  33 , and is located between the shrinkage zone  25  and the external shoulder  15 . This ensures that the securing sleeve  31  covers the shrinkage zone  25  and that its reduced cross-section is likewise protected. The securing sleeve  31  contains a screw-in mechanism  34  in the form of an external hexagon for application of a tightening tool. The tightening torque is transmitted through the securing sleeve  31  and the weld seam  33 , past the reduced cross-section of the shrinkage zone  25 , to the body  2 . 
     When the spark plug  1  is manufactured, the back edge  20  of the body  2  has initially not yet been flanged, and the passage  6  does not yet have a narrowing at the back end  4 . The seal ring  18  and the insulator  8  are inserted into the passage  6 . Next, the edge  20  is flanged and forms the retaining mechanism for the insulator  8 . After that, the shrinkage zone  25  is heated by a current pulse flowing through the body  2  while axial force is applied between the front end  3  and the back end  4 . In this way, the material in the region of the shrinkage zone  25  is upset. The shrinkage zone  25  shrinks further during the subsequent cooling thereof so that an axial clamping of the insulator  8  in the spark plug body  2  occurs, which is indicated by the preloading force Fv and presses the insulator  8  against the seal seat  17 , so that the passage  6  is sealed against inflow and passage through it of combustion gases from the combustion chamber of the internal combustion engine. Next, the securing mechanism  30  is placed on the back end  4  of the body  2  and is joined thereto by the weld seam  33 . The weld seam  33  extends along the entire circumference of the body  2  and the securing sleeve  31 . 
     The body  2  has an external shoulder  45  that faces toward the back end  4  and that the securing sleeve  31  contacts when it is set in place. When the securing sleeve  31  contacts the external shoulder  45 , the gap  41  between the inner contour of the ring-shaped section  32  and the retaining mechanism  20  ensures that the securing mechanism  30  can be installed while ensuring a defined location without being statically overdetermined. In this way, it is possible to ensure an especially stable and secure weld seam  33  at an essentially gap-free line of contact between the bottom edge of the securing sleeve  31  and the external shoulder  45 . A stable weld seam  33  without interruptions or air inclusions is important so that the securing sleeve  31  can actually perform its safety function. 
     It is to be understood that the foregoing is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims. 
     As used in this specification and claims, the terms “for example,” “e.g.,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  spark plug 
           2  body 
           3  front end 
           4  back end 
           5  longitudinal direction 
           6  passage 
           7  ground electrode 
           8  insulator 
           9  center electrode 
           10  igniter 
           11  fused glass element 
           12  passage 
           13  spark gap 
           14  external thread 
           15  external shoulder 
           16  seal ring 
           17  seal seat 
           18  seal ring 
           19  shoulder 
           20  retaining mechanism 
           25  shrinkage zone 
           30  securing mechanism 
           31  securing sleeve 
           32  ring-shaped section 
           33  weld seam 
           34  screw-in mechanism 
           40  gap 
           41  gap 
           45  external shoulder 
         Fv preloading force