Patent Publication Number: US-2023163574-A1

Title: Spark plug for internal combustion engine and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application No. PCT/JP2021/023293 filed on Jun. 21, 2021 which designated the U.S. and claims priority to Japanese Patent Application No. 2020-125644 filed Jul. 22, 2020, the contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a spark plug for an internal combustion engine and a method of manufacturing the same. 
     Related Art 
     For example, a spark plug is known which is configured to form a swirl flow, which is an airflow in the circumferential direction, in an auxiliary combustion chamber provided to a tip of the spark plug. 
     SUMMARY 
     As an aspect of the present disclosure, a spark plug for an internal combustion engine is provided. The spark plug includes: a cylindrical insulator; a center electrode that is held on an inner periphery side of the insulator and projects from the insulator toward a tip side of the insulator; a cylindrical housing that holds the insulator on an inner periphery of the housing; and a plug cover that is provided to a tip portion of the housing. On the tip side of the insulator, an auxiliary combustion chamber is formed which is surrounded by at least the plug cover, the plug cover is provided with nozzle holes that communicate between the auxiliary combustion chamber and the outside of the auxiliary combustion chamber. A central axis of the nozzle hole is inclined with respect to a plug radial direction when viewed in a plug axial direction. At least a part around an outer opening of the nozzle hole is provided with a concave portion that is adjacent to the outer opening, the concave portion being recessed from the outside to the inside of the plug cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG.  1    is a cross-sectional view of a tip portion of a spark plug and is a cross-sectional view taken across a line I-I of  FIG.  3   , according to a first embodiment; 
         FIG.  2    is a cross-sectional view taken across a line II-II of  FIG.  1   ; 
         FIG.  3    is a plan view viewed in the direction of an arrow III of  FIG.  1   ; 
         FIG.  4    is a plan view of the spark plug viewed from a tip side thereof for describing directions in which nozzle holes open, according to the first embodiment; 
         FIG.  5    is a cross-sectional view of the tip portion of the spark plug for describing an angle between a central axis of the nozzle hole and a central axis of the plug, according to the first embodiment; 
         FIG.  6    is an enlarged plan view of the periphery of a concave portion viewed in a direction parallel to a central axis of the concave portion, according to the first embodiment; 
         FIG.  7    is an enlarged cross-sectional view of the periphery of the nozzle hole for describing a direction in which the nozzle hole opens, according to the first embodiment; 
         FIG.  8    is a cross-sectional view of a plug cover before the concave portions are formed, according to the first embodiment; 
         FIG.  9    is a cross-sectional view of the plug cover after the concave portions are formed, according to the first embodiment; 
         FIG.  10    is an enlarged plan view of the periphery of the concave portion viewed in a direction parallel to the central axis of the concave portion, according to a second embodiment; 
         FIG.  11    is a cross-sectional view of the tip portion of the spark plug orthogonal to the central axis of the plug, according to a third embodiment; 
         FIG.  12    is a plan view viewed in the direction of an arrow XII of  FIG.  11   ; 
         FIG.  13    is a plan view of the tip portion of the spark plug, according to a fourth embodiment; and 
         FIG.  14    is a plan view viewed in the direction of an arrow XIV of  FIG.  13   . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For example, as disclosed in DE102018211009, a spark plug is known which is configured to form a swirl flow, which is an airflow in the circumferential direction, in an auxiliary combustion chamber provided to a tip of the spark plug. A plug cover forming the auxiliary combustion chamber is provided with a plurality of nozzle holes, which have a central axis inclined with respect to the radial direction of the spark plug when viewed in the direction parallel to a central axis of the spark plug. Gas is caused to flow from a main combustion chamber of an internal combustion engine to the auxiliary combustion chamber through the nozzle holes to form a swirl flow in the auxiliary combustion chamber. 
     In the spark plug described in DE102018211009, the nozzle holes are formed in a portion having a convex curved surface, which is an outer surface of the plug cover projecting outward. Hence, the nozzle holes are difficult to form in the plug cover by cutting work with a drill, press work with a punch, or the like. Thus, when the nozzle holes are formed, laser beam machining, electrical discharge machining, or the like may be required. In this case, productivity lowers easily due to increase in machining effort. 
     The present disclosure provides a spark plug and a method of manufacturing the same that can increase productivity. 
     First Embodiment 
     An embodiment of a spark plug for an internal combustion engine and a method of manufacturing the same will be described with reference to  FIG.  1    to  FIG.  9   . 
     As illustrated in  FIG.  1   , a spark plug  1  for an internal combustion engine of the present embodiment has a cylindrical insulator  3 , a center electrode  4 , a cylindrical housing  2 , and a plug cover  5 . The center electrode  4  is held on the inner periphery side of the insulator  3  and projects from the insulator  3  toward the tip side thereof. The housing  2  holds the insulator  3  on the inner periphery side thereof. The plug cover  5  is provided to a tip portion of the housing  2 . On the tip side of the insulator  3 , an auxiliary combustion chamber  50  is formed which is surrounded by at least the plug cover  5 . 
     The plug cover  5  is provided with nozzle holes  51  that communicate between the auxiliary combustion chamber  50  and the outside of the auxiliary combustion chamber  50 . As illustrated in  FIG.  2    and  FIG.  3   , a central axis C 2  of the nozzle hole  51  is inclined with respect to a plug radial direction when viewed in a plug axial direction Z. As illustrated in  FIG.  1    to  FIG.  3   , at least a part around an outer opening  511  of the nozzle hole  51  is provided with a concave portion  52  that is adjacent to the outer opening  511 . The concave portion  52  is recessed from the outside to the inside of the plug cover  5 . 
     The spark plug  1  of the present embodiment can be used as, for example, an ignition means of an internal combustion engine for a vehicle such as an automobile. Herein, a plug central axis C 1  means the central axis C 1  of the spark plug  1 . The direction parallel to the plug central axis C 1  is appropriately referred to as a plug axial direction or a Z direction. The side in the Z direction that is connected to an ignition coil (not shown) is referred to as a base end side, and the side that is located in a main combustion chamber (not shown) is referred to as a tip side. The plug radial direction means a radial direction of a circle centering on the plug central axis C 1  on a plane orthogonal to the plug central axis C 1 . 
     As illustrated in  FIG.  1    and  FIG.  3   , the center electrode  4  has a substantially columnar shape as a whole. The insulator  3  holding the center electrode  4  is held by the housing  2  having a substantially cylindrical shape. 
     An earth electrode  6  is joined to the housing  2  so that a discharge gap G is formed between the earth electrode  6  and the center electrode  4 . The earth electrode  6  is fixed to the housing  2  so that the longitudinal direction thereof is along the plug radial direction. The earth electrode  6  projects from an inner periphery  21  of the housing  2  toward the center electrode  4 . The earth electrode  6  and an outer periphery of the center electrode  4  face each other in the plug radial direction. The discharge gap G is formed between the earth electrode  6  and the outer periphery of the center electrode  4 . 
     The tip portion of the housing  2  is provided with the plug cover  5 . In the present embodiment, as illustrated in  FIG.  1   , the plug cover  5  has a bottom wall portion  54 , a peripheral wall portion  55 , and a corner portion  56 . The bottom wall portion  54  covers the tip side of the auxiliary combustion chamber  50 . The peripheral wall portion  55  has a substantially cylindrical shape covering the outer periphery of the auxiliary combustion chamber  50 . The corner portion  56  connects the outer periphery of the bottom wall portion  54  and the tip of the peripheral wall portion  55  in a curved surface shape. In the present embodiment, the plug cover  5  is formed from, for example, iron, nickel, an alloy of iron or nickel, stainless steel, or the like. 
     In the present embodiment, as illustrated in  FIG.  1   , the nozzle holes  51  are formed in the corner portion  56  of the plug cover  5 . The nozzle holes  51  are formed in a portion having a convex curved surface, which is an outer surface  53  of the plug cover  5  projecting outward. When the spark plug  1  is installed in an internal combustion engine (not shown), the outer surface  53  of the plug cover  5  faces the main combustion chamber. That is, when the spark plug  1  is installed in the internal combustion engine, the outer opening  511  of the nozzle hole  51  faces the main combustion chamber. 
     In the corner portion  56  of the plug cover  5 , a plurality of nozzle holes  51  are formed. In the present embodiment, as illustrated in  FIG.  2    and  FIG.  3   , four nozzle holes  51  are formed in the corner portion  56 . As illustrated in  FIG.  3   , the plurality of nozzle holes  51  are arranged in a plug circumferential direction at regular intervals when viewed in the Z direction. The two nozzle holes  51  facing each other in the plug circumferential direction are formed so as to be approximately point symmetrical about the plug central axis C 1  when viewed in the Z direction. The number of the nozzle holes  51  may be three or less. The number of the nozzle holes  51  may be five or more. The plug circumferential direction means a circumferential direction about the plug central axis C 1  on the plane orthogonal to the plug central axis C 1 . 
     As illustrated in  FIG.  4   , the point at which the outer opening  511  of the nozzle hole  51  and the central axis C 2  of the nozzle hole  51  intersect with each other is defined as a point P 2 . When viewed in the Z direction, a straight line passing through the point P 2  and the plug central axis C 1  is defined as a straight line L 1 . That is, the straight line L 1  extends in the plug radial direction. In the present embodiment, when viewed in the Z direction, each of the nozzle holes  51  is formed so that an angle θ 1 , which is a smaller angle between the straight line L 1  and the central axis C 2  of the nozzle hole  51 , is, for example, 20° or more. When viewed in the Z direction, in the nozzle holes  51 , the central axis C 2  is displaced from the straight line L 1  in the same rotational direction by the approximately same angle about the point P 2 . That is, the nozzle holes  51  are formed so that the angles θ 1  are approximately the same when viewed in the Z direction. 
     As described above, when viewed in the Z direction, the central axis C 2  of the nozzle hole  51  is inclined with respect to the plug radial direction. In other words, when viewed in the Z direction, the direction in which the nozzle hole  51  opens is inclined with respect to the plug radial direction. 
     As described in  FIG.  1   , each of the nozzle holes  51  opens with inclination with respect to the Z direction so that the nozzle hole  51  extends outward with respect to the plug radial direction as the nozzle hole  51  extends toward the tip side. 
     The nozzle hole  51  is formed so that when gas externally flows into the auxiliary combustion chamber  50  through the nozzle holes  51 , a swirl flow is generated in the auxiliary combustion chamber  50 . Herein, the swirl flow means an airflow swirling about the plug central axis C 1 . 
     That is, when the spark plug  1  is mounted to the internal combustion engine, in a compression stroke, gas flows from the main combustion chamber into the auxiliary combustion chamber  50  through the nozzle holes  51 . In this case, when the spark plug  1  is viewed from the tip side thereof, a swirl flow in a counterclockwise direction is formed in the auxiliary combustion chamber  50 . In an expansion stroke, since the main combustion chamber becomes negative pressure with respect to the auxiliary combustion chamber  50 , gas flows from the auxiliary combustion chamber  50  to the main combustion chamber through the nozzle holes  51 . In this case, when the spark plug  1  is viewed from the tip side thereof, a swirl flow in a clockwise direction is formed in the auxiliary combustion chamber  50 . 
     As illustrated in  FIG.  1    to  FIG.  3   , in the corner portion  56  of the plug cover  5 , the concave portions  52  are formed. As illustrated in  FIG.  2    and  FIG.  3   , four concave portions  52  are formed in the corner portion  56 . As illustrated in  FIG.  3   , the concave portions  52  are arranged in the plug circumferential direction at regular intervals. In each of the concave portions  52 , the nozzle hole  51  opens on a concave portion forming face  521  on which the concave portion  52  is formed. 
     In the present embodiment, the concave portion  52  has a substantially conical shape. As illustrated in  FIG.  5   , a central axis C 3  of the concave portion  52  is inclined with respect to the Z direction. As illustrated in  FIG.  3    and  FIG.  5   , the central axis C 3  of the concave portion  52  passes through the plug central axis C 1 . The concave portion  52  may have, instead of the substantially conical shape, a substantially quadrangular pyramid shape as described in the second embodiment later. When viewed in a direction parallel to the central axis C 3  of the concave portion  52 , the concave portion  52  may be formed so as to have a polygonal shape such as a substantially semicircular shape, a triangular shape, or the like. 
     As illustrated in  FIG.  1    to  FIG.  3   , the outer opening  511  of the nozzle hole  51  is formed in the concave portion forming face  521  on which the concave portion  52  is formed. As illustrated in  FIG.  6   , viewed in a direction parallel to the central axis C 3  of the concave portion  52 , the center of the outer opening  511  is displaced from the center P 1  of the concave portion  52 . The outer opening  511  is formed at a position separated from the center P 1  of the concave portion  52 . The concave portion forming face  521  is formed so as to surround the outer opening  511 . 
     As illustrated in  FIG.  3   , the outer opening  511  opens at a position deviated from the center P 1  of the concave portion  52  in one of the plug circumferential directions. 
     In the present embodiment, the central axis C 2  of the nozzle hole  51  and the central axis C 3  of the concave portion  52 , in which the nozzle hole  51  is formed, are formed on the substantially same plane. Hence, as illustrated in  FIG.  5   , when the spark plug  1  is viewed in a predetermined plug radial direction, the central axis C 2  and the central axis C 3  can be aligned. In this case, a smaller angle θ 2  between the central axis C 2  and the plug central axis C 1  is approximately the same as a smaller angle θ 3  between the central axis C 3  and the plug central axis C 1 . That is, the smaller angle between the plane, which includes the central axis C 2  and the central axis C 3 , and the plug central axis C 1  is θ 2  or θ 3 . The angles θ 2  and θ 3  are, for example, 45° to 75°. 
     As illustrated in  FIG.  7   , on a cross section including the central axis C 2  and the central axis C 3 , the nozzle hole  51  opens so that the contour of the outer opening  511  of the nozzle hole  51  formed in the concave portion forming face  521  is approximately orthogonal to central axis C 2  of the nozzle hole  51 . 
     Next, a method of manufacturing the spark plug  1  of the present embodiment will be described. 
     In the method of manufacturing a spark plug for an internal combustion engine, when the nozzle holes  51  are formed in the plug cover  5 , the concave portions  52  are formed in the plug cover  5 . After the concave portion  52  is formed, the nozzle hole  51  is produced in at least a part of the concave portion forming face  521  on which the concave portion  52  is formed. 
     In the present embodiment, the nozzle hole  51  is produced in part of the concave portion forming face  521 . The nozzle hole  51  may be produced in the whole concave portion forming face  521 . 
     In the present embodiment, the concave portion  52  is formed by using a drill. Performing cutting work with a drill for the unprocessed plug cover  5  as illustrated in  FIG.  8    forms the concave portions  52  in the plug cover  5  as illustrated in  FIG.  9   . Specifically, cutting work with a drill is performed along a normal direction of the outer surface  53  of the plug cover  5 . Hence, the concave portions  52  having a substantially conical shape are formed. As described in second and third embodiments later, the concave portions  52  can also be formed by press work with a punch. 
     Next, the nozzle hole  51  is produced in the concave portion forming face  521 , on which the concave portion  52  is formed, from the outside toward the auxiliary combustion chamber  50 . In the present embodiment, the nozzle hole  51  is formed by cutting work with a drill. Part of the concave portion forming face  521  of the plug cover  5  is subjected to cutting work with a drill along the normal direction of the part of the concave portion forming face  521 . Hence, as illustrated in  FIG.  1    to  FIG.  3    and  FIG.  6   , the nozzle hole  51  can be formed so that the concave portion  52  is adjacent to the outer opening  511 . 
     Next, effects of the present embodiment will be described. 
     In the spark plug  1  for an internal combustion engine of the present embodiment, the concave portion  52  is formed in at least a part around the outer opening  511  of the nozzle hole  51  so as to be adjacent to the outer opening  511 . Hence, when viewed in the plug axial direction Z, even if the central axis C 2  of the nozzle hole  51  is inclined with respect to the plug radial direction, the plug cover  5  can be processed easily. As a result, productivity in manufacturing the spark plug  1  can be increased. 
     In the method of manufacturing the spark plug  1  for an internal combustion engine according to the present embodiment, after the concave portion  52  is formed in the plug cover  5 , the nozzle hole  51  is produced in at least a part of the concave portion forming face  521 . Hence, when viewed in the plug axial direction Z, even if the central axis C 2  of the nozzle hole  51  is inclined with respect to the plug radial direction, the plug cover  5  can be processed easily. As a result, the spark plug  1  can be manufactured effectively. 
     That is, if processing of the plug cover  5  is attempted without forming the concave portion  52 , the nozzle hole  51  is difficult to form in a portion having a convex curved surface, which is the outer surface  53  of the plug cover  5  projecting outward, by cutting work or the like. That is, even if producing the nozzle hole  51  is attempted in the direction inclined with respect to the normal direction of the outer surface  53 , since a tip of a drill or a punch slips, the nozzle hole  51  is difficult to form. In contrast, the spark plug  1  of the present embodiment can be manufactured by producing the nozzle hole  51  in the concave portion forming face  521  after the concave portion  52  is formed in the plug cover  5 . That is, providing the concave portion  52  can form a surface approximately orthogonal to central axis C 2  of the nozzle hole  51  to be formed in part of the outer surface  53  of the plug cover  5 . In addition, the nozzle hole  51  can be produced in the surface, that is, on the part of the concave portion forming face  521  along the normal direction thereof. Hence, the nozzle hole  51  can be formed easily even if the central axis C 2  of the nozzle hole  51  is inclined with respect to the plug radial direction when viewed in the Z direction. As a result, productivity in manufacturing the spark plug  1  can be increased. 
     In addition, changing the shape of the drill or the like used for forming the concave portion  52  can form the concave portion  52  in advance depending on the inclination of the nozzle hole  51  to be formed. That is, a desired direction in which the nozzle hole  51  opens and the normal direction of part of the concave portion forming face  521  can be closed to each other. Hence, the nozzle hole  51  having a desired inclination can be easily produced in the plug cover  5 . 
     The outer opening  511  opens at a position deviated from the center P 1  of the concave portion  52  in one of the plug circumferential directions. Hence, when viewed in the Z direction, even if the central axis C 2  of the nozzle hole  51  is inclined with respect to the plug radial direction, the plug cover  5  can be formed easily. As a result, the spark plug  1  can be manufactured effectively. 
     That is, the concave portion  52  can be easily formed by cutting work with a drill along the normal direction of the outer surface  53  of the plug cover  5 . Then, the nozzle hole  51  is produced in the concave portion forming face  521  at the position, which is deviated from the center P 1  in one of the plug circumferential directions, along the normal direction of the part of the concave portion forming face  521 . Hence, the nozzle hole  51  having the central axis C 2  inclined with respect to the plug radial direction when viewed in the Z direction can be easily formed. As a result, the spark plug  1  can be manufactured effectively. 
     In the present embodiment, the nozzle holes  51  and the concave portions  52  are formed so that the angle θ 2  and the angle θ 3  are the same. Hence, before the nozzle hole  51  is formed, the concave portion forming face  521  having a normal line along the central axis C 2  of the nozzle hole  51  to be formed can be formed easily. As a result, the nozzle hole  51  can be reliably formed at a desired position. 
     In the present embodiment, the concave portion  52  has a substantially conical shape. Hence, the nozzle hole  51  can be formed easily by cutting work with a drill. Thus, using a multiaxial drill processing machine can easily perform forming the concave portion  52  and forming the nozzle hole  51  consistently. As a result, the nozzle hole  51  can be produced effectively. 
     As described above, according to the present embodiment, the spark plug  1  and a method of manufacturing the same that can increase productivity can be provided. 
     Second Embodiment 
     In the present embodiment, as illustrated in  FIG.  10   , the shape of the concave portion  52  of the first embodiment is modified. 
     In the present embodiment, as illustrated in  FIG.  10   , the concave portion  52  has a substantially quadrangular pyramid shape. The concave portion  52  includes four flat concave portion forming faces  521 . Each of the four concave portion forming face  521  has a substantially triangular shape. 
     In the present embodiment, the concave portion  52  is formed by using a punch whose tip portion has a substantially quadrangular pyramid shape, and subjecting press work to the plug cover  5 . That is, the punch is pressed along the normal of the plug cover  5 . Hence, part of the plug cover  5  pressed by the punch is plastically deformed, whereby the concave portion  52  is formed. 
     After the concave portion  52  is produced, the nozzle hole  51  is produced by a drill along the normal direction of one concave portion forming face  521 . That is, the nozzle hole  51  is produced by a drill in one concave portion forming face  521  having a substantially triangular shape along the direction orthogonal to the concave portion forming face  521 . The nozzle hole  51  may be formed by punching out part of the plug cover  5  by press work with a punch. 
     Other configurations are similar to those of the first embodiment. In the second and later embodiments, the same reference signs as those used in the aforementioned embodiments indicate elements similar to those in the aforementioned embodiments unless otherwise indicated. 
     In the present embodiment, the concave portion  52  is formed of the flat concave portion forming face  521 . Hence, the nozzle hole  51  can be easily produced in the concave portion forming face  521  along the normal direction of the concave portion forming face  521 . As a result, the nozzle hole  51  can be produced further effectively. 
     The present embodiment provides other effects similar to those of the first embodiment. 
     Third Embodiment 
     In the present embodiment, as illustrated in  FIG.  11    and  FIG.  12   , the shape of the concave portion  52  of the second embodiment is modified. 
     In the present embodiment, as illustrated in  FIG.  12   , when viewed in the direction parallel to the central axis C 2  of the nozzle hole  51 , the concave portion  52  has a substantially square shape. As illustrated in  FIG.  11    and  FIG.  12   , the concave portion  52  has the flat concave portion forming face  521 . 
     In the present embodiment, the concave portion  52  is formed by using a punch whose tip portion has a substantially quadrangular pyramid shape, and subjecting press work to the plug cover  5 . After the concave portion  52  is formed, the nozzle hole  51  is produced by a drill in the direction orthogonal to the flat concave portion forming face  521 . 
     The present embodiment provides other configurations and effects similar to those of the second embodiment. 
     Fourth Embodiment 
     In the present embodiment, as illustrated in  FIG.  13    and  FIG.  14   , the position at which the concave portion  52  of the plug cover  5  is formed in the first embodiment is modified. 
     In the present embodiment, as illustrated in  FIG.  13   , the concave portion  52  is formed in the peripheral wall portion  55  of the plug cover  5 . As illustrated in  FIG.  13    and  FIG.  14   , the concave portion  52  is formed so that the central axis C 3  of the concave portion  52  is along the plug radial direction. 
     That is, the concave portion  52  is formed in the peripheral wall portion  55  of the plug cover  5  by performing cutting work in the plug radial direction with a drill. Then, after the concave portion  52  is formed, the nozzle hole  51  is produced in part of the concave portion forming face  521  along the normal direction of the part of the concave portion forming face  521 . 
     The present embodiment provides other configurations and effects similar to those of the first embodiment. 
     The present disclosure is not limited to the above-described embodiments and can be applied to various embodiments within a scope not deviating from the gist of the present disclosure. 
     The present disclosure has so far been described based on some embodiments. However, the present disclosure should not be construed as being limited to these embodiments or the structures. The present disclosure encompasses various modifications, or modifications within the range of equivalence. In addition, various combinations and modes, as well as other combinations and modes, including those which include one or more additional elements, or those which include fewer elements should be construed as being within the scope and spirit of the present disclosure. 
     As an aspect of the present disclosure, a spark plug ( 1 ) for an internal combustion engine is provided. The spark plug includes: a cylindrical insulator ( 3 ); a center electrode ( 4 ) that is held on an inner periphery side of the insulator and projects from the insulator toward a tip side of the insulator; a cylindrical housing ( 2 ) that holds the insulator on an inner periphery of the housing; and a plug cover ( 5 ) that is provided to a tip portion of the housing. On the tip side of the insulator, an auxiliary combustion chamber ( 50 ) is formed which is surrounded by at least the plug cover, the plug cover is provided with nozzle holes ( 51 ) that communicate between the auxiliary combustion chamber and the outside of the auxiliary combustion chamber. A central axis (C 2 ) of the nozzle hole is inclined with respect to a plug radial direction when viewed in a plug axial direction (Z). At least a part around an outer opening ( 511 ) of the nozzle hole is provided with a concave portion ( 52 ) that is adjacent to the outer opening, the concave portion being recessed from the outside to the inside of the plug cover. 
     As another aspect of the present disclosure, a method of manufacturing a spark plug for an internal combustion engine is provided. The spark plug has a cylindrical insulator ( 3 ), a center electrode ( 4 ) that is held on an inner periphery side of the insulator and projects from the insulator toward a tip side of the insulator, a cylindrical housing ( 2 ) that holds the insulator on an inner periphery of the housing, and a plug cover ( 5 ) that is provided to a tip portion of the housing. The method includes forming, on the tip side of the insulator, an auxiliary combustion chamber ( 50 ) that is surrounded by at least the plug cover, and forming, in the plug cover, nozzle holes ( 51 ) that communicate between the auxiliary combustion chamber and the outside of the auxiliary combustion chamber. A central axis (C 2 ) of the nozzle hole is inclined with respect to a plug radial direction when viewed in a plug axial direction (Z). When the nozzle holes are formed in the plug cover, after a concave portion ( 52 ) that is recessed from the outside to the inside of the plug cover is formed in the plug cover, the nozzle hole is produced in at least a part of a concave portion forming face ( 521 ) on which the concave portion is formed. 
     In the spark plug for an internal combustion engine, the concave portion is formed in at least a part around the outer opening of the nozzle hole so as to be adjacent to the outer opening. Hence, when viewed in the plug axial direction, even if the central axis of the nozzle hole is inclined with respect to the plug radial direction, the plug cover can be processed easily. As a result, productivity in manufacturing the spark plug can be increased. 
     In the method of manufacturing the spark plug for an internal combustion engine, after the concave portion is formed in the plug cover, the nozzle hole is produced in at least a part of the concave portion forming face. Hence, when viewed in the plug axial direction, even if the central axis of the nozzle hole is inclined with respect to the plug radial direction, the plug cover can be processed easily. As a result, the spark plug can be manufactured effectively. 
     As described above, a spark plug and a method of manufacturing the same that can increase productivity can be provided.