JP4182078B2 - Glow plug manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a glow plug used for promoting start-up of a diesel engine.

  One such glow plug is shown in FIG. 6 (Patent Documents 1 and 2). The glow plug 1 has a heat generating tube (hereinafter also simply referred to as a tube) 3 for a heater (a heat generating portion of the glow plug) disposed inside a cylindrical metal fitting body (hereinafter also simply referred to as a main body) 2. The structure fixed in the state protruded from the front-end | tip (illustration lower end) 2a of No.1 is shown. In addition, the metal fitting body 2 includes a terminal shaft 4 that is coaxially insulated from the metal fitting body 2 and is fixed to a portion near the rear end 3d in the heat generating tube 3. The terminal shaft 4 is fixed by tightening a nut 17 to a screw 4c formed at a position near the rear end through an O-ring packing 18 and an insulating ring 16 at the rear end 2d of the main body 2.

  The heat generating tube 3 constituting the glow plug 1 is made of Inconel or stainless steel, has a total length (from 3a to 3d shown in FIG. 1) of 20 to 80 mm, and an outer diameter of 3 to 6 mm (thickness 0.5 mm). ) Is formed in a bottomed cylindrical shape formed in a hemispherical shape with the tip 3a being convex. Further, a spiral heat generating coil (or heat generating coil and control coil) member 5 is provided in the interior from the front end to the rear end, and the front end of the coil member (hereinafter also simply referred to as a coil) 5 is provided. 5a is joined to the front end of the heat generating tube 3 by welding, and the rear end is connected to the terminal shaft 4 for energization inserted and fixed in the rear end 3d of the heat generating tube 3. The heat generating coil 5 and the terminal shaft 4 are electrically insulated from the inner surface of the heat generating tube 3 by an insulating material (magnesia powder or the like) (not shown) filled in the heat generating tube 3. A rubber tube (not shown) is inserted between the inner peripheral surface near the rear end 3d of the heat generating tube 3 and the outer peripheral surface of the terminal shaft 4, and the heat generating tube 3 is sealed while ensuring insulation therebetween. The terminal shaft 4 is fixed. The exothermic tube 3 shown in FIG. 6 has a cylindrical shape with a different diameter having a concentric middle portion and a slightly thick large-diameter portion 3b, but there is also a tube having the same diameter (straight) as a whole.

As shown in FIG. 7, the glow plug 1 having such a configuration has a terminal shaft 4 fixed to a portion near the heating tube 3 and the rear end 3d of the heater inside the cylindrical metal fitting body 2. Assembling or manufacturing is performed by press-fitting a predetermined amount of an assembly (part) that forms a heat generating portion including the heat from the rear end 3d of the heat generating tube 3 (Patent Documents 1 and 2). Specifically, after the terminal shaft 4 is inserted inside the metal fitting body 3, the metal fitting body 2 and the terminal shaft 4 are made coaxial (concentric), and the heat generating tube 3 is directed to the inside of the metal fitting body 2 with an arrow. From the tip 3a in the direction, the tip support portion 101 in the press-fitting device (press device) applies force F and pushes it in the direction of the axis G to press-fit.
JP 2003-51371 A JP 2003-17230 A

  However, in the glow plug 1 manufactured by the above-described conventional manufacturing method, as shown in FIG. 8, the adjacent spiral portions L1, L2, L3... May cause a problem such as causing contact S and changing its resistance value. As a result of investigating and examining the cause, the present inventors have come to know the following. This is because, when examining the problematic sample among the glow plugs manufactured by the above-described conventional manufacturing method, as shown in an exaggerated manner in FIG. Many of them were crushed (deformed).

  This is because, when the heat generating tube 3 is press-fitted into the metal fitting body (fitting main body forming a glow plug) 2, the tip 3a of the heat generating tube 3 is pushed in the direction of the axis G to be press-fitted into the metal fitting main body 2. The tip 3a has a convex hemispherical surface. On the other hand, since the tip support portion 101 of the press-fitting device that supports and pushes the tip is flat, a load is locally applied to the top of the hemispherical surface that forms the tip 3a due to the load F during press-fitting. It is thought that crushing occurs due to the action. The load required for this press-fitting is generally 150 to 500 kgf although it depends on the specific structure and type of the glow plug and the set-up allowance in the press-fitting. As a countermeasure against the collapse, it is conceivable to reduce the press-fitting load by reducing the press-fitting allowance (press-fitting tightening allowance). Cannot be used due to performance degradation. Further, the increase in the thickness of the heat generating tube 3 cannot be adopted because it is contrary to the demands for reduction in size and weight and cost.

  Thus, as described above, the helical coil member 5 is arranged in the heat generating tube 3 from the front end to the rear end side. Since the helical pitch of the coil is small, the heat generating tube 3 When the tip 3a is crushed, the distance (pitch) between the adjacent spiral portions L1, L2,... In the coil 5, particularly in the portion near the tip, becomes small, or they come into contact with each other. For these reasons, the conventional manufacturing method described above has a risk of reducing the production yield of the glow plug and the reliability of the product. In addition, although the crushing of the tip is minute, it causes a poor appearance as well as a decrease in dimensional accuracy.

  In the manufacturing process of the metal glow plug, when the heat generating tube formed on the hemispherical surface having a convex tip is press-fitted into the metal fitting body while supporting the tip, the tip of the heat generating tube is crushed. It is an object of the present invention to prevent the adjacent spiral portions of the coil in the same heat generating tube from contacting each other.

In order to achieve the above object, the manufacturing method according to claim 1 is characterized in that a heat generating tube formed on a hemispherical surface having a convex tip is provided with a coil member from the inner tip toward the rear is provided from the rear end side. In a method of manufacturing a glow plug, which is press-fitted inside a cylindrical metal fitting body and fixed with a tip protruding from the tip of the metal fitting body,
Of the press-fitting device used for press-fitting the heat-generating tube inside the metal fitting body, the tip support part that supports the tip of the heat-fitting tube in press-fitting is a recess into which a hemispherical surface that is a convex of the tip of the heat-generating tube fits. A spherical surface having a radius of curvature smaller than the radius of curvature of the hemispherical surface that is convex of the tip of the heat generating tube, and the tip of the heat generating tube is supported by the spherical surface formed by the tip support portion. The heat generating tube is press-fitted into the metal fitting body.

Further, in the manufacturing method according to claim 2, the heat generating tube which is formed in a hemispherical surface having a convex tip and is provided with a coil member from the inner tip toward the rear is formed into a cylindrical body from the rear end side. In a method of manufacturing a glow plug that is press-fitted inside and fixed by protruding the tip from the tip of the metal fitting body,
Of the press-fitting devices used for press-fitting the heat generating tube inside the metal fitting body, a mortar in which a hemispherical surface that is a convex of the tip of the heat generating tube is fitted into a tip support portion that supports the tip of the heat generating tube in press fitting A tapered surface that is formed into a concave shape so that the tip of the heat generating tube is supported by the taper surface except for the top thereof, and the tip of the heat generating tube excluding the top is supported by the taper surface. The heat generating tube is press-fitted into the metal fitting body.

According to the production method of the present invention, the following remarkable effects can be obtained. That is, among the press-fitting devices used in the conventional press-fitting, the tip support part that supports the hemispheric surface that is the convex of the tip of the heat generating tube has a flat surface. The load is concentrated on a small area at the top of the hemispheric surface that is the convex of the tip, which causes the tip surface to be crushed or deformed. On the other hand, in the present invention, the tip support portion is a spherical surface that is a concave surface into which the hemispherical surface that is convex at the distal end of the heat generating tube is fitted, and the curvature radius of the spherical surface is set to be the same as that of the heat generating tube. It is formed in a spherical surface smaller than the radius of curvature of the hemispherical surface that is convex at the tip, and the spherical surface that forms the tip of the heat generating tube is supported by this spherical surface, and press-fitted in that state. For this reason, since the hemispheric surface formed by the convex at the tip of the heat generating tube can receive a load at the time of press-fitting on a wide surface, the load does not concentrate on the top portion but spreads over the whole. Therefore, the occurrence of crushing of the tip as in the prior art can be prevented, or even if it occurs, the deformation can be reduced. Thus, according to the present invention, among the coil members provided in the heat generating tube, it is possible to prevent the adjacent spiral portions spirally wound around the distal end portion from being compressed and brought into contact with each other.

  Embodiments of the present invention will be described in detail with reference to FIGS. 1 is a longitudinal sectional view and an enlarged view of a main part of a glow plug 1 to be manufactured. FIG. 2 is an explanatory view of a state in which the heat generating tube 3 is press-fitted into the metal fitting body 2 in the manufacture and a tip support part 101 of the press-fitting device. FIG. 3 is an enlarged cross-sectional view of the tip portion and the tip support portion 101 of the press-fitting device showing the press-fitted state of the heat generating tube 3 and after the press-fitting. In this embodiment, the glow plug 1 includes a cylindrical metal fitting body 2 extending in the axis G direction and a cylinder extending in the axis G direction with the tip 3a closed and fixed (fixed) to the tip 2a side of the metal fitting body 2. The heat generating tube 3 and the round shaft terminal shaft 4 are configured as follows.

  That is, the metal fitting body 2 has a cylindrical shape that extends substantially straight, and a heat generating tube formed in a cylindrical shape that forms a bottom with a hemispherical surface with a convex tip 3a at a portion closer to the inner tip 2a. 3 is fixed. However, in this embodiment, the heat generating tube 3 has a large diameter (large diameter portion 3b) at a portion slightly closer to the rear end 3d than the middle in the direction of the axis G, while the metal fitting body 2 at a portion corresponding to the large diameter portion 3b. Is formed into a small diameter (small diameter portion 2b), and the heat generating tube 3 is press-fitted into the inside of the metal fitting body 2 from the rear end 3d side through the large diameter portion 3b, as will be described later, The tip 3 a is fixed by protruding from the tip 2 a of the metal fitting body 2. The outer diameter of the large-diameter portion 3b before press-fitting is, for example, φ4.40 mm, the inner diameter of the small-diameter portion 2b is φ4.35 mm, and the design press-fitting allowance (tightening allowance) is 0.05 mm. Further, a heating coil 5 (or a heating coil and a control coil connected in series to the rear end thereof, hereinafter also referred to as a coil at the end) is disposed at the front end of the heating tube 3 so as to form a coil member toward the rear. The tip 5a is fixed to the tip in the heat generating tube 3 by welding.

  On the other hand, a round bar (shaft) -like terminal shaft 4 arranged concentrically (coaxially) is provided in the main body 2, and the front end side (lower side in FIG. 1) is the rear end of the heating tube 3. It is inserted in 3d and fixed via insulating rubber (not shown), and is connected to the rear end of the heating coil 5 in the heating tube 3. However, the terminal shaft 4 has a large diameter about half of its rear end (upper end in the figure), and has a predetermined length on the outer peripheral surface of the rear end (upper end in the figure) of the large diameter portion 4b. 4c is cut off and is a screw terminal for connecting a power cable (not shown) (not shown). Although not shown, the heat generating tube 3 is filled with an insulating material (magnesia powder or the like) to ensure insulation between the coil 5 and the inner surface of the heat generating tube 3, and the terminal shaft 4 and the metal fitting body. By energizing between the two, the heat generating coil is heated by resistance, and the heat generating tube 3 forms a heat generating portion of the glow plug 1. In manufacturing the heat generating part including the heat generating tube 3, the heat generating coil (a coil composed of two materials of the heat generating coil and the control coil) 5 and the terminal shaft 4 are inserted into the heat generating tube 3 depending on the specifications. After fixing as described above and filling the interior with insulating powder, swaging processing is performed to compress and compress the outer periphery of the heat generating tube itself, and an assembly of the heat generating portion integrally provided with the terminal shaft 4 is formed. Make it.

  In addition, a stepped hole 15 is formed in the opening on the rear end 2d side of the metal fitting body 2 forming the glow plug 1 of the present embodiment, and the diameter of the step is increased toward the rear end 2d. A portion near the rear end of the terminal shaft 4 is supported at the center of the metal fitting body 2 by a bush-like insulating ring 16 fitted in the attachment hole 15 and both are electrically insulated. Further, the terminal shaft 4 is fixed to the metal fitting body 2 via the insulating ring 16 by screwing and tightening the nut 17 to the screw 4 c of the terminal shaft 4. Note that an O-ring packing 18 is disposed on the tip end side of the insulating ring 16 and between the inner side of the stepped hole 15 and the terminal shaft 4, and a seal therebetween is ensured.

  A tool engaging portion 8 that forms the head of a hexagon bolt is provided on the outer periphery of the body portion of the rear end 2d of the metal fitting body 2, and a diesel engine (lower side in the drawing 1) is provided on the tip end side (lower side in the drawing). A male screw 9 for mounting to a not shown) is formed around the axis G. In the above description, the screw 4c is provided at the rear end of the terminal shaft 4 to form a screw terminal, and the power cable is directly connected to the power terminal. However, as the glow plug, for example, A terminal structure may be used in which a terminal electrode of another component is screwed and fixed to the screw 4c so as to cover the screw terminal of the terminal shaft 4, and the terminal electrode and the power cable are connected.

  Now, in such a glow plug 1, in the manufacturing process, the heat generating tube (in this embodiment, an assembly of the heat generating portion including it) 3 is connected from the rear end 3d side to the inside of the metal fitting body 2 from the front end 2a side. In the press-fitting device (press device) used for the press-fitting, as shown in FIG. 2, the tip support portion 101 that supports the tip 3a of the heat generating tube 3 has a convexity of the tip 3a. The concave spherical surface (hemispherical surface) 101a is formed with substantially the same radius (spherical R) so that the spherical hemispherical surface is fitted. Therefore, in the press-fitting, the tip 3a of the heat generating tube 3 is supported by the spherical surface 101a, and is pressed into the metal fitting body 2 under this state.

  That is, as shown in FIG. 2, the main body 2 is set vertically on a main body support jig (not shown) fixed to an upper presser plate of a press-fitting device (not shown) with its tip 2a facing down. On the other hand, in the present embodiment, of the assembly of the heat generating portion including the heat generating tube 3, the front end 3a of the heat generating tube 3 fixed on a lower presser board of a press-fitting device (not shown) with the front end 3a of the heat generating tube 3 facing down. The tip 3a is supported by the tip support portion 101 formed on the spherical surface 101a which is a concave to which the hemispherical surface which is the convex of the tip 3a is fitted. At this time, the main body 2 and the heat generating tube 3 are coaxially supported by a positioning or guide member (not shown) so that the terminal shaft 4 fixed to the heat generating tube 3 enters the main body 2 concentrically. Then, under this state, the press-fitting device is driven, for example, the lower presser plate is moved up by a predetermined stroke, and the heat generating tube 3 has a predetermined position in the small diameter portion 2b in the main body 2 with the large diameter portion 3b. The two are relatively pushed in the direction of the axis G with a predetermined load F until they are press-fitted into the shaft G. Thus, a semi-finished product in which the assembled body of the heat generating portion including the heat generating tube 3 is fixed in the main body 2 in the above-described glow plug 1 is obtained. Thereafter, as described above, the glow plug 1 shown in FIG. 1 can be obtained by fitting the O-ring 18 and the insulating ring 16 and screwing and tightening the nut 17 to the screw 4c of the terminal shaft 4.

The glow plug 1 manufactured as described above includes a tip support portion 101 that supports the tip 3a of the heat generating tube 3 in the press-fitting device in the press-fitting of the heat generating tube 3 into the main body 2 in the manufacturing process. A hemispherical surface which is a convex portion of the spherical surface 101a is formed on the concave spherical surface 101a. However, as shown in the enlarged view of FIG. 2, the radius of curvature R2 of the concave spherical surface (hemispherical surface) 101a is smaller than the radius of curvature R1 of the convex spherical surface of the tip 3a. For this reason, compared with the case of the manufacturing method using the conventional press-fitting device in which the tip support portion 101 of the press-fitting device is a flat surface, the load F is not concentrated only on the top of the tip 3a. That is, the load F is received distributed over substantially the entire hemispherical surface. As a result, as shown in FIG. 3, the tip 3a of the heat generating tube 3 press-fitted by such a manufacturing method is prevented from being crushed and deformed at the tip (lower end in the drawing) forming the top. Therefore, since the adjacent spiral portions L1, L2, L3,... Of the internal coil member 5 near the tip 5a are also maintained at an appropriate pitch P, they are brought into contact with each other and the resistance value fluctuates. It is possible to effectively prevent the occurrence of such problems.

In consideration of the processing accuracy of the spherical surface of the tip 3a of the heat generating tube 3, the radius of curvature of both of them is the spherical surface of the concave portion of the tip support portion 101 with respect to the radius of curvature (R1) of the hemispheric surface that is convex of the tip 3a. The curvature radius ( R2) of 101a is slightly smaller (1 to 20%) . In this way, at the beginning of the press-fitting, the load at the time of press-fitting at the outer peripheral annular portion of the top of the spherical surface (the lowest end of the spherical surface of the tip 3a in FIG. 3) of the tip 3a of the heat generating tube 3 Is received, and the spherical surface located inside thereof has a gap with the spherical surface 101 a of the support portion 101. Thereafter, as the press-fitting load increases, the surrounding annular portion is deformed slightly (reduced in diameter) so as to conform to the spherical surface 101a. Finally, the tip 3 a is deformed so as to be pressed over substantially the entire area (entirely) of the spherical surface 101 a that is the recess of the tip support portion 101. In this case, the top portion of the tip 3a of the heat generating tube 3 is basically not easily crushed. Therefore, the adjacent spiral portions L1, L2,. Contact can be particularly effectively prevented. In this case, the depth h of the spherical surface 101a formed as the concave portion of the distal end support portion 101 is smaller than the radius R1 of the hemispheric surface formed as the convex portion of the distal end 3a of the heat generating tube 3, specifically, the size of R1. On the other hand, it is preferably set to 80 to 99%. In addition, the hemispherical surface of the tip 3a of the heat generating tube 3 and the spherical surface 101a of the tip support portion 101 mean those recognized as a hemispherical surface or a spherical surface in general industrial products.

  Further, at the beginning of the press-fitting, the heat-generating tube surrounds the portion near the opening edge of the concave spherical surface 101a so that the press-fitting load is received by the annular portion around the top of the spherical surface of the tip 3a. 3 is the same as the radius of curvature R1 of the tip 3a of the sphere 3, while the other portion of the spherical surface 101a near the center of the bottom surface of the spherical surface 101a is smaller than the radius of curvature R1 of the tip 3a of the heat generating tube 3, The spherical surface 101a may be a spherical surface having two radii so that when the tip 3a of the heat generating tube 3 is brought into contact with the spherical surface 101a except for the periphery of the tip 3a. Good. Specifically, in the tip 3a of the heat generating tube 3, as shown in FIG. 3, the annular portion W1 corresponding to the thickness of the side wall (tube portion wall) of the tube 3 located around the top portion. The portion near the opening edge of the spherical surface 101a to be recessed is made the same as the radius of curvature R1 of the tip 3a of the heating tube 3 so that the load at the beginning of press-fitting can be received at the portion including A portion closer to the bottom center of the spherical surface 101a may be smaller than the radius of curvature R1 of the tip 3a of the heat generating tube 3.

  As can be understood from the above, the tip support portion 101 in the press-fitting device may have a tapered surface 101b that forms a mortar-shaped recess as shown in FIG. That is, even in this case, the load F is concentrated only on the top of the tip 3a as compared with the case of the manufacturing method using the conventional press-fitting device in which the tip support portion 101 of the press-fitting device is a flat surface. Nothing will happen. For this reason, the tip 3a is prevented from being crushed and deformed at the tip (lower end in the figure) forming the top. Therefore, since the adjacent spiral portions L1, L2, L3,... Of the internal coil member 5 near the tip 5a are also maintained at an appropriate pitch P, they are brought into contact with each other and the resistance value fluctuates. This is because it is possible to effectively prevent the occurrence of such problems. Even in this case, at the beginning of the press-fitting, a load is applied to a portion closer to the annular portion (outer periphery) corresponding to the thickness of the side portion (wall) of the tip 3a of the heat generating tube 3. Is preferred. The tapered surface of the tip support portion 101 in the press-fitting device according to the present invention may be a tapered surface formed as a concave formed of two stages of tapered surfaces 101b and 101c as shown in FIG.

  The method for manufacturing a glow plug according to the present invention is not limited to the above-described embodiment, and can be embodied with appropriate modifications without departing from the scope of the invention. As a matter of course, the glow plug to which the present manufacturing method is applied is not limited to the structure described above. For example, in the above-described glow plug, the heat generating tube used in the glow plug is embodied as having a different diameter portion, but it goes without saying that it can be embodied even in a straight cylindrical shape except for the tip surface.

The longitudinal cross-sectional view and principal part enlarged view of the glow plug manufactured by embodiment of this invention. Explanatory drawing of the state which press-fits a heat generating tube to a metal fitting main body, and the enlarged view of the front-end | tip support part of a press-fit apparatus. The expanded sectional view of the front-end | tip part and the front-end | tip support part of a press-fitting apparatus which show the press-fit state of a exothermic tube, and after press-fit. The expanded sectional view of another example of a tip support part. The expanded sectional view of another example of a tip support part. The longitudinal cross-sectional view and principal part enlarged view of the conventional glow plug. It is a figure explaining the conventional manufacturing method, Comprising: The explanatory view of the state which press-fits a heat generating tube to a metal fitting main body, and the enlarged view of the front-end | tip support part of a press-fit apparatus. The expanded sectional view of the front-end | tip part of the heat generating tube explaining the problem by the conventional press fit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glow plug 2 Metal fitting body 2a Tip of metal fitting body 3 Heat generating tube 3a Heat generating tube tip 3d Heat generating tube rear end 5 Coil member 101 Tip supporting portion 101a for supporting the tip of the heat generating tube of the press-fitting device Spherical surface 101b of the tip supporting portion 101c Tapered surface of tip support portion G axis R1 Radius of curvature of the hemisphere at the tip of the heating tube (sphere R)
R2 Radius of curvature of the spherical surface formed by the tip support (sphere R)

Claims (2)

A heat generating tube, which is formed in a hemispherical shape with a convex tip and is provided with a coil member from the inner tip toward the rear, is press-fitted into the inner side of the cylindrical fitting body from the rear end side, and the tip is attached to the fitting body. In a method of manufacturing a glow plug that is fixed by protruding from the tip of
Of the press-fitting device used for press-fitting the heat-generating tube inside the metal fitting body, the tip support part that supports the tip of the heat-fitting tube in press-fitting is a recess into which a hemispherical surface that is a convex of the tip of the heat-generating tube fits. A spherical surface having a radius of curvature smaller than the radius of curvature of the hemispherical surface that is convex of the tip of the heat generating tube, and the tip of the heat generating tube is supported by the spherical surface formed by the tip support portion. Then, the method for manufacturing a glow plug is characterized in that the heat generating tube is press-fitted into the metal fitting body. A heat generating tube, which is formed in a hemispherical shape with a convex tip and is provided with a coil member from the inner tip toward the rear, is press-fitted into the inner side of the cylindrical fitting body from the rear end side, and the tip is attached to the fitting body. In a method of manufacturing a glow plug that is fixed by protruding from the tip of
Of the press-fitting devices used for press-fitting the heat generating tube inside the metal fitting body, a mortar in which a hemispherical surface that is a convex of the tip of the heat generating tube is fitted into a tip support portion that supports the tip of the heat generating tube in press fitting A tapered surface that is formed into a concave shape so that the tip of the heat generating tube is supported by the taper surface except for the top thereof, and the tip of the heat generating tube excluding the top is supported by the taper surface. A method of manufacturing a glow plug, wherein the heat generating tube is press-fitted into the metal fitting body .

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