JP4295164B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug used for preheating a diesel engine and a glow plug used for heating a liquid.

  Conventionally, the glow plug is a ceramic glow plug that constitutes a heater made of conductive ceramic as a heating element, a metal glow plug that constitutes a heater by containing a heating coil at the tip of a bottomed cylindrical metal tube, etc. There are various forms. All of these glow plugs are used for preheating a diesel engine, and are conventionally used by being attached to the engine in a form in which a heat generating portion at the front end of the heater protrudes into the sub-combustion chamber.

Such a glow plug is provided with a connector portion at the rear end portion to which power from an external power source is supplied as power supply means to the heater located on the front end side. This connector part is formed by joining a pin-shaped terminal or screwing a nut to a middle shaft whose rear end part protrudes from the rear end part of the metal shell (for example, Patent Document 1). reference.). This middle shaft adopts the structure shown in FIG. 6A as a fixing method. According to FIG. 6 (a), the middle shaft 101 protrudes from the rear end portion of the metal shell 102, and the gap between the large diameter hole 103 at the rear end portion forming a part of the shaft hole of the metal shell 102 and the middle shaft 101 is O. The ring 104 is inserted, and the O-ring 104 is pressed from the rear end side to the front end side by the insulating member 105. And the round nut 106 is being fixed so that the state which pressed the O-ring 104 may be hold | maintained. In addition, the pin terminal 107 shown to the same figure (b) may be used for the round nut 106. FIG. The glow plug is attached so that its rear end protrudes to the outside of the engine (see, for example, Patent Document 2).
JP 2002-367760 A JP-A-7-71310

  By the way, in recent years, a direct injection type diesel engine has been developed. For this reason, the heater tip tends to be elongated so that the front end of the heater can be directly projected into the combustion chamber. However, since it is difficult to make the glow plug longer in manufacturing the glow plug, which may cause a decrease in the yield, it is desirable that the glow plug is not made longer.

  From such a background, as an attachment structure in which the rear end portion of the glow plug does not protrude outside the engine, an attachment structure in which the rear end portion is accommodated in the engine head has been proposed. By adopting this mounting structure, the glow plug can be relatively shortened in overall length as compared with a structure used for mounting the glow plug with its rear end protruding outside the engine. In the case of this mounting structure, the power supply means for the glow plug has a structure in which a cord connected to an external power source is directly connected to the connector portion at the rear end portion of the glow plug so as to conduct electricity.

  However, this mounting structure causes the following new problem. That is, since the rear end portion of the glow plug is accommodated in the engine head, the rear end portion is attached to the engine oil. For this reason, there may be a problem that engine oil enters the interior from the gap between the metal shell, the insulating member, the center shaft, and the like at the rear end of the glow plug.

  In order to avoid this problem, the glow plug shown in FIG. 6 employs a seal structure in which an O-ring 104 is inserted from the rear end side. However, in spite of this, engine oil sometimes penetrated into the glow plug. This is because the O-ring 104 is pressed against the insulating member 105 even though the O-ring 104 is pressed against the front end surface of the insulating member 105 so as to be in close contact with the surface of the metal shell side taper 107 and the middle shaft 101. This is because the magnitude of the stress on the central shaft 101 is smaller than the magnitude of the stress on the metal shell side taper 108 due to the above. Therefore, there is a possibility that a problem that airtightness cannot be ensured may occur. In this way, if the engine oil penetrates into the glow plug, the engine oil is contaminated and contains conductive materials such as iron powder, so there is a risk that the central shaft side and the metal shell side will be electrically connected to each other. It was.

  The present invention has been made to solve the above-described problems, and can improve the adhesion between the O-ring center shaft and the metal shell, and can keep the airtightness of the rear end portion of the glow plug more firmly. An object of the present invention is to provide a glow plug having a seal structure.

In order to achieve the above object, the glow plug of the invention described in claim 1 has a large-diameter hole at the rear end and passes through the metal shell side taper that tapers to the large-diameter hole. a cylindrical metal shell diameter hole of small diameter is provided with a shaft hole formed on the distal end side is inserted into the axial hole of the metal shell, to name a rod having one end projecting from the rear end side thereof, the metallic The center shaft that faces the metal taper side taper is straight, the O-ring made of an elastic member that is in close contact with the metal taper side taper and the straight shaft portion of the medium shaft, and the medium shaft is inserted through its own hole. And an insulating member having an end face that is fitted into the large-diameter hole of the metal shell and presses the O-ring, and a terminal metal that surrounds the rear end of the middle shaft and is fixed to the middle shaft. A glow plug provided,
An angle formed by the metal shell side taper on the front end side is an acute angle, and an end surface that presses the O-ring of the insulating member forms a taper that decreases in diameter toward the rear end.

The glow plug of the invention described in claim 2 is characterized in that the O-ring is spaced apart from the boundary between the metal shell side taper and the small diameter hole and is in close contact with the metal shell side taper .

The glow plug according to a third aspect of the invention is characterized in that the taper angle of the insulating member is 25 ° or more.

A glow plug as a reference example (corresponding to Reference Example 1 described later) has a metal shell side taper provided on the inner peripheral surface of the shaft hole of the metal shell and a center shaft side taper provided on the surface of the center shaft on the axis. Since it is substantially line symmetric with respect to the parallel straight lines, the O-ring in contact with these two tapers has a configuration in which substantially the same area abuts on the metal shell side and the central shaft side. Since this O-ring is pressed from the rear end side by a plane parallel to the radial cross section of the O-ring (that is, a plane perpendicular to the axis), either the metal shell side taper or the middle shaft side taper is biased. It does not occur and stress is not applied from the O-ring, and the O-ring has a structure that adheres to both sides with a substantially uniform area. Therefore, the gap between the metal shell and the central shaft can be closed, and the airtightness can be improved.

  In addition, the substantially line symmetry means that both the metal shell side taper and the central shaft side taper have substantially the same taper angle, and the assembly of both is the position that becomes the base point of each taper (for example, the metal shell and the central shaft). The base point at which the gap between the two is substantially the same at the axial position.

In addition, a glow plug as another reference example (which corresponds to Reference Example 2 to be described later) has a configuration in which the metal shell side taper and the central shaft side taper are axisymmetric with respect to a straight line parallel to the axis. That is, unlike the configuration of Reference Example 1, the taper angles of the metal shell side taper and the central shaft side taper are different. For this reason, the end face of the insulating member that presses the O-ring should not be a plane parallel to the radial cross section of the O-ring (a plane perpendicular to the axis) so that the stress applied from the O-ring to each taper becomes substantially equal. Is tilted. That is, when it is difficult to form and assemble the metal shell side taper and the central shaft side taper so that they are line-symmetric, the taper may be formed in advance so that the taper angles of both are different. However, in this case, it is necessary to incline the end surface of the insulating member that presses the O-ring with respect to a plane parallel to the radial section. In this way, the O-ring is configured to press both the metal shell-side taper and the central shaft-side taper with substantially equal stress, so that the metal shell and the O-ring and the middle shaft and the O-ring are in close contact with each other, Airtightness can be improved. In addition, there is an advantage that the tight tolerance management as in the configuration described in the reference example 1 is not necessary.

In addition, a glow plug as another reference example (corresponding to Reference Example 3 described later) is provided with either one of the metal shell side taper or the central shaft side taper so that either taper comes into contact with the O-ring, An end face of the insulating member that presses the O-ring has an inclination that is substantially line-symmetric with the taper with respect to a radial section passing through the O-ring. Specifically, for example, when the metal shell side taper is provided without forming the central shaft side taper, the end surface of the insulating member forms a taper that decreases in diameter toward the rear end side. In the case where the central shaft side taper is provided without forming the taper, an insulating member may be used in which the end surface of the insulating member forms a taper whose diameter increases toward the rear end side.

  That is, the end surface of the insulating member having an inclination presses the O-ring, so that the O-ring tends to be displaced obliquely with respect to the axial direction. The O-ring presses either the metal shell-side taper or the central shaft-side taper and receives a reaction force from the taper. Then, the O-ring tends to be displaced in the direction perpendicular to the axis by the force received from the insulating member and the reaction force. As a result, the O-ring is pressed with the same degree of force against either the taper on the metal shell side or the taper on the central shaft side and the surface where the taper is not formed, and airtightness is improved. Can be improved. And in the manufacturing method which implement | achieves this structure, since it is only necessary to give a taper process to either one of a main metal fitting and a center axis | shaft, a man-hour can be reduced and an inexpensive glow plug can be provided by extension.

Further, it is desirable to provide a taper (also referred to as a metal shell side taper) on the metal shell side as in the configuration of claim 1 with respect to the configuration of the reference example 3. That is, as described in claim 1 , the central shaft has a straight portion such that a plane parallel to the axis is its surface, and the metal shell side taper is formed. Then, the O-ring is placed so as to be supported by the metal shell-side taper and the surface of the central shaft, and the insulating member presses the O-ring with a taper formed so as to reduce the diameter toward the rear end. . Further, the angle formed by the metal shell side taper is an acute angle.

  With this configuration, the O-ring of the glow plug is pressed against the center shaft together with the stress received from the insulating member and the reaction force from the metal shell side taper. As a result, the force with which the O-ring is pressed against the metal shell-side taper and the force with which the O-ring is pressed against the central shaft are approximately the same, and as a result, airtightness can be improved. In addition, since the metal shell having a diameter larger than that of the center shaft is processed, it is possible to meet the demand for reducing the diameter of the glow plug without reducing the strength of the center shaft. Furthermore, there is an advantage that it is easy to determine the position where the O-ring pressed by the insulating member is locked.

In the first or second aspect, the taper provided on the end face of the insulating member is preferably provided with a taper angle of 25 ° or more with respect to the axis. If it is less than 25 °, the strength of the insulating member that presses the O-ring may be insufficient and may break. Therefore, the taper angle of the end face of the insulating member is desirably 25 ° or more.

The glow plug of the present invention will be described below with reference to the drawings.
FIG. 1 is a half sectional view showing the entire glow plug 1 according to the first embodiment of the present invention. The glow plug 1 is generally configured by combining a metal shell 10, a middle shaft 20, a heater 30, an insulating member 40, an O-ring 50, an outer cylinder 60, and a pin terminal 70.

  A cylindrical middle shaft 20 with one end protruding toward the rear end side is accommodated on the inner peripheral side of the cylindrical metal shell 10, and a heater 30 is connected to the front end side of the middle shaft 20. In addition, an outer cylinder 60 is joined to the tip of the metal shell 10, and the heater 30 is held on the outer cylinder 60. On the other hand, the O-ring 50 and the insulating member 40 are inserted in the gap between the middle shaft 20 and the metallic shell 10 on the rear end side of the metal shell 10, and the pin terminal 70 fixes the middle shaft 20 on the rear end side of the insulating member 40. .

  The metal shell 10 has a cylindrical shape made of an iron-based material equivalent to S45C, and has a male screw 11 for attachment to a diesel engine (not shown) and a tool engagement with which an attachment tool is engaged on its outer peripheral surface. Part 12 is formed. On the other hand, a shaft hole 13 is formed on the inner periphery of the metal shell, and a metal shell side taper 14 that expands the shaft hole 13 toward the rear end side at the rear end portion, and a further rear of the metal shell side taper 14. A large-diameter hole 15 is formed adjacent to the end side.

  The middle shaft 20 has a rod-like shape made of S430. A tip end small diameter portion is formed at the tip end portion so that the ring member 21 for conduction with the heater 30 is fitted, while a rear end small diameter portion to which the pin terminal 70 is attached is formed at the rear end portion. Yes.

  In the heater 30, a heating element 32 and a lead portion 33 made of conductive ceramic are embedded in a rod-shaped insulating ceramic base 31. The heating element 32 located on the front end side of the heater 30 is formed of a conductive ceramic in a U-shape, and two lead portions 33 extending rearward from each base end of the heating element 32 are formed. One of the lead portions 33 is formed so that the electrode extraction portion 34 is exposed on the surface of the ceramic base 31 in the radial direction so as to be electrically connected to the ring member 21 at the rear end portion of the heater 30 and the other is the electrode extraction. An electrode extraction portion 35 is similarly formed in the radial direction so as to be electrically connected to the outer cylinder 60 on the tip side from the portion 34.

  The outer cylinder 60 has a cylindrical shape made of SUS430. A shaft hole 61 into which the heater 30 is press-fitted is formed in the outer cylinder 60, and the inner peripheral surface of the shaft hole 61 and the electrode extraction portion 35 are brought into contact with each other. is doing. Further, the rear end portion of the outer cylinder 60 is formed with a small-diameter portion 62 that fits into the metal shell 10. A rear end-facing end surface 64 that forms a radially projecting flange 63 is formed on the rear end side of the outer cylinder 60, and a taper 65 that decreases in diameter toward the front end side is formed on the front end side of the flange 63. The taper 65 plays a role as a seal that ensures airtightness with the combustion chamber when attached to a diesel engine (not shown).

  The glow plug 1 is arranged with a predetermined gap 80 so that the metal shell 10 and the middle shaft 20 do not come into contact with each other and become conductive. A seal structure using an O-ring 50 is employed at the rear end of the glow plug 1 so that rainwater from the outside, oil from the internal combustion engine, and the like do not enter the gap 80 during use of the glow plug 1. is doing. Next, this seal structure will be described with reference to FIG.

FIG. 2 is a half sectional view of the enlarged rear end portion of the glow plug 1.
An O-ring 50 is fitted at the rear end of the glow plug 1 in order to prevent the above-described liquid or the like from entering the gap 80 from the outside. The O-ring 50 is made of an elastic member (for example, fluorine rubber or silicon rubber). After the members on the tip end side of the glow plug such as the metal shell 10, the middle shaft 20, the heater 30, and the outer cylinder 60 are assembled, The middle shaft 20 is inserted from the end into its own inner hole and inserted into a predetermined position.

  A taper 16 is formed at the rearmost end of the large-diameter hole 15 located at the rear end of the metal shell 10, and the O-ring 50 is damaged when the O-ring 50 is inserted into the gap between the metal shell 10 and the central shaft 20. It has a structure that will not be damaged. The O-ring 50 is inserted to a position where it comes into contact with the metal shell taper 14. The metal shell-side taper 14 formed on the metal shell 10 is formed so that α = 15 ° at an acute angle with respect to the axis O.

  Further, a tubular insulating member 40 made of a resin such as PPS, PPA, or nylon having a taper 41 (hereinafter referred to as an insulating member taper 41) for pressing the O-ring 50 from the rear end side is fitted. The insulating member 40 includes a flange 42 that protrudes in the radial direction at the rear end portion, and is disposed so that an end surface facing the front end contacts the rear end surface of the metal shell 10. In addition, the portion β which is an acute angle of the insulating member taper 41 is set to 25 ° or more, thereby reducing the occurrence of defects in the insulating member 40 itself. That is, if the O-ring 50 can be pressed by the insulating member taper 41, the surrounding structure may be appropriately changed.

  On the further rear end side of the insulating member 40, a pin terminal 70 connected to an energization cord (not shown) extending from an external power source (not shown) is disposed. The pin terminal 70 includes a flange 71 projecting in the radial direction that presses the insulating member 40 at the tip. The portion adjacent to the rear end side of the flange 71 is caulked from the outer periphery, so that the small rear end diameter portion of the middle shaft 20 is held in its inner hole 73. In addition, when crimping, the pin terminal 70 is pressed from the rear end side to the front end side so that the O-ring 50 is pressed through the insulating member 40 and then crimped.

  Further, a flange 72 is formed on the rear end side of the flange 71 with the above-described caulked portion having a diameter smaller than that of the flange 71. A convex portion of a cap (not shown) of the energizing cord is fitted into a small diameter portion sandwiched between the two flanges 71 and 72 and mechanically connected to the pin terminal 70. Note that a conductive plate connected to the conductive cord lead wire protrudes into the cap of the conductive cord, and the conductive plate contacts the small diameter portion 74 of the pin terminal 70 for electrical connection.

  Hereinafter, a method for manufacturing the glow plug 1 will be described. First, as shown in FIG. 3A, a heating part powder molded body 300 is prepared in which the heating element 32 and the lead part 33 are integrally formed by injection molding from ceramic powder as a raw material. On the other hand, as the ceramic base 31, ceramic powder as a raw material is press-molded in advance to form divided molded bodies 311 and 312 having concave portions in which the heat generating portion powder molded bodies 300 are accommodated on their mating surfaces. . Then, the heat generating part powder molded body 300 is held between the divided molded bodies 311 and 312, and after press compression, the outer peripheral surface is polished into a cylindrical shape through a baking process such as binder removal processing and hot pressing. Thus, the heater 30 shown in FIG.

  Then, fitting is performed by press fitting, interference fitting, or the like so that one electrode extraction portion 34 of the lead portion 33 is electrically connected to the inner peripheral surface of the tip portion of the ring member 21. Similarly, in order to establish the electrical connection of the electrode extraction portion 35, the outer cylinder 60 is fitted into the outer periphery of the heater 30 by press fitting, interference fitting or the like, and the heater 30, the outer cylinder 60, and the ring member 21 are integrated. (FIGS. 3C and 3D).

  Next, the small diameter end portion of the middle shaft 20 is inserted into the rear end portion of the ring member 21, and the overlapping portion is laser-welded over the entire circumference in the radial direction. Then, the metal shell 10 is inserted from the rear end side of the middle shaft 20 and is fitted so that the front end surface of the main metal shell 10 and the rear end-facing end surface 64 of the outer cylinder 60 come into contact with each other. Are welded to the small diameter portion 62 of the outer cylinder 60 by laser welding.

  On the other hand, on the rear end side of the glow plug 1, as shown in FIG. 4, the O-ring 50 and the insulating member 40 are sequentially inserted from the rear end side of the middle shaft 20, and the pin terminal 70 is pressed toward the front end side. The glow plug 1 is completed by caulking and fixing to the middle shaft 20. The insulating member 40 is formed to have a taper 41 by injection molding raw material powder.

  The glow plug 1 formed in this way has a configuration in which the insulating member 40 presses the O-ring 50 to the metal shell side taper 14 because the pin terminal 70 is pressed and assembled to the tip side. The O-ring 50 sandwiched between the metal shell-side taper 14 and the insulating member taper 41 tends to be displaced toward the middle shaft 20, thereby maintaining airtightness with the side surface of the middle shaft 20. As in the present embodiment, by being sandwiched between two tapers, the O-ring has improved adhesion to the central shaft, and as a result, a glow plug with improved airtightness can be provided.

The present invention is not limited to the above-described embodiment, and the concept of the present invention can be realized in various forms .

A reference example is described below. The same parts as those in the above embodiment will be described using the same reference numerals.

(Reference Example 1)
Reference Example 1 shown in FIG. This reference example 1 shows a form in which the conventional insulating member 105 can be used as it is without the insulating member taper 41 being tapered, that is, the tip surface having a plane parallel to the cross section of the O-ring 50. In this embodiment, unlike the above-described embodiment, the middle shaft side taper 22 is also formed on the middle shaft 20. The middle shaft side taper 22 is formed so as to be substantially line symmetric with the metal shell side taper 14 with a straight line O ′ parallel to the axis O as the axis of symmetry. With this configuration, in the actual manufacture of the glow plug 1, it is possible to improve the airtightness by the O-ring 50 without changing the manufacturing method of the insulating member 40.

(Reference Example 2)
Next, Reference Example 2 shown in FIG. In this example, unlike the reference example 1, it is not necessary to arrange the central taper side taper 22 and the metal shell side taper 14 so as to be line-symmetric with respect to the straight line O ′, so that the airtightness can be improved. An insulating member taper 41 is formed on the front end surface of the insulating member 40 in order to adjust the pressing force against each taper of the O-ring 50 by making the both tapers not symmetrical. The insulating member taper 41 is not limited to the taper in the direction of the central axis shown in FIG. 5B, and may be a taper in the direction of the metal shell as appropriate.

(Modification 3)
Moreover, the reference example 3 shown in FIG.5 (c) shows that it is not necessary to provide both the metal shell side taper 14 or the center shaft side taper 22. That is, in the case of the above-described embodiment, the metal shell side taper 14 is provided, and the middle shaft 20 has a straight shape . As the reference example 3, the middle shaft side taper 22 may be provided, and the shaft hole 13 of the metal shell 10 may be straight. In this case, the insulating member taper 41 is formed so as to face the metal shell 10 so that the O-ring 50 is pressed to the distal end side by the insulating member taper 41 and displaced to the shaft hole 13 of the straight metal shell 10. ing.

  Each of the above modifications has a structure that improves the airtightness of the shaft hole at the rear end portion of the glow plug, and any form that is suitable for the form of the engine to which the glow plug is attached may be adopted as appropriate. However, the airtightness of the shaft hole at the rear end of the glow plug can be improved as compared with the conventional configuration shown in FIG.

The present invention is not limited to the case where the rear end portion of the glow plug is accommodated and attached to the engine head, but may be applied to a conventional case where the rear end portion of the glow plug protrudes from the engine head and is attached. Good. In this case, the effect of preventing raindrops or the like from entering the inside of the glow plug is exhibited.

  In the above-described embodiments and modifications, the heater 30 is described as a ceramic heater. However, a heater that accommodates a heating coil that generates heat when energized may be used.

Figure 1 is a half cross-sectional view showing the entire glow plug 1 of the implementation of the embodiment of the present invention. It is. Figure 2 is an enlarged view of the glow plug 1 of the implementation of the embodiment of the present invention. FIG. 3 is a schematic view showing a manufacturing method of the structure on the tip side of the glow plug 1 of the present invention. FIG. 4 is a schematic view showing a manufacturing method of the configuration of the rear end side of the glow plug 1 of the present invention. FIG. 5 is an enlarged view of a main part showing a reference example . FIG. 6 is a partial cross-sectional view showing the structure of a conventional glow plug.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glow plug 10 Main metal fitting 14 Main metal fitting side taper 20 Middle shaft 22 Middle shaft side taper 30 Heater 40 Insulation member 41 Insulation member taper 50 O-ring 60 Outer cylinder 70 Pin terminal

Claims (3)

A cylindrical shape having a large-diameter hole at the rear end, and a shaft hole in which a small-diameter hole smaller in diameter than the large-diameter hole is formed on the front end side through a taper on the metal shell side that is tapered to the large-diameter hole. A metal shell,
Is inserted into the axial hole of the metal shell, and the center shaft to name a rod having one end projecting from the rear end side, a portion opposed to the metal shell side taper is straight,
An O-ring made of an elastic member in close contact with the taper side taper and the straight portion of the central shaft;
An insulating member having an end face that is inserted into the inner hole of the metal shell and fitted into the large-diameter hole of the metal shell and presses the O-ring;
A terminal fitting that surrounds the rear end of the middle shaft and is fixed to the middle shaft;
A glow plug comprising
While the angle formed by the metal shell side taper on the tip side is an acute angle,
An end surface that presses the O-ring of the insulating member forms a taper that decreases in diameter toward the rear end;
Glow plug characterized by The glow plug according to claim 1, wherein the O-ring is spaced apart from a boundary between the metal shell side taper and the small diameter hole and is in close contact with the metal shell side taper. Claim 1 or 2 glow plug, wherein said taper angle of the insulating member is 25 ° or more.

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