JP5903005B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug used for an internal combustion engine or the like.

  A glow plug used for starting assistance of a diesel engine includes a housing having a shaft hole extending in the axial direction, and a heater member that is inserted into the shaft hole with its front end protruding from the front end of the housing and generates heat when energized. And. The heater member may be a sheath heater including a cylindrical tube and a heating coil disposed inside the tube, a cylindrical base made of an insulating ceramic, and a conductive ceramic. There is known a ceramic heater provided with a heat generating element disposed in the box.

  In addition, the housing includes a threaded portion (male threaded portion) for attachment to the engine, and a tapered portion that is provided on the distal end side with respect to the threaded portion and gradually decreases in outer diameter toward the distal end side. . When the threaded portion is screwed into the mounting hole provided in the engine head, the tapered portion is pressed against the seat surface of the engine head so that airtightness in the combustion chamber is ensured. It has become. In addition, a plating layer made of a predetermined metal may be provided on the outer surface of the housing (including the outer surfaces of the threaded portion and the tapered portion) in order to improve corrosion resistance (see, for example, Patent Document 1). .

JP 2008-8607 A

  By the way, when attaching the glow plug to the engine head, in order to ensure good airtightness, generally, the screw portion is screwed into the mounting hole until the rotational torque of the glow plug becomes equal to or higher than a preset tightening torque. (That is, the glow plug is attached by torque management). However, when processing oil remains in the engine head, the gap between the glow plug and the engine head with respect to the rotation angle of the glow plug is determined even though the tapered portion is in contact with the seat surface of the engine head with sufficient pressure. In this case, the degree of increase in the friction coefficient is moderate, and as a result, the increase rate of the rotational torque of the glow plug with respect to the rotational angle of the glow plug may be relatively small. In this case, since the thread portion is excessively screwed into the mounting hole, the compressive stress along the axial direction is excessive with respect to the portion of the housing located between the thread portion and the taper portion. There is a risk that the housing will be deformed. Further, an excessively large torsional force is applied to the housing, and the housing may be broken.

  Accordingly, the inventors of the present invention diligently studied the factors that cause the increase rate to be relatively small. When the glow plug is attached to the engine head, the plating layer provided on the outer surface of the housing is subjected to shearing due to rotation. It has been found that one factor is that the plating layer peels off due to the stress.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make the increase rate of the rotational torque of the glow plug sufficiently large with respect to the rotational angle of the glow plug when attached to the engine head. An object of the present invention is to provide a glow plug capable of more reliably preventing deformation and breakage of a housing while ensuring good airtightness by applying a sufficiently large tightening torque to the glow plug.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The glow plug of this configuration includes a cylindrical housing having an axial hole extending in the axial direction,
A heater member inserted into the shaft hole in a state in which at least a tip portion thereof protrudes from a tip of the housing;
The housing is
A threaded portion for screwing into a mounting hole provided in the engine head;
A glow plug having a tapered portion that decreases in outer diameter toward the tip end in the axial direction and that presses against a seating surface of the engine head when the screw portion is screwed into a mounting hole of the engine head. There,
A plating layer having a hardness higher than that of the engine head is provided on at least the outer surface of the screw portion and the taper portion of the housing, and is provided on the outer surface of the screw portion and the taper portion. The ten-point average roughness Rz of the surface of the plating layer is 5 μm or less.

  According to the configuration 1, the plating layer is provided on the outer surface of at least the threaded portion and the tapered portion (that is, the portion that contacts the engine head when the glow plug is attached to the engine head) of the housing. Is considered to be greater than the hardness of the engine head. Therefore, the plating layer has a strength capable of sufficiently resisting the shearing stress generated when the glow plug is attached to the engine head, and the plating layer can be more reliably peeled off when being mounted on the engine head. Can be prevented. As a result, even when the friction coefficient between the glow plug and the engine head tends to decrease, such as when oil adheres to the engine head, when the glow plug is attached to the engine head, The coefficient of friction of the glow plug tends to increase, and the rate of increase of the rotational torque of the glow plug with respect to the rotational angle of the glow plug can be made sufficiently large. As a result, by applying a sufficiently large tightening torque to the glow plug, it is possible to more reliably prevent deformation and breakage of the housing while ensuring good airtightness.

  Moreover, according to the said structure 1, the 10-point average roughness Rz of the surface of a plating layer is 5 micrometers or less. Therefore, at the time of mounting, the adhesion of the housing (screw portion and taper portion) to the engine head can be further improved, and the coefficient of friction between the engine head and the glow plug can be further increased. As a result, the rate of increase of the rotational torque of the glow plug with respect to the rotational angle of the glow plug can be further increased, and deformation and breakage of the housing can be prevented more reliably.

  Configuration 2. The glow plug of this configuration is characterized in that, in the above configuration 1, the plated layer is made of an alloy containing zinc as a main component and nickel.

  The “main component” refers to a component having the highest mass ratio in the material.

  According to the above configuration 2, since the plating layer contains Zn as a main component, excellent corrosion resistance can be realized.

  On the other hand, when the plating layer is made of Zn, the hardness of the plating layer is lowered, and the function and effect of the configuration 1 may not be sufficiently exhibited. In this regard, according to the configuration 2, the alloy constituting the plating layer contains Ni, and the hardness of the plating layer can be made sufficiently large. Therefore, the effect by the said structure 1 can be exhibited more reliably. Moreover, since Ni is contained in the alloy constituting the plating layer, the heat resistance of the plating layer can be improved.

  In addition, in order to exhibit the effect by the said structure 2 more reliably, it is preferable that the eutectoid rate of Ni in the said alloy shall be 5% or more and 20% or less.

(A) is a partially broken front view of the glow plug, and (b) is a partially broken enlarged front view of the tip portion of the glow plug. It is a partially broken front view which shows the glow plug attached to the engine head. (A) is a partially broken enlarged front view showing a plated layer and the like provided on the outer surface of the threaded portion, and (b) is a partially broken view showing the plated layer and the like provided on the outer surface of the tapered portion. It is an enlarged front view. It is a partially broken front view which shows the structure of the jig | tool for a test, etc. It is a graph which shows the result of a rotation angle measurement test. It is a graph which shows the relationship between 10-point average roughness Rz of a plating layer surface, and Tq / F.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1A is a partially broken front view of the glow plug 1, and FIG. 1B is a partially broken enlarged front view of the tip portion of the glow plug 1. 1 and the like, the direction of the axis CL1 of the glow plug 1 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side will be described as the rear end side.

  As shown in FIGS. 1A and 1B, the glow plug 1 includes a cylindrical housing 2 and a heater member 3 fixed to the housing 2 in a state where the tip end of the glow plug 1 protrudes from the tip of the housing 2. And.

  The housing 2 has a shaft hole 4 extending in the direction of the axis CL1, and has a relatively long length L (for example, 100 mm or more) along the axis CL1. Further, on the outer peripheral surface of the housing 2, when the glow plug 1 is attached to an engine head of an internal combustion engine (diesel engine or the like), a screw portion 5 screwed into an attachment hole of the engine head and a tool such as a torque wrench are provided. A tool engaging portion 6 having a hexagonal cross section for engagement is formed. Further, the outer diameter of the distal end portion of the housing 2 gradually decreases toward the distal end side in the direction of the axis CL1, and as shown in FIG. 2, the mounting hole HO (having a female thread portion on the inner periphery) of the engine head EN. A taper portion 7 is provided that presses against the seating surface ES of the engine head EN when the screw portion 5 is screwed. In addition, the taper part 7 press-contacts to the seat surface ES, and ensuring of airtightness in a combustion chamber will be aimed at.

  In the present embodiment, the housing 2 is formed of a metal having relatively low strength (for example, free-cutting steel) in order to improve workability. Further, the housing 2 is reduced in diameter in order to reduce the size (smaller diameter) of the glow plug 1, and as a result, the screw diameter of the screw portion 5 is set to a predetermined value (for example, M8) or less.

  Returning to FIG. 1, the heater member 3 is provided in a tube 8 having a cylindrical shape with a distal end portion made of a predetermined metal (for example, a metal containing Fe or Ni as a main component) closed, and the tube 8. A heating coil 9 and a control coil 10 are provided, and a central shaft 11 forming an energization path to both the coils 9 and 10 is connected.

  The heating coil 9 is connected in series with the control coil 10, and its tip is joined to the tip of the tube 8. The heating coil 9 is configured by spirally winding a resistance heating wire made of a predetermined metal (for example, an alloy containing Fe as a main component and containing Al, Cr, or the like).

  The control coil 10 is provided between the heat generating coil 9 and the middle shaft 11 and has a material having a temperature coefficient of electrical specific resistance larger than that of the material of the heat generating coil 9 (for example, Co represented by Co—Ni—Fe alloy). Alternatively, a resistance heating wire made of a metal containing Ni as a main component is spirally wound. Thereby, the control coil 10 increases the electric resistance value by receiving its own heat generation and heat generation from the heat generation coil 9, and controls the power supplied to the heat generation coil 9. More specifically, relatively large power is supplied to the heat generating coil 9 in the initial stage of energization, and the temperature of the heat generating coil 9 rises rapidly. Then, the control coil 10 is heated by the heat generation and its own heat generation, the electric resistance value of the control coil 10 is increased, and the power supplied to the heat generation coil 9 is decreased. As a result, the temperature rise characteristic of the heater member 3 becomes a form in which, after the temperature is rapidly raised in the initial stage of energization, the supply power is suppressed by the action of the control coil 10 and the temperature is saturated. In other words, the presence of the control coil 10 is configured to make it difficult for excessive heating (overshoot) of the heating coil 9 to occur while improving rapid temperature rising.

  The middle shaft 11 is made of a predetermined conductive metal and has a rod shape extending along the direction of the axis CL1. Further, the front end of the middle shaft 11 is inserted into the tube 8 and joined to the rear end of the control coil 10, and the rear end protrudes from the rear end of the housing 2. At the rear end of the housing 2, an O-ring 14 made of rubber or the like, an insulating bush 15 made of resin or the like, a pressing ring 16 for preventing the insulating bush 15 from falling off, and an energizing cable are connected. Therefore, the nut 17 is inserted into the middle shaft 11 in this order.

  Furthermore, an insulating powder 12 mainly composed of magnesium oxide (MgO) is enclosed in the tube 8, and the insulating powder 12 is interposed so that the outer peripheral surfaces of the heating coil 9 and the control coil 10 and the tube 8 are The inner peripheral surface is insulated. Further, the rear end of the tube 8 is sealed with an annular rubber 13 between the tube 8 and the middle shaft 8.

  In addition, the tube 8 is formed with a small-diameter portion 8A that accommodates the heating coil 9 and the like at the distal end thereof by swaging or the like, and its outer diameter is smaller than the outer diameter of the small-diameter portion 8A at the rear end portion. The large-diameter portion 8B is also formed. The heater member 3 is fixed to the housing 2 by pressing the large-diameter portion 8B into the small-diameter portion 4A having a relatively small inner diameter in the shaft hole 4.

  Further, in the present embodiment, as shown in FIG. 3, at least the outer surface of the screw portion 5 and the taper portion 7 (in the present embodiment, the entire outer surface of the housing 2) of the housing 2 has a predetermined range of thickness. A plating layer 21 (for example, 5 μm or more and 20 μm or less) is provided. Further, at least portions of the plated layer 21 provided on the outer surfaces of the screw portion 5 and the taper portion 7 are configured to have a hardness greater than the hardness of the engine head EN.

Furthermore, in this embodiment, the plating layer 21 is formed of an alloy (Zn—Ni alloy) containing zinc (Zn) as a main component and containing a predetermined amount of Ni (for example, a eutectoid rate of 5% or more and 20% or less). Has been. The material constituting the plating layer 21 is not limited to a Zn—Ni alloy. For example, a metal mainly composed of Ni may be used. In addition, the plating layer 21 is made of a predetermined brightener. After the housing 2 is immersed in a predetermined plating aqueous solution containing Zn or Ni into which is introduced, a direct current is passed through the housing 2. The hardness of the plating layer 21 is determined based on the composition of the metal constituting the plating layer 21 (components and concentration of the plating aqueous solution) and the conditions for providing the plating layer 21 on the outer surface of the housing 2 (for example, an energization current value) ) Can be adjusted by changing. When the plating layer 21 is formed of a Zn-Ni alloy, examples of the brightener include triethanolamine, saccharin, butyne, naphthalene sulfonate, thiourea, benzoic acid, citrate, glucose, dextrin, gelatin, etc. Can be mentioned. When the plating layer 21 is formed of a metal having Ni as a main component, the brightener includes benzenesulfonic acid, p-toluenesulfonamide, saccharin, formaldehyde, allylsulfonic acid, 2-butyne 1,4-diol. And ethyl cyanohydrin.

  In addition, in the present embodiment, the ten-point average roughness Rz of the surface of the plating layer 21 provided on the outer surface of the screw portion 5 and the taper portion 7 is configured to be 5 μm or less. The ten-point average roughness Rz of the surface of the plating layer 21 can be changed by changing the content of the brightener in the plating aqueous solution or the processing method for forming the outer surface of the housing 2. it can. For example, the roughness of the outer surface of the screw part 5 can be reduced by forming the screw part 5 not by cutting but by rolling, and as a result, the plating layer 21 provided on the outer surface of the screw part 5 can be reduced. The ten-point average roughness Rz of the surface can be reduced.

  As described above in detail, according to the present embodiment, at least the screw portion 5 and the taper portion 7 of the housing 2 (that is, the portion that contacts the engine head EN when the glow plug 1 is attached to the engine head EN). A plated layer 21 is provided on the surface, and the hardness of the plated layer 21 is greater than the hardness of the engine head EN. Therefore, the plating layer 21 has a strength capable of sufficiently resisting the shearing stress generated when the glow plug 1 is attached to the engine head EN, and the plating layer 21 when attached to the engine head EN. Can be more reliably prevented. As a result, when the glow plug 1 is attached to the engine head EN, the friction coefficient between the glow plug 1 and the engine head EN is likely to increase, and the rate of increase in the rotational torque of the glow plug 1 relative to the rotational angle of the glow plug 1 is sufficient. Can be large. As a result, by applying a sufficiently large tightening torque to the glow plug 1, it is possible to more reliably prevent deformation and breakage of the housing 2 while ensuring good airtightness.

  Furthermore, since the ten-point average roughness Rz of the surface of the plating layer 21 is 5 μm or less, the adhesion of the housing 2 (the screw portion 5 and the taper portion 7) to the engine head EN can be further improved. As a result, the increase rate of the rotational torque of the glow plug 1 with respect to the rotational angle of the glow plug 1 can be further increased, and the housing 2 can be more reliably prevented from being deformed or broken.

  In particular, in the present embodiment, the length L of the housing 2 is relatively large, and the screw diameter of the screw portion 5 is relatively small (the thickness of the housing 2 is relatively small). Although there is a greater concern about the deformation of the housing 2 and the like, the ten point average roughness Rz of the surface of the plating layer 21 is 5 μm or less while the hardness of the plating layer 21 is equal to or higher than the hardness of the engine head EN. Can be wiped off. In other words, when the hardness of the plating layer 21 is equal to or higher than the hardness of the engine head EN and the ten-point average roughness Rz of the surface of the plating layer 21 is 5 μm or less, the length L of the housing 2 is relatively large ( This is particularly effective when the length L is 100 mm or more) and when the screw diameter of the screw portion 5 is relatively small (when the screw diameter is M8 or less).

  In addition, since the plating layer 21 is mainly composed of Zn, excellent corrosion resistance can be realized.

  Further, since the alloy constituting the plated layer 21 contains Ni, the hardness of the plated layer 21 can be made sufficiently large. Therefore, the peeling prevention effect of the plating layer 21 can be exhibited more reliably. Furthermore, since Ni is contained in the alloy constituting the plated layer 21, the heat resistance of the plated layer 21 can be improved.

  Next, in order to confirm the effects achieved by the above embodiment, a plating layer is provided over the entire outer surface of the housing, and the hardness of the plating layer is varied by changing the constituent material of the plating layer. Plug samples 1 to 4 were prepared, and a rotation angle measurement test was performed for each sample. The outline of the rotation angle measurement test is as follows.

  That is, as shown in FIG. 4, a cylindrical jig JG simulating an engine head having a hole FS simulating the mounting hole is prepared, and a portion corresponding to the seating surface of the jig JG. And a lubricant was applied to the inner peripheral surface of the hole FS, and a sample was inserted into the hole FS (in this state, the sample was not screwed into the hole FS). Next, the socket SC was engaged with the tool engaging portion of the sample, and the sample was not allowed to rotate relative to the socket SC. Further, the rotational torque of the socket SC can be measured by a predetermined load cell LC. After that, by rotating the jig JG, the thread portion of the sample is screwed into the hole FS, and when a rotational torque starts to be applied from the sample to the socket SC (that is, the taper portion on the seating surface). The angle of rotation of the jig JG when the rotational torque of the socket SC reaches 10 N · m (10 N · m reached rotation angle) was measured. Here, the smaller the 10 N · m arrival rotation angle is, the larger the frictional force generated between the glow plug (especially the threaded portion and taper portion in contact with the engine head) and the engine head when the glow plug is attached to the engine head. It can be said that the rate of increase in the rotational torque of the glow plug with respect to the rotational angle of the glow plug tends to be large. Therefore, when the glow plug is attached to the engine head by torque management, it is possible to suppress an excessively large compressive stress or torsional force from being applied to the housing, and to prevent deformation and breakage of the housing. -The smaller the m rotation angle, the better.

  FIG. 5 shows the result of the rotation angle measurement test. The jig JG was made of aluminum, and its hardness was 130 Vv in terms of Vickers hardness. Sample 1 forms a plating layer from Zn, Sample 2 forms a plating layer from an alloy containing Zn as a main component and containing Ni at a predetermined value (eutectoid rate of 3%), and Sample 3 contains Zn. A plating layer is formed of an alloy containing Ni as a main component and containing a predetermined value (eutectoid rate of 5%). Sample 4 is a plating layer made of an alloy containing Zn as a main component and containing Ni as a main value (eutectoid rate of 10%). Formed. In addition, the sample 5 forms a plating layer made of a metal mainly composed of Ni by performing electrolytic plating, and the sample 6 is made of a metal mainly composed of Ni by performing electroless plating. A plating layer was formed. In FIG. 5, the test result of sample 1 is indicated by a white circle, the test result of sample 2 is indicated by a black circle, the test result of sample 3 is indicated by a white triangle, and the test result of sample 4 is shown. The test result of sample 5 is indicated by a white square mark, and the test result of sample 6 is indicated by a white diamond mark.

  Further, in each sample, the thread diameter of the thread portion was M8, and the 10-point average roughness Rz of the plated layer surface was 5 μm.

  As shown in FIG. 5, the sample (sample 1) in which the hardness of the plating layer is smaller than the hardness of the jig JG (130 Hv) has a relatively large rotation angle of 10 N · m, leading to the engine head. It was found that there was a concern about deformation and breakage of the housing at the time of mounting. This is considered to be because the plating layer peeled off due to the shear stress generated between the plating layer and the jig JG, and the friction coefficient between the sample and the jig JG became small.

  Further, when the above-mentioned rotation angle measurement test was performed on a sample in which the plating layer was formed from a metal containing tin (Sn) as a main component and the hardness of the plating layer was 90 Hv, the rotation torque reached 6 N · m. At that time, the housing had broken.

  On the other hand, Samples 2 to 6 in which the hardness of the plating layer is larger than the hardness of the jig JG, the 10 N · m reaching rotation angle is suppressed to 100 ° or less, and the glow plug rotation angle relative to the rotation angle of the glow plug is It became clear that the rate of increase in rotational torque can be increased sufficiently. This is considered to be because the plating layer has a strength capable of resisting the shear stress generated between the sample and the jig JG, and the peeling of the plating layer is effectively suppressed.

  Moreover, when the said rotation angle measurement test was done after using the jig | tool formed with cast iron, when the hardness of a plating layer shall be larger than the hardness of a jig | tool, 10 N * m arrival rotation angle can be set. It could be suppressed to 100 ° or less, and it was confirmed that peeling of the plating layer can be effectively suppressed.

  From the results of the above test, from the viewpoint of more reliably preventing the deformation of the housing and the like by increasing the increase rate of the rotation torque of the glow plug with respect to the rotation angle of the glow plug when attaching the glow plug to the engine head. In addition, it can be said that it is preferable to provide a plated layer having a hardness higher than that of the engine head on the outer surface of at least the threaded portion and the tapered portion (the portion that comes into contact with the engine head during mounting) of the housing.

  Next, a sample of a glow plug having a plating layer with various changes in the ten-point average roughness Rz (μm) of the surface is prepared, and for each sample, the portion corresponding to the seating surface and the hole FS When the sample is screwed into the jig JG having a lubricant applied to the peripheral surface, a force (axial force) F (kN) along the axial direction applied to the sample housing and a rotational torque Tq (N M) was measured. And the value of Tq / F was computed about each sample. Here, Tq / F corresponds to the rotational torque of the sample that increases per unit axial force. As Tq / F increases, the glow plug is attached to the engine head with sufficient tightening torque while suppressing deformation of the housing. It can be said that it can be attached.

  In addition, the elastic limit along the axial direction in the housing where the thread diameter of the thread portion is M8 (maximum axial force that the housing that is elastically deformed when the axial force is released without causing plastic deformation in the housing) Is about 5N. In terms of ensuring airtightness, it is preferable that the tightening torque when the glow plug is attached to the engine head is 10 N · m or more in consideration of engine vibration and heat. Therefore, if Tq / F is 2.0 or more, the glow plug can be attached to the engine head with a sufficient tightening torque without exceeding the elastic limit of the housing, and while maintaining good airtightness, It can be said that deformation and the like can be effectively suppressed. Therefore, in this test, each sample was evaluated based on Tq / F = 2.0.

  FIG. 6 is a graph showing the relationship between the ten-point average roughness Rz (μm) of the plated layer surface and Tq / F. In each sample, the thread diameter of the thread portion was M8, and the plating layer was formed of an alloy containing Zn as a main component and containing Ni (Zn—Ni alloy). Further, the hardness of the plating layer was set to be equal to or higher than the hardness of the jig JG.

  As shown in FIG. 6, a sample with a 10-point average roughness Rz of 5 μm or less on the surface of the plating layer has a Tq / F of 2.0 or more, and glow with a sufficient tightening torque while suppressing deformation of the housing. It has been found that the plug can be attached to the engine head. This is because the adhesion of the housing (screw part and taper part) to the engine head has increased, and the coefficient of friction between the glow plug and the jig JG with respect to the rotation angle of the glow plug (that is, This is considered to be due to the fact that (rotational torque) is more likely to increase.

  In addition, for samples with various screw diameter changes, the relationship between the 10-point average roughness Rz of the plating layer surface and Tq / F was examined, and the 10-point average roughness Rz of the plating layer surface was 5 μm or less. Thus, it was confirmed that Tq / F was 2.0 or more.

  From the results of the above test, when attaching the glow plug to the engine head, the ten-point average roughness of the surface of the plating layer is set so that a sufficient tightening torque can be applied to the glow plug while suppressing deformation of the housing. It can be said that Rz is preferably 5 μm or less.

  Next, a sample of a glow plug in which a plating layer is formed with Zn (Zn plating sample), a sample of a glow plug in which a plating layer is formed with an alloy containing Zn as a main component and containing Ni (Zn-Ni alloy plating sample), Samples of glow plugs (Ni plating samples) in which a plating layer was formed of a metal containing Ni as a main component were prepared, and a neutral salt spray test based on JIS Z2371 was performed on each sample. Then, 24 hours, 48 hours, and 96 hours after the start of the test, the surface of the housing was observed to confirm whether red rust had occurred. Table 1 shows the test results of the test. In Table 1, “◯” means that the occurrence of red rust was not confirmed, and “x” means that the occurrence of red rust was confirmed.

  As shown in Table 1, it was confirmed that the samples (Zn plating sample and Zn-Ni alloy plating sample) in which the plating layer was formed of a metal mainly composed of Zn had excellent corrosion resistance. However, as shown in FIG. 5 (same test result of sample 1), when a plated layer is formed of Zn, friction generated between the engine head and the glow plug when the glow plug is attached to the engine head. The force is unlikely to increase, and there is a concern about deformation of the housing during installation. Therefore, it can be said that the plating layer is preferably formed of an alloy containing Zn as a main component and containing Ni from the viewpoint of realizing both good corrosion resistance and suppressing deformation of the housing at the time of mounting.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the control coil 10 is interposed between the heating coil 9 and the middle shaft 11 in order to prevent overheating of the heating coil 9, but the middle shaft 11 is brought into direct contact with the heating coil 9 for control. The coil 10 may be omitted.

  (B) In the above embodiment, the heater member 3 is constituted by the tube 8 and the heat generating coil 9 disposed inside the tube 8, and the technical idea of the present invention is applied to a so-called metal glow plug. Has been. On the other hand, the heater member is constituted by a cylindrical base made of an insulating ceramic, and a heating element that is provided in the base and is formed of a conductive ceramic and generates heat when energized from the central shaft 11, The technical idea of the present invention may be applied to a so-called ceramic glow plug. In this case, a heater member (a so-called surface heating type heater) in which a conductive film serving as a heating element is provided on the outer surface of the substrate may be used. Further, at least a part of the heat generating element may be formed of a conductive metal having excellent heat resistance (for example, an alloy containing tungsten as a main component).

  (C) In the above embodiment, the tool engaging portion 6 has a hexagonal cross section, but the shape of the tool engaging portion 6 is not limited to such a shape. Therefore, for example, the tool engaging portion 6 may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)] or the like.

  (D) The shape of the heater member 3 is not particularly limited, and may be, for example, an elliptical cross section, an elliptical cross section, or a polygonal cross section. Further, as the heater member, a so-called plate heater in which a plurality of insulating bases are formed in a plate shape and a heating element is sandwiched therebetween may be used.

  (E) In the above-described embodiment, a metal mainly composed of Fe or Ni is cited as the metal material constituting the tube 8, but this is an example, and the metal material constituting the tube 8 is limited to this. Is not to be done. Moreover, although the metal which has Fe etc. as a main component is mentioned as a metal material which comprises the heating coil 9 and the control coil 10, the constituent materials, such as the heating coil 9, are not limited to this.

  (F) In the above embodiment, a chromate layer may be provided on the surface of the plating layer 21. By providing the chromate layer, it is possible to prevent discoloration of the plating layer 21 and to improve the corrosion resistance.

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 2 ... Housing, 3 ... Heater member, 4 ... Shaft hole, 5 ... Screw part, 7 ... Tapered part, 21 ... Plated layer, CL1 ... Axis, EN ... Engine head.

Claims (2)

A cylindrical housing having an axial hole extending in the axial direction;
A heater member inserted into the shaft hole in a state in which at least a tip portion thereof protrudes from a tip of the housing;
The housing is
A threaded portion for screwing into a mounting hole provided in the engine head;
A glow plug having a tapered portion that decreases in outer diameter toward the tip end in the axial direction and that presses against a seating surface of the engine head when the screw portion is screwed into a mounting hole of the engine head. There,
A plating layer having a hardness higher than that of the engine head is provided on at least the outer surface of the screw portion and the taper portion of the housing, and is provided on the outer surface of the screw portion and the taper portion. A glow plug having a ten-point average roughness Rz of 5 μm or less on the surface of the plating layer.   The glow plug according to claim 1, wherein the plating layer is made of an alloy containing zinc as a main component and nickel.

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