JP3810876B2 - Glow plug for diesel engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a glow plug for a diesel engine used to improve the startability of a diesel engine, and in particular, a cylindrical housing body or a sheath type heater (hereinafter referred to as a “sheath type heater”) in order to cope with a direct injection multiple valve of a diesel engine. The present invention relates to a glow plug for a diesel engine in which a rod-like heater such as a sheathed heater is lengthened and further reduced in diameter.
[0002]
[Prior art]
Recent diesel engines tend to be of direct injection type, so-called direct injection, and accordingly, a glow plug for improving startability of the engine at low temperatures is also attached to the cylinder head together with the fuel injection nozzle. And the front-end | tip part of the sheathed heater which is a rod-shaped heater faces a main combustion chamber, It is comprised so that it may become an ignition assistance source by preheating this chamber.
Since the glow plug used in such a direct injection type diesel engine faces the main combustion chamber through the wall surface of the cylinder head, it is necessary to form the entire length longer than the type that preheats the auxiliary combustion chamber. is there.
[0003]
Conventionally, in this type of glow plug, since the housing body is screwed into a mounting hole having a threaded portion formed in the cylinder head and fastened, the following problems occur. That is, this type of glow plug has a seat surface portion that ensures airtightness in the main combustion chamber by abutting the end surface of the housing body against a stepped portion formed by a small-diameter hole provided in the mounting hole on the cylinder head side. In addition, the screw portion formed on the rear end side of the housing main body is screwed into the screw portion provided on the inner wall of the mounting hole to be fastened and fixed.
[0004]
However, in such a structure, as the length between the seat surface portion and the screw portion becomes longer, the compressive load due to the tightening torque to the screw portion of the housing body acts in the axial direction, so that the housing main body has an outer diameter. There is a risk of buckling deformation due to bending or bending in the direction or the inner diameter direction. When such buckling deformation occurs, the overall length of the housing body is substantially shortened, and the insulating bush that closes the outer end of the external connection terminal inserted into the housing body is detached from the end of the housing body, There is a possibility that the sealing performance at the rear end of the housing cannot be secured, or that the lead wire is disconnected due to the wobbling of the external connection terminal.
[0005]
[Problems to be solved by the invention]
For this reason, according to Japanese Utility Model Publication No. 4-5896, the present applicant configures the insulating bush so as to be movable with respect to the external connection terminal, thereby causing the above-mentioned problem associated with the buckling deformation due to the compressive load in the axial direction of the housing body. Proposes a solution to the problem. However, such conventional glow plugs are only premised on buckling deformation accompanying the compressive load of the housing body. In particular, recent glow plugs are required to have a smaller diameter and a longer length than conventional ones, and the housing body is likely to buckle and deform, and more aggressive measures are desired. Yes.
[0006]
For example, in a conventional glow plug, free cutting steel such as a carbon steel material for machine structure (low carbon steel) that is easy to cut is mainly used for the housing body. Further, M10 screws are mainly used as screw portions for screwing the housing body into the cylinder head.
However, such materials and threaded parts tend to have insufficient strength against tightening torque, and in particular with modern glow plugs, where the length of the housing body tends to be long and small, tightening of the threaded parts Insufficient strength is a problem.
[0007]
Further, the glow plug is particularly long and has a length on the tip side that is longer than the screw portion on the outer peripheral portion of the housing body, resulting in insufficient strength against the tightening torque. The above-described buckling deformation has been dealt with by using S45C or the like as the material of the housing body.
[0008]
However, future diesel engines tend to have a direct-injection multi-valve system, and even glow plugs tend to have longer and thinner housing bodies and rod heaters, which can improve the strength of the housing body. It is necessary to take such measures.
In particular, in the above-described glow plug for which a reduction in diameter is required, it is difficult to use the M12 screw, and even if a material such as S45C is used, it is difficult to compensate for the aforementioned insufficient strength against the tightening torque.
[0009]
Here, the lengthening of the glow plug described above is necessary by adopting it in a direct injection diesel engine. Further, the reduction in diameter is necessary when dealing with the increase in the number of valves, and it is necessary to reduce both the sheath diameter (heater diameter) and the housing diameter, so that such a request can be met. It is hoped that some measures will be taken.
[0010]
The present invention has been made in view of such circumstances, and in order to cope with the direct injection multi-valve of a diesel engine, the length of a rod-shaped heater such as a cylindrical housing body or a sheathed heater is further increased. It is possible to easily cope with the diameter increase, and to compensate for the lack of strength that occurs in the housing body against the tightening torque due to screwing into the mounting hole of the cylinder head of the housing body even with such a long and thin diameter. The purpose is to obtain a diesel engine glow plug that is excellent in processability, strength and cost.
[0011]
[Means for Solving the Problems]
In order to meet such an object, a glow plug for a diesel engine according to the present invention includes a cylindrical housing body having a screw portion for fixing to a mounting hole provided in a cylinder head of the diesel engine, and a tip of the housing body. Glow plug for diesel engine, comprising a rod-like heater press-fitted to the side, and having a seat surface portion that keeps the airtightness of the combustion chamber of the engine by pressing the tip of the housing body against the stepped portion provided in the mounting hole In the inner peripheral portion of the housing body, a large-diameter hole extending from the front end of the housing main body to the rear end side, and a heater holding portion that is adjacent to the large-diameter hole and into which a bar heater is press-fitted, are formed. the heater holding portion, and the threaded portion positioned at a position spaced apart in the axial direction of the housing body, the outer periphery of the housing body A distal end side of the threaded portion in and to the portion of the at least between the sheet surface and the heater holding portion, were subjected to heat treatment such as induction hardening.
[0012]
Here, the glow plug is tightened and fixed by screwing the outer peripheral thread portion of the housing body into the mounting hole provided in the cylinder head so that the tip of the rod heater faces the main combustion chamber in the direct injection type diesel engine. Yes.
[0013]
According to the present invention, when the outer peripheral thread portion of the housing body is screwed into the cylinder head mounting hole and tightened, even if a compressive load is applied in the axial direction, the housing body is subjected to heat treatment such as induction hardening to increase the strength. Therefore, buckling deformation does not occur.
[0014]
According to the present invention, in order to cope with the direct injection multi-valve operation, even if the rod-shaped heater such as the cylindrical housing main body or the sheathed heater in the glow plug is elongated or further reduced in diameter, the housing main body It is possible to obtain a glow plug for a diesel engine that can make up for a lack of strength in the housing body against a tightening torque caused by screwing into the mounting hole of the cylinder head.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
1 to 3 show one embodiment of a glow plug for a diesel engine according to the present invention. In these drawings, an outline of the configuration of the glow plug for a diesel engine, indicated as a whole by reference numeral 10, is shown in FIGS. This will be further described with reference to FIG.
In the figure, reference numeral 11 denotes a sheath made of a heat-resistant metal material, which will be described later, and reference numerals 12 and 13 denote first and second heating elements embedded in the sheath 11 with a heat-resistant insulating powder 14 such as magnesia as shown in FIGS. A sheath heater 15 as a rod heater is constituted by the second spiral heating wire.
[0016]
In this embodiment, the sheathed heater 15 has a two-stage structure in which the distal end side of the sheath 11 is a small diameter portion 11a and the rear end side is a large diameter portion 11b. In addition, the first spiral heating wire 12 is embedded on the distal end side of the small diameter portion 11a of the sheath 11, and the second spiral heating wire 13 extends from the rear end side of the small diameter portion 11a to the large diameter portion 11b. Are buried. The second spiral heating wire 13 is formed of a material having a positive resistance temperature coefficient larger than that of the first spiral heating wire 12, and supplies a large current to the first spiral heating wire 12 in the initial energization. In addition to rapidly generating heat, after a certain period of time has elapsed, the energization current is reduced by its own heat generation and functions as a control body that controls the energization current to the first spiral heating wire 12.
[0017]
Reference numeral 16 denotes a cylindrical housing body that holds the sheathed heater 15 at the tip, and an electrode rod 18 is concentrically disposed at the rear end of the housing body 16 via an insulating bush 17 as shown in FIG. The tip end side of the electrode rod 18 is inserted into the sheath 11. In this embodiment, the case where the electrode rod 18 is formed by joining the distal electrode rod 18a inserted into the rear end portion of the sheath 11 as a separate member and covered with the insulating tube 18b is shown.
[0018]
As shown in FIG. 2, the distal end portion 16 a of the cylindrical housing body 16 is formed on a seat portion 2 a formed by a small-diameter step portion provided in the plug mounting hole 2 in the cylinder head 1 of the engine that is not shown in its entirety. It is a part which becomes the seat surface part for obtaining the airtightness of the combustion chamber 3 by being attached.
Further, a screw portion 16b for screwing and fixing the glow plug 10 to the cylinder head 1 is formed at a portion near the rear end of the housing body 16 by being screwed into a screw portion formed in the plug mounting hole 2. Has been. In FIG. 2, reference numeral 19 denotes a nut that is screwed into a threaded portion on the outer end side of the electrode rod 18.
[0019]
According to the present invention, in the glow plug 10 for a diesel engine having the above-described configuration, at least the screw portion 16b is provided at the outer peripheral portion of the housing body 16 having the screw portion 16b for screwing and fixing to the mounting hole 2 provided in the cylinder head 1. Excluded is induction hardening as a heat treatment for the portion (the portion indicated by A in FIGS. 1 and 2) reaching the leading end portion 16a which becomes the sheet surface portion.
[0020]
According to such a configuration, the plug mounting hole 2 in which the outer peripheral thread portion 16b of the housing body 16 is provided in the cylinder head 1 so that the tip of the sheathed heater 15 faces the main combustion chamber 3 in the direct injection diesel engine. In the glow plug 10 that is fastened and fixed by being screwed into the housing, particularly the strength between the screw portion 16b of the housing main body 16 and the tip end portion 16a serving as the seat surface portion can be improved. Accordingly, when the outer peripheral threaded portion 16b of the housing body 16 is screwed into the threaded portion 2b of the mounting hole 2 of the cylinder head 1 to be fastened and fixed, even if a compressive load is applied in the axial direction between the seat surface portions 16a and 2a. Thus, the conventional buckling deformation of the housing body 16 is eliminated.
[0021]
Here, heat treatment such as induction hardening as described above may be performed on the housing body 16 as a single unit before assembly by press-fitting the glow plug 10.
However, the present invention is not limited to this, and after assembling the sheathed heater 15, the portion excluding the heater holding portion 20 due to the press-fitting of the sheathed heater 15 ( portions indicated by B and C in FIGS. 1 and 2 ) is subjected to heat treatment. Induction hardening may be performed. Also by such a method, the strength can be increased in the same manner as described above, and the buckling deformation due to the compressive load in the axial direction due to the tightening torque can be prevented.
[0022]
In the case where the sheathed heater 15 is held on the housing body 16 by brazing, it is necessary to control the quenching temperature to such an extent that the fixing portion by the brazing material is not melted when heat treatment such as induction quenching is performed after brazing. Also, when brazing after quenching, it is necessary to manage the brazing width because there is annealing during brazing .
[0023]
In particular, in the glow plug 10 described above, the length from the threaded portion 16b of the cylindrical housing body 16 to the tip end portion 16a serving as the seat surface portion (portion indicated by X in FIG. 2) is increased by direct injection of the diesel engine. In addition, as a result of the increase in the number of valves of the engine, the portion protruding from the housing body 16 of the sheathed heater 15 that is a rod heater (portion indicated by Y in FIG. 2 ) tends to be elongated. This heat treatment is effective in securing strength.
[0024]
Further, the recent glow plug 10 described above has a tendency to reduce the diameter of the housing main body 16 as well as the sheathed heater 15, and the above-described heat treatment is effective to compensate for the insufficient strength in such a case. It is.
[0025]
The induction hardening as the heat treatment described above may be such that a hardened layer is formed in the entire thickness, but in some cases, it may be a surface hardening that forms a hardened layer only on the surface layer. In the case of this surface quenching, it is possible to quench the portion indicated by A in the figure including the heater holding portion 20 in a state where the sheathed heater 15 is fixed and held in the housing body 16 by press fitting . Since such a housing body 16 is a cylindrical body and has a small thickness, it is advantageous to quench the entire thickness, but it is also possible to perform surface quenching.
[0026]
According to such a configuration, even if the glow plug 10 is elongated and further reduced in diameter, the housing main body 16 can withstand the tightening torque caused by screwing the housing main body 16 into the mounting hole 2 of the cylinder head 1. It is possible to compensate for the lack of strength, and it is possible to obtain a long glow plug which is excellent in workability and cost as well as strength. In particular, when induction hardening is adopted as the heat treatment described above, there is an advantage that mass productivity of the glow plug 10 can be secured. However, the present invention is not limited to this, and any heat treatment that can secure the strength of a necessary portion of the housing body 16 can be freely adopted.
[0027]
In the configuration described above, a general structural material such as S45C can be used as the material of the housing body 16, which is advantageous in terms of workability. If the strength is simply ensured, a material having high hardness may be used. However, since the housing body 16 has the above-described distal end portion 16a to be the sheet surface portion and needs to be threaded, header processing or cutting processing is required. It is necessary to consider such workability. According to the present invention, heat treatment such as induction hardening is performed in terms of cost, which is advantageous in terms of securing such workability and further ensuring strength.
[0028]
When heat treatment such as induction hardening as described above is performed after the assembly of the glow plug 10, attention must be paid to intrusion of rubber parts and cooling water. In consideration of removal of oxide scale, surface treatment, etc., it is advantageous to perform heat treatment when the housing body 16 is a single body.
[0029]
Here, in the above-described embodiment, the first spiral heating wire 12 has a positive resistance such as an iron chromium alloy material (Fe—Cr alloy material) or a nickel chromium alloy material (Ni—Cr alloy material). It is made of a conductive material having a relatively small temperature coefficient and functions as a heating element. One end of the first spiral heating wire 12 is electrically connected to the inner wall on the distal end side in the sheath 11.
At the other end of the first spiral heating wire 12, a second spiral heating wire 13 is provided between the electrode rod 18a and a predetermined interval. The second spiral heating wire 13 is formed of a conductive material having a large positive resistance temperature coefficient, such as a cobalt-based alloy material, and is configured to function as a control body.
[0030]
In this embodiment, as shown in FIG. 3, the connecting portion 23 for connecting the heat generating wires 12 and 13 is provided with straight portions extending from the ends of the spiral portions of the heat generating wires 12 and 13, respectively. It welds by welding etc. in the contacted state, and has provided a gap between them. However, such a connecting portion between the heat generating wires 12 and 13 may be a connection method that has been widely known conventionally. For example, a separate member for connection is provided between the heat generating wires, Various modifications, such as changing the helical pitch at the end and other parts, can be considered. FIG. 4 shows an example in which the spiral pitch is widened.
[0031]
Note that the present invention is not limited to the structure described in the above-described embodiment, and it goes without saying that the shape and structure of each part can be appropriately modified and changed.
For example, in the above-described embodiment, the sheathed heater 15 has been described in which the first spiral heating wire 12 serving as a heating element and the second spiral heating wire 13 serving as a control body are connected in series and embedded. However, the present invention is not limited to this. For example, the present invention may be a kind of material in which only a helical heating wire serving as a heating element is embedded, or may be the first and second control bodies together with the heating element as shown in FIG. Even if it is based on three kinds of materials in which the spiral heating wires 13 and 21 are embedded, it can be applied.
[0032]
In the embodiment described above, the sheathed heater 15 is illustrated with the tip of the narrow-diameter portion 11a. However, the present invention is not limited to this, and the sheathed heater using the sheath 11 having the same diameter as shown in FIG. It may be 15. Furthermore, it goes without saying that such a rod-shaped heater may be a ceramic heater that has been widely known.
[0033]
【The invention's effect】
As described above, according to the glow plug for a diesel engine according to the present invention, the front end side of the screw portion in the outer peripheral portion of the housing body having the screw portion for screwing and fixing to the mounting hole provided in the cylinder head of the diesel engine. In addition, since at least a portion between the sheet surface portion and the heater holding portion is subjected to a heat treatment such as induction hardening, the following excellent effects can be obtained.
[0034]
According to the present invention, it is possible to compensate for a lack of strength against the compressive load in the axial direction of the housing body with respect to the tightening torque of the glow plug by simply performing heat treatment (quenching treatment such as induction hardening) on at least a part of the housing body. Such buckling deformation can be prevented.
Therefore, according to the present invention, a long glow plug excellent in processability, strength, and cost can be obtained. In particular, according to the present invention, since a general structural material such as S45C can be used as the material of the housing body, the workability is excellent. In addition, according to the present invention, sufficient strength can be ensured by quenching, and the mass production effect of glow plugs can be enhanced by induction quenching as heat treatment.
[0035]
In particular, according to the present invention, in a diesel engine that is a direct injection type and is designed to be multi-valve, a long length of a rod-shaped heater such as a cylindrical housing body or a sheathed heater in a glow plug is required to cope with them. Even if the diameter is further reduced and the diameter is further reduced, it is possible to compensate for the lack of strength in the housing body against the tightening torque caused by screwing the housing body into the mounting hole of the cylinder head.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a side view showing a cross section of a main part of an embodiment of a glow plug for a diesel engine according to the present invention.
FIG. 2 is a cross-sectional view showing an embodiment of a glow plug for a diesel engine according to the present invention and showing an assembled state to a cylinder head.
FIG. 3 is an essential part cross-sectional view showing an example of a sheathed heater, showing an embodiment of a glow plug for a diesel engine according to the present invention.
FIG. 4 is a cross-sectional view of a main part of a sheathed heater showing another embodiment of a glow plug for a diesel engine according to the present invention.
FIG. 5 is a cross-sectional view of a main part of a sheathed heater showing still another embodiment of a glow plug for a diesel engine according to the present invention.
FIG. 6 is a cross-sectional view of a main part of a sheathed heater showing another embodiment of a glow plug for a diesel engine according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cylinder head, 2 ... Plug attachment hole, 2a ... Seat surface part, 3 ... Main combustion chamber, 10 ... Glow plug for diesel engines, 11 ... Sheath, 11a ... Small diameter part, 11b ... Large diameter part, 12, 13, DESCRIPTION OF SYMBOLS 21 ... Spiral heating wire, 14 ... Heat-resistant insulating powder, 15 ... Sheath heater (bar heater), 16 ... Housing main body, 16a ... Front-end | tip part used as a sheet | seat surface part, 16b ... Outer periphery screw part, 20 ... Heater holding part by press fit .

Claims (4)

Includes a tubular housing body having a threaded portion for fixing to the mounting hole provided in the cylinder head of a diesel engine, and a rod-like heater is pressed into the distal end side of the housing body, wherein the distal end portion of the housing body In the glow plug for a diesel engine, which is a seat surface portion that maintains the airtightness of the combustion chamber of the engine by being pressed against the stepped portion provided in the mounting hole,
A large-diameter hole that extends from the front end of the housing main body to the rear end side, and a heater holding portion that is adjacent to the large-diameter hole and into which a rod-shaped heater is press-fitted are formed on the inner peripheral portion of the housing main body.
The heater holding portion is positioned at a position separated from the screw portion in the axial direction of the housing body,
A glow plug for a diesel engine, characterized in that a heat treatment is applied to at least a portion between the seat surface portion and the heater holding portion on the front end side of the screw portion in the outer peripheral portion of the housing body. The glow plug for a diesel engine according to claim 1,
A glow plug for a diesel engine, wherein a heat treatment is performed on a portion of the outer peripheral portion of the housing body excluding a portion corresponding to a heater holding portion. In the glow plug for diesel engines according to claim 1 or 2,
Glow plug for diesel engines, characterized in that heat treatment is induction hardening. In the glow plug for diesel engines according to claim 1, claim 2 or claim 3,
The glow plug is tightened and fixed by screwing the outer peripheral thread portion of the housing body into the mounting hole provided in the cylinder head so that the tip of the rod heater faces the main combustion chamber in the direct injection type diesel engine. Glow plug for diesel engines.

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