JP6263406B2 - Glow plug with pressure sensor - Google Patents

Description

  The present invention relates to a glow plug with a pressure sensor having a function of detecting combustion pressure in addition to a function of promoting ignition in a combustion chamber of an engine.

2. Description of the Related Art Conventionally, a glow plug with a pressure sensor that also has a function of detecting a combustion pressure is known as a glow plug used for assisting starting of a diesel engine. This glow plug with a pressure sensor (hereinafter also simply referred to as a glow plug) is attached to the engine head with a heater exposed in the combustion chamber, and in addition to promoting the ignition of fuel, the combustion pressure ( (Combustion gas pressure) is received by the heater, and the displacement of the heater is detected by a sensor unit having a piezoelectric element, a strain sensor (gauge), or the like. The glow plug includes, for example, a cylindrical metal shell, a cylindrical metal outer cylinder held on the front end side of the metal shell, a rod-shaped ceramic heater held in the outer cylinder, a sensor unit, Have Among these, the ceramic heater and the outer cylinder are disposed so as to be displaceable in the axial direction according to the combustion pressure, and the displacement of the ceramic heater is detected by the sensor unit.
In the conventional glow plug, the outer cylinder is fixed to the ceramic heater by press-fitting (an interference fit), brazing, or the like in the entire axial direction. For example, Patent Document 1 discloses such a glow plug (see FIG. 1 of Patent Document 1 and the description thereof).

WO2013 / 099226A1 publication

  However, in the form in which the ceramic heater is held in the whole axial direction of the outer cylinder by press-fitting, since the portion to be press-fitted in the outer cylinder is long, a large press-fitting load is required for press-fitting, and the press-fitting property is poor. On the other hand, in the form in which the ceramic heater is held in the entire axial direction of the outer cylinder by brazing, the brazed portion becomes longer, which increases the cost.

Therefore, the inventors hold the ceramic heater by press-fitting, brazing, or the like at the front end side portion of the outer cylinder, while the outer cylinder does not hold the ceramic heater at the rear end side portion of the outer cylinder ( A configuration in which the outer cylinder was separated from the ceramic heater was considered.
However, in this embodiment, the following problems occur. That is, since the glow plug is attached to the engine head with the heater tip of the ceramic heater and the outer cylinder protruding portion of the outer cylinder exposed in the combustion chamber, the ceramic heater and the outer cylinder are heated toward the tip side. It becomes. Since the outer cylinder is made of metal, it expands greatly as compared to a ceramic heater when exposed to high temperatures. For this reason, even if the outer cylinder is initially fixed to the ceramic heater at the tip end portion by press fitting, the tip end portion of the outer cylinder expands greatly and its diameter increases. There is a possibility that a gap may be formed between the outer peripheral surface of the ceramic heater. Alternatively, even if the outer cylinder is initially fixed to the ceramic heater at the tip side portion by brazing, when the brazing material is melted by heat, the gap between the inner peripheral surface of the outer cylinder and the outer peripheral surface of the ceramic heater is similarly reduced. There may be gaps. Then, the combustion gas may enter the rear end side of the glow plug from the glow plug through the gap.

  The present invention has been made in view of such a current situation, and can hold the ceramic heater by the outer cylinder reliably and at low cost, and can also be used when the inner peripheral surface of the outer cylinder and the outer peripheral surface of the ceramic heater are in use. An object of the present invention is to provide a glow plug with a pressure sensor that can prevent combustion gas from entering the rear end side of the outer cylinder through the gap.

One aspect of the present invention for solving the above-described problems is a cylindrical metal shell having an axial hole extending in the axial direction, and a metal body that is cylindrical and is disposed in the shaft hole of the metal shell. An outer cylinder having an outer cylinder projecting portion that protrudes from the distal end of the metallic shell to the distal end side in the axial direction from the distal end of the metal shell, and a rod-like ceramic made of ceramic and held by the outer cylinder, from the distal end of the outer cylinder A ceramic heater that has a heater tip projecting toward the tip side in the axial direction and is held in the metal shell together with the outer cylinder so as to be displaceable in the axial direction, and a sensor unit that detects the displacement of the ceramic heater And a holding member that is cylindrical and made of metal, is arranged in the shaft hole and is held by the metal shell, and holds the outer cylinder and the ceramic heater in the inside thereof so that the displacement is possible. With pressure sensor A Ropuragu, internal the outer tube hole of the outer cylinder, and the heater holding portion for holding the ceramic heater to the inside of itself, to the distal end side of the axial direction than the heater holding portion, the outer tube projecting A heater separating portion that surrounds and surrounds the ceramic heater, and the outer cylinder protruding portion of the outer cylinder surrounds the ceramic heater inside itself in a loose-fitting manner. The holding member is located closer to the tip end side in the axial direction than the position held by the metal shell, and from the heater holding portion among the heater separating portions inside the outer cylinder hole of the outer cylinder. It is a glow plug with a pressure sensor welded to a position separated from the tip end side in the axial direction .

  In the glow plug with a pressure sensor of the present invention, the inside of the outer cylinder hole of the outer cylinder has a heater holding part for holding the ceramic heater therein, while the outer cylinder protruding part of the outer cylinder has the ceramic heater inside thereof. Is enclosed in a loose fit. For this reason, for example, in the form in which the ceramic heater is held by the heater holding portion by press-fitting, compared to the case where the ceramic heater is held in the entire axial direction of the outer cylinder, the portion to be press-fitted in the outer cylinder (that is, heater holding) Part) is shortened, so that the press-fit load can be reduced and the press-fit property can be improved. Further, in the form in which the ceramic heater is held by the heater holding portion by brazing, the brazing portion can be shortened as compared with the case where the ceramic heater is held in the entire axial direction of the outer cylinder, so that the cost can be reduced.

In addition, since the heater holding portion of the outer cylinder is disposed in the shaft hole of the metal shell, it is less likely to be exposed to high temperatures during use than the outer cylinder protrusion protruding from the metal shell. For this reason, for example, in the form in which the ceramic heater is held by the heater holding portion by press fitting, the heater holding portion is largely thermally expanded to prevent a gap from being generated between the inner peripheral surface of the heater holding portion and the outer peripheral surface of the ceramic heater. it can. Further, in the form in which the ceramic heater is held by the heater holding portion by brazing, it is possible to prevent the brazing material from being melted due to high temperature and causing a gap between the inner peripheral surface of the heater holding portion and the outer peripheral surface of the ceramic heater. Therefore, it is possible to prevent the combustion gas from entering the rear end side of the outer cylinder through the gap between the inner peripheral surface of the outer cylinder and the outer peripheral surface of the ceramic heater.
Further, when the holding member is welded to the heater holding portion in the outer cylindrical hole, heat generated during welding is transmitted to the ceramic heater, and problems such as cracking and cracking of the ceramic heater are likely to occur.
On the other hand, in this glow plug with a pressure sensor, a heater separation portion separated from the ceramic heater is provided inside the outer cylinder hole, and a holding member is welded to the heater separation portion. For this reason, the heat generated during welding is not easily transmitted to the ceramic heater, and a reliable glow plug is obtained in which problems such as cracking and cracking of the ceramic heater are prevented.
When the glow plug is attached to the engine and the engine is operated, high-temperature and high-pressure combustion gas repeatedly reaches the holding member through the gap between the glow hole, the heater tip, and the outer cylinder projection. Then, the holding member instantaneously expands thermally, and the dimension in the axial direction increases (extends in the axial direction). With this expansion, the outer cylinder and the ceramic heater held by the holding member are displaced in the axial direction. Since the displacement accompanying this thermal expansion is superimposed on the displacement of the ceramic heater according to the combustion pressure, the detection accuracy of the combustion pressure may be reduced. More specifically, when a holding member in a form welded to the outer cylinder at a position on the distal end side in the axial direction from the position held by the metal shell is used as the holding member, the heated holding member is Since the outer cylinder and the ceramic heater are expanded so as to move to the tip side, unnecessary fluctuations (fluctuations in the direction in which the displacement and pressure increase appear to be small) are added to the displacement of the ceramic heater according to the combustion pressure. For this reason, the detection precision of combustion pressure falls.
On the other hand, in the above-described glow plug with a pressure sensor, the holding member is on the tip end side in the axial direction from the position of the holding member held directly or indirectly by the metal shell, and the heater is separated from the inside of the outer cylinder hole. Among the portions, the welding is performed at a position spaced apart from the heater holding portion toward the distal end side in the axial direction. When the holding member is exposed to the combustion gas as described above, the holding member is thermally expanded and extends toward the tip end side in the axial direction. On the other hand, among the outer cylinders, the combustion gas reaches also between the ceramic heater and the outer cylinder protruding part that surrounds the ceramic heater while being separated from each other. It extends toward the tip side. That is, the portion from the portion where the holding member is welded to the heater holding portion in the heater separating portion is also thermally expanded and extends toward the tip end side in the axial direction. Therefore, at the same time that the holding member extends toward the tip end side with the combustion gas, the portion from the portion where the holding member is welded to the heater holding portion in the heater separation portion also extends toward the tip end side, so that the holding member The displacement of the outer cylinder and the ceramic heater due to the extension is partially offset. Thus, unnecessary fluctuations in the outer cylinder and the ceramic heater (variations in the direction in which the displacement and pressure increase appear to be small) are less likely to be added to the displacement of the ceramic heater according to the combustion pressure, so that the detection accuracy of the combustion pressure can be improved. .

In the form of the “heater holding part”, only a part in the axial direction inside the outer cylinder hole is used as the heater holding part . A plurality of heater holding portions can be provided inside the outer cylinder hole.

  Moreover, as a form which hold | maintains a ceramic heater with a "heater holding | maintenance part", the form which hold | maintains a ceramic heater by press-fitting a ceramic heater to an outer cylinder and making it an interference fit is mentioned, for example. Further, there is a mode in which the ceramic heater is held by caulking the outer cylinder radially inward after the ceramic heater is loosely inserted into the outer cylinder. Moreover, after the ceramic heater is loosely inserted into the outer cylinder, the ceramic heater is held by filling the brazing material in the gap between the outer cylinder and the ceramic heater and brazing.

  The outer cylinder protruding portion surrounds the ceramic heater inside itself in a loose-fitting manner. The outer cylinder protruding portion and the inner ceramic heater are in the axial direction without the outer cylinder protruding portion holding the inner ceramic heater. The outer cylinder protruding portion surrounds the internal ceramic heater so as to be relatively movable. Specifically, the outer cylinder protruding portion surrounds the inner ceramic heater while being separated, or the outer cylinder protruding portion and the inner ceramic heater are in contact with each other, and the outer cylinder protruding portion is the inner ceramic heater. The form which does not hold | maintain is mentioned.

The “outer cylinder” may have a metal layer such as a plating layer mainly composed of Au, Ag, Cu, Ni or the like on the inner peripheral surface thereof.
As a form of the “ceramic heater”, there may be mentioned one in which a heating resistor is integrated with a ceramic base made of insulating ceramic. Specifically, a form in which the heat generating resistor is embedded in the ceramic base and a form in which the heat generating resistor is exposed to the outside of the ceramic base are exemplified. Moreover, as a heating resistor, what consists of metals, such as an electroconductive ceramic and W (tungsten), is mentioned.
The “sensor unit” is configured using, for example, a strain sensor (strain gauge), a semiconductor strain gauge having a piezoresistor, a displacement sensor such as a piezoelectric element, and a member that guides the displacement of the ceramic heater to the displacement sensor. Things.

The position where the “holding member” is welded in the “heater separating portion” can be appropriately selected. For example, it may be in the form with a welded retaining member to the distal end portion of the heater spaced portion, Or, the holding members at positions spaced from each leading end and the trailing end of the heater spaced portion (for example, a central portion of the heater spaced portion) It is good also as a form which welded.

The “holding member” may be welded to the “heater separating portion” of the outer cylinder over the entire circumference in the circumferential direction, or may be welded at a plurality of locations with a gap in the circumferential direction.
The “holding member” may be directly held by the metal shell, or may be indirectly held by the metal shell through another member. Further, the holding member may be fixed to the metal shell or the like over the entire circumference in the circumferential direction, or may be fixed at a plurality of locations with gaps in the circumferential direction. Examples of the fixing form of the holding member to the metal shell include welding, brazing, and caulking.
However, when the “holding member” has a function as a seal member that hermetically divides the annular space between the inner peripheral surface of the metal shell and the outer peripheral surface of the outer cylinder in the axial direction, the holding member is removed. While welding to the cylinder over the entire circumference, the holding member may be welded or brazed to the metal shell or the like over the entire circumference.

In addition, as a form of the “holding member”, for example, an outer cylinder side part welded to the outer cylinder, a metal part side part positioned on the rear end side in the axial direction than this, and held by the metal shell, etc., A form having an intermediate deformation part which is located between these and which is deformed in accordance with the axial displacement of the ceramic heater and the outer cylinder can be mentioned . Further, as the form of the intermediate deformable section include the form of the ring-shaped diaphragm (thin film) and bellows of the bellows.

  As described above, the holding member may be directly held by the metal shell, or may be indirectly held by the metal shell via another member. In the form in which the holding member is directly held by the metal shell, the position in the axial direction of the portion of the holding member that is fixed to the metal shell (for example, the welded portion of the holding member) is Corresponding to “position held in”. Moreover, in the form in which the holding member is indirectly held by the metal shell via another member, the position in the axial direction of the portion of the holding member that is fixed to the other member (for example, the welded portion of the holding member) is Corresponds to “the position where the (holding member) is held by the metal shell”.

It is a partial fracture longitudinal cross-sectional view of the glow plug with a pressure sensor which concerns on embodiment. It is the expansion longitudinal cross-sectional view which expanded the site | part of a heater front-end | tip part and an outer cylinder protrusion part vicinity among the glow plugs with a pressure sensor which concerns on embodiment. It is the expansion longitudinal cross-sectional view which expanded the site | part of the holding member, the outer cylinder hole inside, and the heater rear-end part vicinity among the glow plugs with a pressure sensor which concern on embodiment. It is the expansion longitudinal cross-sectional view which expanded the site | part in the vicinity of a heater rear end part, a connection ring, and a center shaft front-end | tip part among the glow plugs with a pressure sensor which concerns on embodiment. It is explanatory drawing explaining the motion of a holding member, an outer cylinder, and a ceramic heater when heated with combustion gas.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 4 show a glow plug 1 with a pressure sensor according to the present embodiment (hereinafter also simply referred to as a glow plug 1). 1 to 4, the direction along the axis AX of the glow plug 1 and its metal shell 10 is defined as the axial direction HJ, and the side (lower side in the figure) on which the ceramic heater 20 is disposed in the axial direction HJ. The front end side GS and the opposite side (upper side in the figure) are defined as the rear end side GK.

  The glow plug 1 is attached to the engine head with the ceramic heater 20 and the outer cylinder 30 exposed in the combustion chamber of a diesel engine (not shown), and in addition to promoting the ignition of fuel, combustion in the combustion chamber Used to detect pressure (combustion gas pressure). The glow plug 1 includes a metal shell 10, a ceramic heater 20, an outer cylinder 30, a holding member 40, a sensor unit 50, and the like.

  Among these, the metal shell 10 is a cylindrical metal member (specifically, carbon steel) having a shaft hole 10h penetrating in the axial direction HJ. The metal shell 10 is positioned between the cylindrical front end cap member 11 located on the front end side GS, the cylindrical rear end cap member 15 located on the rear end side GK, and extends in the axial direction HJ. It consists of a cylindrical metal fitting body member 13 (see FIG. 1). The rear end portion 11k of the front end cap member 11 and the front end portion 13s of the metal fitting body member 13 are joined (specifically, welded) via a flange portion 53c of a sensor support member 53 described later (see FIG. 3). . The rear end portion 13k of the metal fitting body member 13 and the front end portion 15s of the rear end cap member 15 are directly joined (specifically, welded) (see FIG. 1).

  The distal end portion 11s (see FIG. 3) of the distal end cap member 11 has a tapered shape with a diameter decreasing toward the distal end side GS. When the glow plug 1 is attached to the engine head (not shown), the outer peripheral surface 11sm having a tapered shape at the tip end portion 11s is pressed against the seat surface of the plug hole to ensure airtightness in the combustion chamber. Further, an attachment portion 13d having a male screw for attaching the glow plug 1 to the engine head is provided in a portion of the metal fitting body member 13 on the rear end side GK (see FIG. 1). The rear end side GK portion of the rear end cap member 15 is provided with a tool engaging portion 15e that has a hexagonal cross section and engages a tool when the glow plug 1 is attached to the engine head. Yes. The rear end cap member 15 is loaded with a cylindrical sealing rubber member 17 in such a manner as to protrude to the rear end side GK from the rear end 15b of the rear end cap member 15.

  Next, the ceramic heater 20 will be described. The ceramic heater 20 is a ceramic heater having a round bar shape with a diameter d1 = 3.1 mm extending in the axial direction HJ and having a tip that is curved into a hemispherical shape. Specifically, the ceramic heater 20 includes a conductive ceramic (specifically, tungsten carbide as a conductive component) in a ceramic base 26 made of an insulating ceramic (specifically, a silicon nitride ceramic). A heating resistor 27 made of silicon ceramic is embedded.

  Of these, the heating resistor 27 includes a heating portion 27c, a pair of lead portions 27d and 27e, and a pair of electrode extraction portions 27f and 27g. The heat generating portion 27c (see FIG. 2) is disposed on the distal end side GS, has a U-shaped bent shape, and generates a high temperature when energized. The pair of lead portions 27d and 27e (see FIGS. 2 to 4) is connected to both ends of the heat generating portion 27c and extends in parallel to the rear end side GK. The pair of electrode extraction portions 27f and 27g (see FIGS. 3 and 4) are connected to the pair of lead portions 27d and 27e on the rear end side GK, and are exposed to the outer peripheral surface 26m of the ceramic base 26. One electrode extraction portion 27g is located on the rear end side GK with respect to the other electrode extraction portion 27f.

  The ceramic heater 20 is held by the outer cylinder 30. Specifically, in the ceramic heater 20, the heater front end portion 21 (see FIG. 2) protrudes toward the front end side GS from the front end 31 a of the outer cylinder 30, and the heater rear end portion 23 (see FIGS. 3 and 4) is outside. A heater intermediate portion 22 (see FIGS. 2 to 4) that protrudes to the rear end side GK from the rear end 33 b of the tube 30 and is located between the heater front end portion 21 and the heater rear end portion 23 is located inside the outer tube 30. It is held by the outer cylinder 30 in the form of being arranged. Moreover, the ceramic heater 20 is hold | maintained at the metal shell 10 so that it can displace to the axial direction HJ with the outer cylinder 30 so that it may mention later.

  The heater rear end 23 of the ceramic heater 20 is connected to an intermediate shaft member 83 (see FIG. 4) via a connection ring 81 (see FIGS. 3 and 4). The connection ring 81 is a cylindrical metal member (specifically, stainless steel) that extends in the axial direction HJ. The connection ring 81 is disposed inside the shaft hole 10 h of the metal shell 10 on the radially inner side of the displacement transmission member 51 and the sensor support member 53 described later. The heater rear end portion 23 of the ceramic heater 20 is press-fitted into the tip side GS portion of the connection ring 81. On the other hand, a fitting portion 83sa of the middle shaft front end portion 83s of the middle shaft member 83 is press-fitted into a portion of the connection ring 81 on the rear end side GK. Thereby, one electrode extraction portion 27 g of the ceramic heater 20 is electrically connected to the central shaft member 83 via the connection ring 81.

  The middle shaft member 83 is a round bar-shaped metal member (specifically, stainless steel member) extending in the axial direction HJ. The middle shaft member 83 is inserted into the shaft hole 10 h of the metal shell 10 while being separated from the metal shell 10. Further, a portion of the middle shaft member 83 on the front end side GS is disposed on the radially inner side of a displacement transmission member 51 and a sensor support member 53 to be described later and spaced apart from these. The middle shaft member 83 includes a middle shaft front end portion 83s having a large diameter located on the front end side GS, and a middle shaft body portion 83c having a smaller diameter than the middle shaft front end portion 83s and extending from the middle shaft front end portion 83s to the rear end side GK. . As described above, the connection ring 81 is press-fitted into the fitting portion 83sa of the distal end GS in the middle shaft distal end portion 83s.

  Next, the outer cylinder 30 will be described. The outer cylinder 30 (see FIGS. 2 to 4) is a cylindrical metal member extending in the axial direction HJ. Specifically, the outer cylinder 30 includes a cylindrical metal body (specifically, stainless steel) outer cylinder body 37 and an Au plating layer formed on the inner peripheral surface of the outer cylinder body 37. And a metal layer 38. The outer cylinder 30 has a stepped shape in which the outer diameter is equal in the axial direction HJ, while the inner diameter is larger at the front end side GS portion and smaller at the rear end side GK portion. Specifically, the outer diameter d2 of the outer cylinder 30 is d2 = 4.1 mm. Further, the inner diameter d3 of the distal end side GS portion of the outer cylinder 30 (the outer cylinder protruding portion 31 and the heater separating portion 34 described later) is d3 = 3.3 mm. On the other hand, the inner diameter (equal to the diameter d1 of the ceramic heater 20) in the interference-fitted state in the rear end side GK portion (heater holding portion 35 described later) of the outer cylinder 30 is 0.2 mm smaller than the inner diameter d3. 1 mm.

  The outer cylinder 30 is held by the metal shell 10 together with the ceramic heater 20 so as to be displaceable in the axial direction HJ. Specifically, the outer cylinder protruding portion 31 (see FIG. 2) protrudes toward the distal end GS from the distal end 11sa of the metal shell 10, and the outer cylinder hole interior 33 (see FIGS. 3 and 4) is the shaft hole of the metal shell 10. In a state of being disposed within 10h, the metal shell 10 is held so as to be displaceable in the axial direction HJ via a holding member 40, a displacement transmission member 51, a sensor support member 53, and the like which will be described later.

  On the other hand, the outer cylinder 30 holds the heater intermediate portion 22 of the ceramic heater 20 by press-fitting (interference fitting). Specifically, the outer cylinder protruding portion 31 of the outer cylinder 30 surrounds the ceramic heater 20 inside thereof while being separated. As described above, the inner diameter d3 of the outer cylinder protruding portion 31 is d3 = 3.3 mm. On the other hand, the diameter d1 of the ceramic heater 20 is d1 = 3.1 mm. Accordingly, a gap SA of 0.1 mm is formed over the entire circumference between the inner peripheral surface 31 n of the outer cylinder protruding portion 31 and the outer peripheral surface 20 m of the ceramic heater 20.

  On the other hand, the outer cylinder hole inside 33 of the outer cylinder 30 is located at the front end side GS and is connected to the above-described outer cylinder protruding portion 31, and the heater holding portion 35 located at the rear end side GK. It consists of. Among these, the heater separation part 34 surrounds the ceramic heater 20 inside itself while being separated. Specifically, as described above, the inner diameter d3 of the heater separating portion 34 is d3 = 3.3 mm, similar to the inner diameter d3 of the outer cylinder protruding portion 31 described above. On the other hand, the diameter d1 of the ceramic heater 20 is d1 = 3.1 mm. Therefore, a 0.1 mm gap SB is also formed over the entire circumference between the inner peripheral surface 34 n of the heater separating portion 34 and the outer peripheral surface 20 m of the ceramic heater 20.

Note that a holding member 40 described later is welded to the heater separating portion 34. A portion of the heater separating portion 34 where the holding member 40 is welded is referred to as a welded portion 34c. In addition, a portion of the heater separating portion 34 that is located on the front end side GS from the welding portion 34c and continues to the outer cylinder protruding portion 31 is a front end side portion 34s and is located on the rear end side GK from the welding portion 34c. A portion connected to the heater holding portion 35 is defined as a rear end side portion 34k.
On the other hand, the heater holding unit 35 holds the ceramic heater 20 therein by press-fitting (interference fitting). In the heater holding portion 35, one electrode extraction portion 27 f of the ceramic heater 20 is in contact with the metal layer 38 of the outer cylinder 30 and is electrically connected to the outer cylinder 30.

  Next, the holding member 40 will be described. The holding member 40 (see FIG. 3) is a cylindrical member made of metal (specifically, stainless steel). The holding member 40 is disposed in an annular space KA between the inner peripheral surface of the metal shell 10 (specifically, the inner peripheral surface 11n of the tip cap member 11) and the outer peripheral surface 30m of the outer cylinder 30. The holding member 40 is held by a sensor support member 53, which will be described later, at a position W1 in the axial direction HJ, and held by the metal shell 10 via this, while the holding member 40 is outside at a position W2 on the distal side GS from the position W1. The cylinder 30 is held.

  Specifically, the holding member 40 includes an outer cylinder side part 41, a metal part side part 45, and an intermediate deformation part 43 positioned therebetween. Outer cylinder side part 41 of holding member 40 is a cylindrical part located in tip side GS, and holds outer cylinder 30 inside itself. Specifically, the outer cylinder side portion 41 is welded to the welding portion 34c of the heater separating portion 34 of the outer cylinder 30 over the entire circumference in the outer circumferential direction 30 at a position W2 on the distal end side GS with respect to the position W1 in the axial direction HJ. Has been. Further, the metal part side portion 45 is a part having a cylindrical shape larger in diameter than the outer cylinder side part 41 and located on the rear end side GK, and is held by the metal shell 10 via a sensor support member 53 described later. Specifically, the metal side portion 45 is externally fitted to the support tip portion 53s of the sensor support member 53 and welded over the entire circumference in the axial direction HJ at a position W1. Further, since the sensor support member 53 is welded to the metal shell 10 over the entire circumference in the circumferential direction as will be described later, the metal fitting side portion 45 of the holding member 40 is indirectly fixed to the metal shell 10 by welding. .

  In such a form, the holding member 40 holds the outer cylinder 30 and the ceramic heater 20 on the metal shell 10, and at the same time, the inner peripheral surface 11n of the tip cap member 11 of the metal shell 10 and the outer peripheral surface 30m of the outer cylinder 30. It functions as a seal member that hermetically divides the annular space KA therebetween in the axial direction HJ. For this reason, it is possible to prevent the combustion gas that has entered the annular space KA from the front end side GS of the glow plug 1 from entering the rear end side GK of the outer cylinder 30 through the annular space KA.

Furthermore, the intermediate deformation portion 43 of the holding member 40 is a portion that deforms with the displacement of the ceramic heater 20 and the outer cylinder 30 in the axial direction HJ. Specifically, the intermediate deformation portion 43 forms an annular plate-like diaphragm (thin film), and the intermediate deformation portion 43 is deformed to allow displacement of the ceramic heater 20 and the outer cylinder 30 in the axial direction HJ. To do.
In addition, since this holding member 40 also electrically connects between the outer cylinder 30 and the metal shell 10, one electrode extraction portion 27f of the ceramic heater 20 is interposed via the outer cylinder 30 and the holding member 40. It is electrically connected to the metal shell 10. The holding member 40 also functions as a heat transfer member that releases the heat of the ceramic heater 20 to the engine head via the metal shell 10.

  Next, the sensor unit 50 will be described. The sensor unit 50 includes a displacement transmission member 51, a sensor support member 53, a diaphragm member 55, a sensor element 57, a pair of wirings 58, and an integrated circuit 59. Of these members, the displacement transmission member 51 (see FIGS. 3 and 4) is a cylindrical metal member (specifically, stainless steel member) extending in the axial direction HJ. The displacement transmission member 51 is disposed inside the shaft hole 10 h of the metal shell 10 on the radially inner side of the sensor support member 53 and on the rear end side GK with respect to the holding member 40. The displacement transmission member 51 is welded to the outer cylinder 30 over the entire circumference in the axial direction HJ at a position W3. On the other hand, a diaphragm member 55 is connected to the rear end side GK of the displacement transmitting member 51.

  The sensor support member 53 (see FIGS. 3 and 4) is a cylindrical metal member (specifically, stainless steel) that extends in the axial direction HJ. The sensor support member 53 is disposed outside the displacement transmitting member 51 in the axial hole 10 h of the metal shell 10. The sensor support member 53 includes a cylindrical support front end portion 53s, a large flange portion 53c located on the rear end side GK, and a cylindrical support main body portion 53k extending from the flange portion 53c to the rear end side GK. Consists of. Among these, the metal fitting side portion 45 of the holding member 40 is externally fitted and welded to the support tip portion 53s as described above. Further, the flange portion 53 c is welded to the metal shell 10 while being sandwiched between the rear end portion 11 k of the front end cap member 11 of the metal shell 10 and the tip portion 13 s of the metal body member 13. Further, a diaphragm member 55 is connected to the rear end side GK of the support main body portion 53k.

  The diaphragm member 55 (see FIG. 4) is a metal (specifically, stainless steel) member, and the sensor element 57 is joined to the main surface of the rear end side GK. The sensor element 57 is a semiconductor strain gauge having a piezoresistor, and its own resistance value changes as the diaphragm member 55 is bent and deformed. Further, the integrated circuit 59 is disposed inside the rear end cap member 15 of the metal shell 10 as indicated by a broken line in FIG. 1, and a pair of wirings 58 drawn from the sensor element 57 to the rear end side GK. The sensor element 57 is connected via The integrated circuit 59 outputs an electrical signal to the outside using the resistance value of the sensor element 57.

  As described above, in the sensor-equipped glow plug 1 of the present embodiment, the outer cylinder hole inside 33 of the outer cylinder 30 has the heater holding portion 35 that holds the ceramic heater 20 inside thereof, while the outer cylinder 30. The outer cylinder protruding portion 31 surrounds the ceramic heater 20 inside thereof while being separated. For this reason, compared with the case where the ceramic heater 20 is held in the entire axial direction HJ of the outer cylinder 30, the portion to be press-fitted in the outer cylinder 30 (that is, the heater holding portion 35) is shortened, so that the press-fitting load is reduced. And press fit can be improved.

  In addition, since the heater holding portion 35 of the outer cylinder 30 is disposed in the shaft hole 10h of the metal shell 10, it is exposed to a higher temperature during use than the outer cylinder protrusion 31 protruding from the metal shell 10. hard. For this reason, it is possible to prevent the heater holding portion 35 from undergoing a large thermal expansion and generating a gap between the inner peripheral surface 35 n of the heater holding portion 35 and the outer peripheral surface 20 m of the ceramic heater 20. Therefore, it is possible to prevent the combustion gas from entering the rear end side GK of the outer cylinder 30 through the gap between the inner peripheral surface 30n of the outer cylinder 30 and the outer peripheral surface 20m of the ceramic heater 20.

  Further, in the present embodiment, a heater separating portion 34 separated from the ceramic heater 20 is provided in the outer cylinder hole inside 33 of the outer cylinder 30, and the holding member 40 is welded to the heater separating portion 34. For this reason, compared with the case where the holding member 40 is welded to the heater holding portion 35, heat generated during welding is hardly transmitted to the ceramic heater 20, and problems such as cracking and cracking of the ceramic heater 20 are prevented. A reliable glow plug 1 is obtained.

  Further, in the present embodiment, the holding member 40 is located on the distal side GS from the position W1 of the holding member 40 held by the metal shell 10 via the sensor support member 53, and the heater is separated from the inside 33 of the outer cylinder hole. The portion 34 is welded to a position W2 spaced from the heater holding portion 35 to the tip side GS. When the holding member 40 is exposed to the combustion gas, the holding member 40 is thermally expanded and extends toward the distal end side GS. This displacement is defined as Δa1 (see FIG. 5). On the other hand, the combustion gas reaches between the outer cylinder 30 and the ceramic heater 20 between the outer cylinder protrusion 31 that surrounds the ceramic heater 20 while being separated, and the heater separation section 34 that is connected to the outer cylinder protrusion 20. It thermally expands and extends toward the tip side GS. That is, in the heater separating portion 34, the portion 34ka (a part of the axial direction HJ of the rear end side portion 34k) from the position W2 where the holding member 40 is welded to the position W3 where the displacement transmission member 51 is welded is also heated. It expands and extends to the tip side GS. Let this displacement be Δa2.

  Accordingly, at the same time when the holding member 40 extends toward the front end side GS with the combustion gas (displacement Δa1), the position W3 where the displacement transmission member 51 is welded from the position W2 where the holding member 40 is welded in the heater separating portion 34. The part 34ka up to the end also extends toward the distal end GS (displacement Δa2), so that the displacement of the outer cylinder 30 and the ceramic heater 20 due to the extension of the holding member 40 is partially offset, and the displacement Δa3 = Δa1−Δa2. Thus, unnecessary fluctuations in the outer cylinder 30 and the ceramic heater 20 (variations in the direction in which the displacement and the pressure increase appear to be small) are difficult to be added to the displacement of the ceramic heater 20 according to the combustion pressure. Can be good.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the heater holding portion 35 and the ceramic heater 20 of the outer cylinder 30 are fixed by press-fitting, but the present invention is not limited to this. For example, the heater holding part of the outer cylinder and the ceramic heater may be fixed by brazing.

Moreover, although the outer cylinder protrusion part 31 of the outer cylinder 30 illustrated the form which surrounds the ceramic heater 20 inside, separating in the embodiment, it is not restricted to this. The outer cylinder protruding part and the internal ceramic heater may be in contact with each other, and the outer cylinder protruding part may not hold the internal ceramic heater .

DESCRIPTION OF SYMBOLS 1 Glow plug 10 Main metal fitting 10h Shaft hole 11sa Tip 20 (of main metal fitting and front end cap member) Ceramic heater 21 Heater front end portion 22 Heater intermediate portion 23 Heater rear end portion 30 Outer cylinder 31 Outer cylinder protrusion 31a (Outer cylinder and outer Front end 33 of outer tube hole (between cylinder protrusion) Rear end 34b (inside outer tube and outer tube hole) Heater separating portion 34s Front end side portion 34k Rear end side portion 34c Welding portion 35 Heater holding portion 40 Holding member 41 Outer tube Side part 43 Intermediate deformation part 45 Metal part side part 50 Sensor part AX Axis line HJ Axis direction GS (Axial direction) Front end side GK (Axial direction) Rear end side KA Annular space W1, W2, W3 Position

Claims (1)

A cylindrical metal shell having an axial hole extending in the axial direction;
An outer cylinder having a cylindrical shape and made of metal and having an outer cylinder projecting portion projecting from the distal end of the metallic shell to the distal end side in the axial direction inside the outer cylindrical hole disposed in the axial hole of the metallic shell. When,
The metal shell is made of ceramic and is held by the outer cylinder, has a heater tip protruding from the tip of the outer cylinder to the tip side in the axial direction, and is displaceable in the axial direction together with the outer cylinder A ceramic heater held in
A sensor unit for detecting the displacement of the ceramic heater;
A cylindrical member made of metal, disposed in the shaft hole and held by the metal shell, and a holding member that holds the outer cylinder and the ceramic heater in the interior thereof so that the displacement is possible. A glow plug with a pressure sensor,
The inside of the outer cylinder hole of the outer cylinder is
A heater holding part for holding the ceramic heater inside itself ;
A heater separating portion that is continuous with the outer cylinder projecting portion and surrounds the ceramic heater while separating from the heater holding portion on the tip end side in the axial direction ;
The outer cylinder protrusion of the outer cylinder is
Ri Na surrounds its interior of the ceramic heater loosely fitted,
The holding member is
The tip end side in the axial direction from the position held by the metal shell, and the tip end side in the axial direction from the heater holding portion of the heater separating portion inside the outer cylinder hole of the outer cylinder A glow plug with a pressure sensor , welded to a position spaced apart from each other .

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