JP2014016142A - Glow plug with pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the breakage of a center shaft, to improve an insertion property of the center shaft in a through-hole, and to prevent a short-circuit of the center shaft.SOLUTION: A glow plug 1 includes: a housing 2 having a shaft hole 7; a heater member 5; a center shaft 4; and a pressure sensor 6. While the center shaft 4 is inserted in a cylindrical portion 21 provided at a rear end portion of the heater member 5, the center shaft 4 and the heater member 5 are connected. The pressure sensor 6 has a through-hole 18A, and is disposed in the shaft hole 7. The center shaft 4 has a thick diameter portion 41 formed in a range across a rear end 21E of the cylindrical portion 21, and a thin diameter portion 42 having a smaller diameter than the thick diameter portion 41. The thin diameter portion 42 is formed from a rear end of the center shaft 4 to at least a part of the center shaft 4 inserted in the through-hole 18A. On an outer periphery of at least the part of the thin diameter portion 42 inserted in the through-hole 18A, an insulation member 43 having an outer diameter smaller than that of the thick diameter portion 41 is provided.

Description

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

  2. Description of the Related Art Conventionally, a glow plug used for starting assistance of a diesel engine has a cylindrical housing having an axial hole extending in an axial direction, a heater member inserted through the axial hole, and a heater member inserted through the axial hole. It has a central shaft that forms an energization path. Further, the central shaft is connected to the heater member in a state where the front end portion is inserted into a cylindrical portion provided at the rear end portion of the heater member. In addition, a ceramic heater or a metal heater is employed as the heater member. As a ceramic heater, a ceramic heater in which a conductive ceramic heating element is arranged inside a ceramic base is known. In addition, a metal heater is known in which a heating coil that generates heat when energized is disposed in a cylindrical metal tube. In the case where a ceramic heater is used as the heater member, the cylindrical portion is a metal ring member in which the rear end portion of the ceramic heater is inserted on the front end side and the front end portion of the central shaft is inserted on the rear end side. Can be mentioned. Moreover, when using a metal heater as a heater member, the said cylindrical part can mention the rear-end part of the tube in which the front-end | tip part of a center axis is penetrated.

  In addition, in recent years, a glow plug with a pressure sensor has been proposed in which a function for detecting pressure such as combustion pressure is provided for the glow plug. In such a glow plug with a pressure sensor, the heater member is attached in a state of being relatively displaceable with respect to the housing, and a tip portion thereof protrudes from the tip of the housing. When the heater member receives the combustion pressure or the like and the heater member is relatively displaced, the relative displacement is transmitted to the pressure sensor, and a signal corresponding to the relative displacement amount of the heater member (that is, the pressure applied to the heater member). Is output from the pressure sensor.

  By the way, in terms of accurately transmitting the relative displacement of the heater member to the pressure sensor and increasing the pressure detection accuracy, the transmission member for transmitting the relative displacement from the heater member to the pressure sensor is made shorter. It is preferable to configure so that a loss does not occur as much as possible in the transmitted relative displacement. Therefore, a method has been proposed in which a pressure sensor is provided in the shaft hole to reduce the distance between the heater member and the pressure sensor and shorten the transmission member (see, for example, Patent Document 1). When the pressure sensor is provided in the shaft hole in this way, the middle shaft is inserted into a through hole provided in the pressure sensor and penetrating in the axial direction.

JP 2006-336918 A

  By the way, when the pressure sensor is provided in the shaft hole, it is necessary to use a relatively small pressure sensor. In such a small pressure sensor, the through hole has a small diameter. Therefore, it is very difficult to insert the center shaft into the through hole, and the center shaft is poorly inserted. Even if the center shaft can be inserted into the through-hole, the distance between the inner peripheral surface of the through-hole and the outer peripheral surface of the center shaft is small, so the center shaft contacts the pressure sensor, and the center shaft short-circuits to the pressure sensor. There is a risk that.

  On the other hand, it is conceivable that by making the central shaft have a small diameter, it is possible to improve the insertability of the central shaft and to prevent a short circuit of the central shaft. However, since stress is particularly easily applied to a portion of the central shaft that is located on the inner peripheral side of the rear end of the cylindrical portion due to vibration caused by the operation of the internal combustion engine or the like, the rigidity of the central shaft is reduced when the central shaft has a small diameter. May decrease, and the central shaft may break at the portion.

  Although it is conceivable to increase the diameter of the through hole in order to improve the insertability of the central shaft, in this case, the detection accuracy of the pressure sensor may be reduced.

  The present invention has been made in view of the above circumstances, and an object thereof is to effectively suppress breakage of the central shaft, improve the insertability of the central shaft into the through hole, and prevent short-circuiting of the central shaft. An object of the present invention is to provide a glow plug with a pressure sensor.

  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 with a pressure sensor of this configuration includes a cylindrical housing having an axial hole extending in the axial direction,
A heater member that is inserted into the shaft hole in a state where at least a tip portion of the housing protrudes from a tip of the housing, and is relatively displaceable along the axial direction with respect to the housing;
A central shaft that forms a rod shape extending in the axial direction, is inserted through the shaft hole, and forms an energization path to the heater member;
A pressure sensor that is directly or indirectly fixed to the housing, is disposed on the rear end side of the heater member, and detects a pressure based on a relative displacement of the heater member;
A glow plug with a pressure sensor to which the middle shaft and the heater member are connected in a state in which a tip portion of the middle shaft is inserted into a cylindrical portion provided at a rear end portion of the heater member,
The pressure sensor has a through hole penetrating in the axial direction, and is disposed in the axial hole.
The middle shaft is inserted through the through hole,
A large diameter portion formed in a range straddling the rear end of the cylindrical portion along at least the axial direction;
It is located on the rear end side from the large diameter portion, and has a small diameter portion whose own outer diameter is smaller than the outer diameter of the large diameter portion,
The narrow-diameter portion is formed from a rear end of the middle shaft to a portion inserted through the through hole in at least the middle shaft,
A cylindrical insulating member whose outer diameter is smaller than the outer diameter of the large-diameter portion is provided at least on the outer periphery of the portion inserted through the through-hole in the small-diameter portion.

  The “tubular portion” may be a part of the heater member or a member provided separately from the heater member. For example, when the heater member includes a heating element and a cylindrical tube that accommodates the heating element therein, and the distal end portion of the central shaft is inserted into the rear end portion of the tube, The rear end corresponds to a “tubular portion”. In addition to the heater member, a cylindrical ring member into which the rear end portion of the heater member is inserted is provided. When the tip end portion of the central shaft is inserted into the ring member, the ring member is Corresponds to the “cylindrical part”.

  According to the said structure 1, the large diameter part with a comparatively large outer diameter is provided in the site | part which straddles the rear end of a cylindrical part among center shafts. Therefore, the rigidity of the middle shaft located on the inner peripheral side of the rear end of the cylindrical portion can be further increased, and the breakage of the middle shaft can be more reliably prevented when stress is applied due to vibration of the internal combustion engine or the like. it can.

  Moreover, according to the said structure 1, between the rear end of a center axis | shaft to the site | part inserted by the through-hole of a pressure sensor at least, the small diameter part whose own outer diameter is smaller than the outer diameter of a large diameter part is Is provided. Therefore, when the center shaft is inserted into the through hole from the front end side of the housing, the center shaft can be inserted into the through hole very easily, and the insertability of the center shaft can be remarkably improved.

  Furthermore, according to the said structure 1, the cylindrical insulating member is provided in the outer periphery of the site | part inserted by the through-hole at least among the narrow diameter parts. Therefore, it is possible to more reliably prevent a short circuit between the pressure sensor and the center shaft (small diameter portion) located on the inner periphery of the pressure sensor, due to contact with the center shaft pressure sensor.

  In addition, when an insulating member is provided on the outer periphery of the small-diameter portion, there is a concern that the insertability may be deteriorated. However, according to the configuration 1, the outer diameter of the insulating member is smaller than the outer diameter of the large-diameter portion. It is supposed to be. Therefore, good insertability can be maintained without impairing the above-described improvement effect of insertability.

  Moreover, according to the said structure 1, since it is not necessary to enlarge the outer diameter of a through-hole, it can prevent that the detection accuracy of a pressure sensor falls.

  Configuration 2. The glow plug with pressure sensor of this configuration is characterized in that, in the above configuration 1, the insulating member is made of a material having heat shrinkability.

  According to the said structure 2, the insulating member is formed with the material which has heat shrinkability. Therefore, by heating the insulating member, the insulating member can be thermally contracted, and the adhesion of the insulating member to the middle shaft, and thus the friction force generated between the middle shaft and the insulating member can be increased. As a result, it is possible to more reliably prevent the insulating member from shifting to a position deviated from the inner peripheral side of the pressure sensor due to vibration caused by the operation of the internal combustion engine or the like, and to prevent a short-circuit of the central shaft by providing the insulating member. The effect can be exhibited more reliably.

Configuration 3. The glow plug with a pressure sensor of this configuration has the step portion positioned between the large-diameter portion and the small-diameter portion in the above-described configuration 1 or 2,
A tip portion of the insulating member is in contact with the stepped portion.

  According to the said structure 3, it is comprised so that the front-end | tip part of an insulating member may contact with the step part located between a large diameter part and a small diameter part. Therefore, when the central shaft is inserted into the through hole or when vibration is applied to the central shaft, it is possible to effectively suppress the insulating member from moving toward the distal end side. As a result, the effect of preventing the short-circuit of the central shaft by providing the insulating member can be more reliably exhibited.

  Configuration 4. In the glow plug with a pressure sensor according to this configuration, in any one of the above configurations 1 to 3, the middle shaft is directed toward the rear end side at a portion connecting the rear end of the large diameter portion and the front end of the small diameter portion. It has a tapered portion that tapers.

  When the outer diameter of the central shaft changes abruptly when providing the large diameter portion and the small diameter portion on the central shaft, when stress is applied to the central shaft due to the operation of the internal combustion engine etc. There is a possibility that stress is locally applied to the stepped portion and the vicinity thereof, and the central shaft is broken.

  In this regard, according to the above-described configuration 4, a taper portion that is tapered toward the rear end side is formed at a portion connecting the rear end of the large-diameter portion and the tip of the small-diameter portion of the middle shaft, The outer diameter of the central shaft is gradually changed from the portion to the small diameter portion. Therefore, when stress is applied to the central shaft, it is possible to more reliably prevent stress from being locally applied to a part of the central shaft. As a result, when the stress is applied to the central shaft due to the operation of the internal combustion engine or the like, the central shaft can be more reliably prevented from breaking.

  Configuration 5. The glow plug with pressure sensor of this configuration is characterized in that, in the above configuration 4, the distal end portion of the insulating member is in contact with the tapered portion.

  According to the said structure 5, it is comprised so that the front-end | tip part of an insulating member may contact a taper part. Therefore, it is possible to prevent the insulating member from moving toward the distal end side when the central shaft is inserted into the through hole or when vibration is applied to the central shaft. As a result, the effect of preventing the short-circuit of the central shaft by providing the insulating member can be more reliably exhibited.

It is a partially broken front view of a glow plug. It is a partial expanded sectional view of a glow plug. It is a partial expanded sectional view of the glow plug in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view of a glow plug 1 with a pressure sensor (hereinafter simply referred to as “glow plug 1”). In FIG. 1 and the like, the lower side of the figure will be described as the front end side of the glow plug 1, and the upper side will be described as the rear end side.

  As shown in FIG. 1, the glow plug 1 includes a housing 2, a cap member 3, a middle shaft 4, a heater member 5, a pressure sensor 6, and the like.

  The housing 2 is formed of a predetermined metal material (for example, an iron-based material such as S45C) and has a shaft hole 7 extending along the direction of the axis CL1. Further, a male screw portion 8 for attaching the glow plug 1 to an engine cylinder head or the like is formed on the outer periphery of the housing 2. In addition, a tool engaging portion 9 having a hexagonal cross section is formed on the outer periphery of the rear end portion of the housing 2. When the glow plug 1 (male thread portion 8) is attached to the cylinder head or the like, the tool engaging portion The tool used for 9 is engaged.

  Furthermore, a metal sensor fixing member 10 having a cylindrical shape extending along the direction of the axis CL1 is inserted into the inner periphery of the distal end portion of the housing 2. The sensor fixing member 10 has a distal end portion joined to the distal end portion of the housing 2 and a rear end portion joined to a diaphragm 18 described later of the pressure sensor 6. Thereby, the pressure sensor 6 is in a state of being indirectly fixed to the housing 2 via the sensor fixing member 10.

  The cap member 3 has a cylindrical shape and is joined to the distal end portion of the housing 2 via the distal end portion of the sensor fixing member 10. Further, the outer peripheral surface on the front end side of the cap member 3 is tapered so as to taper toward the front end side in the direction of the axis CL1, and when the glow plug 1 is attached to the engine, the tapered portion becomes the seat surface of the engine. By pressure-contacting, the airtightness in the combustion chamber is ensured.

  The middle shaft 4 is inserted into the shaft hole 7 and has a rod shape extending along the axis CL1. Further, the middle shaft 4 is a portion that forms an energization path to the heater member 5 and is formed of a conductive metal (for example, an iron-based alloy). The configuration of the middle shaft 4 will be described in detail later.

  The heater member 5 has a rear end portion inserted into the shaft hole 7 and a front end portion protruding from the front end of the housing 2 (cap member 3). The heater member 5 includes a tube 11 and a heating coil 12 and a control coil 13 disposed inside the tube 11.

  The tube 11 is a cylindrical tube formed of a metal (for example, nickel-base alloy or stainless steel alloy) whose main component is iron (Fe) or nickel (Ni) and having a closed end. In addition, inside the tube 11, the heating coil 12 whose tip is joined to the tip of the tube 11 and the control coil 13 connected in series to the rear end of the heating coil 12 are oxidized. It is enclosed with an insulating powder 14 containing magnesium powder. Although the heat generating coil 12 is electrically connected to the tube 11 at the tip, the outer peripheral surface of the heat generating coil 12 and the control coil 13 and the inner peripheral surface of the tube 11 are insulated by the interposition of the insulating powder 14. It has become.

  Further, an annular rubber 15 made of a predetermined rubber (for example, silicone rubber, fluorine rubber, etc.) is provided between the inner periphery of the rear end side of the tube 11 and the middle shaft 4, and the inside of the tube 11 is sealed. Has been.

  The heating coil 12 is connected in series with the middle shaft 4 via the control coil 13, and 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) spirals. It is comprised by winding in the shape. The heating coil 12 generates heat when energized through the middle shaft 4.

  The control coil 13 is interposed between the heat generating coil 12 and the middle shaft 4 and has a material having a temperature coefficient of electrical specific resistance larger than that of the heat generating coil 12 [for example, a cobalt (Co) -Ni-Fe alloy or the like. It is configured by spirally winding a resistance heating wire made of a metal containing Co or Ni as a main component. Thereby, the control coil 13 increases the electric resistance value by receiving its own heat generation and heat generation from the heat generation coil 12, and controls the power supplied to the heat generation coil 12. Specifically, in the initial energization period, relatively large power is supplied to the heating coil 12, and the temperature of the heating coil 12 rises rapidly. Then, the control coil 13 is heated by the heat generation, the electric resistance value of the control coil 13 increases, and the power supplied to the heat generating coil 12 decreases. As a result, the temperature rise characteristic of the heater member 5 is such that the temperature is saturated after the temperature is rapidly raised in the initial stage of energization, and thereafter, the supplied power is suppressed by the action of the control coil 13. That is, the presence of the control coil 13 is configured so that the rapid rise in temperature rise is improved, and overheating (overshoot) of the heating coil 12 is less likely to occur.

  In the present embodiment, the heater member 5 is attached to the housing 2 via a cylindrical movable member 16 that can be expanded and contracted along the axis CL1. Therefore, the heater member 5 can be relatively displaced along the axis CL <b> 1 with respect to the housing 2 when a pressure such as a combustion pressure is applied to the tip portion thereof.

  In addition, the movable member 16 has an opening on one end side having a relatively small diameter, and an opening on the other end is formed in a relatively large diameter. In the embodiment, it has two bent portions. For this reason, the movable member 16 can be stretched and deformed along the axis CL1 in combination with being formed thin with a predetermined metal (for example, stainless steel or nickel alloy).

  In this embodiment, one end of the movable member 16 is welded to the heater member 5 (tube 11) over the entire circumference, and the other end of the movable member 16 is connected to the tip of the housing 2 over the entire circumference. Are welded. Thereby, it is possible to more reliably prevent the combustion gas that has entered from the gap between the cap member 3 and the heater member 5 (tube 11) from entering the housing 2 and leaking to the outside. It has become.

  In addition, a cylindrical transmission member 17 is joined to the outer peripheral portion of the heater member 5 on the rear end side of the joined portion of the movable member 16. The transmission member 17 has its rear end connected to the pressure sensor 6 (diaphragm 18), and the relative displacement of the heater member 5 is transmitted to the pressure sensor 6 via the transmission member 17. . In the present embodiment, as described above, since the pressure sensor 6 is provided in the shaft hole 7, the length of the transmission member 17 along the axis CL1 can be made relatively small. As a result, the transmission member 17 has a large natural frequency and is less likely to vibrate. Therefore, the displacement of the heater member 5 is accurately transmitted to the pressure sensor 6, and as a result, the pressure detection accuracy is improved. It has become.

  The pressure sensor 6 is provided on the tip side of the central portion of the housing 2 in the direction of the axis CL1, and as shown in FIG. 2, a metal (for example, stainless steel) having a through hole 18A penetrating in the direction of the axis CL1. And a sensor element 19 (in this embodiment, a piezoresistor) joined to the rear end surface of the diaphragm 18. The rear end portion of the transmission member 17 is joined to the diaphragm 18, and when the heater member 5 is displaced due to a pressure such as a combustion pressure, the diaphragm is corresponding to the amount of displacement of the heater member 5. 18 is bent and deformed. In the present embodiment, the inner diameter of the through hole 18A is configured to be constant along the axis line CL1.

  Further, the sensor element 19 has its own resistance value that changes as the diaphragm 18 is bent and deformed. The resistance value of the sensor element 19 is converted / amplified into a voltage value by an integrated circuit 20 (see FIG. 1) provided inside the housing 2, and a signal of the converted / amplified voltage value (that is, received by the heater member 5). A signal indicating the pressure) is output to an external circuit (not shown) such as an ECU via a cable or the like (not shown).

  By the way, when the glow plug 1 is manufactured, first, the pressure sensor 6 attached to the sensor fixing member 10 is provided in the housing 2. Next, in a state where the central shaft 4 is inserted into a cylindrical portion 21 provided in the rear end portion of the heater member 5 (in this embodiment, the rear end portion of the tube 11 corresponds to the cylindrical portion 21), the heater Connected to the member 5, the middle shaft 4 and the heater member 5 are integrated. Then, the middle shaft 4 integrated with the heater member 5 is inserted from the front end side opening of the housing 2, and the middle shaft 4 is inserted into the through hole 18 </ b> A of the pressure sensor 6 (diaphragm 18). In the present embodiment, the intermediate shaft 4 is configured as follows in order to improve the insertion property of the intermediate shaft 4 into the through hole 18A.

  That is, the middle shaft 4 is positioned in the range extending across the rear end 21E of the cylindrical portion 21 along the axis CL1, and the outer diameter of the middle shaft 4 is located on the rear end side of the large diameter portion 41. Is provided with a small-diameter portion 42 that is smaller than the outer diameter of the large-diameter portion 41. The small-diameter portion 42 is formed from the rear end of the middle shaft 4 to at least a portion of the middle shaft 4 that is inserted into the through hole 18A. That is, the entire region of the portion of the middle shaft 4 that passes through the through hole 18 </ b> A is the small diameter portion 42.

  Furthermore, in this embodiment, in order to prevent a short circuit with the pressure sensor 6 of the middle shaft 4 due to the contact between the middle shaft 4 and the pressure sensor 6, a portion (final part) inserted through at least the through hole 18 </ b> A in the small diameter portion 42. In addition, a cylindrical insulating member 43 made of a predetermined insulating material is provided on the outer periphery of a portion located on the inner periphery of the through hole 18A. The insulating member 43 is provided on the outer periphery of the small-diameter portion 42 before the intermediate shaft 4 is inserted into the through-hole 18A. When the intermediate shaft 4 is inserted into the through-hole 18A, the thin-diameter portion having the insulating member 43 on the outer periphery. 42 is inserted through the through-hole 18A. In addition, the insulating member 43 has an outer diameter that is smaller than the outer diameter of the large-diameter portion 41 when it is provided on the outer periphery of the small-diameter portion 42.

  In addition, the insulating member 43 is made of a material having predetermined heat shrinkability (for example, Teflon (registered trademark) PFA, Teflon (registered trademark) EFP, or the like). In this embodiment, when the inner diameter of the insulating member 43 before heat shrinkage is 2.0 mm or more and 2.5 mm or less, the inner diameter of the insulating member 43 after heat shrinkage is 1 as the material having the heat shrinkability. The thickness of the insulating member 43 after heat shrinkage is 0.13 mm or less and the shrinkage rate is 20% or more and 45% or less. By forming the insulating member 43 with such a material, the insulating member 43 is heated, so that the adhesion of the insulating member 43 to the outer peripheral surface of the central shaft 4 is remarkably increased.

  Further, the distal end portion of the insulating member 43 is configured to come into contact with a stepped portion 44 located between the large diameter portion 41 and the small diameter portion 42 of the middle shaft 4.

  As described above in detail, according to the present embodiment, the portion of the middle shaft 4 that straddles the rear end of the tubular portion 21 is provided with the large-diameter portion 41 having a relatively large outer diameter. Therefore, the rigidity of the middle shaft 4 positioned on the inner peripheral side of the rear end of the cylindrical portion 21 can be further increased, and the breakage of the middle shaft 4 can be more reliably prevented when stress is applied with vibration of the internal combustion engine or the like. can do.

  In addition, a small-diameter portion 42 whose outer diameter is smaller than the outer diameter of the large-diameter portion 41 is provided between the rear end of the middle shaft 4 and at least a portion inserted through the through-hole 18A of the pressure sensor 6. ing. Therefore, when the middle shaft 4 is inserted into the through hole 18A from the front end side of the housing 2, the middle shaft 4 can be inserted into the through hole 18A very easily, and the insertability of the middle shaft 4 can be remarkably improved.

  Further, in the present embodiment, a cylindrical insulating member 43 is provided on the outer periphery of at least a portion of the small diameter portion 42 that is inserted through the through hole 18A. Therefore, the short circuit with the pressure sensor 6 of the center shaft 4 accompanying the contact with the pressure sensor 6 and the center shaft 4 (small diameter part 42) can be prevented more reliably.

  In addition, in the present embodiment, the outer diameter of the insulating member 43 is smaller than the outer diameter of the large diameter portion 41. Therefore, good insertability can be maintained without impairing the above-described improvement effect of insertability.

  Further, since it is not necessary to increase the outer diameter of the through hole 18A, it is possible to prevent the detection accuracy of the pressure sensor from being lowered.

  Furthermore, the insulating member 43 is formed of a material having heat shrinkability. Therefore, by heating the insulating member 43, the adhesion of the insulating member 43 to the middle shaft 4, and thus the friction force generated between the middle shaft 4 and the insulating member 43 can be increased. As a result, it is possible to more reliably prevent the insulating member 43 from moving to a position deviated from the inner peripheral side of the pressure sensor 6 due to vibrations caused by the operation of the internal combustion engine or the like. The effect of preventing short circuit 4 can be exhibited more reliably.

  In addition, since the tip end portion of the insulating member 43 is configured to contact the stepped portion 44, the insulating member 43 is insulated when the middle shaft 4 is inserted into the through hole 18A or when vibration is applied to the middle shaft 4. It is possible to effectively suppress the member 43 from shifting toward the distal end side. As a result, the effect of preventing the short-circuit of the center shaft by providing the insulating member 43 can be more reliably exhibited.

  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 step portion 44 is provided between the large diameter portion 41 and the small diameter portion 42. However, as shown in FIG. It is good also as providing the taper part 46 which tapers toward the rear-end side in the site | part which connects the front-end | tip of the diameter part 42. As shown in FIG. In this case, when stress is applied to the central shaft 4, it is possible to more reliably prevent stress from being locally applied to a part of the central shaft 4. As a result, it is possible to more reliably prevent the middle shaft 4 from being broken when stress is applied.

  Further, when the tapered portion 46 is provided, the distal end portion of the insulating member 43 may be configured to contact the tapered portion 46. In this case, it is possible to prevent the insulating member 43 from moving toward the distal end side when the central shaft 4 is inserted through the through hole 18A. As a result, the effect of preventing the short-circuit of the central shaft 4 by providing the insulating member 43 can be more reliably exhibited.

  (B) In the above embodiment, a metal heater having the heating coil 12 is used as the heater member. However, as the heater member, a ceramic heater including a base made of insulating ceramic and a heating element made of conductive ceramic. It is good also as using. In this case, the heater member 5 can be an assembly of a ceramic heater and a cylindrical metal outer cylinder fixed to the outer peripheral surface of the ceramic heater. The movable member 16 is coupled to the outer cylinder. Further, in the case of using a ceramic heater, when connecting the ceramic heater and the center shaft, a cylindrical ring member in which the rear end portion of the ceramic heater is inserted into the front end side and the front end portion of the center shaft is inserted into the rear end side May be used. In this case, the ring member corresponds to the cylindrical portion of the present invention.

  (C) In the above embodiment, the inner diameter of the through-hole 18A is constant along the axis CL1, but the inner diameter of the through-hole 18A is configured to gradually increase toward the front end side in the direction of the axis CL1. Also good. In this case, the insertability of the central shaft 4 into the through hole 18A can be further enhanced.

  (D) The arrangement position of the pressure sensor 6 in the above embodiment is an example, and the arrangement position of the pressure sensor 6 is not particularly limited as long as it is within the shaft hole 7. Therefore, for example, a pressure sensor may be provided on the rear end side of the shaft hole 7.

  (E) In the above embodiment, a piezoresistor is cited as the sensor element, but usable sensor elements are not limited to this. Therefore, for example, a piezoelectric element or the like may be used as the sensor element.

  (F) The movable member 16 only needs to be deformable along the direction of the axis CL1, and the shape thereof is not particularly limited. Therefore, for example, a movable member having a bellows-like cylindrical portion extending along the direction of the axis CL1 may be used. Moreover, it is good also as using the cyclic | annular member which extends in the direction which cross | intersects the axis line CL1, and can bend and deform in the direction of the axis line CL1.

  (G) The insulating member may be made of an insulating material coated on the outer periphery of the central shaft 4.

  (H) The part corresponding to the large-diameter part 41 and the part corresponding to the small-diameter part 42 may be prepared separately, and the two parts may be joined to obtain the central shaft 4.

DESCRIPTION OF SYMBOLS 1 ... Glow plug (Glow plug with a pressure sensor), 2 ... Housing, 4 ... Medium shaft, 5 ... Heater member, 6 ... Pressure sensor, 7 ... Shaft hole, 18A ... Through-hole, 21 ... Cylindrical part, 41 ... Thick diameter Part, 42 ... small diameter part, 43 ... insulating member, 44 ... step part, 46 ... taper part, CL1 ... axis.

Claims (5)

A cylindrical housing having an axial hole extending in the axial direction;
A heater member that is inserted into the shaft hole in a state where at least a tip portion of the housing protrudes from a tip of the housing, and is relatively displaceable along the axial direction with respect to the housing;
A central shaft that forms a rod shape extending in the axial direction, is inserted through the shaft hole, and forms an energization path to the heater member;
A pressure sensor that is directly or indirectly fixed to the housing, is disposed on the rear end side of the heater member, and detects a pressure based on a relative displacement of the heater member;
A glow plug with a pressure sensor to which the middle shaft and the heater member are connected in a state in which a tip portion of the middle shaft is inserted into a cylindrical portion provided at a rear end portion of the heater member,
The pressure sensor has a through hole penetrating in the axial direction, and is disposed in the axial hole.
The middle shaft is inserted through the through hole,
A large diameter portion formed in a range straddling the rear end of the cylindrical portion along at least the axial direction;
It is located on the rear end side from the large diameter portion, and has a small diameter portion whose own outer diameter is smaller than the outer diameter of the large diameter portion,
The narrow-diameter portion is formed from a rear end of the middle shaft to a portion inserted through the through hole in at least the middle shaft,
A pressure sensor having a cylindrical insulating member whose outer diameter is smaller than the outer diameter of the large-diameter portion is provided on an outer periphery of at least a portion of the small-diameter portion that is inserted into the through-hole. With glow plug.   The glow plug with a pressure sensor according to claim 1, wherein the insulating member is made of a material having heat shrinkability. The middle shaft has a step portion located between the large diameter portion and the small diameter portion,
The glow plug with a pressure sensor according to claim 1, wherein a distal end portion of the insulating member is in contact with the stepped portion.   The said center axis | shaft has the taper part which tapers toward the rear end side in the site | part which connects the rear end of the said large diameter part, and the front-end | tip of the said small diameter part, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. A glow plug with a pressure sensor as described in the paragraph. The glow plug with a pressure sensor according to claim 4, wherein a distal end portion of the insulating member is in contact with the tapered portion.

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