JP5608014B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug used for preheating or the like of a diesel engine.

  2. Description of the Related Art Conventionally, glow plugs used for diesel engine start-up assistance and the like include a cylindrical housing and a heater incorporating a heating element that generates heat when energized. Moreover, a ceramic heater may be employed as the heater.

  The ceramic heater is configured by housing a conductive ceramic heating element in a cylindrical base made of an insulating ceramic. In the glow plug having such a ceramic heater, the outer periphery of the intermediate portion of the ceramic heater is generally held by a cylindrical outer cylinder, and the outer cylinder is fixed to the housing. In addition, a member (for example, a lead wire) is provided to electrically connect the rear end portion of the ceramic heater protruding from the rear end of the outer cylinder and the front end portion of the metal center shaft inserted into the housing. The middle shaft and the ceramic heater are electrically connected (for example, see Patent Document 1).

  Furthermore, in recent years, a method has been proposed in which a cylindrical connecting member is used as a member for connecting the rear end portion of the ceramic heater and the front end portion of the central shaft (see, for example, Patent Document 2). According to this method, the ceramic heater and the middle shaft can be firmly connected, and the vibration resistance and the like can be improved.

JP 2002-364842 A JP 2010-73417 A

  However, in the technique described in Patent Document 2, when an impact is applied to the glow plug due to vibration caused by dropping or engine operation, the stress associated with the swinging motion of the center shaft is caused by the rear end of the ceramic heater via the connecting member. There is a risk of being transmitted with a greater force to the part. Further, in the portion of the ceramic heater held by the outer cylinder, a holding force directed radially inward is working, and on the rear end side of the portion of the ceramic heater held by the outer cylinder, As the holding force is released, a relatively large stress is applied. Therefore, there is a possibility that stress associated with dropping or vibration and stress associated with release of the holding force may be applied in a superimposed manner on a portion of the ceramic heater located between the connecting member and the outer cylinder. . As a result, breakage of the ceramic heater is likely to occur, and it may be difficult to ensure sufficient impact resistance.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ceramic heater in which a rear end portion protrudes from an outer cylinder and the rear end portion is connected to a central shaft via a cylindrical connecting member. It is an object of the present invention to provide a glow plug that can realize excellent impact resistance.

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

Configuration 1. The glow plug of this configuration includes a rod-shaped ceramic heater extending in the axial direction,
A cylindrical outer cylinder that holds the outer periphery of the ceramic heater in a state in which the front end and the rear end of the ceramic heater protrude from itself,
A cylindrical housing in which the outer cylinder is fixed to its tip,
A rod-shaped center shaft inserted into the housing;
A cylindrical connecting member that connects the ceramic heater and the central shaft in a state where the rear end portion of the ceramic heater is fitted into the front end portion of the ceramic heater and the front end portion of the middle shaft is fitted into the rear end portion of the ceramic heater. A glow plug with
Of the ceramic heater, when the distance along the axis between the rear end of the portion that contacts the outer cylinder and the tip of the portion that contacts the connecting member is A (mm),
0.10 ≦ A ≦ 1.50
It is characterized by satisfying.

  According to the above configuration 1, the distance A along the axis of the ceramic heater located between the outer tube and the connecting member (hereinafter referred to as “exposed portion”) is sufficiently small, 1.50 mm or less. It is said that. Therefore, in the ceramic heater (base), a portion having a slightly low strength (that is, a portion serving as a base point of breakage) is scattered, so that a situation in which the low strength portion is located in the exposed portion is less likely to occur. The durability of the exposed portion against stress can be increased. As a result, it is possible to achieve excellent breakage resistance in the ceramic heater, and effectively improve the impact resistance of the glow plug.

  In addition, as the distance A is reduced, the breakage resistance of the ceramic heater can be increased, and the impact resistance can be further improved. However, if the distance A is excessively small (that is, if the connecting member is excessively close to the outer cylinder), leakage of current transmitted through the surface of the base is likely to occur between the outer cylinder and the connecting member. As a result, the heat generation performance of the ceramic heater may be reduced. Therefore, it is preferable that the distance A is set to 0.10 mm or more from the viewpoint of maintaining sufficient insulation between the outer cylinder and the connecting member and preventing deterioration in heat generation performance.

The structure of the glow plug in this embodiment is shown, (a) is sectional drawing of a glow plug, (b) is a front view of a glow plug. It is a partial expanded sectional view which shows the front-end | tip part of a glow plug.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1A is a longitudinal sectional view of the glow plug 1, and FIG. 1B is a front view of the glow plug 1. FIG. 2 is a partially enlarged cross-sectional view centering on the ceramic heater 4. In FIGS. 1 and 2, 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 FIGS. 1A and 1B, the glow plug 1 includes a housing 2, a middle shaft 3, a ceramic heater 4, an outer cylinder 5, a terminal pin 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 the cylinder head of the engine is formed on the outer periphery of the central portion of the housing 2 in the longitudinal direction. In addition, a hook-shaped tool engaging portion 9 having a hexagonal cross section is formed on the outer periphery of the rear end portion of the housing 2, and when the glow plug 1 (male screw portion 8) is attached to the cylinder head, A tool used in the tool engaging portion 9 is engaged.

  The shaft hole 7 of the housing 2 accommodates the middle shaft 3 made of a metal and having a round bar shape with a clearance from the inner peripheral surface of the housing 2. The front end portion of the middle shaft 3 is fitted into the rear end portion of the cylindrical connection member 10 formed of a metal material (for example, an iron-based material such as SUS), and the front end portion of the connection member 10 The rear end portion of the ceramic heater 4 is fitted. Thereby, the middle shaft 3 and the ceramic heater 4 are mechanically and electrically connected via the connection member 10. Note that a constricted portion 13 whose outer diameter is narrowed toward the distal end side is formed on the distal end side of the intermediate shaft 3, and stress transmitted to the intermediate shaft 3 is relaxed by the constricted portion 13.

  On the other hand, a metal terminal pin 6 is fixed by caulking to the rear end portion of the middle shaft 3. Further, an insulating bush 11 made of an insulating material is provided between the front end portion of the terminal pin 6 and the rear end portion of the housing 2 in order to prevent direct electrical conduction between the two. . Further, an O-ring 12 made of an insulating material is provided between the housing 2 and the middle shaft 3 so as to contact the tip of the insulating bush 11 in order to improve the airtightness in the shaft hole 7 and the like. Yes.

  In addition, the outer cylinder 5 is formed in a cylindrical shape from a predetermined metal material. The outer cylinder 5 holds an intermediate portion along the direction of the axis CL1 of the ceramic heater 4, and the front end of the ceramic heater 4 protrudes from the front end of the outer cylinder 5, and the rear end of the ceramic heater 4 Protrudes from the rear end of the outer cylinder 5. Further, the outer cylinder 5 has a relatively small diameter and thin small diameter portion 14 at its rear end. With the small diameter portion 14 inserted into the shaft hole 7, laser welding is performed along the contact surface between the front end surface of the housing 2 and the outer cylinder 5, whereby the housing 2 and the outer cylinder 5 are joined. Yes.

  As shown in FIG. 2, the ceramic heater 4 is made of an insulating ceramic (for example, silicon nitride as a main component), has a cylindrical base 21 extending in the direction of the axis CL1, and is embedded in the cylindrical base 21. And a long thin U-shaped heating element 22 made of conductive ceramic. The base body 21 is formed so as to have substantially the same outer diameter (for example, about 3.1 mm to 3.3 mm) except for its front end. The heating element 22 includes a pair of rod-shaped lead portions 23 and 24 and a connecting portion 25 that connects the tip portions of the lead portions 23 and 24, and the tip portion of the connecting portion 25 particularly generates heat. It becomes part 26. The heat generating part 26 is a part that functions as a so-called heat generating resistor, and has a substantially U-shaped cross section along the curved surface at the tip of the ceramic heater 4 (base 21) formed in a curved surface. . Further, the cross-sectional area of the heat generating portion 26 is configured to be smaller than the cross-sectional area of the lead portions 23 and 24, and the heat generating portion 26 actively generates heat when energized.

  Further, the lead portions 23 and 24 extend substantially parallel to each other toward the rear end side of the ceramic heater 4. In addition, on the rear end side of one lead portion 23, an electrode extraction portion 27 is projected in the outer peripheral direction, and the electrode extraction portion 27 is exposed on the outer peripheral surface of the ceramic heater 4. Similarly, the other lead portion 24 also has an electrode extraction portion 28 protruding in the outer peripheral direction, and the electrode extraction portion 28 is exposed on the outer peripheral surface of the ceramic heater 4. Note that the electrode extraction portion 27 of one lead portion 23 is formed on the rear end side in the direction of the axis CL <b> 1 with respect to the electrode extraction portion 28 of the other lead portion 24.

  In addition, the exposed portion of the electrode extraction portion 27 is in contact with the inner peripheral surface of the connection member 10, and as a result, the middle shaft 3 connected to the connection member 10 and the lead portion 23 are electrically connected. ing. Further, the exposed portion of the electrode extraction portion 28 is in contact with the inner peripheral surface of the outer cylinder 5, and electrical conduction between the housing 2 joined to the outer cylinder 5 and the lead portion 24 is achieved. Yes. That is, in the present embodiment, the middle shaft 3 and the housing 2 function as an anode and a cathode for energizing the heat generating portion 26 of the ceramic heater 4.

  In the present embodiment, among the ceramic heaters 4, the distance along the axis CL <b> 1 of the exposed portion 29 that is located between the connecting member 10 and the outer cylinder 5 and whose outer peripheral surface is exposed to the space in the shaft hole 7 is set. It is said to be relatively small. Specifically, the distance along the axis CL <b> 1 between the rear end of the portion that contacts the outer cylinder 5 and the tip of the portion that contacts the connecting member 10 in the ceramic heater 4 is defined as A (mm). At this time, it is configured to satisfy 0.10 ≦ A ≦ 1.50 (more preferably, 0.10 ≦ A ≦ 1.00). In the present embodiment, the distance A is 1 by forming the small diameter portion 14 of the outer cylinder 5 slightly longer toward the rear end side (for example, 2.0 mm or more along the axis CL1). .50 mm or less.

  As described in detail above, according to the present embodiment, the distance A along the axis CL1 of the exposed portion 29 located between the outer cylinder 5 and the connecting member 10 in the ceramic heater 4 is sufficiently sufficient as 1.50 mm or less. It is supposed to be small. Accordingly, in the ceramic heater 4 (base 21), there are cases where portions with slightly low strength (that is, portions that become the base points of breakage) are scattered, and the portions with low strength are located in the exposed portion 29. The durability of the exposed portion 29 against stress can be increased. As a result, excellent breakage resistance can be ensured in the ceramic heater 4, and as a result, the impact resistance of the glow plug 1 can be effectively improved.

  On the other hand, since the distance A is set to 0.10 mm or more, sufficient insulation can be maintained between the outer cylinder 5 and the connection member 10, and the heat generation performance in the ceramic heater 4 is more reliably reduced. Can be prevented.

  Further, in the portion of the ceramic heater 4 held by the outer cylinder 5, a holding force directed radially inward is working. In the present embodiment, the relatively thin small-diameter portion 14 is on the rear end side. It is comprised so that it may become comparatively long toward. Therefore, the holding force can be gradually released toward the rear end side, and the holding force applied to the portion of the ceramic heater 4 held by the outer cylinder 5 can be more reliably prevented from changing suddenly. it can. Further, since the holding force is gradually released, the stress applied to the exposed portion 29 of the ceramic heater 4 with the release of the holding force can be reduced. By these effects, the breakage resistance of the ceramic heater 4 can be further improved, and the impact resistance can be further improved.

  Next, a leak resistance evaluation test and an impact resistance evaluation test were performed in order to confirm the operational effects exhibited in the above embodiment.

  The outline of the leak resistance evaluation test is as follows. That is, samples of glow plugs with various changes in the distance A were prepared, and a voltage necessary for setting the heat generating portion of the ceramic heater to a predetermined high temperature (for example, 1200 ° C.) was applied to each sample. And the presence or absence of the electric current leakage between the connection member and the outer cylinder at the time of voltage application was confirmed. Here, a sample in which current leakage did not occur was evaluated as “◯” as having sufficient insulation, while a sample in which current leakage occurred was evaluated as “x” as inferior in insulation. I gave it. Table 1 shows the test results of the test.

  The outline of the impact resistance evaluation test is as follows. That is, 100 samples of glow plugs with various changes in the distance A were prepared, and each sample was dropped from a height of 50 cm or 100 cm onto a concrete surface with the axis line horizontal. And the presence or absence of the damage of the exposed part by dropping was confirmed, and the ratio (damage ratio) of the number in which the damage in 100 was produced was calculated. Here, a sample with a breakage rate of 1.0% or less is evaluated as “◯” as being excellent in impact resistance, while a sample with a breakage rate exceeding 1.0% is inferior in impact resistance. An evaluation of “x” was made. Table 2 shows the test results of the test. In both tests, the outer diameter of the cylindrical portion of the substrate (portion having substantially the same outer diameter) was set to 3.1 mm to 3.3 mm.

  As shown in Table 1, it was confirmed that the sample having the distance A of 0.10 mm or more has sufficient insulation between the connection member and the outer cylinder without causing current leakage.

  On the other hand, as shown in Table 2, a sample with a distance A of 1.50 mm or less has excellent impact resistance with almost no damage to the exposed portion when dropped from a height of 50 cm. Became clear. This is because the distance A is set to 1.50 mm or less and the exposed portion of the ceramic heater is reduced, so that it is less likely that a slightly lower portion of the ceramic heater (substrate) is located in the exposed portion. This is thought to be because of

  In particular, it was found that the sample having the distance A of 1.00 mm or less has extremely excellent impact resistance with almost no damage to the exposed portion even when dropped from a height of 100 cm. .

  From the above test results, it can be said that it is preferable to configure to satisfy 0.10 mm ≦ A ≦ 1.50 mm from the viewpoint of improving impact resistance while ensuring sufficient insulation. Further, in order to further improve the impact resistance, it can be said that it is more preferable to configure so as to satisfy A ≦ 1.00 mm.

  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) The ceramic heater 4 of the above embodiment is embodied in the case of a round bar shape, that is, a circular cross section, but is not necessarily a circular cross section, for example, an elliptical cross section or an elliptical cross section. The shape may be a polygonal cross section. The technical idea of the present invention may be applied to a so-called plate heater in which a plurality of insulating bases are formed in a plate shape and a heating element is sandwiched therebetween.

  (B) In the above embodiment, the ceramic heater 4 is configured such that the heating element 22 is embedded in the base body 21, but the heating element 22 does not necessarily have to be embedded in the base body 21. The heating element 22 may be exposed on the outer surface of the heater 4.

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 2 ... Housing, 3 ... Medium shaft, 4 ... Ceramic heater, 5 ... Outer cylinder, 10 ... Connection member, CL1 ... Axis line.

Claims (1)

A rod-shaped ceramic heater extending in the axial direction;
A cylindrical outer cylinder that holds the outer periphery of the ceramic heater in a state in which the front end and the rear end of the ceramic heater protrude from itself,
A cylindrical housing in which the outer cylinder is fixed to its tip,
A rod-shaped center shaft inserted into the housing;
A cylindrical connecting member that connects the ceramic heater and the central shaft in a state where the rear end portion of the ceramic heater is fitted into the front end portion of the ceramic heater and the front end portion of the middle shaft is fitted into the rear end portion of the ceramic heater. A glow plug with
Of the ceramic heater, when the distance along the axis between the rear end of the portion that contacts the outer cylinder and the tip of the portion that contacts the connecting member is A (mm),
0.10 ≦ A ≦ 1.50
Glow plug characterized by satisfying.

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