JP3796905B2 - Glow plug - Google Patents

Description

【００４２】
表１より知られるごとく，凹部４０の外径寸法ｄが小さいほど，また，２面巾Ｗが小さいほどクラックの発生率が高くなった。しかしながら，上記外径寸法ｄがハウジング６の上端開口部の内径寸法Ｄと同じまたはこれよりも大きい場合（ｄが７ｍｍ以上の場合）には，全くクラックが発生しなかった。
【００４３】
この理由は次のように考えられる。
即ち，上記内径寸法Ｄよりも上記外径寸法ｄが小さくなった場合には，そのナットとブッシングとの当接位置が，ブッシングとハウジングとの当接位置よりも内径側にまで広がる。
【００４４】
そのため，かしめ固定によってナットからブッシングへ強い押圧力作用した場合には，ハウジングの上端面からオーバーハングされた状態のブッシングの内径部分においては上記押圧力が単純な圧縮応力ではなく曲げ応力として作用する。それ故，この曲げ応力によりクラックが発生してしまう。そして，上記曲げ応力は，上記外径寸法ｄが小さいほど大きくなり，上記のようなクラック発生状況となると考えられる。
【００４５】
したがって，本例によれば，ブッシング４に凹部４０を設けるに当たり，その外径寸法ｄをハウジング６の上記内径寸法Ｄ以上の大きさにすることが，クラック発生防止にさらに有効であることがわかる。
【００４６】
実施形態例６
本例は，図１１に示すごとく，ブッシングとして従来と同形状のブッシング９４をそのまま用い，ナット５０５のブッシング当接面５４に凹部５０を設けたものである。その他は実施形態例１と同様である。
この場合には，ブッシング９４を従来のままの形状とし，ナット５０５の形状を変更することにより間隙部７を形成することができる。この間隙部７形成による効果は，実施形態例１と同様である。
【図面の簡単な説明】
【図１】実施形態例１における，ブッシング，ナットの配設部分の断面を示す説明図。
【図２】実施形態例１における，ブッシングの斜視図。
【図３】実施形態例２における，ブッシング，ナットの配設部分の断面を示す説明図。
【図４】実施形態例２における，ブッシングの斜視図。
【図５】実施形態例３における，ブッシング，ナットの配設部分の断面を示す説明図。
【図６】実施形態例４における，ナットの２面巾Ｗを示す説明図。
【図７】実施形態例４における，ナットの２面巾Ｗ変化と厚み変化の関係を示す説明図。
【図８】実施形態例４における，ブッシング形状とクラック発生率との関係を示す説明図。
【図９】実施形態例４における，ブッシング形状とクラック発生率との関係を示す説明図。
【図１０】実施形態例５における，各寸法位置を示す説明図。
【図１１】実施形態例６における，ブッシング，ナットの配設部分の断面を示す説明図。
【図１２】従来例のグロープラグの構成を示す説明図。
【図１３】従来例の他のグロープラグのブッシング，ナットの配設部分の断面を示す説明図。
【図１４】従来例における，ナットのかしめ固定方法を示す，（ａ）平面図，（ｂ）正面図。
【図１５】従来例における，ナットのかしめ固定後の不具合を示す，（ａ）平面図，（ｂ）正面図。
【図１６】従来例における，クラックが発生したブッシングの斜視図。
【図１７】従来例における，クラックが発生した他のブッシングの斜視図。
【符号の説明】
１．．．グロープラグ，
３．．．中軸，
３１．．．端子ネジ部，
４，４０２，４０３．．．ブッシング，
４０．．．凹部，
４５．．．ナット当接面，
５，５０５．．．ナット，
５０．．．凹部，
５４．．．ブッシング当接面，
６．．．ハウジング，[0001]
【Technical field】
The present invention relates to a glow plug for preheating the inside of a cylinder of a diesel engine.
[0002]
[Prior art]
As shown in FIG. 12, the conventional glow plug 9 has a housing 6, a heater 2 fitted into the housing 6, and a middle shaft 3 inserted into the housing 6 toward the upper end of the heater 2. Yes. Further, the center shaft 3 has a terminal screw portion 31 protruding from the upper end of the housing 6, and a ring-like bushing 94 is inserted into this and a nut 5 is screwed.
[0003]
Since the nut 5 is a metal conductor, if the nut 5 is brought into direct contact with the housing 6, electrical insulation between the center shaft 3 and the housing 6 cannot be achieved. Therefore, a resin bushing 94 having electrical insulation is interposed between the nut 5 and the housing 6. As this bushing 94, there is a type having a protruding portion 941 inserted into the opening of the housing 6 as shown in FIG.
[0004]
Further, in the glow plug 9, as disclosed in Japanese Patent Laid-Open No. 53-25742, there is a measure of caulking and fixing the nut 5 in order to prevent the nut 5 from being loosened due to vibration during use. It was taken.
That is, as shown in FIGS. 14A and 14B, the screwed nut 5 was pressure-deformed from the left and right using the pressure jig 8. Thereby, the inner diameter shape of the nut 5 is flattened and cannot be easily rotated. Therefore, loosening due to vibration or the like of the nut 5 can be avoided reliably.
[0005]
As shown in FIG. 12, the middle shaft 3 and the heater 2 are connected by a connection fitting 81, and the middle shaft 3 and the housing 6 are fixed by an insulating ring 84 and a glass seal 83. A metal sleeve 28 is interposed between the housing 6 and the heater 2.
[0006]
[Problems to be solved]
However, the conventional glow plug 9 has the following problems.
That is, as shown in FIGS. 15A and 15B, when the nut 5 is fixed by caulking, a crack 99 may occur in the bushing 94.
The cause is considered as follows.
As shown in FIG. 15B, the nut 5 is not only deformed in the pressure direction by the pressure deformation, but also swells in the thickness direction.
[0007]
Therefore, as shown in FIGS. 15B and 16, the swelling of the nut 5 becomes a strong pressing force (bending stress) against the bushing 94, and the bushing 94 cannot withstand this pressing force and generates a crack 99. .
As shown in FIG. 17, the crack 99 is similarly generated by caulking and fixing the nut 5 in the case of the bushing 94 of the type provided with the protruding portion 941.
[0008]
As a countermeasure for preventing cracks, it is conceivable to change the material of the bushing 94 to a tough material. For example, using a tough material such as alumina or Teflon as a material for the bushing 94 is effective for crack prevention. However, changing the material leads to an increase in the cost of the bushing and, in turn, an increase in the cost of the glow plug.
[0009]
The present invention has been made in view of such conventional problems, and it is an object of the present invention to provide an inexpensive glow plug that does not crack in the bushing even if the nut is caulked and fixed.
[0010]
[Means for solving problems]
The invention of claim 1 includes a housing, a heater fitted in the housing, a current-carrying central shaft inserted into the housing toward the upper end of the heater, and a ring-shaped bushing contacting the upper end of the housing In a glow plug having a nut screwed to the terminal screw portion of the middle shaft through
The glow plug is characterized in that a gap is formed around the central axis between the bushing and the nut.
[0011]
The most notable aspect of the present invention is that the gap is provided between the bushing and the nut.
This gap can be formed, for example, by bringing only the outer periphery of the bushing and the nut into contact with each other. Specifically, as described later, the gap can be formed by forming a recess on one or both contact surfaces of the bushing or the nut. Moreover, the said clearance part can also be formed by interposing the spacer which has an internal diameter larger than a bushing and a nut between a bushing and a nut.
[0012]
Next, the operation of the present invention will be described.
In the glow plug of the present invention, the gap is provided between the bushing and the nut. Therefore, as in the conventional case, when the nut is caulked and fixed, cracks do not occur in the bushing.
[0013]
That is, when the nut is caulked and fixed, it is deformed by pressure from the left and right sides while the nut is in contact with the bushing. As a result, the nut is deformed in the pressurizing direction so that the inner diameter shape becomes flat, and the nut is also deformed and expanded in the thickness direction. At this time, conventionally, the bushing received a strong pressing force due to the bulging of the nut in the thickness direction.
[0014]
On the other hand, in the present invention, as described above, the gap is provided between the bushing and the nut. Therefore, when the caulking is fixed, even if the nut is deformed in the thickness direction, it can be absorbed by the gap. Therefore, the bushing is not subjected to a strong pressing force due to the caulking of the nut, and the occurrence of cracks can be prevented.
[0015]
Further, in the present invention, since the occurrence of the cracking of the bushing can be prevented by the formation of the gap portion, it is not necessary to apply a material that is particularly tougher than the conventional one to the bushing. Therefore, it is possible to avoid an increase in bushing cost and, in turn, an increase in glow plug cost.
[0016]
Therefore, according to the present invention, even if the nut is caulked and fixed, cracks are not generated in the bushing, and an inexpensive glow plug can be provided.
[0017]
Next, as in a second aspect of the invention, the gap is preferably ring-shaped. As a result, it is possible to provide a non-biased gap between the ring-shaped bushing and the nut, and the effects of the gap described above can be more fully exhibited.
[0018]
According to a third aspect of the present invention, the gap is preferably formed by a recess provided in an inner peripheral portion of a nut contact surface of the bushing. That is, it is preferable that the contact surface of the bushing with the nut is not a horizontal plane, but a shape having a recess formed by recessing the central inner peripheral portion. Thereby, the said clearance gap can be easily formed only by changing the shape of a bushing.
[0019]
According to a fourth aspect of the present invention, the gap portion can be formed by a concave portion provided in an inner peripheral portion of the bushing contact surface of the nut. In this case, a bushing having the same shape as the conventional one can be used as it is.
[0020]
According to a fifth aspect of the present invention, the gap portion preferably has an outer diameter dimension equal to or larger than the inner diameter dimension of the upper end opening of the housing with which the bushing abuts. In this case, it is possible to avoid the contact position between the nut and the bushing from being closer to the inner diameter side than the contact position between the bushing and the housing. That is, it is possible to avoid contact of the nut with the portion where the bushing is overhanged on the inner diameter side of the opening of the housing.
[0021]
Therefore, even if a strong pressing force is applied from the nut to the bushing, the bushing is only subjected to a simple compressive stress, and no bending stress is generated on the overhang portion. Therefore, the occurrence of bushing cracks can be prevented more reliably.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A glow plug according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the glow plug 1 of this example includes a housing 6, a heater 2 (see FIG. 12) fitted into the housing 6, and a current-carrying central shaft inserted into the housing toward the upper end of the heater 2. 3 and a nut 5 screwed onto a terminal screw portion 31 of the middle shaft 3 via a ring-shaped bushing 4 that contacts the upper end of the housing.
[0023]
As shown in FIG. 1, a gap 7 is formed between the bushing 4 and the nut 5.
Specifically, as shown in FIGS. 1 and 2, the gap 7 is formed by a ring-shaped recess 40 provided on the inner periphery of the nut contact surface 45 of the bushing 4.
[0024]
Further, as shown in FIG. 1, the bushing 4 is of a type having a protruding portion 41 inserted into the opening 61 of the housing 6. In addition, an inner hole 43 for allowing the terminal screw portion 31 to pass therethrough is provided at the center as in the conventional case.
Others are the same as the conventional example.
[0025]
Next, the operation of this example will be described.
Also in the glow plug 1 of this example, the nut 5 is caulked and fixed as in the prior art after the assembly. Specifically, similarly to the method shown in FIG. 14 described above, the nut 5 is pressed and deformed from the left and right using the pressing jig 8.
[0026]
At this time, the nut 5 is not only deformed in the pressurizing direction but also deformed and inflated in the thickness direction. Here, in the present example, the gap portion 7 is provided between the bushing 4 and the nut 5. Therefore, as shown in FIG. 1, the deformation (dotted line portion) in the thickness direction of the nut 5 is absorbed by the gap portion 7.
[0027]
Therefore, the bushing 4 is not subjected to a strong pressing force as in the prior art, and no cracks are generated.
Further, in this example, it is possible to take a countermeasure against cracking of bushing simply by providing the gap 7. There is no significant cost increase.
Therefore, according to this example, it is possible to obtain an inexpensive glow plug 1 that does not cause cracking to the bushing due to the nut caulking.
[0028]
Embodiment 2
In this example, as shown in FIGS. 3 and 4, in place of the bushing 4 of the first embodiment, a bushing 402 of a type having no protrusion is applied. Also in the bushing 402, the ring-shaped recess 40 similar to that of the first embodiment is provided on the nut contact surface 45. Others are the same as the first embodiment.
[0029]
In this case, the cost of the bushing 402 can be reduced by not providing the protruding portion.
Therefore, the cost of the glow plug can be further reduced.
Other effects are the same as those of the first embodiment.
[0030]
Embodiment 3
In this example, as shown in FIG. 5, instead of the bushing 4 in the first embodiment, a bushing 403 of a disk shape having no protrusion and provided with ring-shaped recesses 40 on both sides is applied. It is. Others are the same as the first embodiment.
[0031]
In this case, as in the case of the second embodiment, the cost reduction effect of the bushing 403 can be obtained by not providing the protrusions, and the assembly process of the glow plug can be rationalized.
That is, in the case of Embodiments 1 and 2, it is necessary to manage the assembly direction so that the ring-shaped recess 40 of the bushings 4 and 402 is positioned on the nut 5 side.
[0032]
On the other hand, the bushing 403 of the present example has the same shape on both sides, and ring-shaped recesses 40 are provided on both sides thereof. Therefore, it is not necessary to manage the assembly direction in the bushing assembly process, and the manufacturing process can be streamlined and the cost of the glow plug can be reduced.
Other effects are the same as those of the first embodiment.
[0033]
Embodiment 4
In this example, the effect of the gap 7 in the glow plugs of the first to third embodiments was evaluated by experiments.
Specifically, the correlation between the amount of deformation of the nut and the occurrence of cracks during the caulking of the nut was investigated. This is a study of the occurrence of cracks in each bushing with respect to changes in the thickness of the nut, taking advantage of the fact that the bulge in the thickness direction increases as the amount of pressure deformation of the nut increases.
[0034]
First, the amount of deformation of the nut 5 in the pressurizing direction was defined by the distance between two opposing surfaces (two-surface width W) as shown in FIG. The two-sided width W before deformation is 9 mm. Further, FIG. 7 shows the result of obtaining the thickness change in advance with respect to the change in the two-surface width W. In the figure, the horizontal width is the two-surface width W, and the vertical axis is the thickness deformation amount B. In addition, in the same figure, the change of the width dimension deformation amount C in the direction which makes 90 degree | times with the pressing direction of a nut is also shown for reference.
[0035]
Next, as shown in FIGS. 8 and 9, a nut caulking fixing test is performed on glow plugs (sample Nos. E31 to E33, C31, and C32) having bushings of various shapes, and the two-surface width W and The crack occurrence situation was investigated. The caulking fixation test was performed four times for each two-surface width W. In FIGS. 8 and 9, the case where no cracks occurred is shown as ◯, and the case where any cracks occurred is shown as x.
[0036]
In addition, sample No. in FIG. C31 and C32 use the conventional bushing 94, E31 uses the bushing 402 of the second embodiment, E32 uses the bushing 403 of the third embodiment, E33 uses the bushing 4 of the third embodiment. It is what was used.
[0037]
As is known from FIG. 8 and FIG. 9, the product of the present invention (E31 to E33) did not generate any cracks in the bushing over the entire test range, resulting in a very good result. On the other hand, in the conventional products (C31, C32) using the conventional bushing 94 without the recess 40, the crack generation rate increased as the width W of the two surfaces was reduced. In particular, in C31 which does not have a protruding portion, a crack occurred from the stage where the two-surface width W was relatively large.
[0038]
From the above results, it is possible to prevent the occurrence of cracking of the bushing when the nut is fixed by caulking, by providing the ring-shaped recess 40 on the nut abutting surface of the bushing and thereby providing the gap portion between the bushing and the nut. It became clear that it was extremely effective.
[0039]
Embodiment 5
In this example, as shown in FIG. 10, in the glow plug 1 of the first embodiment, the outer diameter d of the recess 40 of the bushing 4 was changed, and the influence was examined. The inner diameter D of the upper end opening of the housing 6 is 7 mm. Further, the depth T of the recess 40 of the bushing 4 was all set to 0.3 mm.
[0040]
Specifically, a glow plug using a bushing 4 having each outer diameter dimension d is prepared, and a nut caulking fixation test similar to that of the embodiment 4 is performed to check whether or not a crack is generated in the bushing. went.
The results are shown in Table 1. The test was carried out four times for each dimension. The case where no cracks occurred was indicated by ◯, the case where cracks occurred only once in four times, and the others were indicated by ×.
[0041]
[Table 1]

[0042]
As is known from Table 1, the smaller the outer diameter dimension d of the recess 40 and the smaller the two-surface width W, the higher the crack generation rate. However, when the outer diameter d was the same as or larger than the inner diameter D of the upper end opening of the housing 6 (when d was 7 mm or more), no crack was generated.
[0043]
The reason is considered as follows.
In other words, when the outer diameter dimension d is smaller than the inner diameter dimension D, the contact position between the nut and the bushing extends further to the inner diameter side than the contact position between the bushing and the housing.
[0044]
Therefore, when a strong pressing force is applied from the nut to the bushing by caulking, the pressing force acts not as a simple compressive stress but as a bending stress at the inner diameter portion of the bushing overhanged from the upper end surface of the housing. . Therefore, cracks are generated by this bending stress. The bending stress becomes larger as the outer diameter dimension d is smaller, and it is considered that the above-described crack generation situation occurs.
[0045]
Therefore, according to this example, when the recess 40 is provided in the bushing 4, it is more effective to prevent the occurrence of cracks by setting the outer diameter dimension d to be larger than the inner diameter dimension D of the housing 6. .
[0046]
Embodiment 6
In this example, as shown in FIG. 11, the bushing 94 having the same shape as the conventional one is used as a bushing, and the recess 50 is provided on the bushing contact surface 54 of the nut 505. Others are the same as the first embodiment.
In this case, the gap portion 7 can be formed by changing the shape of the nut 505 to the bushing 94 having the conventional shape. The effect of forming the gap 7 is the same as that of the first embodiment.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram showing a cross section of a bushing and nut arrangement part in Embodiment 1;
FIG. 2 is a perspective view of a bushing in the first embodiment.
FIG. 3 is an explanatory view showing a cross section of a bushing and nut arrangement portion in Embodiment 2.
4 is a perspective view of a bushing in Embodiment 2. FIG.
FIG. 5 is an explanatory view showing a cross section of a bushing and nut arrangement portion in Embodiment 3.
FIG. 6 is an explanatory view showing a two-surface width W of a nut in the fourth embodiment.
FIG. 7 is an explanatory diagram showing a relationship between a change in the two-surface width W and a change in thickness of the nut in the fourth embodiment.
FIG. 8 is an explanatory diagram showing a relationship between a bushing shape and a crack occurrence rate in Embodiment Example 4;
FIG. 9 is an explanatory diagram showing the relationship between the bushing shape and the crack occurrence rate in Embodiment Example 4;
FIG. 10 is an explanatory diagram showing each dimension position in Embodiment 5.
FIG. 11 is an explanatory view showing a cross-section of a bushing and nut arrangement portion in a sixth embodiment.
FIG. 12 is an explanatory view showing a configuration of a conventional glow plug.
FIG. 13 is an explanatory view showing a cross section of another conventional glow plug bushing and nut arrangement portion.
FIGS. 14A and 14B are a plan view and a front view, respectively, showing a nut caulking and fixing method in a conventional example.
15A is a plan view and FIG. 15B is a front view showing a defect after caulking and fixing of a nut in a conventional example.
FIG. 16 is a perspective view of a bushing in which a crack has occurred in a conventional example.
FIG. 17 is a perspective view of another bushing in which a crack has occurred in a conventional example.
[Explanation of symbols]
1. . . Glow plug,
3. . . Middle shaft,
31. . . Terminal screw,
4,402,403. . . Bushing,
40. . . Recess,
45. . . Nut contact surface,
5,505. . . nut,
50. . . Recess,
54. . . Bushing contact surface,
6). . . housing,

Claims (5)

A housing, a heater fitted in the housing, a current-carrying central shaft inserted into the housing toward the upper end of the heater, and a terminal of the central shaft via a ring-shaped bushing that contacts the upper end of the housing For glow plugs with nuts threaded on the thread
A glow plug characterized in that a gap is formed at the periphery of the central axis between the bushing and the nut. The glow plug according to claim 1, wherein the gap portion has a ring shape. 3. The glow plug according to claim 1, wherein the gap portion is formed by a concave portion provided in an inner peripheral portion of a nut contact surface of the bushing. 3. The glow plug according to claim 1, wherein the gap portion is formed by a concave portion provided in an inner peripheral portion of a bushing contact surface of the nut. 5. The glow plug according to claim 1, wherein the gap portion has an outer diameter dimension equal to or larger than an inner diameter dimension of an upper end opening portion of the housing with which the bushing abuts.

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