JPH0645144Y2 - Seed glow plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a sheath glow plug which is improved in diameter so as to be slimmed down as a whole.

[Prior Art] As is well known, an internal combustion engine, especially a diesel engine, is provided with a seed glow plug as a start assisting device. As shown in FIG. 3, this sheath glow plug is provided with a tubular mounting member 1 having a threaded portion 1b and a heat generating tube 3. The tube 3 is fitted into the mounting member 1 and heat is generated by brazing 4 in this state. Tube 3
And the mounting bracket 1 are connected in an airtight state.

Also, a glow plug has been proposed in which a heating tube is press-fitted into a metal shell without welding.

[Problems of the prior art] Generally, the outer diameter of the threaded portion of the conventional glow plug of this kind is set to 10 mm or more and the outer diameter of the heat generating tube is set to about 5 mm, but in order to remove restrictions on the mounting space, etc. In recent years, it has been desired to set the threaded portion to 9 mm or less.

By the way, when the glow plug is attached, the threaded portion 1b of the mounting bracket 1 is connected to the female threaded portion of the cylinder block 5 of the engine.
5a and screw the lower end of the mounting bracket to the taper
It is necessary to contact the 5b in an airtight state. Therefore, during the screwing operation, the mounting bracket 1 is tightened with a tightening torque of about 1.0 kg · m to 1.5 kg · m.

At this time, if the mounting bracket 1 is reduced in diameter to about 8 mm in response to recent demands to make it slimmer, the above-mentioned conventional glow plug may be annealed by being heated by brazing. Therefore, the lower end 1a of the mounting member 1 may be deformed abnormally, making it impossible to attach / detach, or in the worst case, breaking. Also, in the glow plug in which the heat-generating tube is press-fitted into the fitting, no consideration has been given to work-hardening due to the reduction in diameter of the threaded portion and press-fitting.

[Object of the Invention] The present invention was made in order to solve the above problems, and the purpose thereof is to allow the threaded portion to hold a corresponding strength, and to prevent the attachment / detachment from deteriorating without being damaged. The diameter can be set to a small diameter such as about 8 mm, the entire body can be slimmed down to be compact, a wide degree of freedom can be secured for mounting, and the mechanical strength of the mounting bracket is increased by work hardening, which is excellent. It is to provide a seed glow plug that produces an effect.

[Means for Solving Problems] In order to solve the above problems, the present invention inserts a center electrode into a metal sheath tube having a closed front end and an open rear end via an electrical insulator. Together with a heat-generating tube in which an electric resistor is connected between the center electrode and the bottom portion of the tip of the sheath tube, the inner peripheral surface has a step portion as a boundary, and the tip has a large diameter portion and an intermediate portion. The heating tube is provided with a tubular fitting that forms a small-diameter portion and that corresponds to the small-diameter portion at a substantially central portion of the outer peripheral surface and that has a threaded portion provided at a position that is not outside the small-diameter portion. A sheath glow plug having a rear end portion press-fitted into the small-diameter portion of the mounting member via the large-diameter portion and connected in an airtight state, wherein the mounting member contains S10C to S35C or carbon C. Made of non-heat treated steel that causes work hardening when the amount is 0.2% by weight or less, Serial screw portion has an outer diameter of 7mm or more, 9 mm or less, the thickness is 1.5mm or more, 2.5
mm or less, the outer diameter of the sheath tube is set to be larger than the inner diameter of the small diameter portion of the mounting member by 0.05 mm or more and 0.2 mm or less. The screw portion has a structure in which work hardening is caused by press fitting the rear end portion of the heat generating tube.

[Advantage and effect of the invention] According to the invention configured as described above, when the heat generating tube and the mounting bracket are press-fitted, the screw portion is bulged and deformed to receive an initial stress, and the work hardening is caused by the work hardening. It is reinforced to increase mechanical strength, and since the mounting bracket does not become annealed, it is possible to maintain appropriate strength and reduce the outer diameter of the mounting bracket without impairing good detachability. It is possible to provide a sheath glow plug which has an excellent effect such that it can be set to a small size, downsizing can be achieved by slimming down the entire body, restrictions on a mounting space can be reduced, and a wide degree of freedom in mounting can be secured.

[Embodiment] A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In Fig. 1, 10 is a sheath glow plug for a diesel engine.
Reference numeral 10 denotes a metal mounting bracket made of non-heat treated steel that causes work hardening, for example, S10C to S35C or C of 0.2% or less, and a metal heating tube 13 is press-fitted into the mounting bracket 16. . The heat generating tube 13 is configured by inserting a center electrode 15 into a metal sheath tube 13a having a closed front end and an open rear end through an electrical insulator 11 such as magnesium oxide. And shes tube 13a
The inner electrical insulator 11 is sealed by a packing g, and a coil-shaped electrical resistor 12 is connected between the center electrode 15 and the bottom of the sheath tube 13a. 16 is a tubular mounting bracket,
This forms a screw part 16c with an outer diameter Ld of 8 mm on the outer periphery,
A chamfered taper portion 16d is formed on the outer periphery of the lower end. Reference numeral 17 is an insulator enclosed between the fitting 16 and the center electrode 15, and 19 is a nut for connecting a lead wire.

On the other hand, 21 is a cylinder block of a sub-chamber diesel engine, which has a mounting hole 2 that communicates with the swirl chamber and the pre-combustion chamber 21a.
2 is formed. A female screw portion 22a is formed on the inner peripheral surface of the mounting hole 22, and a tapered receiving surface 22b is provided on the lower end portion in a direction to reduce the hole diameter.

Now, the mounting state of the mounting bracket 16 and the heat generating tube 13 is performed by press-fitting the heat generating tube 13 into the mounting bracket 16. In order to make this state, on the inner surface of the mounting bracket 16, the large diameter portion 16a is formed at the tip and the small diameter portion 1 is formed in the middle with the step portion 20 as a boundary.
6b are continuously formed.

At this time, the outer diameter dimension J of the heating tube 13 is 4.4 mm, the length T40 mm and the thickness t0.5 mm, and the height M of the mounting bracket 16 is 35 mm.
The length of the threaded portion 16c is N17mm, and the thickness K is 1.83mm to 1.9mm
Within the range (pitch 1.0 mm to 0.75 mm), and the inside diameter 1 of the large diameter portion 16a is set within the range of 4.5 mm to 4.7 mm, which is slightly larger than the outside diameter J of the heating tube 13. There is. The diameter H of the small diameter portion 16b of the mounting member 16 is set to 4.2 mm to 4.35 mm, which is smaller than the outer diameter J of the heat generating tube 13 by about 0.05 mm to 0.2 mm.

Then, at the time of connection, the heating tube 13 in the state shown in FIG. 1 is passed through the large-diameter portion 16a of the mounting member 16 from the rear end opening to the step portion 20.
And then press-fitted into the small diameter portion 16b. Then, the diameter H of the small diameter portion 16b is 0.05 mm to 0.
Since the diameter is set to about 2 mm, the screw part 1
6c is bulged and deformed, compared to the original state before press fitting, for example, 0.
The diameter is about 05 mm. In this state, the mounting bracket 16 and the heating tube 13 overlap each other by a length of about 7 mm as shown by the predetermined length dimension Ov as shown in FIG.
Both the inner and outer peripheral surfaces of 6 and the heat generating tube 13 are in airtight contact with each other.

In the glow plug 10 thus assembled, the threaded portion 16c of the fitting 16 is screwed into the female threaded portion 22a of the cylinder block 21 with a predetermined tightening torque as shown in FIG. The surface 22b is brought into contact with the airtight state.

[Constitution described above] Since the heating tube 13 is connected to the metal fitting 16 by press fitting, the sheath tube and the mounting metal fitting are connected by brazing, and unlike the conventional case where the mounting metal fitting is heated and annealed, the screw portion 16c is Even if the diameter is small, the corresponding strength is maintained and the fitting 16 does not abnormally deform or break due to the predetermined tightening torque applied when the glow plug is attached.
As a result, good detachability that is the same as before can be obtained, and the outer diameter dimension Ld of the screw part 16c of the mounting bracket 16 is 8 mm.
For example, the diameter can be set to be small, and the entire body can be made smaller by slimming down to reduce the restrictions on the mounting space and ensure a wide degree of freedom in mounting.

In addition, the press-fitting of the heat-generating tube 13 causes the threaded portion 16c to bulge and deform to increase the diameter by about 0.05 mm, so that the mounting member 16 is subjected to work hardening and has an initial stress, and the mechanical strength is increased.

In the above embodiment, while setting the outer diameter Ld of the threaded portion 16c of the mounting bracket 16 to 8 mm to achieve overall slimming,
Normally, the torque value is required for the tightening torque when mounting.
It has been found that it can withstand up to 2.5 kg · m to 3.0 kg · m, which is larger than 1.0 kg · m to 1.5 kg · m.

Here, the threaded portion 16c of the mounting bracket 16 is not limited to the outer diameter dimension Ld of 8 mm as in the above embodiment, and is 7 mm or more.
It is known that the size range of 9 mm or less is sufficient, and the reason for setting such a size range is as follows.

That is, if the outer diameter of the threaded portion 16c exceeds 9 mm, the overall effect of downsizing is small, and if it is 6 mm or less, the strength becomes less than a predetermined value with respect to the tightening torque, and mounting becomes impossible.

The applicable range of the glow plug is not limited to the pre-combustion chamber type and the swirl chamber type, but can also be applied to the direct injection type diesel engine.

In addition, in concrete implementation, various modifications can be made without departing from the scope of the invention.

[Brief description of drawings]

1 and 2 show a first embodiment of the present invention.
FIG. 1 is an exploded vertical sectional view of a glow plug in a diesel engine, FIG. 2 is a vertical sectional view showing a mounted state of the glow plug on a cylinder block, and FIG. 3 is a vertical sectional view showing a mounted state of a conventional glow plug. In the figure, 10 ... Diesel engine sheath glow plug, 12 ... Electric resistor, 13 ... Heat generating tube, 13a ... Sheath tube, 16 ... Mounting bracket, 16c ... Screw part

Claims (1)

[Scope of utility model registration request] 1. A center electrode is inserted through an electric insulator into a metal sheath tube having a closed front end and an open rear end, and the center electrode is disposed between the center electrode and the bottom of the front end of the sheath tube. A heat-generating tube with an electric resistor connected to it, with a large-diameter portion at the tip and a small-diameter portion in the middle, with the stepped portion as the boundary on the inner peripheral surface, and the small-diameter portion at the approximate center of the outer peripheral surface A tubular mounting metal fitting corresponding to a portion and provided with a threaded portion at a position not protruding from the small diameter portion, wherein the rear end of the heating tube is the large diameter portion in the small diameter portion of the mounting metal fitting. It is a sheath glow plug press-fitted through and connected in an airtight state, wherein the mounting metal fitting has a content of S10C to S35C or carbon C of 0.
It is made of non-heat treated steel that causes work hardening at 2% by weight or less, and the screw part has an outer diameter of 7 mm or more, 9 mm or less, and a wall thickness of 1.5 mm
As described above, each is set to 2.5 mm or less, and the outer diameter of the sheath tube is set to be larger than the inner diameter of the small diameter portion of the mounting bracket by 0.05 mm or more and 0.2 mm or less, and the mounting is performed. The sheath glow plug, wherein the threaded portion of the metal fitting causes work hardening by press fitting the rear end portion of the heat generating tube.