JPH05187634A - Glow plug - Google Patents

Abstract

PURPOSE:To obtain a glow plug having a prolonged lifetime upto a tracking breakdown on the surface of a bush by a construction wherein an insulative bush keeps a state of insulation of a core shaft from a housing and fixes the core shaft, making it engage with the housing. CONSTITUTION:A glow plug 10 is provided with an insulative bush 4 through which a core shaft 2 is inserted and by which the core shaft 2 is fixed, being made to engage with a housing 1 in an electrically insulated state. A thread part 23 of the core shaft 2 is inserted into a bush main body 41 of resin of the glow plug 10, a metal nut 51 is fitted thereon by screwing by this resin bush 41 and the core shaft 2 is fixed to the housing 1 in an insulated state by the bush. Since the metal nut is covered with the bush main body 41 made of resin, occurrence of dielectric breakdown due to sticking of a stain of a conductive substance on the surface of the insulative bush 4 made to engage with the core shaft on which a plus potential is impressed in electrification is suppressed.

Description

Detailed Description of the Invention

[0001]

This invention relates to glow plugs for diesel engines.

[0002]

2. Description of the Related Art A glow plug is a plug that preheats combustion gas when starting a diesel engine, as shown in FIG.
A cylindrical housing 100 having an engine mounting screw 101 on the outer peripheral surface, a heater rod 210 protruding from the housing 100 at the lower end of the housing 100 and enclosing a heating element 220 inside, and a heater rod 210 at one end.
And the other end projecting from the housing 100 and having a screw 201 for tightening and fixing a harness or a metal plate from the power supply of the vehicle, and a middle shaft 200.
Is fixed to the housing 100 in an electrically insulated state.

The heater rod 210 is fixed to the housing 100 by welding or the like.
Housing 1 through insulating bush 400 at opening 0
It is fixed at 00. The insulating bush 400 is usually made of resin, and insulates and locks the center shaft 200 to the housing 100 together with the O-ring 300 that prevents invasion of water and oil. The insulating bush 400 is further fixed to the opening end of the housing by pressing the metal nut 500 onto the threaded portion of the center shaft 200.

As shown in FIG. 6, the glow plug described above includes a screw portion 101 of a housing 100 on an engine 8.
The power supply harness 71 or the metal plate 72 is sandwiched on the metal nut 500 which is attached (not shown), and the metal nut 7 is fastened to the center shaft 200 at the upper portion. As a result, when the glow plug is energized, a current flows to the center shaft 200, the heating element 220, the heater rod 210, the housing 100, and the engine 8, and the heater rod 210 is heated. Here, the center shaft 200 is at the same potential as the + potential of the power source, but the housing 100 is at the ground potential, and the insulating bush 400 existing between them is between the current loaded on the center shaft 200 and the ground current flowing through the housing 100. It has a function to prevent the leak.

[0005]

By the way, a leisure vehicle such as a four-wheel drive vehicle may travel along a shore of a waterway or a beach, in which case the frequency of the engine being flooded with water or seawater is low. high. Also in general passenger cars, when the vehicle travels in a flooded canal covered with an antifreezing agent in winter, the engine is flooded with water containing salt, but this frequency is high in some regions.

When seawater or water containing a salt such as an antifreezing agent is repeatedly exposed to water in this manner, the surface of the insulating bush 4 is contaminated by conductive deposits, resulting in a decrease in the insulating property of the surface. When electricity is applied in a state where it is soiled with conductive deposits in this manner, current leaks between the metal nut 500 and the housing 100. The leakage of current generated on the surface of the bush 400 is accompanied by a partial spark discharge, and when it is repeated, the surface of the bush 400 is carbonized and tracking breakdown occurs. Especially when the engine is equipped with a slant, the mounting position of the glow plug becomes relatively low with respect to the road surface, the frequency of water contact increases, and depending on the model, the energizing terminal part of the glow plug is covered as shown in Fig. 7. The water 9 that has been drained may collect. When energized in such a state, depending on the depth of the accumulated water and the salt concentration in the water, the metal nut 500 to which a + potential is applied or the energizing metal plate 72 is melted by the electric corrosion and adheres to the surface of the bush 400. The life until the above-mentioned tracking breakdown is remarkably reduced.

Also, in the glow plug of FIG. 8 according to the prior art, the above-mentioned salt water intrudes through the gap between the housing 100 and the bush 400 or the gap between the center shaft 200 and the bush 400 above the O-ring 300 to cause similar tracking damage. There was a problem that. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a glow plug which has a long life until tracking breakdown occurs on the bush surface even when the glow plug is exposed to salt water or the like.

[0008]

A glow plug of the present invention comprises a heater rod for heat generation, a rod-shaped center rod capable of conducting electricity to a heater whose one end is electrically connected to the heater rod, and the heater rod. A cylindrical housing that encloses the inner shaft inside, projects and holds the heater rod at the lower end opening, and locks by protruding the central shaft at the upper end opening, and the inner shaft is locked to the housing in an insulated state In a glow plug including an insulating bush to be fixed, the insulating bush is formed by a resin bush main body, the inner shaft, and a metal nut that can be fixed at a predetermined position and is enclosed by the resin bush main body. It is characterized in that the central shaft is locked and fixed to the housing while maintaining an insulating state from the housing.

[0009]

In the glow plug of the present invention, the resin bush body is formed by including the outer peripheral surface of the metal nut. For this reason, since the metal nut enclosed in the resin bush body is screwed onto the center shaft, the creepage distance on the outer peripheral surface of the bush becomes longer compared to the case where the conventional metal nut for locking the bush is exposed. The exposed area of the metal part is reduced, and the occurrence of tracking due to dielectric breakdown can be suppressed. Therefore, the insulating property of the bush is increased, the durability of the glow plug is increased, and the life can be extended. Further, since the resin bush main body includes the metal nut, the liquid tightness is improved, and thus the durability of the plug is improved.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples. As shown in FIG. 1, the glow plug 10 includes a cylindrical housing 1, a heater rod 21 held in a lower end opening of the housing 1, an upper end opening of the housing 1, a screw connected to the heater rod 21, and a side surface. A center shaft 2 for energization having a portion 23;
An insulating bush 4 which is inserted into the center shaft 2 and locks and fixes the center shaft 2 to the housing 1 in an electrically insulated state.

The housing 1 is made of a tubular metal, and a screw portion 11 for attaching to an engine is formed at a substantially center of a side surface thereof, and a heater rod 21 is locked and fixed to the housing 1 at a lower end opening portion by means of brazing or the like. ing. In the heater rod 21, a heating element 22 such as a nickel wire, which is welded to an opening by a metal tube such as SUS310S, which is connected to the inner shaft 2 for energization by welding inside the housing 1, is made of an insulating powder such as magnesia. It is configured by filling with the method of. The inner shaft 2 for energization protrudes from the upper end opening of the housing 1, and the protrusion is a metal for electrically connecting the harness 71 from the power source or the glow plug 10 in parallel as in the conventional glow plug shown in FIG. A screw portion 23 for tightening and fixing the plate 72 is formed.

As shown in FIG. 2, the insulating bush 4 comprises an insulating resin bush body 41 and a metal nut 51, and an O-ring 32 is interposed between the resin bush body 41 and the metal nut 51. . The metal nut 51 is made of brass having a screw formed on the inner surface for screwing with the threaded portion 23 of the center shaft 2, and the outer circumference is enclosed by a resin bush main body 41 via an O-ring 32 made of silicon rubber or the like. The main body 41 is screwed into the center shaft 2 and locked. An anaerobic sealing agent 61 is provided on the thread surface of the inner peripheral surface of the metal nut 51,
A predetermined amount is applied to the threaded portion 23 of the center shaft 2 in advance, and the metal nut 51 in the resin bush main body 41 is screwed into the screw of the center shaft 2 and tightened, and then cured at the threaded surface to seal the threaded surface. An adhesive layer having a function of preventing loosening is formed.

The O-ring 32 has a bottom surface of the metal nut 51,
By being compressed and deformed by a predetermined amount between the upper surfaces of the stepped portions of the resin bush main body 41, the liquid tightness of the interface between the metal nut 51 and the resin bush main body 41 is secured. Further, between the upper end surface of the housing 1 and the insulating bush 4, an O-ring 31 made of silicon rubber or the like is arranged in a triangular groove portion formed by the tapered hole portion of the housing 1 and the side surface of the resin bush main body 41. The insulating bush 4 is preliminarily attached to the small diameter portion and then assembled by tightening the resin bush main body 41 to secure liquid tightness between the inner surface of the tapered hole of the housing 1 and the outer surface of the insulating bush main body 41.

The resin bush body 4 of the glow plug 10
1 is formed by inserting it into the threaded portion 23 of the center shaft 2 and screwing a metal nut 51 with this resin bush 41 to insulate and fix the center shaft 2 to the housing 1. As shown in FIG. 2, a method of manufacturing the insulating bush 4 is made of PPS resin having a hexagonal portion for facilitating screw tightening formed on the upper end side and a large-diameter and small-diameter two-stage hole formed on the inner surface. After the resin bush main body 41 is formed by injection molding or the like, the O-ring 32 is inserted into the bottom surface of the large diameter portion, and thereafter the threaded portion is formed on the inner surface and the flange portion 52 and the knurled portion 53 are formed on the outer surface. It is obtained by inserting 51 into the resin bush main body 41 and welding by ultrasonic welding.

In the glow plug 10 described above, the outer upper end portion of the housing 1 is a ground potential portion when energized, and the metal nut 51 enclosed in the energizing center shaft 2 and the insulating bush 4 is a + potential portion. Since the housing 1 and the metal nut 51 have their outer peripheral surfaces enclosed by an insulating resin,
Compared with the case of the conventional metal nut, the insulation creepage distance can be increased and the insulation property is improved. Further, the adhesiveness between the inside of the housing 1 and the insulating bush 4 and the adhesiveness between the center shaft 2 and the insulating bush 4 are enhanced, and the lower end portion of the insulating bush 4 and the O
Prevents ingress of water etc. between the ring. Therefore, the glow plug 10 has enhanced insulation and prevents tracking damage, and has excellent durability. As another embodiment of the bush, a metal nut 54 having a tapered outer peripheral surface may be inserted without using the O-ring 32 as shown in FIG. In this case, liquid tightness can be secured at the interface between the resin bush 42 and the metal nut 54 without the O-ring. Further, as shown in FIG. 4, the joint surface between the metal nut 51 and the resin bush main body 41 may be fixed by interposing an adhesive layer 62 to secure liquid tightness. In the above-described embodiment, the example in which the liquid tightness in the housing is ensured has been described, but it is used under the environmental condition in which only the tracking damage on the outer surface of the resin bush main body 41 which occurs in the conventional glow plug is considered. In some cases, it is not necessary to use an insulating bush for a completely liquid-tight structure. In that case, the O-rings 31 and 32 may not be used. Further, the adhesive 61 may be used when necessary to prevent the loosening of the metal nut 51.

Further, the present invention relates to an insulating bush 4 for insulating and fixing between the current-carrying inner shaft 2 and the housing 1, and the structure of the glow plug is not limited to this embodiment. A ceramic heater 23 containing a heating element 22 is used as the heater rod 21 as shown, and a known self-temperature control type ceramic glow plug having a resistor 24 which is connected in series with the ceramic heater 23 and integrally formed therein is used. The same effect can be obtained by applying an insulating bush.

[0017]

As described above, according to the present invention, since the metal bush is covered with the insulating resin bush main body, the insulating bush locked to the center shaft to which + potential is applied during energization has almost no exposed portion. , Even if the glow plug is energized with salt water adhering to or immersed in the insulating bush, the electrical corrosion of the metal nut is very small, and the contamination of the surface of the insulating bush due to corrosion products is extremely small. . Therefore, it is possible to suppress the occurrence of dielectric breakdown due to the attachment of the dirt of the conductive substance on the surface of the insulating bush.

Further, as compared with the conventional glow plug, the creepage distance of the surface of the insulating bush becomes longer, the insulating distance becomes longer, the insulating effect is enhanced, and the tracking breakdown on the outer surface of the insulating bush is suppressed, and the life of the glow plug is dramatically increased. Can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a glow plug of an embodiment.

FIG. 2 is a perspective view illustrating the structure of a bush.

FIG. 3 is a sectional view of an example of a bush in which the outer peripheral surface of the metal nut is tapered.

FIG. 4 is a sectional view of a bush of an example in which a metal metal nut and a resin bush are joined with an adhesive.

FIG. 5 is a cross-sectional view of an example in which a heater rod is applied to a glow plug that is a ceramic heater including a heating element.

FIG. 6 is a schematic diagram for explaining a state in which a glow plug is attached to an engine and a harness for energization is arranged.

FIG. 7 is a schematic diagram illustrating a state in which a glow plug is mounted on an engine and immersed in salt water or the like.

FIG. 8 is a schematic sectional view of a conventional glow plug.

[Explanation of symbols]

1 housing, 2 center shaft, 4 insulating bush, 4
1, 42 Resin bush main body, 51, 54 Metal nut, 31, 32 O-ring, 21 Heater rod,

Claims (1)

[Claims] 1. A heater rod for heat generation, a rod-shaped center rod capable of energizing a heater whose one end is electrically connected to the heater rod, and the heater rod and the center rod being internally enclosed and having a lower end opening. A glow plug comprising: a cylindrical housing that projects and holds the heater rod, and projects and locks the central shaft at an upper end opening; and an insulating bush that locks and fixes the central shaft to the housing in an insulated state, The insulating bush is formed of a metal nut that can be fixed at a predetermined position on the resin bush main body and the center shaft and is enclosed by the resin bush main body, and maintains the insulation state between the center shaft and the housing. A glow plug characterized in that a center shaft is locked and fixed to the housing.