JP2005061828A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug having a structure that is excellent in strength despite the small diameter of a sheath tube, that can easily secure necessary heat generation characteristics, and that does not easily cause a short circuit between a heat generation coil and a sheath tube.
In a glow plug 1, a sheathed heater 2 is connected in series with a sheathed tube 11 whose tip end is closed, a heating coil 21 disposed on the leading end side in the sheathing tube, and a rear side of the heating coil 21. A control coil 23 is connected and increases the electrical resistance value by receiving heat generated from the heat generating coil 21 and controls energization of the heat generating coil 21. The axial cross-sectional diameter of the heat generating coil housing portion 11a of the sheath tube 11 is 3.0 to 4.4 mm, and the wall thickness t is 0.3 to 0.75 mm. Further, the value of t / D1 when the axial cross-sectional diameter is D1 is 0.08 to 0.2.
[Selection] Figure 2

Description

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

  A glow plug as described above is generally known that uses a sheathed heater in which a heating coil formed of a resistance heating wire is enclosed with an insulating powder inside a sheathed tube formed of a heat-resistant metal. Then, the metal shell is attached to the sheathed heater, and is used by being attached to the engine block of the diesel engine so that the heat generating part at the tip is located in the combustion chamber by the screw part formed on the outer peripheral surface thereof.

  By the way, in recent years, with the high performance and miniaturization of the diesel engine, the glow plug is required to be small, and the outer diameter of the protruding portion from the metal shell of the sheath tube is also less than 5 mm, for example. Tend to be smaller. However, when the diameter of the sheath tube is reduced, the strength is insufficient. For example, when a large impact is applied by accidentally dropping the sheath tube, there is a problem that the heater is easily damaged. Further, since the size of the heating coil is reduced, it may be difficult to obtain necessary heat generation performance or temperature rise characteristics. On the other hand, as the diameter of the sheath tube is reduced, the heat generating coil easily comes into contact with the inner surface of the sheath tube, and a problem of short circuit is likely to occur.

  An object of the present invention is to provide a glow plug having a structure that is excellent in strength despite the small diameter of the sheath tube, that can easily ensure the necessary heat generation performance, and that does not easily cause a short circuit between the heat generation coil and the sheath tube. There is.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the first configuration of the glow plug of the present invention is:
A sheathed tube with a closed tip,
The outer diameter of the portion (the heat generating coil accommodating portion) that accommodates the heat generating coil of the sheathed tube is 3.0 to 4.4 mm. The thickness t is 0.3 to 0.75 mm, and the value of t / D1 when the outer diameter is D1 is 0.08 to 0.2.

  That is, in the structure of the glow plug of the present invention, the outer diameter of the heat generating coil housing portion of the sheath tube is set to a numerical value of 3.0 to 4.4 mm in order to meet the needs for downsizing. In the first configuration, the thickness t of the heat generating coil housing portion of the sheath tube is 0.3 to 0.75 mm, and the value of t / D1 when the outer diameter is D1 is 0.08 to 0.00. By setting it to 2, sufficient strength can be ensured even though the sheath tube is reduced in diameter, and as a result, breakage or the like when receiving an impact due to dropping or the like is less likely to occur. In addition, by setting the numerical range, the outer diameter of the heat generating coil can be set to be relatively large even if the sheath tube is reduced in diameter, and the required heat generation performance can be easily secured.

  When the thickness t is less than 0.3 mm, the strength of the sheath tube is insufficient. For example, if a large impact is applied by accidentally dropping the sheath tube, the heater is likely to be damaged. On the other hand, in the present invention, since the outer diameter of the sheath tube is limited to 4.4 mm or less, when the wall thickness t exceeds 0.75 mm, the inner diameter of the sheath tube becomes too small, and the diameter of the heating coil is sufficiently increased. It may not be possible to secure the necessary heat generation performance. In this case, it goes without saying that if the diameter of the heat generating coil is forcibly increased, a short circuit is likely to occur between the inner surface of the sheath tube and the heat generating coil and the control coil. The wall thickness t is desirably adjusted within a range of 0.45 to 0.6 mm.

Next, the second configuration of the glow plug of the present invention is:
A sheathed tube with a closed tip,
The outer diameter of the portion (the heat generating coil accommodating portion) that accommodates the heat generating coil of the sheathed tube is 3.0 to 4.4 mm. When the inner diameter of the heating coil housing part is D2 and the outer diameter of the heating coil is d1, the radius difference CG = (D2−d1) / 2 is adjusted within the range of 0.1 to 0.8 mm. It is characterized by being.

  In the second configuration, by adjusting the CG within a range of 0.1 to 0.8 mm, a short circuit occurs between the heat generating coil and the sheath tube even though the sheath tube is reduced in diameter. Can be difficult. If the CG is less than 0.1 mm, a short circuit is likely to occur between the inner surface of the heat generating coil housing and the outer surface of the heat generating coil, and the heat generating performance may be deteriorated. On the other hand, when CG exceeds 0.8 mm, for example, when a glow plug is manufactured by encapsulating a heat generating coil and a control coil together with an insulating material (for example, magnesia powder) in a seed tube, and further reducing the diameter by forging. The coil is likely to meander in the sheath tube, and similarly, a short circuit is likely to occur. Note that the value of CG is desirably adjusted within a range of 0.2 to 0.6 mm.

  It is further desirable to combine the first configuration with the second configuration, in addition to the effect of preventing the short circuit, since the effect of improving the strength of the sheath tube or easily ensuring the heat generation performance is also achieved.

  In any of the first and second configurations, when the outer diameter of the heat generation coil housing portion of the sheath tube is less than 3.0 mm, the outer diameter of the heat generation coil becomes too small, and sufficient heat generation performance is obtained. Therefore, the outer diameter is set in a range of 3.0 mm or more.

  The outer diameter d1 of the heating coil is preferably 1.5 to 3.0 mm. When the outer diameter d1 is less than 1.5 mm, necessary heat generation performance may not be obtained. On the other hand, if it exceeds 3.0 mm, the outer diameter of the heat generating coil housing part of the sheath tube is limited to 4.4 mm or less, so that the thickness t becomes too small, leading to a problem that the strength is insufficient. Further, the ratio d1 / D2 between the outer diameter d1 of the heat generating coil and the inner diameter D2 of the heat generating coil housing portion is preferably adjusted in the range of 0.5 to 0.8. If d1 / D2 exceeds 0.8, the heat generation performance may be deteriorated, and a short circuit is likely to occur between the inner surface of the heating coil housing and the outer surface of the heating coil. Further, when d1 / D2 is less than 0.5, the coil is likely to meander in the sheath tube, and similarly, a short circuit is likely to occur.

  The sheath tube can be made of, for example, any one of stainless steel, iron-base heat-resistant alloy, and Ni-base heat-resistant alloy. For example, when a sheathed heater is used as a glow plug, the durability of the sheathed tube can be improved by forming the sheathed tube made of these materials directly exposed to a high-temperature gas flow in the engine combustion chamber. As the stainless steel, various austenitic stainless steels can be suitably used in the present invention because they have particularly good corrosion resistance.

  In this case, particularly when heat resistance is required, a Ni-based heat-resistant alloy such as Inconel 601 (Inconel is a trade name) can be suitably used. In addition, when used in an environment with a high swirl flow rate, such as a high-speed injection type diesel engine, in order to suppress oxidation consumption due to a high-temperature gas flow, a composition having a particularly high Ni content among austenitic stainless steels is used. Austenitic heat resistant steel (for example, SUH309, SUH310, SUH330, etc.) having a composition similar to that (for example, SUS310S) or the like can be suitably used.

  The material of the heating coil is the same as that of a known glow plug, for example, an iron-chromium alloy (for example, an alloy mainly containing iron and containing 13 to 30% by weight of chromium), a nickel-chromium alloy (for example, mainly nickel). As an alloy containing 8 to 22% by weight of chromium. On the other hand, as the material of the control coil, a material having a temperature coefficient of electrical specific resistance larger than that of the heat generating coil is used. For example, a cobalt-iron alloy (containing about 6 to 18% by weight of iron mainly containing cobalt). However, since it is excellent in durability, it can be suitably used in the present invention. In addition, nickel-plated iron wires, nickel wires, and the like can also be used.

  The heating coil and the control coil can be selected from appropriate materials, wire diameters, and coil lengths, with the resistance value of the heating coil as RH and the resistance value of the control coil as RC, respectively. It is preferable that the value of (RH / RC) RT is 1 or more and the value of the electric resistance ratio (RH / RC) 800 at 800 ° C. is 0.1 to 0.4. If the value of (RH / RC) RT is less than 1, the heater may not be able to ensure sufficient rapid heat characteristics. On the other hand, if the value of (RH / RC) 800 is less than 0.1, the energization control by the control coil becomes excessive, and the heating coil may not be able to generate heat sufficiently. On the other hand, if (RH / RC) 800 exceeds 0.4, the energization control effect by the control coil becomes insufficient, and the heating coil is likely to overheat.

  Next, the length of the protrusion from the metal shell of the sheath tube is preferably 24 to 50 mm. If the length of the protruding portion is less than 24 mm, the space for accommodating the heating coil and the control coil in the protruding portion becomes insufficient, and as a result, the coil length necessary to obtain the desired temperature rise characteristic (or heating performance) can be secured. It may disappear. On the other hand, when the length exceeds 50 mm, since the sheath tube diameter is small, the strength of the protruding portion is insufficient, and breakage or the like is likely to occur when an impact or the like is applied. The protruding length is desirably 28 to 40 mm.

  In the above glow plug, the resistance wire coil (heating coil or heating coil and control coil) arranged in the sheath tube is energized via an energizing terminal shaft inserted into the sheath tube from the base end side. It is common to do it. In this case, while the front-end | tip of the electricity supply terminal axis | shaft can be connected to the rear end of a resistance wire coil, the front-end | tip of the current supply terminal axis | shaft can be located protruding from a metal fitting end surface. For example, when a lateral force acts on the projecting portion of the sheath tube, a strong bending force tends to concentrate on the contact position with the opening inner edge of the metal shell. Therefore, by projecting the tip of the energizing terminal shaft from the end face of the metal shell, the contact portion of the sheath tube is reinforced, and the strength against bending is improved. In this case, the concentrated position of the force on the sheath tube when a bending force is applied is rather near the tip position of the current-carrying terminal shaft. Therefore, the length from the position to the tip of the sheath tube is preferably 24 to 50 mm, preferably It is good to set it as 24-42 mm.

  Next, in the above glow plug, when the outer diameter of the sheath tube is reduced, its assembling property to the metal shell may be deteriorated. In this case, the inner diameter of the hole portion in which the sheath tube is disposed of the metal shell is formed larger than the protruding portion from the metal shell of the sheath tube, and the base end portion of the sheath tube is the hole portion of the metal shell. The diameter can be increased to a size corresponding to the inner diameter, and the expanded diameter portion can be joined into the hole of the metal shell by brazing, welding, or press fitting. The assembling property can be improved by expanding the diameter of the base end portion of the sheath tube and joining the metal shell to the metal shell at the expanded diameter portion.

  In the glow plug, a plurality of resistance wire coils are arranged in the axial direction in the sheath tube, and the resistance wire coil is disposed in the sheath tube at the front end side thereof and on the rear side of the heat generation coil. In addition to being connected in series with this, it can be configured to include a control coil that increases the electric resistance value by receiving heat generated from the heat generating coil and controls energization to the heat generating coil.

  In order to improve the startability of the engine, the so-called rapid heating property that reaches the saturation temperature in as short a time as possible is often required for the heater temperature raising performance in the glow plug. One possible method is to increase the rate of temperature rise by passing a large current through the heating coil at the beginning of energization, but the coil temperature tends to rise excessively, leading to problems such as coil disconnection and sheath tube melting. There is. In the glow plug having the above structure, since the temperature of the control coil is low and the electrical resistance value is small at the initial stage of energization, a relatively large current flows through the heating coil to rapidly raise the temperature. Then, when the temperature of the heating coil rises, the control coil is heated by the heat generation, the electrical resistance value increases, and the energization current value to the heating coil decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature rises rapidly at the beginning of energization, the current is suppressed by the action of the control coil and the temperature is saturated. Ascent can also be made difficult to occur.

  When the glow plug of the present invention is used as a glow plug of a diesel engine for a vehicle, it has a temperature rise characteristic that has a peak temperature TP at the beginning of energization and saturates at or below the peak temperature TP (hereinafter referred to as overheating prevention) It is desirable to have a mold temperature rise characteristic). That is, in a vehicle or the like, a battery is used as a power source for the glow plug. In this case, the glow plug is not always energized at a constant battery voltage (for example, 12V), but usually a superimposed voltage from an alternator or the like is added to the glow plug, so that it is higher than the battery voltage (for example, about 14V at the maximum). It is more often energized in a fluctuating manner. In this case, since the temperature rise characteristics are as described above, it is possible to effectively prevent overheating of the heater.

  Further, the control coil can be directly connected to the rear end of the heat generating coil with a gap between the coils larger than the winding pitch of the heat generating coil. In this case, the size of the gap between the coils is preferably adjusted to 0.8 to 3 mm. When the gap between the coils exceeds 3 mm, the heating of the control coil by the heating coil is difficult to proceed, and the heating coil is likely to rise excessively. On the other hand, if the gap between the coils is less than 0.8 mm, the resistance value of the control coil becomes too large and rapid heating cannot be ensured, or the saturation temperature becomes too low to obtain sufficient heat generation performance. It may disappear. The size of the inter-coil gap is more preferably adjusted to 1 to 2 mm. In the present invention, the inter-coil gap is a coil between a position moved half a turn along the heating coil from the connection point between the heating coil and the control coil and a position moved half a turn to the control coil side. It is defined as the distance in the axial direction.

  Next, the glow plug of the present invention has a peak temperature TP of 800 ° C. or higher when the temperature rise characteristic is measured at an energization voltage of 11 V at room temperature in order to satisfy the requirement for rapid thermal performance. On the way to reach TP, the energization time t800 until reaching 800 ° C. is desirably 8 seconds or less (preferably 5 seconds or less).

  In the glow plug, when the temperature rise characteristic is measured at room temperature with an energization voltage of 11 V, the peak temperature TP and the temperature after 60 seconds from the start of energization (hereinafter referred to as the temperature after 60 seconds) TS. The difference TP-TS is preferably 50 to 200 ° C. When TP−TS is less than 50 ° C., when the energization voltage fluctuates in the direction of increasing, the heater is likely to rise excessively. On the other hand, if TP-TS exceeds 200 ° C., the saturation temperature becomes too low, and the necessary heat generation performance cannot be ensured. TP-TS is desirably 80 to 150 ° C.

  The peak temperature TP is preferably 900 to 1150 ° C. When the peak temperature TP is less than 900 ° C., heat generation is insufficient, and functions such as engine preheating may not be performed sufficiently. On the other hand, if the peak temperature TP exceeds 1150 ° C., the heat generation becomes too large, and the life of the heat generating coil may be reduced. The peak temperature TP is desirably 80 to 150 ° C.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings.
FIG. 1 is an overall view showing an example of a glow plug of the present invention and a longitudinal sectional view thereof. The glow plug 1 includes a sheathed heater 2 and a metal shell 3 disposed on the outside thereof. As shown in FIG. 2, the sheathed heater 2 is connected in series with two resistance wire coils, that is, a heating coil 21 disposed on the distal end side, and a rear end thereof by welding or the like inside a sheathed tube 11 whose distal end is closed. The control coil 23 is enclosed together with a magnesia powder 27 as an insulating material.

  As shown in FIG. 1, the main body portion 11 a of the sheath tube 11 that accommodates the heat generating coil 21 and the control coil 23 projects from the metal shell 3 to form a protruding portion. The main body 11a is formed in a cylindrical shape having a substantially uniform outer diameter D1 (however, the tip is rounded), and the D1 is 3.0 to 4.4 mm (preferably 3.5 to 4). 4.0 mm). Here, although the heat generating coil 21 is electrically connected to the sheath tube 11 at the tip, the outer peripheral surface of the heat generating coil 21 and the control coil 23 and the inner peripheral surface of the sheath tube 11 are insulated by the intervention of magnesia powder. It has become.

  In FIG. 2, the heating coil 21 has an electrical resistivity ρ20 at 20 ° C. of 80 to 180 μΩ · cm, an electrical resistivity at 800 ° C. of ρ800, and ρ800 / ρ20 of about 0.9 to 1.2. It is made of a material, specifically, an iron-chromium alloy wire or a nickel-chromium alloy wire. The coil has a wire diameter k of 0.15 to 0.4 mm, a coil length CL1 of 5 to 12 mm, a coil outer diameter d1 of 1.5 to 3.0 mm, a winding pitch P of 0.2 to 0.8 mm, The number of line turns N is 8-15.

  The control coil 23 is made of, for example, a material having an electric specific resistance ρ20 at 20 ° C. of 5 to 25 μΩ · cm, an electric specific resistance at 800 ° C. of ρ800, and ρ800 / ρ20 of about 7 to 12, specifically An iron-chromium alloy wire or a nickel-chromium alloy wire is used. The coil wire diameter k is 0.17 to 0.3 mm, coil length CL2 is 10 to 32 mm, coil outer diameter d1 is 1.5 to 3.0 mm, winding pitch P is 0.2 to 0.8 mm, winding The number N of line turns is 25-40.

  Further, the heating coil 21 and the control coil 23 have an electrical resistance ratio (RH / RC) RT of 1 or more at room temperature, where RH is the resistance value of the heating coil and RC is the resistance value of the control coil. In addition, the value of the electric resistance ratio (RH / RC) 800 at 800 ° C. is adjusted to be 0.1 to 0.4. Between the heat generating coil 21 and the control coil 23, an inter-coil gap 25 larger than the winding pitch of the heat generating coil 21 is formed. The size JL of the inter-coil gap 25 is adjusted in the range of 0.8 to 3 mm, preferably 1 to 2 mm. Moreover, when this is caught by the winding pitch P of the heat generating coil 21, it is adjusted in the range of 0.2 to 0.8 pitch (preferably 0.3 to 0.6 pitch).

  Next, the sheath tube 11 has the above-mentioned main body part 11a and a diameter-enlarged part 11b formed larger in diameter on the base end side. The thickness t of the main body 11a is 0.3 to 0.75 mm (desirably 0.45 to 0.6 mm), and the value of t / D1 is 0.08 to 0.2 (desirably 0). .11 to 0.17 mm). Further, when the inner diameter of the main body 11a is D2, and the outer diameters of the heating coil 21 and the control coil 23 are d1, the value of the radius difference CG = (D2-d1) / 2 is 0.1-0. It is 8 mm (desirably 0.2 to 0.6 mm). Further, the ratio d1 / D2 between the outer diameter d1 of the coils 21 and 23 and the inner diameter D2 of the main body 11a is set to 0.5 to 0.8 (preferably 0.6 to 0.7).

  A rod-shaped energizing terminal shaft 13 is inserted into the sheath tube 11 from the base end side, and the tip thereof is connected to the rear end of the control coil 23 by welding or the like. On the other hand, as shown in FIG. 1, a male screw portion 13 a is formed at the rear end portion of the energizing terminal shaft 13.

  Such a structure of the sheathed heater 2 can be manufactured as follows, for example. That is, as shown in FIG. 3B, a heat generating coil and a control coil are enclosed together with magnesia powder in a sheath tube 11 ′ formed with a diameter larger than the final dimension by the machining allowance. The main body part 11a and the enlarged diameter part 11b are formed by subjecting 11 'to a rotary forging process (swage process).

  The swaging process can be performed using, for example, a swaging machine 70 shown in FIG. In the swaging machine 70, a plurality of dies 73 arranged so as to surround the sheath tube 11 ′ are supported by corresponding hammers 72, and these dies are arranged in the rotation main shaft 74 to rotate integrally. It is done. The rotating main shaft 74 is configured to rotate inside a cage 75 having a plurality of rollers 71 made of hardened steel or the like. When the hammer 72 comes to the position of the roller 71 while rotating with the rotating main shaft 74. When the die 73 is compressed and the hammer 72 comes between the adjacent rollers 71, 71, the die 73 is opened by centrifugal force. Therefore, if the rotation speed of the rotation spindle 74 is increased to a certain level or more, the compression process using the die 73 can be repeated many times.

  Next, as shown in FIG. 1, the metal shell 3 is formed in a cylindrical shape having an axial through hole 4, where the sheathed heater 2 extends from one opening end to the distal end side of the sheathed tube 11 by a predetermined length. Inserted and fixed in a protruding state. A tool engaging portion 9 having a hexagonal cross section for engaging a tool such as a torque wrench when the glow plug 1 is attached to the diesel engine is formed on the outer peripheral surface of the metal shell 3. A screw part 7 for attachment is formed.

  The through hole 4 of the metal shell 3 includes a large-diameter portion 4b positioned on the opening side from which the sheath tube 11 protrudes, and a small-diameter portion 4a following the large-diameter portion 4a. The small-diameter portion 4a is formed on the proximal end side of the sheath tube 11b. The large diameter portion 11b is press-fitted and fixed. On the other hand, a counterbore 3a is formed in the opening on the opposite side of the through hole 4, and here, a rubber O-ring 15 and an insulating bush (for example, nylon) 16 which are sheathed on the energizing terminal shaft 13; Is inserted. On the further rear side, the energizing terminal shaft 13 is provided with a pressing ring 17 for preventing the insulation bush 16 from falling off. The holding ring 17 is fixed to the energizing terminal shaft 13 by a caulking portion 17a formed on the outer peripheral surface, and a knurled portion 13b for increasing the caulking coupling force is provided on a corresponding surface of the energizing terminal shaft 13. Is formed. Reference numeral 19 denotes a nut for fixing the energizing cable to the energizing terminal shaft 13.

  The protruding length L2 of the sheath tube 11 from the metallic shell 3 is adjusted to 24 to 50 mm (desirably 28 to 40 mm). In addition, as shown in FIG. 2, the tip end position of the energizing terminal shaft 13 substantially coincides with the open end surface of the metal shell 3.

Hereinafter, the dimensions and the like of each part of the glow plug 1 of FIG. 1 will be specifically exemplified (see also FIG. 2).
・ Total length L1 = 145 mm.
(Heating coil 21)
Material: Iron-chromium alloy (composition: Al = 7.5% by weight; Cr = 26% by weight; Fe = balance, ρ20 = 160 μΩ · cm, ρ800 / ρ20 = 1.0).
Dimension: k = 0.22 mm, CL1 = 10 mm, d1 = 1.7 mm, P = 1.0 mm, N = 10. The electrical resistance RH of the entire coil at 20 ° C is 1Ω.
(Control coil 23)
・ Material: Cobalt-iron alloy (Composition: Fe = 8% by weight; Co = remainder, ρ20 = 8 μΩ · cm, ρ800 / ρ20 = 9.8, resistance increases to 800 ° C. as the temperature rises) .
Dimensions: k = 0.2 mm, CL2 = 15 mm, d1 = 1.7 mm, P = 0.5 mm, N = 30. The electric resistance value RC of the entire coil at room temperature is 0.33Ω.

(RH / RC) RT: 3.
(RH / RC) 800: 0.3.
(Gap between coils 25)
-JL: 2 mm.

(Seeds tube 11)
-Material: SUS310S.
Dimension: D1 = 3.5 mm, t = 0.5 mm, t / D1 = 0.14 mm, CG = 0.4 mm, outer diameter D3 = 4.4 mm of the expanded portion, L2 = 36 mm.

(Metal fitting 3)
-Material: Carbon steel for machine structure (S45C).
Dimension: length L3 = 53 mm of a portion 5 (hereinafter referred to as a main portion) located on the tip side from the screw portion 7, outer diameter D4 = 8.2 mm of the main portion, length L4 of the screw portion 7 = 27 mm, The outer diameter D5 of the threaded portion 7 = 10 mm.

Hereinafter, the operation of the glow plug 1 of FIG. 1 will be described.
The glow plug 1 is attached to a cylinder block of a diesel engine at a threaded portion 7 of the metal shell 3. Thereby, the front-end | tip part of the sheath tube 11 in which the heat generating coil 21 and the control coil 23 were accommodated is positioned in the combustion chamber (or auxiliary combustion chamber) of the engine. In this state, when a voltage is applied to the energizing terminal shaft 13 by using an in-vehicle battery as a power source, the energizing terminal shaft 13 → the control coil 23 → the heating coil 21 → the sheath tube 11 → the metal shell 5 → (grounded through the engine block). Energized along the route.

  As a result, in the sheathed heater 2 of the glow plug 1, since the temperature of the control coil 23 is low and the electrical resistance value is small at the initial stage of energization, a relatively large current flows through the heating coil 21 to rapidly raise the temperature. When the temperature of the heat generating coil 21 rises, the control coil 23 is heated by the heat generation, the electric resistance value increases, and the current value supplied to the heat generating coil 21 decreases. As a result, the temperature rise characteristic of the heater is such that after the temperature is rapidly raised in the initial stage of energization, the energization current is suppressed by the action of the control coil and the temperature is saturated.

  The body portion 11a of the sheath tube 11 has a cylindrical shape having a substantially uniform outer diameter D1, and D1 is set to a value of 4.4 mm or less. Specifically, the difference TP-TS between the peak temperature TP and the temperature TS after 60 seconds is 50 to 200 ° C., and the energization time t800 until the peak temperature TP reaches 900 to 1150 ° C. and 800 ° C. is 8 seconds or less. Thus, it is possible to stably realize the characteristics excellent in rapid heating.

  Further, the thickness t of the sheath tube 11 is 0.3 to 0.75 mm, and the value of t / D1 when the outer diameter is D1 is 0.08 to 0.2. Despite being a small heater, the desired heat generation performance is ensured, and the strength of the sheath tube 11 becomes sufficient. For example, even if the sheath tube 11 is dropped during installation, the heater is not easily damaged. Further, the clearance CG between the heating coil 21 and the control coil 23 in the main body 11a of the sheath tube 11 is adjusted in the range of 0.1 to 0.8 mm, so that the inner surface of the sheath tube 11 and each coil 21 are adjusted. , 23 are less likely to be short-circuited, and the manufacturing yield can be improved.

  Here, in FIG. 2, the ratio CL1 / D1 between the coil length CL1 of the heating coil 21 and the outer diameter D1 of the body portion of the sheath tube 11 is set to 1.6 to 3.5 (about 2.5 in this embodiment). It is good to do. That is, since the sheath tube 11 has a small diameter, heat dissipation from the tube surface proceeds more actively than a conventional large-diameter sheath heater. In addition, the heat generation performance of the control coil becomes unstable, and good overheating prevention type temperature rise characteristics may not be expected. On the other hand, if CL1 / D1 exceeds 4, there may be a problem that the tip of the sheath tube does not become the highest heat generation portion.

  FIG. 4 shows a modification of the glow plug 1 of FIG. 1 (common members are given the same reference numerals and description thereof is omitted). In the glow plug 100, the enlarged diameter portion 11 b on the base end side of the sheath tube 11 is formed longer than the glow plug 1 of FIG. 1, and the projecting side of the sheath tube 11 is formed in the through hole 4 of the metal shell 3. Is not formed with the large-diameter portion 4b as shown in FIG. The enlarged diameter portion 11 b of the sheath tube 11 is joined to the through hole 4 by brazing.

  Further, a countersink portion 3a similar to that shown in FIG. 1 is formed in the opening on the opposite side of the through hole 4. Here, instead of the insulating bush 16 shown in FIG. And a washer-shaped first insulating ring (for example, a heat-resistant resin such as bakelite) 12 is fitted. In this state, a cylindrical projecting portion formed on the peripheral edge of the opening of the spot facing portion 3a is crimped to the first insulating ring 14 side to form a crimped portion 13b. The shaft 13 has a structure in which a second insulating ring 14 (the same material and shape as the first insulating ring 12) and a holding ring 17 are mounted and fixed in this order.

  On the other hand, as shown in FIG. 5, the distal end portion of the energizing terminal shaft 13 protrudes a predetermined length from the corresponding open end portion of the metal shell 5, and the sheath tube 11 extends from the distal end of the energizing terminal shaft 13. The length L2 ′ up to the tip of is adjusted to 24 to 50 mm (preferably 24 to 42 mm).

  In the glow plug 100, the following effects not achieved in the glow plug 1 in FIG. 1 are achieved. That is, the tip end portion of the energizing terminal shaft 13 enters the protruding portion from the metal shell 3 of the sheath tube 11. As a result, the sheath tube 11 has a shape in which the contact portion with the inner edge of the opening of the metal shell 3 to which a strong bending force is easily applied when a lateral force is applied is reinforced by the current-carrying terminal shaft 13. Even if an impact or the like is applied, breakage or the like hardly occurs.

  On the other hand, it can be said that the glow plug 1 of FIG. 1 is superior to the glow plug 100 of FIG. 4 in the following points. First, since the rear end side of the energizing terminal shaft 13 is structured to be clamped by the crimping ring 17 via the insulating bush 16, the first insulating ring 12 and the seal ring 10 are stopped by the crimping portion 3b. Further, the number of parts is smaller than that of the glow plug 100 of FIG. 4 reinforced by the second insulating ring 14 and the caulking ring 17, and the manufacture is easy. Further, in the glow plug 100 of FIG. 4, since the distance between the inner edge of the caulking portion 3b protruding inward and the outer surface of the energizing terminal shaft 13 is relatively small, the insulating ring 12 is prevented from causing a short circuit due to water leakage or the like. , 14 needs to be considered. On the other hand, in the glow plug 1 of FIG. 1, the distance from the inner edge of the opening of the metal shell 3 to the outer surface of the energizing terminal shaft 13 is increased by the flange portion 16 a of the insulating bush 16, and Since water that tries to leak into the energizing terminal shaft 13 side from the gap with the metal fitting 3 is blocked by the O-ring 15, the structure is less likely to cause a short circuit. Furthermore, in the glow plug 100 of FIG. 4, since the sheath tube 11 is joined to the metal shell 3 by brazing, it is necessary to design the strength in anticipation of softening of the sheath tube 11a due to the thermal effect during brazing. On the other hand, in the glow plug 1 of FIG. 1, the sheath tube 11 is press-fitted to the metal shell 3, so there is no fear of softening due to thermal influence, and there is an advantage that the strength improvement effect by processing can be used more effectively. .

  The embodiment of the glow plug including the heating coil and the control coil has been described above. However, the present invention is not limited to this. For example, the present invention similarly applies to a glow plug that includes only the heating coil and omits the control coil. Applicable.

(Example 1)
Various glow plugs shown in FIG. 1 were produced according to the dimensions and materials exemplified above, except for the conditions described below. That is, the outer diameter D1 of the main body 11a of the sheath tube 11 was changed in the range of 3.0 to 4.4 mm. Further, the thickness t of the main body 11a was changed in the range of 0.25 to 0.75 mm. Further, the heating coil 21 and the control coil 23 were changed in the range of 1.5 to 3.0 mm only for the outer diameter d1. Specific numerical values of D1, t, and d1 of each glow plug are shown in Table 3 together with t / D1, D2 (seed tube inner diameter), CG (radius difference between the coil and the inner surface of the sheath tube), and d1 / D2. It shows.

Fifty glow plugs were produced for each condition, and the following tests were performed. The results are shown in Table 3.
(1) Probability of short circuit occurrence At room temperature, first, a pulse voltage of 50 V (pulse length 0.1 seconds) is applied to the glow plug to measure the glow plug resistance, and the measured value is R0. . Next, energization is continued for 30 seconds at a voltage of 11 V, and then a similar pulse voltage is applied to measure the resistance value of the glow plug. The measured value is R1. If a short circuit occurs between the sheath tube and the heating coil or control coil due to heating, the resistance of the measured resistance R1 decreases because the length of the actual energizing coil is shortened. When the rate of decrease of R1 with respect to R0 {(R0−R1) / R0} × 100 is 10% or more, it is determined that a short circuit has occurred, and the measured number of short circuits in 50 glow plugs is zero. Pass (○), even one short-circuited was rejected (x).
(2) Strength evaluation (I)
Each glow plug is dropped while holding it vertically so that the initial distance from the concrete test surface to the tip of the seed tube is 1 cm, with the seed tube at the bottom, and then the above distance is gradually increased by 1 cm. While falling, repeat. After each drop, visually check whether the sheath tube has been broken or broken. And the thing of the maximum drop distance which does not produce a fracture | rupture was determined to be excellent ((double-circle)), the thing of 3 cm-4 cm is good ((circle)), and the thing of 2 cm or less is impossible (x).
(3) Strength evaluation (II)
Hold the main metal fitting of each glow plug with a chuck so that the sheath tube is horizontal, set it on the bending tester, and at the position of 1 mm along the axial direction from the tip of the sheath tube protruding sideways. The value of the maximum bending load when the tip of the bending punch was brought into contact and a cantilever bending test was performed at a crosshead speed of 1 mm / min was measured as a bending strength value. FIG. 8 shows a graph in which the strength value when the outer diameter D1 of the main body portion 11a of the sheath tube 11 is fixed to 3.5 mm and the thickness t is changed is plotted together with the short-circuit occurrence probability.

From the results in Table 1, the following can be understood.
(1) When the wall thickness t is 0.3 mm or more and t / D1 is 0.08 or more, the strength of the sheath tube becomes sufficient, and damage in the drop test is less likely to occur.
(2) When CG is 0.1 mm to 0.8 mm, it is difficult to cause a short circuit.

  Moreover, in order not to cause breakage in the drop test, it is necessary that t / D1 be 0.08 or more. However, from the result of FIG. 8, it is sufficient that a corresponding strength value of 5 kg or more is secured. I understand that. It can be seen that when t / D1 exceeds 0.2, the probability of occurrence of a short circuit increases rapidly.

(Example 2)
Various glow plugs shown in FIG. 1 were produced according to the dimensions and materials exemplified above, except for the conditions described below. First, only the outer diameter D1 of the main body portion 11a of the sheath tube 11 is changed by various values of 2.5 to 5.0 mm, and the heating coil 21 and the control coil 23 are adapted to the outer diameter d1 only from 1.5 to 5.0. It changed suitably in the range of 2.5 mm. Further, as the material of the control coil 23, a nickel-plated iron wire (the wire diameter is the same, the plating thickness is about 1 μm) and a nickel wire (the wire diameter is the same) were used instead of the cobalt-iron alloy. Things were made.

  And the temperature rise characteristic curve (temperature-time curve) when these glow plugs were kept at room temperature and energized at an energization voltage of 11 V was measured as follows. The temperature measurement was performed with the glow plug 1 attached to a jig 200 as shown in FIG. The jig 200 is made of carbon steel having a vertically long cylindrical shape (outer diameter: 23 mm), and an axial plug mounting hole 201 is formed in the center part in a penetrating form. The glow plug 1 shown in FIG. 1 has a distal end side inserted into the plug mounting hole 201 and the threaded portion 7 is screwed into a female threaded portion 201 a formed on one end side of the plug mounting hole 201. Is attached to the jig 200. The dimensions of each part of the jig 200 are as described in the drawing (unit: mm). Further, the tip of the sheath tube 11 of the glow plug 1 protrudes 10 mm from the end face of the jig 200 in the mounted state.

  And in the protrusion part of the sheath tube 11, the measurement area to 8 mm is set to the axial direction from the front-end | tip, and while checking the highest temperature position in the measurement area beforehand, a thermocouple (Pt / Pt-Rh) is set to this position. ) Was fixed and the sheathed heater 2 was continuously energized, and the temperature change with time was measured to obtain a temperature rise characteristic curve (the above measurement method is based on the method specified in ISO 7578 (1986)). ). Further, from the obtained temperature rise characteristic curve, the above-mentioned 800 ° C. arrival time (t800), peak temperature (TP), and temperature after 60 seconds (TS) were calculated. The results are shown in Table 2.

  That is, the glow plug of No. 1 whose outer diameter D1 of the main body 11a exceeds 4.4 mm has a large t800, lacks rapid thermal performance, and has a temperature TS after 60 seconds (which reflects the saturation temperature) TS. It is low and TP-TS is also less than 50 ° C., and it is understood that good overheating prevention type temperature rise characteristics are not obtained. In contrast, glow plugs (numbers 2 to 6, 8 to 10) using the sheathed heater of the present invention having an outer diameter D1 of the main body 11a of 3 to 4.4 mm have a small t800 and excellent quick heat performance. It can be seen that the temperature rise prevention type temperature rise characteristic is also good. On the other hand, in a glow plug having an outer diameter D1 of the main body portion 11a of less than 3 mm, the temperature TS is low after 60 seconds because the size of the heating coil is small, and it is understood that the performance of the glow plug is insufficient.

  FIG. 6 shows the temperature rise characteristic curve of the glow plug of No. 5. FIG. 7 shows a temperature rise characteristic curve of the glow plug of the comparative example of No. 1.

(Example 3)
The glow plug shown in FIG. 1 was produced according to the dimensions and materials exemplified above, except that the inter-coil gap length JL was changed to 0.5 to 5 mm. Then, a temperature rise characteristic curve (temperature-time curve) was measured for these glow plugs in the same manner as in Example 2, and values of t800, TP and TS were calculated. The results are shown in Table 2.

  That is, it can be seen that by adjusting JL in the range of 0.8 to 3 mm, a glow plug that is particularly excellent in rapid thermal performance and overheating prevention type temperature rise characteristics is realized.

The whole figure and longitudinal section showing an example of the glow plug of the present invention. Sectional drawing which shows the internal structure of the sheathed heater, and its principal part enlarged schematic diagram. Explanatory drawing which shows the concept of a swaging machine and the effect | action of swaging. The longitudinal cross-sectional view which shows the modification of the glow plug of FIG. Sectional drawing which shows the internal structure of the sheathed heater. 6 is a temperature rise characteristic curve of a glow plug of No. 5 in Example 3. FIG. 6 is a temperature rise characteristic curve of the glow plug of No. 1 in Example 3. FIG. The graph which shows the bending strength test result of Example 1 with the probability of short-circuit occurrence. Schematic diagram of a conventional glow plug. The longitudinal cross-sectional view of the jig | tool used for the temperature measurement of a glow plug.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glow plug 2 Seeds heater 3 Main metal fitting 7 Screw part 11 Seed tube 11a Main body part 11b Expanded diameter part 13 Current supply terminal shaft 21 Heating coil 23 Control coil

Claims (10)

A sheathed tube with a closed tip,
A heat generating coil disposed on the distal end side of the sheath tube, and an outer diameter of a portion of the sheath tube accommodating the heat generating coil (hereinafter referred to as a heat generating coil housing portion) is 3.0 to 4. 4 mm, the thickness t is 0.3 to 0.75 mm, and the value of t / D1 when the outer diameter is D1 is 0.08 to 0.2. Glow plug. A sheathed tube with a closed tip,
A heat generating coil disposed on the distal end side of the sheath tube, and an outer diameter of a portion of the sheath tube accommodating the heat generating coil (hereinafter referred to as a heat generating coil housing portion) is 3.0 to 4. When the inner diameter of the heat generating coil housing portion is D2 and the outer diameter of the heat generating coil is d1, the radius difference CG = (D2-d1) / 2 is 0.1 to 0.8 mm. Glow plug characterized by being adjusted in the range. T when the outer diameter of the heat generating coil housing portion of the sheath tube is 3.0 to 4.4 mm, the wall thickness t is 0.3 to 0.75 mm, and the outer diameter is D1. The glow plug according to claim 2, wherein the value of / D1 is 0.08 to 0.2. A plurality of resistance wire coils are arranged in the axial direction in the sheath tube,
In the sheath tube, the resistance wire coil is connected in series with the heating coil disposed on the distal end side of the sheathing coil and on the rear side of the heating coil. The glow plug according to claim 1, further comprising a control coil that increases a value and controls energization of the heating coil. The outer diameter d1 of the heating coil is adjusted to 1.5 to 3.0 mm, and the ratio d1 / D2 between the outer diameter d1 and the inner diameter D2 of the heating coil housing portion is adjusted in the range of 0.5 to 0.8. The glow plug according to any one of claims 1 to 4, wherein the glow plug is provided. The glow plug according to any one of claims 1 to 5, wherein the sheath tube is made of any one of stainless steel, iron-base heat-resistant alloy, and Ni-base heat-resistant alloy. A metal shell is provided to cover the sheath tube in a state where the tip side protrudes,
The glow plug according to any one of claims 1 to 6, wherein a length of the protruding portion of the sheath tube from the metal shell is 24 to 50 mm. A metal shell is provided to cover the sheath tube in a state where the tip side protrudes,
The tip of the energizing terminal shaft inserted from the base end side in the sheath tube is connected to the rear end of the resistance wire coil, the tip of the energizing terminal shaft is located protruding from the end surface of the metal shell, and the energization The glow plug according to any one of claims 1 to 7, wherein a length from the tip of the terminal shaft to the tip of the sheath tube is 24 to 50 mm. An inner diameter of the hole in which the sheath tube is disposed of the metal shell is formed larger than a protruding portion of the sheath tube from the metal shell, and a base end portion of the sheath tube is formed of the main metal The diameter is expanded so as to have a size corresponding to the inner diameter of the hole of the metal fitting, and the enlarged diameter part is joined to the hole of the metal shell by brazing, welding, or press fitting. Item 10. The glow plug according to any one of Items 1 to 8. The glow plug according to any one of claims 4 to 9, wherein the temperature rise characteristic on the surface of the tip portion of the sheath tube has a peak temperature TP at the beginning of energization and is saturated below the peak temperature TP. .

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