JPH0311067B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ignition device for an engine.

In recent years, in response to engine exhaust gas countermeasures and consumption regulations, the shape of engine combustion chambers has become more complex, and the mounting locations of spark plugs are also becoming more restricted.

Therefore, miniaturization of spark plugs has recently been considered. One way to achieve this miniaturization is to eliminate the spark plug mounting bracket.

As described above, an example of a device that eliminates the mounting hardware is described in US Pat. No. 2,543,961. This is a structure in which a threaded portion is provided around the outer periphery of the insulator, and the insulator is directly screwed and fixed into a screw hole in the cylinder head of the engine.

Although this type of conventional structure can be made smaller by eliminating the mounting bracket, since the insulator is screwed into the screw hole of the cylinder head, if the insulator is removed frequently, the screws of the insulator may become damaged. This causes problems such as parts becoming worn or missing.

An object of the present invention is to provide an engine ignition device that solves these problems.

An embodiment according to the present invention is shown in FIG. 1, and an enlarged view of the vicinity of the spark portion is shown in FIG. 2, which will be explained below. Reference numeral 1 denotes a cylinder head made of iron or aluminum, and a through hole b having a threaded portion 1a is bored at the inner upper end thereof. 2 is an insulator made of alumina porcelain, which has a screw hole 2a and an unthreaded hole 2b in the center, and an annular large diameter portion 2c on the outer periphery.
As shown in the figure, it has a straight portion projecting from the cylinder head 1. Reference numeral 3 designates a mounting annular nut for screwing and fixing the insulator 2 to the through hole 1b of the cylinder head 1, and is composed of a tightening portion 3a and a threaded portion 3b. In this embodiment, the threaded portion 3b has a nominal diameter of 6 mm. Insulator 2
4 at the rear end is a terminal made of iron, which is screwed and fixed into the screw hole 2a.

The tip 2d of the straight portion of the insulator 2 is made into a semiconductor by injecting Cr, Ni, etc. by ion implantation, or by coating with a semiconductor such as SiC. The resistance value is set to 3 to 10 kΩ. 5
is a ring-shaped electrode made of a heat-resistant alloy such as Ni, and its discharge surface is coated with a noble metal (e.g. Pt80wt%-
Ir20wt%) is bonded. This electrode 5 is screwed onto the tip 2d of the insulator 2. Reference numeral 6 denotes a ring-shaped ground electrode made of a heat-resistant alloy such as Ni, and a noble metal made of the same material as the electrode 5 is bonded to its discharge surface. This ground electrode 6 is connected to the cylinder head 1.
It is driven into and fitted into the through hole 1b. Reference numeral 7 formed inside the insulator 2 is a conductive thin wire made of piano wire or Ni alloy wire that electrically connects the semiconductor portion 2d and the terminal 3. This thin line 7
is inserted into the semiconductor portion 2d to maintain electrical continuity. Furthermore, an electrical conductor path 8 is formed on the end surface of the terminal 3 by baking a metal paste such as silver paste, so that the end surface of the thin wire 7 and the end surface of the terminal 3 are brought into direct contact.

In the above configuration, the operation will be explained next. The procedure for assembling the insulator 2 to the cylinder head 1 is as follows. That is, the insulator 2 is inserted into the through hole 1b of the cylinder head 1, and the annular large diameter portion 2a of the insulator 2 is supported in the seat portion 1c of the through hole 1b of the cylinder head 1. After that, the annular nut 3 is inserted into the outer periphery of the insulator 2, and the threaded part 3b of this nut 3 is
is screwed into the threaded portion 1a of the through hole 1b of the cylinder head 1, the tip of the nut 3 contacts the upper surface of the annular large diameter portion 2c of the insulator 2, and the insulator 2 is fixed to the through hole 1b of the cylinder head 1.

By the way, in the above embodiment, the insulator 2
The outermost diameter (large annular diameter part 2c) of the terminal 3 is 4 to 8 mm in terms of withstand voltage, the outer diameter of the terminal 3 is 2 to 4 mm in terms of high voltage cord connection, and the electrode 5 is 2 to 4 mm in terms of spark wear resistance.
Outer diameter of 0.5-2mm, thickness 0.5-1mm, thin wire 7 is 0.3mm
~1.5mm. Therefore, it is very small.
Furthermore, in this embodiment, noble metal is bonded to the electrodes 5 and 6 to suppress their spark consumption in order to achieve maintenance-free operation, so there is no need to check the degree of wear and tear.

Furthermore, in this embodiment, since the semiconductor portion 2d is provided at the tip of the insulator 2, there is also a noise prevention effect.

In this way, in addition to achieving miniaturization, by providing a straight part that protrudes from the cylinder head 1, the spark discharge can easily come into contact with the mixed gas of fuel and air. It is classified as a creeping discharge type. By setting the dimensional relationship described below when using this creeping discharge type, it is possible to cause the sparks to fly and to make it easier for the spark discharge to come into contact with the mixed gas.

That is, as shown in Fig. 2, the thickness of the insulator between the thin wire 7 and the insulator 2 in the straight part is X, the distance from the end surface of the cylinder head 1 to the surface of the electrode 5 facing the ground electrode 6 is Y, and the straight part is When the length between the outer periphery of the electrode 5 and the outer periphery of the electrode 5 is Z, the following relationship holds true.

1.5X≦Y≦3X ……(A) 0.4mm≦X≦1.2mm……(A) 0.2mm≦Z≦0.4mm……(C) The basis for the above relational expression is described below.

Figure 3 shows the ground electrode 6 of the electrode 5 viewed from the end face of the cylinder head 1 when the thickness of the insulator between the thin wire 7 and the insulator 2 in the straight part is varied.
The relationship between Y, which is the distance to the opposing part, and the discharge voltage is shown.

As is clear from Figure 3, the value of wall thickness X is 1.2
If it becomes larger than mm, the discharge voltage will rise rapidly. Furthermore, if the wall thickness X is smaller than 0.4 mm, the insulator will not be sufficiently thick, and the insulator will break down due to the voltage.

Furthermore, if the wall thickness X is less than 1.5 times the distance Y, the fuel flowing into the combustion chamber cannot be sufficiently ignited, resulting in poor ignitability. Also,
If the wall thickness X becomes three times or more the distance Y, the thermal load on the spark plug will be too large and a pre-ignition effect will occur, making it impossible to obtain good ignition.

Furthermore, if the distance Z is 0.2 mm or less, induced discharge will also occur on the surface of the insulator, resulting in poor ignitability. Also, the distance Z is
If it is 0.4 mm or more, the surface area of the center electrode within the combustion chamber becomes large, the center electrode receives a large amount of heat, and the heat resistance of the center electrode deteriorates.

The relationship between the wall thickness X and the distance Y is diagrammed, and the optimum range is shown in the shaded area in FIG.

By satisfying these related dimensions, during the initial discharge (capacitive discharge), the discharge occurs at a low voltage by flying along the creeping surface of the insulator 2, and during the subsequent discharge (inductive discharge), it leaves the surface of the insulator 2. discharge. Therefore,
The overall voltage is low enough to cause sparks, and the ignitability is good.

The present invention is not limited to the above-described embodiments, and various modifications can be made as follows.

(1) Although the terminal 3 and center electrode 6 are fixed by screwing, they may also be bonded and fixed with ceramic adhesive.

(2) The entire ground electrode 4 and center electrode 6 may be made of noble metal.

(3) The thin metal wire 7 may not be straight, but may be curved. In this case, it is made of platinum and the platinum wire is fixed by shrinkage of the insulator 2 by firing.

As described above, according to the present invention, since the insulator is held between the seat portion of the cylinder head and the nut, it is possible to obtain a small-sized spark plug in which the insulator does not break even if it is frequently removed.

Furthermore, in the present invention, since the cylinder head is provided with a protruding straight portion, the creeping discharge generated between the electrode and the ground electrode can easily come into contact with the mixed gas, and therefore, it is possible to obtain a spark plug with excellent ignitability. can.

Furthermore, by limiting the dimensions of the spark plug, it was possible to improve the spark flying and ignitability at low voltages.

Furthermore, by forming the electrode so as to surround the semiconductor portion, it was possible to obtain a spark plug with excellent noise prevention characteristics.

[Brief explanation of drawings]

FIG. 1 is a partially broken sectional view showing an embodiment of the present invention;
Fig. 2 is an enlarged sectional view of the main part of Fig. 1, Fig. 3 is a related part showing the relationship between distance Y and discharge voltage when distance X is changed, and Fig. 4 is an effect of the present invention. It is a characteristic diagram provided for explanation. 1...Cylinder head, 1a...Threaded part, 1b
...Through hole, 2...Insulator, 3...Nut, 3
b...Screw part, 4...Terminal, 5, 6...Electrode, 7
...Thin metal wire.

Claims (1)

[Claims] 1. Has a through hole, at the inner upper end of the through hole,
A cylinder head is formed with a threaded portion, and a seat portion with a smaller diameter than the threaded portion is formed at the inner lower end of the through hole, and the cylinder head is insertable into the through hole of the cylinder head, and a cylinder head is formed on the outer periphery of the cylinder head. is an insulator having a large-diameter annular portion that can be engaged with the seat portion of the through hole, and a straight portion that protrudes from the cylinder head and has a semiconductor portion at the tip thereof. a ring-shaped electrode surrounding the semiconductor portion and having a diameter larger than the straight portion; and a ring-shaped ground electrode that is fitted and fixed to the lower end side of the through hole of the cylinder head so as to face the electrode. , a terminal formed on the rear end side of the insulator, a thin metal wire formed inside the insulator to electrically connect the semiconductor portion and the terminal, and the screw portion of the cylinder head. a nut that clamps the annular large-diameter portion of the insulator together with the seat and fixes the insulator to the cylinder head by screwing, and a nut that fixes the insulator to the cylinder head; Let X be the thickness of the insulator between them, Y be the distance from the end face of the cylinder head to the surface of the electrode facing the ground electrode, and Z be the length between the outer periphery of the straight part and the outer periphery of the electrode. , 1.5X≦Y≦3X 0.4mm≦X≦1.2mm 0.2mm≦Z≦0.4mm, thereby causing creeping discharge between the electrode and the ground electrode. Ignition device.