JP3135710B2 - Spark plug with built-in pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug having a built-in pressure sensor for detecting a combustion pressure in a cylinder of an engine.

[0002]

2. Description of the Related Art Knocking occurs when the engine is operated stably at a lean air-fuel ratio in order to improve fuel efficiency and purify exhaust gas, or when the supercharging amount is increased to improve fuel efficiency in a stoichiometric air-fuel ratio range. Easily, unstable torque causes large torque fluctuation. Therefore, it is necessary to detect the combustion pressure in the cylinder, prevent knocking from occurring, and suppress the torque fluctuation to a certain value or less. For this reason, a spark plug with a built-in pressure sensor that incorporates a pressure sensor that detects a fluctuation in combustion pressure in a cylinder is used to detect torque fluctuations in the engine, knocking, and the like. In the case of a spark plug with a built-in pressure sensor, conventionally, a pressure sensor using a piezoelectric element has a large body of the metal shell of the spark plug and a spark plug mounting seat around the screw hole for mounting the spark plug provided in the cylinder head of the engine. Or a pressure sensor mounting hole provided in the metal shell.

[0003]

However, the former has a disadvantage that the piezoelectric characteristics are affected by the variation of the initial load applied to the piezoelectric element due to the fastening torque of the spark plug to the engine, and the output tends to vary from cylinder to cylinder. Also,
In the latter case, since the through hole for the spark plug and the through hole for the pressure sensor are arranged side by side on the metal shell, complicated machining is required and the manufacturing cost increases, and the metal shell becomes larger in diameter and is mounted on the engine. Has the disadvantage that the properties are reduced.
SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug with a built-in pressure sensor, in which the initial compressive load of a piezoelectric element can be set to be constant, the machining of the metal shell is relatively simple, and the increase in the outer diameter is small.

[0004]

A spark plug with a built-in pressure sensor according to the present invention has an outer peripheral step provided on an outer periphery between a front end portion having a small diameter at the front end and a rear end portion having a large diameter at the rear end. And a metal cylindrical inner housing provided with a male screw on one of the outer periphery of the front end side or the rear end side, a mounting screw for the engine on the front end side of the outer periphery, and a rear end side on the rear end side. A large-diameter portion is provided, an inner thread is screwed into the male screw on the inner periphery, and an inner peripheral step facing the outer peripheral step is formed on the rear-end large-diameter portion, and an outer periphery of the inner housing is formed. A metal cylindrical outer housing fastened to the inner housing; a pressure sensor disposed between the inner peripheral step of the outer housing and the outer peripheral step of the inner housing; And an insulator fitted inside. In this configuration, if the front ends of the inner and outer housings are seam-welded, the sealing performance of the cylinder is improved.

[0005]

According to the present invention, since the inner housing provided with the outer housing and the insulator is provided, and the pressure sensor is provided between the inner and outer housings, the fastening of the spark plug to the engine and the piezoelectric device can be performed. Since the initial compressive load to the element is set independently of each other, variations in output due to variations in fastening torque can be reduced. In addition, since the inner and outer housings are both concentric cylindrical shapes, machining of the housing is easy, and enlargement of the diameter of the spark plug can be minimized.

[0006]

1 and 2 show a spark plug 100 with a built-in pressure sensor according to a first embodiment of the present invention. The spark plug 100 includes a metal cylindrical inner housing 1 which is a metal shell, and an outer housing 2 which is externally fitted to and fastened to the inner housing 1. The inner housing 1 includes a male screw 11 provided on a distal end portion 14 having a small diameter at the distal end, and a large diameter rear end portion 1 having the distal end portion 14 and the rear end.
7, an outer peripheral step portion 12 is provided.
The inner diameter of the female screw 21 screwed to the male screw 11 and the rear end side large diameter portion 24
An inner peripheral step 22 is formed, and the pressure sensor 3 is sandwiched between the inner peripheral step 22 and the outer peripheral step 12. Also,
An insulator 4 including a center electrode 5 is fitted in the inner housing 1.

The inside of the inner housing 1 includes a small-diameter front end portion 14 on which a locking step 13 is formed and a large-diameter rear end portion 15. The outer periphery of the inner housing 1 is cylindrical portion 1 from the tip.
6, the male screw 11, the outer peripheral step portion 12, and a large-diameter rear end portion 17. The rear end side portion 17 is provided with thin portions 18 and 19 serving as crimping allowances. Outer housing 2
A small-diameter fitting portion 23 on the inner periphery from the distal end side,
1, an inner peripheral step portion 22 and a rear end side large diameter portion 24 are provided, and on the outer periphery, a mounting screw 25 from the front end side to the engine, a large diameter body portion 26,
A hexagonal head 27 is formed. In this embodiment, the ground electrode 6 is welded to the distal end of the outer housing 2 and the fitting surface 20 between the distal side portion 14 of the inner housing 1 and the fitting portion 23 of the outer housing 2 is laser-welded. The seam welding by the laser beam irradiation is for preventing the combustion gas in the cylinder from entering around the piezoelectric element, and may be electron beam welding or plasma arc welding.

The pressure sensor 3 has a ring-shaped electrode plate 32 with a lead wire 31 interposed between the ring-shaped piezoelectric elements 30, 30 at a fixed tightening torque, and has a cylindrical insulating layer 33 and 34 are provided. The lead wire 31 is taken out from a gap provided between the outer periphery of the rear end portion 17 of the inner housing 1 and the inner periphery of the large diameter portion 24 on the rear end side of the outer housing 2 or a slit provided in the inner periphery.

The insulator 4 has a rod-like shape with a shaft hole 41, and is composed of a leg 42 having a small diameter, a trunk 43 having a large diameter, and a head 44 having a medium diameter. The tip of the leg 42 is a step 45
, A tapered portion 46 is provided, and a corrugation 47 is formed at the rear end of the head 44. The center electrode 5 is formed by inserting an electrode rod 51, a resistor 52, and a connection terminal 53 into the shaft hole 41 from the front end side, and fixing the center electrode 5 with a filled conductive glass seal 54. The tip of the electrode rod 51 projects from the tip of the insulator 4 and forms a spark discharge gap with the ground electrode 6. The rear end of the connection terminal 53 is a large-diameter plug cap connection terminal 55 protruding from the rear end of the insulator 4.
It has become.

FIG. 3 shows a second embodiment. In this embodiment, the male screw 11 of the inner housing 1 is formed on the large-diameter rear end portion 17 which is the rear end side of the outer peripheral step portion 12, and the female screw 21 of the outer housing 2 is correspondingly formed on the inner peripheral portion. The lead wire 31 is formed on the rear end side of the step portion 22, and the lead wire 31 is exposed to the outside via the inner peripheral groove 28 of the large diameter portion 24 on the rear end side of the outer housing 2, and is formed on the surface of the head 44 of the insulator 4. It is electrically connected to the provided cylindrical electrode 7. The ground electrode 6 is
It may be welded to the tip of the inner housing 1. In the above embodiment, the inner housing 1 and the outer housing 2 have substantially the same overall length, but one of them is shorter than the other. The pressure sensor 3 may be interposed therebetween. Further, the male screw 11 is not limited to the above embodiment, but is screwed on the outer periphery of the rear end portion 17 of the inner housing 1 and provided with a female screw 21 on the inner periphery of the outer housing 2 to be fitted. It may be a structure.

FIG. 4 shows a spark plug with a built-in pressure sensor according to the present invention shown in FIG. 1 and a conventional washer-type spark plug in which a pressure sensor is interposed between a body of a metallic shell and a spark plug mounting seat. This shows the relationship between the output of the spark plug and the tightening torque, and the spark plug of the present invention has less fluctuation of the output due to the tightening torque than the conventional spark plug, so that the output can be measured accurately. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a spark plug with a built-in pressure sensor according to a first embodiment.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a sectional view of a spark plug with a built-in pressure sensor according to a second embodiment.

FIG. 4 is a graph showing a relationship between a tightening torque and an output in a spark plug with a built-in pressure sensor of the present invention and a conventional washer-type spark plug.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner housing 2 Outer housing 3 Pressure sensor 4 Insulator 5 Center electrode 6 Ground electrode 11 Male screw 12 Outer step 21 Female screw 22 Inner step 25 Mounting screw 30 Piezoelectric element

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01T 13/00-21/06

Claims (2)

(57) [Claims] 1. After a small diameter at the front end and a large diameter at the rear end.
The outer peripheral step portion and the destination provided on the outer periphery between the side edge
A male screw is attached to either the end or the outer periphery of the rear end.
And di is provided a metallic cylindrical inner housing, the mounting screws to the engine on the distal end side of the outer circumference end side large diameter on the rear end side
Parts are provided, together with the circumferential stepped portion is formed opposing inner and outer peripheral step portion in the female screw and the rear end side large-diameter portion is screwed to the male thread on the inner periphery, fastened to the outer periphery of the inner housing Metal outer cylindrical housing, the inner peripheral step of the outer housing, and the inner housing
A pressure sensor built-in spark plug comprising: a pressure sensor disposed between the outer peripheral step portion of the housing ; and an insulator including a center electrode and fitted inside the inner housing. 2. The spark plug with a built-in pressure sensor according to claim 1, wherein the tip of the inner housing and the tip of the outer housing are seam-welded.