JP2002151231A - Spark plug unit with built-in pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug unit with a built-in pressure sensor which prevents spark to fly at spark discharge gap of a spark plug main body from leaking to a shield coating of a sensor output lead wire through a gap formed between an elastic polymer material part and a hard polymer material. SOLUTION: The unit is made of an elastic polymer material covering at least a front end part of a terminal fitting 4 protruding from a rear end edge of a jutting part 14a of an insulating body 14 protruding from a rear end edge of a main metal fitting toward the inside of an opening at a front end side of a plug cap 12. An elastic holding part 30 and a reinforcing member 31 integrated with the elastic holding member 30 and made of a polymer material harder than the elastic holding member 30 to reinforce it are formed in a laminated state. When a distance from the front end edge of the terminal fitting 4 to the rear end edge of the main metal fitting 2 measured along the surface of the insulating body 14 is L1, and that from the tail end point at the terminal fitting 4 side to the tail end point at the sensor output lead wire 8 side measured along the outer face of the elastic holding part 30 L2, a formula L2>L1 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spark plug unit with a built-in pressure sensor.

[0002]

2. Description of the Related Art Conventionally, the pressure in a combustion chamber of an internal combustion engine is detected by a pressure sensor built in a spark plug for the purpose of detecting the combustion state and knocking of the internal combustion engine, or improving fuel efficiency and purifying exhaust gas. Have been.
The outline of the spark plug with a built-in pressure sensor used for such a purpose is as follows. That is, a pressure sensor made of a ring-shaped piezoelectric ceramic element is fitted from the outside together with a ring-shaped electrode for output extraction at a base end position of a mounting screw portion formed on a metal shell of the spark plug, and is attached to a flange-shaped sensor holding portion. Receive this,
The whole is covered from outside with a sensor case. The output lead wire from the ring-shaped electrode is taken out of the sensor case backward. When the spark plug is mounted on the plug hole of the internal combustion engine at the mounting screw portion, the pressure sensor is pressed through the sensor case against the outer edge of the opening of the plug hole.
The combustion pressure is transmitted to the pressure sensor via the sensor case. The pressure sensor outputs a voltage corresponding to the detected pressure level via the output lead wire due to the piezoelectric effect.

A spark plug ignites an internal combustion engine by generating a spark discharge by applying a high voltage between the electrodes. The spark discharge is usually a steep pulse containing many harmonic components. Caused by a discharge current in the shape of a circle. Therefore, radio noise due to the harmonic component is constantly leaking from the spark plug during spark discharge. And
In the case of a spark plug having a built-in pressure sensor, radio noise generated from the spark plug body may be picked up by the sensor output lead wire and superimposed on the sensor output signal, causing a reduction in the S / N ratio or erroneous detection. In order to prevent such noise, a shielded cable whose core is covered with a shield covering made of a metal net or the like is generally used as a sensor output lead wire. Shielded.

On the other hand, in a gasoline engine for an automobile or the like, the mechanism around the cylinder head for mounting the spark plug is complicated, and the spark plug is mounted on the bottom of a deep plug hole formed in the cylinder head. Things are increasing. And
For the spark plug fixed to the bottom of the plug hole with a screw, elastic insulation such as rubber is used to insulate and protect the high voltage supply unit such as a spring-like member that applies a high voltage from the ignition coil unit to its terminal fitting. In some cases, a spark plug unit is formed by covering a plug cap made of a polymer material with the spark plug body and the plug cap.

[0005]

In the above-described spark plug unit, if the diameter of the plug hole is reduced due to location restrictions, the thickness of the plug cap may be reduced and buckling may occur. Therefore, the strength is increased by using a member made of a polymer material (for example, synthetic resin) harder than the elastic polymer material as a reinforcing material for the plug cap. In addition, since synthetic resins are generally less expensive to manufacture than silicone rubber, etc., the amount of elastic polymer material used is reduced to reduce costs. In many cases, it is a constituent member. The sensor output lead wire covered with the shield coating is integrally formed in such a form as to be embedded in the plug cap along the axial direction.

However, in some cases, the adhesiveness at the interface between the elastic polymer material and the hard polymer material cannot be sufficiently obtained. In particular, rubber (for example, silicon rubber) and synthetic resin (for example, polyester) have a low linear expansion coefficient. Due to a difference or the like, a gap is easily formed between the two during molding or during use. Further, as the diameter of the plug hole is reduced, the sensor output lead wire embedded in the plug cap and the terminal fitting of the spark plug main body are often arranged close to each other. Therefore, when a high voltage is applied to the spark plug body from the ignition coil unit, the air located in the gap causes an ionization phenomenon and further insulation breakdown due to the high voltage, and the spark to be ignited in the spark discharge gap of the spark plug body. May leak from the terminal fittings to the shield coating of the sensor output lead wire (creepage discharge) through this gap. Due to this spark leak, normal sparks do not fly in the spark discharge gap (missing sparks), and the rated engine output cannot be obtained. This spark leak is a phenomenon peculiar to the spark plug unit with a built-in pressure sensor, which occurs at a place different from flashover, which is a creeping discharge phenomenon on the insulator surface of the spark plug body.

SUMMARY OF THE INVENTION It is an object of the present invention to form a spark to be ignited in a spark discharge gap of a spark plug body from a terminal fitting of the spark plug body between an elastic polymer material portion and a hard polymer material portion of a plug cap. It is an object of the present invention to provide a spark plug unit with a built-in pressure sensor capable of preventing a leak from passing through a gap to a shield coating of a sensor output lead wire and obtaining a stable engine output.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an insulator having a pressure sensor assembled to a cylindrical metal shell, and having a terminal at the tip of a protruding portion projecting from one end of the metal shell. And a spark plug body with
The protrusion has an opening arranged inside, and an elastic holding portion made of an elastic polymer material is disposed on the inner surface of the opening, and a reinforcement made of a polymer material harder than the elastic holding portion is provided. A plug cap detachably attached to the spark plug main body, and at least a part of the reinforcing member and the elastic holding portion are located between the protrusion and itself, and are connected to the pressure sensor. The present invention relates to a spark plug unit with a built-in pressure sensor having a sensor output lead wire that derives a sensor output to the outside and is covered with a shield coating, and is configured as follows to solve the above-described problem. It is characterized by having.

That is, the shortest distance measured along the surface of the protruding portion of the insulator between the terminal fitting and the metallic shell is L1, and the shortest distance from the terminal fitting to the terminal point on the sensor output lead wire side is defined as L1. When the shortest distance measured via the outer surface of the elastic holding portion is L2, the relationship of L2> L1 is satisfied.

As described above, according to the present invention, the distance between the terminal fitting and the terminal point on the sensor output lead wire side is smaller than the shortest distance L1 measured along the surface of the protrusion of the insulator. The shape and the like of the elastic holding portion are adjusted so that the shortest distance L2 measured via the outer surface of the holding portion is larger. In other words, assuming that the above-described spark leak occurs, the process in which the spark leak crawls (that is, passes through the gap formed between the terminal fitting and the elastic holding portion and the reinforcing member, and causes the sensor output Step to reach the shield coating of the lead wire; hereinafter, referred to as the second creepage distance) L
2 is a process in which sparks crawl on the assumption that flashover, which is a creeping discharge phenomenon on the insulator surface, occurs (that is, a process between the terminal fitting and the metal shell; hereinafter, referred to as a first creepage distance). It is larger than L1. Therefore, according to this configuration, the spark to be ignited in the spark discharge gap of the spark plug main body is transferred from the terminal fitting of the spark plug main body to the elastic holding portion (elastic polymer material portion) and the reinforcing member (hard polymer material) in the plug cap. part)
Through the gap formed between the sensor output lead wire and the shield coating of the sensor output lead wire (creepage discharge), and a stable engine output can be obtained. It is necessary that the actual first creepage distance L1 be as large as possible to prevent the occurrence of flashover.

It is desirable that the elastic holding portion has an extension portion extending so as to cover the entire terminal fitting. Since the entire terminal fitting is covered by the extension of the elastic holding part, the leakage of the spark to be ignited in the spark discharge gap of the spark plug body from the terminal fitting to the shield coating of the sensor output lead wire (creepage discharge) is further reduced. It can be prevented more reliably.

[0012]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. In the following description, the side of the spark plug body 5 where the spark discharge gap g is formed in the direction of the axis O of the insulator 14 is defined as the front side. FIG. 1 is a longitudinal sectional view showing the overall configuration of a spark plug unit with a built-in pressure sensor (hereinafter, simply referred to as a spark plug unit) according to one embodiment of the present invention. The spark plug unit 1 is roughly composed of a spark plug body 5 and a plug cap 12. In the spark plug main body 5, the pressure sensor 3 is integrated with the metal shell 2, and a path for applying a high voltage to the spark discharge gap g on the front end side in the direction of the axis O and similarly on the rear end side. The terminal fitting 4 is formed. Further, a sensor output terminal portion 6 for extracting a sensor output from the pressure sensor 3 is formed integrally with the metal shell 2 of the spark plug body 5. The metal shell 2 of the spark plug body 5 is formed in a cylindrical shape, and its axis O
At the front end side in the direction, a mounting portion 16 is formed in which an external thread is cut into the outer peripheral surface to be screwed into the mounting screw hole TH of the cylinder head, and a flange-shaped sensor holding portion is adjacent to the base end side. 17 project in the circumferential direction. A circumferential rib 52 for stopping the cylindrical insulator 14 is formed on the inner peripheral surface of the mounting portion 16.

A through-hole (not shown) is formed in the insulator 14 in the direction of the axis O, and a center electrode 51 is provided at the front end thereof.
A terminal fitting 4 is arranged on the rear end side, and both are electrically connected by a conductive glass seal layer or a resistor composition (not shown) filled in the through hole.

A ground electrode 50 is welded to the front end face of the mounting portion 16 of the metallic shell 2 to form a spark discharge gap g with the center electrode 51. Further, the metal shell 2 has a tool engaging portion 2a for engaging a mounting tool such as a box wrench on the outer peripheral surface of the rear end portion.

The insulator 14 is inserted into the inside of the metal shell 2, and as shown in FIG. 2, the step on the front end side of the middle body portion 14c is engaged with the rib 52, while being formed at an intermediate position in the axial direction. The ring-shaped packings 53 and 54 and the talc-filled layer 55 are arranged on the step on the rear end side of the formed flange 14b, and the circumferential metal caulking portion 2b is formed on the rear end of the metal shell 2 to assemble. Have been.

A sensor output lead wire 8 connected to the pressure sensor 3 is incorporated in the plug cap 12. Further, an end of the spark plug main body 5 connected to the spark plug main body 5 is formed on the side of the spark plug main body 5. A cap-side metal fitting 10 as a cap-side second terminal for electrically connecting the sensor output lead wire 8 to the sensor output terminal 6 is formed. The sensor output lead wire 8 is connected to the cap-side bracket 1.
0 is covered with a shield coating 8b. On the other hand, the connection end 8c of the sensor output lead wire 8 and the cap-side metal fitting 10 integrated with the connection end 8c are not shielded. Is formed.

The spark plug body 5 is provided with a cylinder head S by tightening a male screw cut in the mounting portion 16 into a mounting screw hole TH formed in the bottom of the plug hole PH.
H attached. On the other hand, the plug cap 12 has an insertion hole 15 () for inserting the protrusion 14 a of the insulator 14 protruding from the rear edge of the rear opening 2 c of the metal shell 2 and the terminal fitting 4 protruding from the protrusion 14 a. An opening (opening) is formed in the direction of the axis O, and the inner surface of the insertion hole 15 has at least the cap body 11 serving as an elastic holding portion 30 made of an elastic polymer material (for example, silicone rubber).
The cap main body 11 incorporates the sensor output lead wire 8 of the pressure sensor 3, the cap side first terminal portion 9 for electrically connecting the terminal fitting 4 to the ignition coil IC, and the sensor output lead wire 8. Metal fitting 10 for electrically connecting the sensor to the sensor output terminal 6
(Cap-side second terminal portion). Then, the projection 14a of the insulator 14 is pushed in the direction of the axis O while the insertion hole 15 is elastically enlarged in diameter, so that the projection 14a of the insulator 14 is held on the inner surface of the insertion hole 15. That is, the insulator 1 is inserted into the insertion hole 15 of the elastic holding portion 30.
4 by simply pushing in the protrusion 14a of the plug cap 1
2 can be easily connected to the spark plug body 5. In addition, the protrusion 14a can be closely held on the inner surface of the insertion hole 15 by the elastic force of the elastic polymer material, and flashover (that is, creeping discharge on the surface of the insulator 14) can be achieved.
Are unlikely to occur.

The cap body 11 is made of a polymer material (for example, a polyester resin) harder than the elastic polymer material forming the elastic holding portion 30, and has a core body side hole 31b opened at the front end face in the direction of the axis O. Core body 31
(Reinforcing member). An outer surface covering portion 32 made of an elastic polymer material (for example, silicon rubber) covering the outer peripheral surface of the core 31 and an inner surface of the core side hole portion 31b made of the same elastic polymer material are also held elastically. The inner surface covering portion forming the portion 30 (hereinafter, also referred to as the inner surface covering portion 30) is formed as, for example, an integrally molded body of silicon rubber. Thus, the inner surface covering portion 30 and the core body 31
The outer surface covering portion 32 is integrally formed outside the projecting portion 14a of the insulator 14 so as to be successively stacked radially outward. In addition, the sensor output lead wire 8 is integrally formed so as to be embedded inside the outer surface covering portion 32 along the direction of the axis O (see FIG. 3).

As shown in FIG. 3A in an enlarged manner, the elastic holding portion 30 includes a main body portion 30a for accommodating the protruding portion 14a of the insulator 14 and a rear portion of the terminal fitting 4 at a rear end. And an extension 30b extending to cover the terminal fitting 4.
As a result, in the cross section of FIG. 3A including the axis O of the metal shell 2, the distance measured along the outer surface of the elastic holding portion 30 from the terminal point on the terminal fitting 4 side to the terminal point on the sensor output lead wire 8 side. L2 (second creepage distance) is a distance L1 (first creepage distance) measured from the front edge of the terminal fitting 4 to the rear edge of the rear opening 2c of the metal shell 2 along the surface of the protrusion 14a of the insulator 14. ) Has been adjusted to a greater extent. This means
This means that the second creepage distance L2 is larger than the first creepage distance L1 at which sparks crawl when flashover is assumed to occur in the spark plug body 5. As a result, the spark to be ignited in the spark discharge gap g of the spark plug body 5 leaks as a flashover along the surface of the insulator 14 (surface discharge). Leakage (creeping discharge) to the shield coating 8b of the sensor output lead wire 8 through the gap formed between the elastic holding portion 30 and the core body 31 in 12 is also reliably prevented.

Considering the case of a section not including the axis O of the metal shell 2, the first creepage distance L1 and the second creepage distance L2 can be generalized as follows. That is, the first creepage distance L1 can be rephrased as the shortest distance measured between the terminal fitting 4 and the metal shell 2 along the surface of the protrusion 14a of the insulator 14. The second creepage distance L2 can be translated into the shortest distance measured from the terminal fitting 4 to the terminal point on the sensor output lead wire 8 side via the outer surface of the elastic holding portion 30.

Further, at least one of the outer surface of the extension portion 30b and the main body portion 30a of the elastic holding portion 30
By forming the concave portion or the convex portion in the circumferential direction, the second creepage distance L2 can be increased.
> L1. It is more effective to form a plurality of concave portions or convex portions in parallel along the axial direction.

Here, as shown in FIGS. 3B and 3C, the sensor output lead wire 8 is formed in the concave portion 3 formed in the outer surface coating portion 32.
2a. Then, as shown in FIG. 3A, the front end of the outer surface of the elastic holding portion 30 is connected to the sensor output lead wire 8.
In this case, the end point on the sensor output lead wire 8 side at the second creepage distance L2 means the point P1 at which the outer surface of the elastic holding portion 30 changes direction. In addition, the concave portion 32a is formed over the outer surface covering portion 32 and the core body 31, and as a result, the elastic holding portion 3
The front end of the outer surface is a shield coating 8 of the sensor output lead wire 8.
b, the end point on the sensor output lead wire 8 side at the second creepage distance L2 is the elastic holding portion 30
It means a contact point between the front end of the outer surface and the shield coating 8b.

As shown in FIG. 3A, the elastic holding portion 30
The outer diameter d2 of the extension 30b is smaller than the outer diameter d1 of the main body 30a, and the radial thickness t2 of the core 31 corresponding to the extension 30b is smaller than the core diameter corresponding to the main body 30a. 31 is formed larger than the radial thickness t1. When this gap is narrowed in order to prevent a spark leak passing through a gap formed between the elastic holding section 30 and the core body 31, when the elastic polymer material to be the elastic holding section 30 is molded or used. The core 31 made of a hard polymer material is pressed by thermal expansion, and a crack may be generated in the core 31. This crack may become a new gap through which the spark leak passes. In the present embodiment, the extension 30b that covers the terminal fitting 4 that is a spark leakage source (+ pole)
The radial thickness t2 of the core body 31 corresponding to
Is formed to be larger than the radial thickness t1 of the core body 31 corresponding to the above, cracks are less likely to occur in the core body 31 corresponding to the extension 30b, and the occurrence of spark leakage is suppressed.

Returning to FIG. 1, the core body 31 has a through hole 35 in the direction of the axis O whose front end communicates with the core side hole 31b.
Here, the long spring-shaped cap-side first terminal portion 9 is arranged. On the other hand, a counterbore 3 is provided at the rear end of the core body 31 in the axial direction.
1c is formed, and its inner surface is covered with a coil holding covering portion 36 (in this embodiment, integrated with the outer surface covering portion 32) made of an elastic polymer material (for example, silicon rubber), and a coil mounting hole is formed. 37 are formed. The ignition coil IC is mounted on the mounting portion 8 integrally molded.
0 into the coil mounting hole 37, the terminal fitting 4 of the spark plug main body 5 via the cap-side first terminal 9.
Is electrically connected to Then, a high voltage is applied to the spark discharge gap g formed between the center electrode 51 and the ground electrode 50 by the ignition coil IC via the cap-side first terminal portion 9, the terminal fitting 4, and the center electrode 51. . The spring-like cap-side first terminal portion 9 is compressed and elastically deformed between a high-voltage terminal (not shown) of the ignition coil IC and the terminal fitting 4, and is formed between the inner surface of the insertion hole 15 and the protrusion 14 a. It is held by friction and works to secure electrical contact between the ignition coil IC and the terminal fitting 4 by its elastic return force.

Next, in FIG. 2, a cap-side fitting 1 is provided at the end of the cap body 11 where the insertion hole 15 is opened.
A ring-shaped socket fitting (hereinafter, also referred to as a socket fitting 10) forming 0 is integrated. By pushing the protrusion 14 a of the insulator 14 and the terminal fitting 4 into the insertion hole 15, the sensor output terminal 6 attached on the metal shell 2 and the socket fitting 10 are brought into contact with each other. Further, by engaging and fixing the plug cap 12 to the spark plug body 5 with the cap body 11, the socket fitting 10 as the cap-side first terminal 9 and the cap-side second terminal is provided.
Are detachably coupled to the terminal fitting 4 and the sensor output terminal section 6, respectively, and the plug cap 12 is accommodated in the plug hole PH. When the plug cap 12 is attached to the spark plug main body 5, the rear edge of the ring-shaped socket fitting 10 in the direction of the axis O is located forward of the front edge of the tool engaging portion 2a, and The rear edge of the connection end 8c of the sensor output lead wire 8 coupled to the metal fitting 10 is located forward of the rear edge of the tool engagement portion 2a. Thus, the entire connection end 8c forming the non-shielded portion 71 is positioned so as to overlap with the metal shell 2 in the direction of the axis О.

As described above, the metal shell 2 has a mounting portion 16 for the internal combustion engine formed at the front end side in the direction of the axis O.
A sensor holding portion 17 in the circumferential direction is protrudingly provided corresponding to the rear end position of the mounting portion 16 in the direction of the axis O.

On the other hand, a sensor cover 19 located in front of the sensor holding portion 17 has a bottom portion 19a which contacts and covers the front end surface of the pressure sensor assembly 18, and a bottom portion 19a.
a side wall portion 19 which is formed in a cylindrical shape rising rearward from the outer peripheral edge in the direction of the axis O and covers the outer peripheral surface of the pressure sensor assembly 18.
b are formed. The pressure sensor assembly 18 includes a ring-shaped plate packing 59, a pressure sensor 3 made of a ring-shaped piezoelectric ceramic element, a ring-shaped electrode plate 60, and a ring-shaped electrode plate 60 from the side near the bottom 19 a of the ring-shaped sensor cover 19. The insulating plate 61 has a structure in which the insulating plates 61 are stacked in this order, and the mounting portions 16 of the metal shell 2 are inserted into holes formed in the respective central portions. Further, the lead portion 62 from the electrode plate 60 is pulled out rearward through a slit formed in the insulating plate 61. When the mounting portion 16 of the metal shell 2 is fitted into the ring-shaped sensor cover 19 and the pressure sensor assembly 18 in the direction of the axis O from the front end thereof, the rear end of the pressure sensor assembly 18 becomes the sensor holding portion. 17 is supported in contact with the front end face.

The side wall 19 of the sensor cover 19
“b” extends rearward of the rear end edge of the pressure sensor assembly 18 in the direction of the axis O to form an extension 19c. In the opening 19d formed on the rear end side of the extending portion 19c, a ring-shaped gap between the inner peripheral surface of the extending portion 19c and the outer peripheral surface of the metal shell 2 inside the extending portion 19c is formed by the ring-shaped socket metal 10. The insertion holding section 20 of FIG. Using the extension 19c of the sensor cover 19, the insertion holder 2
If a ring-shaped gap is formed at 0 and the socket fitting 10 is inserted into the gap, the connecting operation with the ring-shaped sensor output terminal 6 can be performed extremely easily with the extension 19c serving as a guide. it can. Further, since the extending portion 19c restrains the movement of the socket fitting 10 in the radial direction, a stable connection state can be maintained.

A ring-shaped sensor output terminal 6 is arranged between the socket fitting 10 and the metallic shell 2 so as to be electrically connected to the end of the lead 62. In particular,
As shown in FIG. 1B, the sensor output terminal portion 6 is integrated as an annular metal plating layer on the outer peripheral surface of a terminal base 63 formed in a ring shape from an insulating material such as resin. As shown in FIG. 2, the sensor output terminal portion 6 is fixed to the metal shell 2 in an insulated state by fitting the terminal base 63 to the outer peripheral surface of the metal shell 2. In the present embodiment, an engaging rib 63a formed in the circumferential direction on the inner circumferential surface of the terminal base 63 is fitted into an engaging recess 2f (see FIG. 2) formed in the outer circumferential surface of the metal shell 2 in the circumferential direction. The terminal base 63 is fixed to the metal shell 2 in such a manner that the terminal base 63 is prevented from coming off in the direction of the axis O.

As shown in FIG. 2, the rear end of the lead portion 62 has a through portion (hole or cutout) 63c (hole or notch) in the direction of the axis O formed on the lead portion holding portion 63b projecting from the front end surface of the terminal base 63. 1 (see FIG. 1 (b)), and the tip is contact-fixed to the sensor output terminal 6. In addition, between the lead part 62 and the penetrating part 63c and the pressure sensor assembly 1
The gap formed between the sensor cover 8 and the sensor cover 19 is filled with a filling seal portion 64 made of an insulating polymer material (rubber, synthetic resin, or the like).

The socket fitting 10 and the sensor output terminal 6 are both formed in a ring shape and are relatively rotatable. When the plug cap 12 (that is, the cap body 11) is rotated about the axis O, , Electrical continuity can be secured at any angular position.

Returning to FIG. 1 again, the inner peripheral edge of the bottom portion 19a of the sensor cover 19 is sealed and connected to the outer peripheral surface of the base end of the mounting portion 16 of the metal shell 2 by a laser welding portion 65 in the circumferential direction. After the sensor cover 19 is covered on the outside of the pressure sensor assembly 18, the bottom 19 a is pressed and adhered to the pressure sensor assembly 18 in the direction of the axis O, and the pressurized state is maintained. A laser weld 165 is formed and fixed. When the spark plug unit 1 is mounted, the bottom portion 19a of the sensor cover 19 is pressed through the gasket GK at the peripheral edge of the mounting screw hole TH on the cylinder head side, and vibration is generated by the pressure sensor assembly 1.
The pressure is transmitted to the pressure sensor assembly 8 to detect the pressure. With the above-described configuration, the state of close contact between the bottom portion 19a and the pressure sensor assembly 18 is increased, and the pressure detection accuracy is improved.

Next, in this embodiment, a cylindrical socket support 21 made of an elastic polymer material (for example, silicon rubber) is formed at the end of the cap body 11 on the side where the insertion hole 15 is opened. , A socket fitting 1 on its inner peripheral surface
0 is integrated. Specifically, the cap body 11
, The opening side end of the insertion hole 15 is enlarged by radially reducing the thickness of a wall portion 136 forming the insertion hole 15, and a tool engagement portion accommodating portion 15 b for accommodating the tool engagement portion 2 a is provided.
Are formed. The wall portion 136 is extended forward in the axial direction, and the extended portion is used as a socket metal support portion 21, to which the socket metal 10 is integrated.

The socket metal support 21 is inserted into the insertion holder 20 together with the socket metal 10 while being compressed in the radial direction, and the socket metal 10 is directed toward the sensor output terminal 6 by its elastic return force. Energize.
According to this configuration, the socket fitting 10 is back-up urged by the elastic restoring force of the socket fitting supporting portion 21 made of rubber or the like, so that the rattling of the socket fitting 10 in the radial direction is prevented and the sensor output terminal section is provided. 6 can be made more reliable.

In this case, when inserted into the insertion holding portion 20 on the outer peripheral surface of the socket metal support portion 21, it comes into contact with the inner peripheral surface of the extending portion (side wall portion) 19c of the sensor cover 19 to be compressed and elastically deformed. Elastic protruding portions 21a (see FIG. 2) can be formed. Due to the elastic return force of the elastic protrusion 21a,
The connection between the socket fitting 10 and the sensor output terminal section 6 can be further ensured. Further, in the present embodiment, the elastic protrusion 21a is an annular ridge formed in the circumferential direction of the socket fitting support portion 21, but by adopting such an annular ridge, the elastic protrusion 21a is elastic. Projection 21
“a” enhances the seal airtightness between the socket metal support 21 and the sensor cover 19, and can improve the waterproof effect. In this case, if two or more protruding ridges are formed at a predetermined interval, more favorable sealing properties can be secured. On the other hand, if not so high sealing property is required, only one protruding ridge is formed, or an intermittent form other than the protruding ridge, for example, a scattered convex is used as the form of the elastic protruding part 21a. You can also.

According to the configuration of the spark plug unit 1, the spark plug main body 5 is first mounted on the side of the internal combustion engine such as an automobile engine at the mounting portion 16, and the plug cap 12 is mounted on the mounted spark plug main body 5. Can be retrofitted. Thereby, when attaching the spark plug main body 5, a trouble such as winding of the lead wire 8 around a tool or the like does not occur at all.
The metal shell 2 is grounded via the cylinder head SH. However, the metal shell 2 and the metal shell 2 are connected to each other so that the entire metal shell 2 is overlapped in the axial direction of the insulator 14. Since the arrangement relationship with the metal shell 2 is determined, the metal shell 2 functions as an auxiliary shield part for shielding the non-shield part 71, and the radio noise leaking from the insulator 14 of the spark plug main body 5 is generated by the lead wire 8. Can be prevented or suppressed from being superimposed on the sensor signal flowing through the sensor.

The rear end of the sensor output lead wire 8 is connected to an output extraction connector (hereinafter, simply referred to as a connector) 13. The shield coating 8b is connected to a ground terminal (not shown) in the connector 13 and is grounded. The plug cap 12 is engaged with the spark plug body 5 so as to be relatively rotatable around the axis O. In the mounting screw hole TH formed in the cylinder head of the automobile engine, the starting position of the thread is often not constant, and when the male screw of the mounting portion 16 is screwed in with a specified tightening torque, a spark is generated. The mounting phase angle of the plug body 5 to the cylinder head SH may vary. In this case, if the connector 13 is non-rotatably connected to the spark plug main body 5 around the axis O, the final circumferential position of the connector 13 varies due to the variation in the mounting phase angle. Depending on the connector 13
When connecting a signal line cable from the control circuit side to the control circuit side, a problem may occur. However, by rotating the plug cap 12 about the axis with respect to the spark plug body 5 as described above, the circumferential position of the connector 13 can be freely adjusted. However, when it is not necessary to adjust the position of the connector 13 in the circumferential direction, the plug cap 12 and the spark plug main body 5 are formed such that a key groove is formed on one side and a convex portion engaging with the other is formed on the other side. O
May be adopted so as to be non-rotatably coupled around.

Hereinafter, various modifications of the spark plug unit according to the present invention will be described. 4 to 7.
In FIG. 1, the spark plug unit 1 shown in FIGS.
Components that are conceptually common to the above are given the same reference numerals, and detailed descriptions thereof will be omitted. In the spark plug units 100 and 200 shown in FIGS. 4 and 6, the spark plug body 5 and the connection end 8 are located at positions corresponding to the connection end 8c.
c, circumferential shield rings 45, 46, 61 separate from the metal shell 2 are arranged.

4A, the front edge of the shield ring 45 formed integrally with the protruding portion 14a of the insulator 14 by plating or the like is connected to the rear edge of the rear opening 2c of the metal shell 2. And crimped portion 2b
Is electrically connected to the rear edge of the rear opening 2c of the metal shell 2. Note that a separate cylindrical shield ring 46 as shown in FIG.
You may fit it. As described above, in the spark plug unit 100 of the first modified example shown in FIG. 4, the shield rings 45 and 46 play a role as a ground conduction portion for grounding the discharge voltage, similarly to the metal shell 2.

That is, as shown in FIG. 5, the metallic shell 2 is electrically connected to and grounded by a shield ring 45,
The shape is extended by 46. Therefore, the first creepage distance L1 in this embodiment is determined by the distance between the terminal fitting 4 and the shield rings 45 and 46.
a Represented by the shortest distance measured along the surface. Also,
In the cross section of FIG. 5 including the axis O of the metal shell 2, the first creepage distance L1 is the distance measured along the surface of the insulator 14 from the front edge of the terminal metal 4 to the rear edge of the shield rings 45 and 46. In other words,

On the other hand, in the spark plug unit 200 of the second modification shown in FIG.
1 is integrated with the shield coating 8b. Specifically, as shown in FIGS. 6B and 6C, the corresponding edge of a shield ring 61 formed by rolling a strip-shaped metal plate into a cylindrical shape is connected to a shield coating 8 b via a folded connection portion 60. It is a structure to be connected to. Further, the socket fitting 10 is integrated with the socket fitting support 21.

In this embodiment, as shown in FIG. 7, the shield ring 61 is arranged so as to be in contact with the outer surface of the main body 30a of the elastic holding portion 30. In such a case, the terminal point on the sensor output lead wire 8 side at the second creepage distance L2 means a contact point P2 between the outer surface of the elastic holding portion 30 and the shield ring 61.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spark plug unit with a built-in pressure sensor according to an embodiment of the present invention, and a perspective view of a terminal ring thereof.

FIG. 2 is a longitudinal sectional view showing a main part of the spark plug unit of FIG.

FIG. 3 is a partially enlarged view of FIG. 2 and a cross-sectional view along XX and YY axes thereof.

FIG. 4 is a longitudinal sectional view showing a first modification of the spark plug unit with a built-in pressure sensor of the present invention, and a perspective view showing a modification of the shield ring.

FIG. 5 is an enlarged longitudinal sectional view of a main part of FIG. 4;

FIG. 6 is a longitudinal sectional view showing a second modification of the spark plug unit with a built-in pressure sensor of the present invention, an enlarged partial sectional view of a shield ring, and a sectional view taken along the line BB of FIG.

FIG. 7 is an enlarged longitudinal sectional view of a main part of FIG. 6;

[Explanation of symbols]

1, 100, 200 Spark plug unit with built-in pressure sensor 2 Metal shell 3 Pressure sensor 4 Terminal fitting 5 Spark plug body 8 Sensor output lead wire 8b Shield coating 12, 112, 212 Plug cap 14 Insulator 14a Projection 15 Insertion hole ( Opening) 30 Inner surface covering part (elastic holding part) 30a Main body part 30b Extension part 31 Core body (reinforcing member) 32 Outer surface covering part 45, 46, 61 Shield ring L1 First creepage distance L2 Second creepage distance d1 Main body part Outer diameter d2 Outer diameter of extension part t1 Radial thickness of core body corresponding to body part t2 Radial thickness of core body corresponding to extension part O Axis

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takahiro Suzuki 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term in Japan Special Ceramics Co., Ltd. 3G019 CA07 KA28 KB09 5G059 AA01 CC02 GG05 JJ18 KK03

Claims (3)

[Claims] 1. A spark plug main body in which a pressure sensor is assembled to a cylindrical metal shell, and an insulator having a terminal metal fitting is disposed at a tip of a protrusion protruding from one end of the metal shell; Has an opening arranged inside, an elastic holding portion made of an elastic polymer material is disposed on the inner surface of the opening, and a reinforcing member made of a polymer material harder than the elastic holding portion is provided. A plug cap detachably attached to the spark plug main body, at least a part of the reinforcing member and the elastic holding portion are located between the projecting portion and itself, and connected to the pressure sensor to provide an external sensor A spark plug unit with a built-in pressure sensor having a sensor output lead wire that derives an output and is covered with a shield coating, wherein the terminal fitting and the metal shell are provided. The shortest distance measured along the surface of the protruding portion of the insulator was L1, and the distance from the terminal fitting to the end point on the sensor output lead wire side was measured via the outer surface of the elastic holding portion. The shortest distance is L
A spark plug unit with a built-in pressure sensor, which satisfies the relationship of L2> L1 when 2. 2. The spark plug unit with a built-in pressure sensor according to claim 1, wherein the elastic holding portion has an extension portion extending so as to cover the entire terminal fitting. 3. The elastic holding portion, wherein an outer diameter of the extension portion is formed smaller than an outer diameter of a main body portion covering the projecting portion, and a radial thickness of the reinforcing member corresponding to the extension portion. 3. The spark plug unit with a built-in pressure sensor according to claim 2, wherein a thickness of the reinforcing member is larger than a radial thickness of the reinforcing member corresponding to the main body.