JPH0127588Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a spark plug with a built-in pressure sensor, and in particular, a spark plug with a built-in pressure sensor that is sensitive without changing the external shape and performance of conventional spark plugs. The present invention provides a spark plug with a built-in pressure sensor that is sensitive to detecting pressure fluctuations and vibrations in the high frequency range such as knocking.

[Prior art] Knowing the combustion pressure of a running internal combustion engine allows the combustion status, torque output, etc. to be detected, and the amount of fuel injection,
Controlling the number of cylinders, gear ratio, etc. is expected to be useful for reducing fuel consumption, preventing knocking, and preventing noise. However, conventional methods for applying pressure sensors to internal combustion engines, such as The spark plug can be installed by drilling a screw hole in the cylinder head separately from the spark plug, or by installing the spark plug through an opening 7 located inside the combustion chamber of the internal combustion engine 3, as shown in FIG.
A spark plug 1 in which a long and narrow combustion pressure propagation passage 7 having a diameter of 1.a is provided in a metal shell 5 up to a pressure sensor 6.
Combustion gas pressure was measured by attaching a

[Problem to be solved by the invention] However, if the above method is adopted, the structure of the internal combustion engine body, which has already been designed most efficiently, will change, or the external shape of the spark plug body will change significantly, causing problems. It became. For example, the former method imposes restrictions on the design around the internal combustion engine, and causes combustion gas to leak from the gap between the cylinder head screw hole and the pressure sensor, resulting in a reduction in output. On the other hand, the shape of the latter method is significantly different from that of conventional spark plugs, and in addition to imposing restrictions on the design around the internal combustion engine 3 as with the former method, there are internal combustion engines in which the spark plug 1 itself cannot be installed. In addition, even if it is possible to attach it, it becomes difficult to attach and detach it, and furthermore, it is necessary to connect pipes or conductive wires (not shown) to the cooling water inlet 8a, outlet 8b, and electrodes 9, 10 of the pressure sensor 6, and various devices for this purpose. Therefore, the area around the internal combustion engine 3 is in a very complicated state, and it takes time to manufacture and repair it.
In addition, in an internal combustion engine 3 equipped with a spark plug 1 like the latter, the propagation passage 7 becomes a so-called quench region where combustion does not occur, leading to an increase in HC during idling, and due to an increase in the clearance volume, the compression ratio decreases. changes, the output of the internal combustion engine 3 decreases,
Furthermore, air column vibration in the propagation path 7 caused deterioration of the S/N ratio. Therefore, although the attachment of pressure sensors to internal combustion engines has great promise for controlling various types of engines, in reality, their use has remained limited to laboratory use. Another problem is that pressure vibrations in a high frequency range such as knocking may be attenuated by absorption depending on the transmission path to the pressure sensor.

Therefore, the inventors of the present invention have conducted extensive studies to apply such useful pressure sensors without adversely affecting conventional internal combustion engines and their surroundings, and as a result, they have found that it is usually not possible to apply sensors with precise measurement performance. It was discovered that by applying a pressure sensor to the center electrode of a spark plug, which had never been considered due to its high voltage, it is possible to make precise measurements without adversely affecting the spark plug itself or other parts. The spark plug with a built-in pressure sensor of the present invention was completed.

[Means for Solving the Problems] That is, the gist of the present invention is to create a plug that ignites fuel in the combustion chamber of an internal combustion engine by causing a discharge between the center electrode and the ground electrode. , the base part to which high voltage is supplied, and the discharging tip part movable along the central axis according to pressure fluctuations on the combustion chamber side, are divided into separate bodies, and the base part and the above part are separated. A pressure sensor having an outer circumferential portion including a pressure-receiving surface made of an electrical conductor is provided between the tip portion and the pressure sensor, with a part of the outer circumferential portion in contact with the base portion and the pressure-receiving surface in contact with the tip portion; The base portion and the tip portion apply a predetermined clamping force to the pressure sensor, and the natural frequency of the vibration system consisting of the pressure receiving surface and the center electrode of the tip portion is increased from 6 to 10K.
Hz, a spark plug with a built-in pressure sensor.

Embodiments of the present invention will be described below based on the drawings.

[Embodiment] FIG. 2 is a longitudinal sectional view of a spark plug 11 showing a first embodiment of the present invention. Here, 12 is a pressure sensor using crystal as a piezoelectric element, and is provided in a center electrode insertion hole 16b in the center of the insulator 16. Among the center electrodes, 13 indicates the base electrode to which a high voltage is supplied, and 14 indicates the distal electrode to which discharge occurs, and the pressure sensor 12 is sandwiched between these two electrodes 13 and 14. . The base end portion 13a of the base electrode 13 is fitted and fixed into the insertion hole 17b of the terminal 17, which is screwed into the hole 16b of the insulator 16. As shown in the figure, the front electrode 14 is inserted into the center electrode insertion hole 16b of the insulator 16 on its outer peripheral surface.
It is supported by coming into contact with the inner surface of and is movably arranged along the central axis. Since the proximal tip 14a of the electrode 14 is in contact with the pressure sensor 12, and the locking protrusion 14b is locked in the step 16e of the insertion hole 16b, the diaphragm actually serves as the pressure receiving surface of the pressure sensor 12. Only 35 deformations can be moved. Therefore, the tip electrode 14 and the diaphragm 35
It is possible for the two to vibrate or move as one. The insulator 16 further has a large diameter central portion 16d.
The distal end portion 16f is covered with the main metal fitting 15 having the ground electrode 15f, and the caulking portion 15a of the metal fitting 15 is attached to the shoulder portion 16g of the insulator 16, and the other caulking portion 1
5c is caulked into the circumferential groove 16c of the insulator 16,
The insulator 16 is fixed to the metal fitting 15, and the gap therebetween is sealed. However, the distal end 16f of the insulator 16 covering the distal electrode 14 and the hand fitting 15
A gap 21 is separated from the threaded portion 15d which is connected to the internal combustion engine. Further, a ring-shaped gasket 20 is provided near the threaded portion 15d to maintain airtightness of the internal combustion engine.

As shown in the enlarged longitudinal cross-sectional view of FIG.
are basically composed of a laminated body sandwiching an anode 33 in which the direction of electromotive force is reversed. The peripheral wall of this laminate is covered with an insulator 34 all around, and its end face 31a on the piezoelectric element 31 side contacts the cathode 36, and its end face 32a on the other piezoelectric element 32 side contacts a conductive diaphragm 35, which is a pressure receiving surface. are in contact. These are housed in a conductive cylindrical case 37, with the cathode 36 in conductive contact with the case 37, and the diaphragm 3
5 is the peripheral edge 35a of the case 37 and the edge 37a of the case 37.
The case 37 serves as a common cathode. Since the outer circumferential portion of the pressure sensor 12 is thus composed of the case 37 and the diaphragm 35, it has electrical conductivity.

A lead wire 18 consisting of a metal wire 18b covered with an insulator 18a is led out from the anode 33.
The spark plug 11 penetrates in an insulated state through a lead-out hole drilled in the center of each of the piezoelectric element 31, the cathode 36, the case 37, the base center electrode 13, and the terminal 17.
It is led outside. This lead wire 18 is arranged up to, for example, a distributor and is connected to an amplifier installed inside or near the distributor. In addition, the case 37 constituting the cathode has its end 1 attached to the center electrode 13 on the base side.
3d, the cathode of the pressure sensor 12 reaches the distributor to which the other end of the high-voltage cable connected to the terminal 17 is connected, where it is connected to the amplifier together with the anode lead 18, and this By connecting the amplifier and the control device, various devices can be controlled based on the signal from the pressure sensor 12.

The pressure sensor 12 is preloaded, that is, a certain amount of clamping force is applied to the pressure sensor 12 in advance in order to increase its sensitivity. The preload is provided by the proximal center electrode 13 pressing the pressure sensor 12 together with the distal center electrode 14 . The preload due to this clamping can be generated, for example, by the screwing pressure of the male threaded portion 17d of the terminal 17. That is, the proximal end portion 13a of the proximal center electrode 13 is inserted into the male threaded portion 17d of the terminal 17. Therefore, when the male threaded portion 17d is screwed into the female threaded portion 16a of the insulator 16, the locking protrusion 14b of the electrode 14 on the distal side locks with the stepped portion 16e of the insertion hole 16b of the insulator 16, thereby preventing movement. Since the pressure sensor 12 is supported by the blocked distal end portion 14a, the pressure sensor 12 can be compressed.

Depending on the material and shape of the center electrode 14 on the front side, the natural frequency at the end surface 32a on the piezoelectric element 32 side, that is, the natural frequency when the electrode 14 and the diaphragm 35 are integrated, is adjusted to 6 to 10 KHz. . This frequency is adapted to the knocking frequency range. The natural frequency is generally expressed by the following formula.

₀ = (1/2π)・√ In this formula, ₀ is the natural frequency of the object, c is its spring constant (N/μm), and m is the resonance mass Kg.
In this embodiment, the pressure receiving surface 3 of the pressure sensor 12 is
The vibration system ahead of 2a, that is, the diaphragm 35
6kHz≦ ₀ ≦ by appropriately selecting c or m of the system in which the and the center electrode 14 on the tip side are integrated.
Set to 10kHz. Generally, most of the materials used as center electrodes have low natural frequencies.
In order to apply it to this embodiment, c is increased or m is decreased by changing the material and shape.

The pressure sensor built-in spark plug 11 configured as described above can be applied as is to internal combustion engines to which conventional spark plugs have been applied.
It can be installed directly into the spark plug installation hole of the cylinder head.

The spark plug 11 of the first embodiment applied to the cylinder head has a high voltage current supplied from the terminal 17 to the center electrode 13 on the base side, the case 37 of the pressure sensor 12, the diaphragm 35, and the center electrode 14 on the front side. The tip portion 14c of the center electrode 14 on the tip side is formed of platinum or conductive ceramic.
By generating a discharge between the ground electrode 15 and the ground electrode 15 facing each other, it functions exactly like a normal spark plug.

When an explosion occurs in the internal combustion engine due to electric discharge, the tip side 14 of the center electrode 14 on the tip side of the spark plug 11 of the first embodiment that is directly exposed in the combustion chamber of the engine
c is subjected to the impact of combustion pressure. At this time, the pressure due to the normal combustion is transmitted to the pressure sensor 12 via the center electrode 14 on the front side, but a vibration system in which the center electrode 14 on the front side and the diaphragm 35 as a pressure receiving surface are integrated is activated. Since the vibration system has a natural vibration of 6 to 10 kHz, the high-frequency pressure vibration when knocking occurs causes resonance, so that the amplitude is amplified and transmitted to the end surface 32a on the piezoelectric element 32 side.

In this way, the end surface 32a of the piezoelectric element 32 in contact with the diaphragm 35 is pressed with a pressure corresponding to the combustion pressure, so that the piezoelectric element generates an electric charge.
Next, another piezoelectric element 3 is connected via the anode 33.
Press 1 to generate a charge. As described above, the pressure signal generated in this manner is transmitted through the lead wire 18 on the positive side to an amplifier located near the distributor, for example, and on the negative side from the case 37 of the pressure sensor 12 to the base side. The signal reaches the center electrode 13, terminal 17, high-voltage cable, and distributor, is connected to an amplifier nearby, and is used as data for various controls. Furthermore, since the pressure sensor 12 is preloaded, detection is extremely sensitive. Here, the pressure sensor 12 and its lead wire 18
are all exposed to high voltage,
Since all have the same potential, even if the center electrode 1 on the base side
Even if a high voltage current for sparking leaks from the lead wire 18 to the metal wire 18b of the lead wire 18, the pressure signal will not be adversely affected unless the pressure signal itself of the pressure sensor 12 is shot.

As described above, the first embodiment can be applied to internal combustion engines in the same way as conventional plugs, and since its outer shape requires almost no changes, it does not cause any trouble to the installation work or to the internal combustion engine itself or peripheral devices. Furthermore, since the pressure sensor is not directly touched by combustion gas, the durability of the piezoelectric element is improved and a forced cooling device such as water cooling is not required. Furthermore, since the vibration system consisting of the diaphragm 35 and the center electrode 14 on the tip side has a high natural frequency of 6 to 10kHz, it can be used not only in the low frequency range, but also in the low frequency range.
Detection of high frequencies such as knocking can be performed with high precision due to resonance, making it possible to detect a wide frequency range.
Furthermore, since the pressure sensor 12 is always preloaded, extremely sensitive measurements can be made. In addition, since the ignition system wiring section such as a high voltage cable is used to extract the pressure signal, the wiring harness can be simplified, and since the ignition system wiring originally has a high insulation resistance, Signal wires such as lead wires of the pressure sensor incorporated therein can maintain high insulation resistance, allowing highly accurate measurements.

Next, FIG. 4 shows a longitudinal cross-sectional view of a main part of a second embodiment of the present invention. The spark plug 41 of the second embodiment has the same structure as the first embodiment except for the center electrode 44 on the front side. In this embodiment, a storage chamber 44a is provided at the center of the center electrode 44 on the front side. This storage chamber 44a is filled with a solid material 44b such as metal, which has an appropriate density and usually has a low density. As a result, the mass m and spring constant c of the center electrode 44 on the tip side are adjusted, and the natural frequency of the combination with the diaphragm 35 is set to 6 to 10 kHz, making it possible to accurately detect pressure at high frequencies. can. Furthermore, in addition to the effects of the first embodiment, the adjustment of the natural frequency has the following effects:
This can be adjusted by changing the amount and properties of the solid 44b sealed in the storage chamber 44a without changing the material or external shape of the front center electrode 44 itself, which affects the discharge performance or lifespan of the spark plug. Never give up. Furthermore, by selecting the solid body 44b that has appropriate thermal conductivity or specific heat, it is possible to prevent the pressure sensor 42 from reaching a high temperature and prevent premature ignition due to overheating of the electrode tip.

Next, FIG. 5 shows a longitudinal cross-sectional view of a main part of a third embodiment of the present invention. The spark plug 51 of the third embodiment has the same structure as the first embodiment except for the center electrode 54 on the front side. In this embodiment, as in the second embodiment, a storage chamber 54a is provided at the center of the center electrode 54 on the front side. An appropriate amount of fluid 54b with an appropriate density is sealed in this storage chamber 54a, and if a smaller amount of fluid 54b is filled than the volume of the storage chamber 54a,
A cavity 54c is formed above the fluid 54b, filled with a vacuum, fluid vapor, air or other gas, or a combination thereof. However, at the combustion temperature, fluid that generates high-pressure gas may expand the front center electrode 54 due to its pressure, which may change the preload to the pressure sensor 52 and affect the measured value. Fluids with low vapor pressure at high temperatures are preferred.

As a result, the mass m of the center electrode 54 on the front side
and the spring constant c is adjusted, and the diaphragm 3
The natural frequency of the combination with 5 is set to 6 to 10 KHz, and high frequency pressure can also be detected with high accuracy. Further, in addition to the effects of the first embodiment, similar to the second embodiment, the natural frequency can be adjusted without changing the material or the outer shape of the center electrode 54 itself on the front side by enclosing it in the storage chamber 54a. Since it can be adjusted by changing the amount and properties of the fluid 54b, it does not affect the discharge performance or life of the spark plug. Further, since the fluid 54b is sealed inside the storage chamber 54a, it is easy to fill the storage chamber 54a and adjust the amount of filling, and the natural frequency can be adjusted more precisely. Furthermore, by selecting the fluid 54b with appropriate heat conduction, specific heat, or heat of vaporization, the pressure sensor 5
Pre-ignition due to high temperature countermeasures and overheating of the electrode tip can be prevented.

[Effects of the invention] As detailed above, according to the spark plug with a built-in pressure sensor of the invention, the pressure sensor whose outer periphery is made of an electrical conductor is attached to the middle part of the high-voltage center electrode divided into two parts. By providing this, it functions similarly to a normal spark plug, and the pressure sensor is not directly exposed to combustion gas. Therefore, the life of the pressure sensor itself is extended, a forced cooling device such as water cooling is not required, and the device does not become unnecessarily complicated. In addition, since the vibration system consisting of the pressure receiving surface of the pressure sensor and the center electrode on the tip side has a natural frequency of 6 to 10 KHz, not only can normal combustion pressure be detected precisely, but also the center electrode Despite its relatively large mass, the vibration system resonates and the signal from the pressure sensor is significantly amplified, making it easy to detect the combustion pressure of abnormal combustion with high frequencies such as knocking. can. Furthermore, since a clamping force is applied to the pressure sensor, highly sensitive measurements can be made. In addition, when a material for adjusting the natural frequency is sealed inside the center electrode on the tip side, by appropriately selecting the material,
It is also possible to adjust the temperature of the pressure sensor by adjusting heat conduction to the pressure sensor, and to prevent premature ignition due to overheating of the electrode tip.

In addition, since a pressure sensor was installed in the center electrode,
Its outer shape is almost the same as that of conventional spark plugs. Therefore, it can be applied without changing the structure of the internal combustion engine. Additionally, a high voltage center electrode can be utilized on one of the pressure sensor leads. In this way, one lead wire can be omitted, contributing to the simplification of the wire harness, and since the pressure sensor and its lead wire are incorporated into the center electrode, which originally has a high insulation resistance, their insulation resistance can be held high.

[Brief explanation of the drawing]

Figure 1 is a vertical sectional view showing the application of a conventional lock that combines a pressure sensor and a spark plug to an internal combustion engine.
2 is a vertical cross-sectional view of the first embodiment of the present invention, FIG. 3 is an enlarged vertical cross-sectional view of the pressure sensor portion thereof, FIG. 4 is a longitudinal cross-sectional view of the main part of the second embodiment of the present invention, and FIG. The figure shows a longitudinal sectional view of the main part of the third embodiment. 11,41,51...Spark plug, 12,4
2, 52... Pressure sensor, 13... Base side center electrode, 14, 44, 54... Tip side center electrode, 15
... Ground electrode, 35 ... Diaphragm (pressure receiving surface), 37 ... Case, 44a, 54a ... Storage chamber, 44b ... Enclosed solid, 54b ... Enclosed fluid.

Claims (1)

[Claims for Utility Model Registration] A plug that ignites fuel in a combustion chamber of an internal combustion engine by discharging between a center electrode and a ground electrode, wherein the center electrode is connected to a base portion to which a high voltage is supplied; A discharging tip part that is movable along the central axis in response to pressure fluctuations on the combustion chamber side; A pressure sensor whose outer periphery is made of an electrical conductor is provided with a part of the outer periphery in contact with the base part and a pressure receiving surface thereof in contact with the tip part, and the pressure sensor is provided with a pressure sensor whose outer periphery is made of an electrical conductor, and the pressure sensor is provided with a pressure receiving surface in contact with the tip part, and a predetermined area is formed by the base part and the tip part. While applying a clamping force of
Hz, a spark plug with a built-in pressure sensor.