JPH08292088A - Knocking detector - Google Patents

Abstract

PURPOSE: To provide a knocking detector that is able to reduce the sharpness in the resonance output of a piezoelectric element. CONSTITUTION: A vibration detecting body 7 consisting of a vibrating plate 9 and a piezoelectric element 8 is clamped tight to a projection 2c of a housing 2. A conductive elastic member 12 with a specified resistance value by a tip part 6a of a terminal 6 is forcibly pressed to the vibration detecting body 7, whereby an electrode at the output side of the piezoelectric element 8 and the terminal 6 are electrically connected to each other via the conductive elastic member 12. On the other hand, the tip of a cylindrical part 12b of the conductive elastic member 12 is pressed to a bottom part 2b of the housing 2 or at the grounding side of the piezoelectric element 8. Accordingly, since the elastic member 12 connected in parallel with the piezoelectric element 8 functions as load resistance, the sharpness Q in resonance output of the element 8 is electrically reduced. Likewise, since the elastic member 12 being pressed by the vibration detecting body 7 functions as a damper member, vibrations in the vibration detecting body 7 is absorbed to some extent and thereby the sharpness Q is mechanically abated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a knocking detection device, for example, an internal combustion engine (hereinafter referred to as "engine").
The present invention relates to a knocking detection device used for ignition timing control.

[0002]

2. Description of the Related Art Conventionally, it has been known to use a knocking sensor for knocking detection performed by engine knock control. Many of these knocking sensors are attached to the cylinder block of the engine, which is a vibrating body, and the vibration due to the knock of the engine transmitted to the cylinder block is converted into an electric signal by the piezoelectric element of the knocking sensor and output to the electronic control unit etc. are doing. A resonance type knocking sensor is known as a typical knocking sensor.

Generally, in a resonance type knocking sensor, the vibration frequency of a piezoelectric element generated due to knocking is maximized by matching the resonance frequency of a vibration detecting body composed of a vibration plate and a piezoelectric element with the knocking frequency. ing. The resonance output generated by the vibration of the piezoelectric element is taken out to the outside through a terminal connected to an electrode provided on the surface of the piezoelectric element. In addition, the actual exploitation Sho 62-128331
The publication discloses a knock sensor in which a brush electrically connected to one end of a terminal is provided and the tip of the brush is elastically contacted with the upper surface of the piezoelectric ceramic to electrically connect the piezoelectric element and the terminal. ing.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Saikai 62-12
According to the knock sensor disclosed in Japanese Patent No. 8331, the brush absorbs the vibration of the knock sensor to maintain the electrical connection between the piezoelectric element and the terminal. However, when absorbing the vibration in this way, the electrode provided on the surface of the piezoelectric element is rubbed by the brush at the contact position between the brush and the piezoelectric element, so that there is a problem that the electrode is worn due to long-term use.

Further, as described above, in the resonance type knocking sensor, the vibration of the piezoelectric element caused by the occurrence of knocking is maximized, so that the sharpness Q of the resonance output is obtained.
Has a problem that the band of the knocking frequency that can be detected is narrowed. An object of the present invention is to provide a knocking detection device with high reliability of electrical connection between a terminal and a piezoelectric element.

Another object of the present invention is to provide a knocking detection device capable of electrically reducing the sharpness Q of the resonance output of the vibration detector. Another object of the present invention is to provide a knocking detection device capable of mechanically reducing the sharpness Q of the resonance output of the vibration detector.

[0007]

In order to solve the above-mentioned problems, the knocking detection device according to claim 1 of the present invention comprises:
A housing having a protrusion on the side opposite to the contact surface with the vibrating body,
A vibration detector, which is composed of the diaphragm and a piezoelectric element and is fixed to the protrusion, a terminal for taking out an output signal of the piezoelectric element to the outside, and a terminal made of a conductive elastic material having a predetermined resistance value. It is arranged between the vibration detecting body and pressed against the vibration detecting body by the terminal, a part of which is electrically connected to one pole of the piezoelectric element and the other part is connected to the other pole of the piezoelectric element. And a conductive elastic member that is electrically connected.

According to a second aspect of the present invention, there is provided the knocking detection device according to the first aspect, wherein the conductive elastic member has a double structure including a central portion and an outer portion of the central portion. The part is a low conductive part and the outer part is a high conductive part. The knocking detection device according to a third aspect is the knocking detection device according to the first aspect, wherein the conductive elastic member has a convex portion that is fitted into the housing.

The knocking detection device according to a fourth aspect is the knocking detection device according to the first aspect, wherein the conductive elastic member is made of conductive rubber.

[0010]

According to the knocking detection device of the first aspect of the present invention, the conductive elastic member having a predetermined resistance value is electrically connected to one pole and the other pole of the piezoelectric element. Therefore, since the conductive elastic member is connected in parallel with the piezoelectric element as a load resistance, the sharpness Q of the resonance output of the vibration detector can be electrically reduced. Further, since the conductive elastic member is pressed against the vibration detecting body, the sharpness Q of the resonance output of the vibration detecting body is mechanically reduced by buffering the vibration of the vibration detecting body by using this elastic member as a damper member. can do.

According to the knocking detection device of the second aspect of the present invention, since the conductive elastic member is formed in the double structure having the high conductive portion and the low conductive portion, vibration occurs through the high conductive portion. The resonance output of the detector can be extracted to the terminal with high sensitivity. Also, by connecting a part of the low conductive part to one pole of the piezoelectric element and electrically connecting the other part of the low conductive part to the other pole of the piezoelectric element, the low conductive part functions as a load resistance. Since it is connected in parallel with the piezoelectric element,
It is possible to electrically reduce the sharpness Q of the resonance output of the vibration detector.

According to the knocking detection device of the third aspect of the present invention, since the convex portion of the conductive elastic member is fitted in the housing, the conductive elastic member is fitted to a predetermined position of the housing by this fitting portion. It is possible to make sure contact. Moreover, the positioning of the conductive elastic member is easy. According to the knocking detection device of the fourth aspect of the present invention, since the conductive elastic member is made of conductive rubber, the vibration of the knocking detection device is absorbed by the conductive elastic member and the contact reliability between the terminal and the vibration detection body is improved. It is possible to improve the sex. Further, this conductive rubber has an effect of preventing abrasion of the terminal and the vibration detecting body.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A knocking detecting device according to a first embodiment of the present invention is shown in FIGS. As shown in FIG. 1, the knocking detection device 1 includes a housing 2, a cover 4, a terminal 6, a vibration detection body 7, and a conductive elastic member 12, and is a space defined by the housing 2 and the cover 4. The vibration detector 7 and the conductive elastic member 12 are housed in the portion 16. Then, the end portion of the terminal 6 that is insert-formed in the housing 2 has the conductive elastic member 1
It is electrically connected to the vibration detector 7 via 2.

The housing 2 made of metal, for example, is formed in a T-shape in vertical cross section, and a male screw portion 2a is formed on the outer peripheral wall of a small-diameter columnar portion located below in FIG. The male screw portion 2a can be screwed into a female screw portion of a mounting hole 31 formed in the cylinder block 30 of the engine, which is a vibrating body. By mounting the housing 2 on the cylinder block 30, vibration from the cylinder block 30 will be described later. Is transmitted to the vibration detector 7. On the other hand, a concave portion having a bottom portion 2b is formed in the upper portion of the large-diameter columnar portion of the housing 2 located above in FIG. A cylindrical protrusion 2c is formed in the center of the bottom 2b, and the vibration plate 9 of the vibration detector 7 is fixed to the upper end surface of the protrusion 2c.

The vibration detector 7 for detecting vibration is a thin disk-shaped diaphragm 9 and a thin disk-shaped member having an outer diameter smaller than the outer diameter of the diaphragm 9, and silver electrodes are formed on both surfaces. And a piezoelectric element 8. The electrode formed on the diaphragm 9 side of the piezoelectric element 8 is used as an electrode on the ground side, and the electrode formed on the side opposite to the diaphragm 9 is used as an electrode on the output side. A communication hole 9a is formed at the center of the diaphragm 9, and a communication hole 8a having a larger diameter than the communication hole 9a is formed at the center of the piezoelectric element 8. The piezoelectric element 8 and the diaphragm 9 are
The piezoelectric element 8 and the vibrating plate 9 may be formed by a conductive adhesive such as a conductive paste or by thinning the adhesive layer to form unevenness on the surface.
When they are conducted, they are concentrically bonded to each other by a non-conductive adhesive. On the other hand, the upper end of the above-mentioned protrusion 2c is connected to the central portion of the diaphragm 9 on the side opposite to the joint surface by ring projection welding. This allows
The ground side electrode of the piezoelectric element 8 is electrically connected to the housing 2 via the diaphragm 9.

The conductive elastic member 12 is made of a conductive elastic material such as silicon rubber containing carbon and has a disk portion 12a.
A cylindrical portion 12b as a convex portion is formed to extend from the center of the. The side surface of the bottom portion 2b of the disk portion 12a is in contact with the electrode on the output side near the peripheral portion of the communication hole 8a. On the other hand, the column portion 12b is loosely inserted into the communication hole 8a and the communication hole 9a, and is inserted into the insertion hole 2f surrounded by the protrusion 2c.
Is fitted. The tip of the column 12b is the bottom 2
touching b. As a result, the load resistance corresponding to the predetermined resistance value of the conductive elastic member 12 is connected between the output side electrode of the piezoelectric element 8 and the ground side electrode.

The cover 4 made of resin or the like is composed of a bottomed cylindrical connector portion 4a which opens upward in FIG. 1, and a container-shaped portion 4b which shares a bottom portion with the connector portion 4a. A space 16 having a convex vertical cross section is formed in the container-shaped portion 4b. The vertical cross-sectional shape of the space portion 16 is a convex shape because the vibration detection body 7 housed in the space portion 16 is
This is to make the volume of the space occupying the upper side of the conductive elastic member 12 as small as possible. As a result, the height of the knocking sensor 1 can be reduced, so that the knocking sensor 1 can be downsized.

A terminal 6 is insert-molded at the bottom shared by the connector portion 4a and the vessel-shaped portion 4b.
One end of the terminal 6 extends into the connector portion 4a. The other end of the terminal 6 extends into the space 16 and the tip 6a is bent so as to extend parallel to the disc 12a. When the cover 4 is attached to the housing 2, the tip portion 6a is pressed against the disk portion 12a, so that the output side electrode of the piezoelectric element 8 and the terminal 6 are electrically connected via the conductive elastic member 12. . Also,
At this time, the tip end of the column portion 12b is elastically pressed against the bottom portion 2b, so that the terminal 6 and the housing 2 are electrically connected via the conductive elastic member 12 as a load resistance. As a result, as shown in FIG. 2, the piezoelectric element 8 and the conductive elastic member 12 as a load resistor are connected in parallel between the terminal 6 and the housing 2 on the ground side.
The voltage generated from the piezoelectric element 8 is sent from this terminal 6 to an electronic control unit or the like (not shown).

Further, as shown in FIG. 1, the vessel-shaped portion 4b.
A flange portion 4c extending outward in the radial direction is formed at the end portion on the opening side. An annular groove 4d into which the O-ring 10 can be fitted is formed on the radially outer portion of the lower end surface of the container-shaped portion 4b. When the cover 4 is placed on the housing 2 and caulked by the caulking portion 2d, the O-ring 10 is sandwiched between the circumferential portion 2e and the outer peripheral portion 4e. The O-ring 10 prevents water, foreign matter, and the like from entering the space 16 through the gap between the cover 4 and the housing 2.

Next, a method of assembling the knocking detection device 1 will be described with reference to FIG. The housing 2 is formed by a forging process or the like so that the vertical cross-section has a T shape. Then, by a cutting process or the like, the male screw portion 2a is formed on the outer peripheral wall of the small diameter portion.
Is formed, and the bottom portion 2b is formed so that the protruding portion 2c remains on the upper portion of the large diameter portion. The vibration detector 7 is assembled in a separate process in which the end faces of the piezoelectric element 8 and the diaphragm 9 are joined together with an adhesive. The assembled vibration detector 7 is placed on the upper end of the protrusion 2c with the diaphragm 9 side facing the bottom 2b direction. Then, the welded portion 9b of the diaphragm 9 that contacts the upper end of the protrusion 2c is subjected to ring projection welding.
As a result, the vibration detector 7 is fixed to the housing 2. Then, the cylindrical portion 12b of the conductive elastic member 12 is fitted into the insertion hole 4d through the communication hole 8a and the communication hole 9a.

A terminal 6 is insert-molded on the cover 4 which is resin-molded in a separate process. Also,
An O-ring 10 is fitted in the groove 4d. The vibration detecting body 7 and the conductive elastic member 12 have a container-shaped portion 4 of the cover 4.
When the cover 4 is placed on the housing 2 so as to cover the housing b, the tip 6a of the terminal 6 is locked to the upper surface of the disk 12a. Then, when the flange portion 4c is pressed to the housing 2 side by caulking and fixing by the caulking portion 2d, the tip end portion 6a is pressed against the conductive elastic member 12 by the force acting in the axial direction by the caulking and fixing. For this reason, the vibration detecting member 7 is projected by the disc portion 12a.
It is elastically pressed to the side. Further, the tip of the column portion 12b is elastically pressed against the bottom surface 2b. Circumferential part 2e and outer peripheral part 4
A liquid-tight seal is made between e and O by an O-ring 10.

Next, the operation of the knocking detection device 1 will be described with reference to FIG.
It will be described based on. Since the cylinder block 30 generates vibration according to the ignition timing of the engine, the knocking detection device 1 mounted on the cylinder block 30
This vibration is transmitted to. Then, the vibration transmitted to the knocking detection device 1 is transmitted to the piezoelectric element 8 via the male screw portion 2a of the housing 2, the projection portion 2c and the vibration plate 9, and the piezoelectric element 8 which has received the vibration responds to the applied stress. Generate a voltage signal. The voltage signal generated in the piezoelectric element 8 is output to the terminal 6 via the conductive elastic member 12.

According to the knocking detection device 1 of the first embodiment, the conductive elastic member 12 having a predetermined resistance value and the piezoelectric element 8 are connected in parallel between the ground side and the output side. As a result, since the conductive elastic member 12 serves as a load resistance, the sharpness Q of the resonance output of the vibration detector 7 is electrically reduced. Therefore, it is possible to improve the S / N ratio with respect to the variation of the vibration frequency that is the detection target.

Further, since the vibration detecting member 7 is pressed toward the protrusion 2c by the conductive elastic member 12, the conductive elastic member 12 dumps the vibration of the vibration detecting member 7 to cause the vibration detecting member 7 to move. The sharpness Q of the resonance output is mechanically reduced. Therefore, it is possible to improve the S / N ratio with respect to the variation of the vibration frequency that is the detection target. Also,
Since the terminal 6 is elastically pressed against the piezoelectric element 8 via the conductive elastic member 12, the conductive elastic member 12
The resilience has the effect of absorbing the vibration of the knocking detection device 1 and improving the contact reliability between the terminal 6 and the piezoelectric element 8. Since the conductive elastic member 12 is arranged between the terminal 6 and the piezoelectric element 8, the electrode of the piezoelectric element 8 is prevented from being rubbed by the terminal 6 and worn.

Further, by covering the housing 2 with the cover 4 and caulking and fixing it, the terminal 6 is pressed onto the conductive elastic member 12, whereby the terminal 6 and the piezoelectric element 8 are electrically connected. Therefore, since a soldering operation for connecting the terminal and the piezoelectric element is not required, the knocking detection device 1 can be easily manufactured. Further, in the conductive elastic member 12, the cylindrical portion 12b as a convex portion is loosely inserted into the communication hole 8a and the communication hole 9a and fitted into the insertion hole 2d, so that the conductive elastic member 12 can be easily positioned. is there.

As the value of the load resistance of the conductive elastic member 12, for example, the size of the piezoelectric element 8 is about 15 in diameter.
mm x thickness about 0.5 mm, resonance center frequency is about 7 kHz
In this case, the resonance gain is about 25 when the voltage when there is no signal is 0 dB.
In order to obtain dB, it is desirable to set the load resistance to about 3 kΩ. (Second Embodiment) A second embodiment of the present invention is shown in FIG. The second embodiment is an example in which the shape of the conductive elastic member is different from that of the first embodiment.

The conductive elastic member 112 made of a conductive elastic material such as silicon rubber containing carbon is disk-shaped,
The vibration detection body 7 fixed to the protrusion 2 c of the housing 2 is placed on the center portion of the vibration detection body 7. Since the conductive elastic member 112 has a smaller amount of carbon added to the silicon rubber in the central portion 112b than in the outer peripheral portion 112a, the outer peripheral portion 112a has high conductivity and the central portion 112b has a higher electric conductivity than the outer peripheral portion 112a. And low conductivity. The composition boundary 112c between the outer peripheral portion 112a and the central portion 112b is provided on the outer peripheral side of the communication hole 8a of the piezoelectric element 8. The outer portions of the outer peripheral portion 112a and the central portion 112b are electrically connected to the output side electrode of the piezoelectric element 8.

The cover 104 has a connector portion 104a and a container-shaped portion 1 which are formed so as to share the bottom portion 104c.
04b, and the terminal 106 is insert-molded on the bottom portion 104c. An insertion hole 104 into which the conductive elastic member 112 can be fitted is formed on the lower surface of the bottom portion 104c in FIG.
d is formed. One end 1 of the terminal 106
06a extends into the connector portion 104a, and the other end portion 106b extends along the bottom surface 104e of the insertion hole 104d. The configuration of the other parts is substantially the same as that of the first embodiment.

When the housing 2 is covered with the cover 104,
The bottom surface 104e of the cover 104 is locked to the top surface of the conductive elastic member 112 via the other end 106b of the terminal 106. Then, when the caulking portion 2d is caulked and fixed so as to press the flange portion 104f toward the housing 2, the bottom portion 104e is sandwiched by the other end portion 106b.
Is pressed by the conductive elastic member 112, and the vibration detecting body 7 is elastically pressed by the conductive elastic member 112 toward the protrusion 2c side. Therefore, the vibration of the vibration detector 7 is buffered, so that the sharpness Q of the resonance output of the piezoelectric element 8 can be mechanically reduced.

Further, the conductive elastic member 112 is elastically deformed by the pressing force generated by the caulking and fixing, so that the bottom portion 2b side of the central portion 112b is pushed into the communication holes 8a and 9a. Since the diameter of the communication hole 8a is larger than the diameter of the communication hole 9a, the central portion 112b comes into contact with the diaphragm 9 in the vicinity of the communication hole 9a, so that the central portion 112b and the piezoelectric element 8 are grounded. A certain vibration plate 9 is electrically connected. On the other hand, as described above, since the outer portions of the outer peripheral portion 112a and the central portion 112b are electrically connected to the output side electrode of the piezoelectric element 9, the central portion is provided between the output side electrode of the piezoelectric element 8 and the ground side electrode. Part 112
This means that the load resistance corresponding to the predetermined resistance value of b is connected. By this load resistance, the sharpness Q of the resonance output of the piezoelectric element 8 can be electrically reduced. On the other hand, since the terminal 106 and the output-side electrode of the piezoelectric element 8 are electrically connected via the highly conductive outer peripheral portion 112a, the resonance output of the piezoelectric element 8 is sensitive to the terminal 1.
It can be taken out from 06.

According to the knocking detection device 101 of the second embodiment, the other end 106b is pressed against the conductive elastic member 112 while being supported by the bottom surface 104e, and the bottom surface 1
Since the whole 04e is pressed against the conductive elastic member 112, there is an effect that the terminal 106 and the conductive elastic member 112 can be brought into stable and reliable contact. Further, since part of the thickness of the conductive elastic member 112 and the other end 106b are housed in the insertion hole 104d, the knocking detection device 101 can be further downsized in the thickness direction.

In the knocking detection device 1 of the first embodiment shown in FIG. 1 as well, the disc portion 1 of the conductive elastic member 12 is used.
The outer peripheral side of the communication hole 8a of 2a is a highly conductive portion, and the inner peripheral side of the communication hole 8a of the disc portion 12a and the columnar portion 12 are formed.
By making b a low conductive portion, the resonance output of the piezoelectric element 8 can be taken out from the terminal 6 with high sensitivity through this high conductive portion, as in the knocking detection device 101 of the second embodiment.

In the first and second embodiments, the silicon rubber containing carbon is used as the conductive elastic member, but the conductive elastic material forming the conductive elastic member has a predetermined resistance value. These types of conductive rubber may be used. As such a material, in addition to silicon rubber containing carbon, for example, other types of rubber containing carbon can be cited.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a knocking detection device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a knocking detection device according to a first exemplary embodiment of the present invention.

FIG. 3 is a vertical sectional view of a knocking detection device according to a second exemplary embodiment of the present invention.

[Explanation of symbols]

 1 Knocking Detection Device 2 Housing 2c Protrusion 4 Cover 6 Terminal 6a Tip 7 Vibration Detector 8 Piezoelectric Element 9 Vibration Plate 12 Conductive Elastic Member 12a Disk Part 12b Column (Convex) 10 O-ring 30 Cylinder Block (Vibration) Body) 104 cover 104d insertion hole 104e bottom surface 106 terminal 112 conductive elastic member 112a outer peripheral portion (high conductive portion) 112b central portion (low conductive portion)

Claims (4)

[Claims] 1. A housing having a protruding portion on the side opposite to the contact surface with the vibrating body, a vibration detecting body comprising the vibrating plate and a piezoelectric element and fixed to the protruding portion, and an output signal of the piezoelectric element to an external device. And a terminal made of a conductive elastic material having a predetermined resistance value, disposed between the terminal and the vibration detecting body and pressed by the vibration detecting body by the terminal, and a part of the piezoelectric element 2. A knocking detection device, comprising: a conductive elastic member electrically connected to one pole of the piezoelectric element and the other part thereof electrically connected to the other pole of the piezoelectric element. 2. The conductive elastic member has a double structure of a central portion and an outer portion of the central portion, wherein the central portion is a low conductive portion and the outer portion is a high conductive portion. The knocking detection device according to claim 1, wherein: 3. The knocking detection device according to claim 1, wherein the conductive elastic member has a convex portion that is fitted into the housing. 4. The knocking detection device according to claim 1, wherein the conductive elastic member is made of conductive rubber.