JP2001235362A - Piezoelectric knock sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric knock sensor having a small number of parts and a structure without lid easily assembled. SOLUTION: In this piezoelectric knock sensor, vibration sensing members 10, 30 are supported on the bottom of an accommodating recessed part 2 having an upper surface of a metal mounting case 1 opened at the center position, and a structure without lid is formed by filling elastic resin 26 in the accommodating recessed part 2. A synthetic resin mounting screw 25 is integrally formed by molding at a lower end of an output terminal 20 outwardly projected from the mounting case 1, and the vibration sensing members 10, 30 are supported at the center with the synthetic resin mounting screw 25 to electrically connected one side electrode of each of piezoelectric elements 13, 32 to the output terminal 20. Required insulation is obtained by the synthetic resin mounting screw 25 to dispense with an insulation plate and an insulation tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric knock sensor fixed to a cylinder or the like of an internal combustion engine and used for detecting occurrence of knocking in the cylinder.

[0002]

2. Description of the Related Art A piezoelectric knock sensor in which a vibration sensing member having a piezoelectric element is supported at the center on the bottom surface of a storage recess in which the upper surface of a metal mounting case is open, and is supported in the metal mounting case. Have been proposed. As this kind of piezoelectric knock sensor, a non-resonant type piezoelectric knock sensor having a vibration sensing member including an element obtained by laminating a piezoelectric element and a weight, and an annular piezoelectric element attached to one surface of a metal sheet for resonance And a resonance-type piezoelectric knock sensor provided with a vibration sensing unit. In the former non-resonance type piezoelectric knock sensor, the displacement of the piezoelectric element in the thickness direction corresponding to the knocking frequency is caused by the inertial force due to the occurrence of knocking, and a signal voltage is generated between the electrodes. In addition, the latter resonance type piezoelectric knock sensor makes the piezoelectric element satisfactorily vibrate with the occurrence of knocking by matching the natural resonance frequency of the vibration sensing member to the frequency of the knocking vibration wave, and The maximum output is generated.

[0003]

As a piezoelectric knock sensor of this type, a vibration sensing member is supported at its center on a seat surface of a storage recess formed inside a metal mounting case, and an upper portion of the storage recess is provided. In general, the opening is shielded by a connector that also serves as a lid to seal the internal space, and an electrode formed on the upper surface of the piezoelectric element is connected to a metal output terminal inserted into the center of the connector. It is a target. By the way, in such a configuration, due to the looseness of the synthetic resin connector, the airtightness in the case is reduced, moisture or the like intrudes, and an output terminal inserted into the center of the synthetic resin connector, Since the electrode of the piezoelectric element is connected to the electrode by a lead wire, there is a problem that complicated insulation treatment is required and the connection means is complicated. Thus, the present inventors
A vibration sensing member having a piezoelectric element is supported on the bottom surface of a storage recess in which the upper surface of a metal mounting case is opened at a center position, and a sealing resin is filled in the storage recess to seal the vibration sensing member. We proposed a non-lid piezoelectric knock sensor embedded in resin.

[0004] In such a configuration, a connector that also serves as a lid is not required because of the lidless structure, and the vibration sensing member is insulated by filling the housing recess with a sealing resin. It becomes simple, and the connection end of the output terminal connected to the electrode of the piezoelectric element protrudes from the sealing resin, and it is only necessary to connect an external electric circuit to the connection end,
There is an advantage that the connection means also has a simple configuration. In addition, sealing is ensured, and each component is protected from moisture, oil, and the like.

FIG. 4 shows a non-resonant type piezoelectric ceramic sensor having a non-lid structure. Here, a vibration sensing member b disposed in a concave metal mounting case a
Is formed by laminating a piezoelectric element c and a weight d. The mounting screw f is inserted through a center hole e formed in the vibration sensing member b, and screwed into a screw hole k formed in the bottom of the mounting case a. The lower end of the tubular output terminal g is sandwiched between the head of the mounting screw f and the weight d, thereby projecting the connection end of the output terminal g out of the mounting case a. Is injected with a sealing resin.

In such a configuration, however, insulation between the mounting screw f and the output terminal g becomes a problem. Therefore, an insulating plate h is inserted between the output terminal g and the screw head of the mounting screw f. Further, an insulating tube i is inserted around the mounting screw f in the center hole e of the vibration sensing member b, thereby preventing a short circuit between the front and back electrodes of the piezoelectric element c. For this reason, although the number of components is reduced by adopting the lidless structure as compared with the conventional lid structure, such a component is required for the insulation treatment, and the problem remains. SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric knock sensor having a lidless structure that has a smaller number of components and is easy to assemble.

[0007]

According to the present invention, there is provided a piezoelectric knock sensor having a metal mounting case in which a vibration sensing member having a piezoelectric element is held in a housing recess filled with an elastic resin. An output terminal protruding outward is screwed to the mounting case in an insulated state, and the vibration sensing member is sandwiched between a holding protrusion formed on a peripheral surface of the output terminal and the mounting case. The piezoelectric knock sensor is characterized in that one of the electrodes held in the housing recess and one of the electrodes formed on the piezoelectric element is electrically connected to the output terminal. Here, in the above-described configuration, in addition to the non-resonant type piezoelectric knock sensor in which the vibration sensing member is formed by laminating a piezoelectric element and a weight, the vibration sensing member is configured such that the piezoelectric element is attached to one surface of a metal sheet for resonance. The present invention can be applied to a resonance type piezoelectric knock sensor.

In this configuration, since the output terminal is screwed into the mounting case in an insulated state, insulation between the mounting screw and the output terminal and insulation between the inner surface of the center hole of the vibration sensing member and the mounting screw are provided. And no insulating plate or insulating tube is required. To screw the mounting case in an insulated state in this manner, a synthetic resin mounting screw is integrally formed at the lower end of the output terminal by molding, and the synthetic resin mounting screw is
It is preferable to insert the screw into the center hole formed in the vibration sensing member and screw it into the screw hole formed in the bottom surface of the case. Further, since the vibration sensing member is insulated and waterproofed by the elastic resin, it is possible to adopt a coverless structure.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a non-resonant type piezoelectric knock sensor S1 for an internal combustion engine according to the present invention. The piezoelectric knock sensor S1 has a vibration sensing member 10 disposed in a concave metal mounting case 1. Here, the structure of the metal mounting case 1 will be described.
Mounting bolt 2 screwed into the cylinder wall of the engine at the center of the outer bottom
Is protruding. A storage recess 3 having an upper opening is formed in the inside thereof. Further, a screw hole 5 is formed in the seat bottom 4 of the storage recess 3 along the center line of the mounting bolt 2.
Are formed.

In the screw hole 5, the vibration sensing member 10 is supported at the center by the synthetic resin mounting screw 25 of the present invention.
The vibration sensing member 10 has a center hole 16 formed by laminating a weight 14 also having an insertion hole formed on the upper surface of an annular piezoelectric element 13 having an insertion hole formed at the center so that the center hole 16 is concentric with the screw hole 5. And is held on the synthetic resin mounting screw 25 as described above.

Next, the main part of the present invention will be described. FIG.
As shown in enlarged form, the mounting screw 25 made of synthetic resin is integrally provided at the lower end of the output terminal 20 in the form of a straight rod by molding. The output terminal 20 has an upper end serving as a connection end 21 protruding from the metal mounting case 1, and further has a large-diameter flange-shaped holding projection 22 on the lower end side peripheral surface.
Is formed, and a connecting protrusion 23 provided with engaging teeth is formed on a peripheral surface on the lower end side from the holding protrusion 22 to form a straight rod. The connecting protrusion 23 is integrally formed with a synthetic resin mounting screw 25 by molding. The synthetic resin mounting screw 25 is made of a hard resin such as PPS resin, and has a screw formed on a peripheral surface thereof.

Then, as described above, the synthetic resin mounting screw 25 is inserted from the center hole 16 of the vibration sensing member 10 and screwed and tightened into the screw hole 5, whereby the holding projection 22 is interposed via the weight 14. To the upper electrode of the piezoelectric element 13, and the lower electrode of the piezoelectric element 13 is brought into contact with the seat bottom 4 to ground the body. At this time, the inner surface of the piezoelectric element 13 is insulated by the mounting screw 25 made of synthetic resin, and the output terminal 20 is not grounded.

In this configuration, after the vibration sensing member 10 is mounted in the housing recess 3, the housing recess 3 is filled with a sealing resin 26 such as silicon. Then, only the connection end 21 of the output terminal 20 protrudes upward from the opening of the storage recess 3. As a result, the vibration sensing member 10 is sealed in the storage recess 3, and the electrodes on the front and back surfaces of the piezoelectric element 13 are insulated and protected by the synthetic resin mounting screws 25 and the sealing resin 26.

In this configuration, since the synthetic resin mounting screw 25 is formed integrally with the output terminal 20, unlike the prior art configuration shown in FIG. 4, an insulating plate and an insulating tube are not required.

In such a configuration, the piezoelectric knock sensor S1 is screwed by a mounting bolt 2 to a place where knocking vibration propagates, such as a cylinder block. And
When the knocking occurs, the vibration sensing member 10, which is held at the center by the synthetic resin mounting screw 25, generates a strain in the thickness direction due to its inertial force, and a potential difference occurs between the electrodes on the front and back surfaces of the piezoelectric element 13. Thus, an output signal is extracted from the connection end 21 of the output terminal 20 connected to the upper electrode of the piezoelectric element 13. Then, the piezoelectric knock sensor S1
As a result, the knocking vibration is detected by extracting an output signal accompanying the knocking vibration, thereby taking measures to prevent the knocking vibration by means such as controlling the ignition timing of the fuel.

FIG. 3 shows a resonance type piezoelectric knock sensor S2 for an internal combustion engine according to the present invention. Here, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted. The piezoelectric knock sensor S2 is configured by disposing a resonance type vibration sensing member 30 in a concave metal mounting case 1. Here, an annular seat 34 is formed concentrically with the screw hole 5 in the seat bottom 4 of the storage recess 3 of the metal mounting case 1, and the vibration sensing member 30 is disposed on the annular seat 34. .

The vibration sensing member 30 has a piezoelectric element 32 adhered to an upper surface of a resonance metal thin plate 31, and the lower surface thereof is held by an annular seat 34. The central hole 33 is formed by through holes formed in the metal thin plate 31 and the piezoelectric element 32, respectively.
Is formed. Then, an annular washer 35 is provided on the lower surface of the holding protrusion 22, and a synthetic resin mounting screw 25 integrally formed on the lower end side of the holding protrusion 22 is inserted into the center hole 33, and the screw hole 5 is formed. To the vibration sensing member 30
Is clamped between the washer 35 and the annular seat 34. In this fixed state, the metal mounting case 1 is filled with the sealing resin 26. Then, the connection end 21 of the output terminal 20 is sealed with the sealing resin 2.
6 protrudes outward.

Here, it is assumed that the sealing resin 26 has such an elasticity that does not hinder the vibration of the vibration sensing member 30 when the vibration occurs due to the occurrence of knocking. Even in the resonance type piezoelectric knock sensor S2 having such a configuration, similarly to the non-resonance type piezoelectric knock sensor S1 of FIG. 1, no insulating material is required and the number of components is reduced.

In such a configuration, the resonance type piezoelectric knock sensor S2 for an internal combustion engine is screwed by a mounting bolt 2 to a place where knocking vibration propagates, such as a cylinder block. When the knocking occurs, the center is held by the synthetic resin mounting screw 25 and the sealing resin 26
Vibration sensing member 30 sealed to such an extent that it is not impeded by
The metal thin plate 31 is bent up and down, and a potential difference is generated between the electrodes on the front and back surfaces of the piezoelectric element 32, and an output signal is taken out from the output terminal 20 connected to the upper electrode of the piezoelectric element 32. At this time, the resonance frequency and the knocking frequency of the vibration sensing member 30 are set so as to match in advance,
When knocking occurs, resonance occurs in a bending vibration mode in which the peripheral edges of the washer 35 and the annular seat portion 34 are vibrating nodes, and a maximum output is generated from the piezoelectric element 32. The output signal accompanying the knocking vibration is taken out by the resonance type piezoelectric knock sensor S2 for the internal combustion engine.
The knocking vibration is detected, so that measures to prevent the knocking vibration are taken by means such as controlling the ignition timing of the fuel.

[0020]

The piezoelectric knock sensors S1, S2 according to the present invention.
As described above, the vibration sensing member is supported at the center position on the bottom surface of the storage recess where the upper surface of the metal mounting case is opened, and the storage recess is filled with a sealing resin to form a non-lid structure. At the lower end of the output terminal projecting outward from the mounting case, a synthetic resin mounting screw is integrally formed by molding, and the vibration sensing member is supported at the center by the synthetic resin mounting screw. Is electrically connected to the output terminal, the required insulation is provided by the synthetic resin mounting screw, and an insulating material such as an insulating plate or an insulating tube is not required. For this reason, the number of components can be reduced as much as possible, and there is an excellent effect that an inexpensive piezoelectric knock sensor can be provided easily.

[Brief description of the drawings]

FIG. 1 shows a non-resonant piezoelectric knock sensor S1 according to the present invention.
It is a vertical side view.

FIG. 2 is an enlarged side view of the output terminal 20 in which a mounting screw 25 made of synthetic resin is integrally formed at a lower end.

FIG. 3 is a vertical sectional side view of a resonance type piezoelectric knock sensor S2 according to the present invention.

FIG. 4 is a longitudinal side view of a piezoelectric resonance knock sensor according to the prior art.

[Explanation of symbols]

 S1, S2 Piezoelectric resonance type knock sensor 1 Metal mounting case 5 Screw hole 10 Vibration sensing member 13 Piezoelectric element 14 Weight 16 Center hole 20 Output terminal 21 Connection end 23 Connecting protrusion 25 Synthetic resin mounting screw 26 Sealing resin 30 Vibration sensing member 31 Thin metal plate 32 Piezoelectric element 33 Center hole

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Claims (3)

[Claims] 1. A piezoelectric knock sensor having a metal mounting case in which a vibration sensing member having a piezoelectric element is held in a housing recess filled with an elastic resin, wherein an output terminal projecting outward from the mounting case is provided. While being screwed to the mounting case in an insulated state, the vibration sensing member is held in the housing recess by being sandwiched between a holding protrusion formed on the peripheral surface of the output terminal and the mounting case. A piezoelectric knock sensor, wherein one electrode formed on the piezoelectric element is electrically connected to the output terminal. 2. The piezoelectric knock sensor according to claim 1, wherein the vibration sensing member has a non-resonant structure in which a piezoelectric element and a weight are laminated. 3. The piezoelectric knock sensor according to claim 1, wherein the vibration sensing member has a resonance type structure in which a piezoelectric element is attached to one surface of a metal sheet for resonance.