JP2003066062A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor capable of flatly enhancing a sensor output with a simple structure. SOLUTION: This acceleration sensor comprises a housing 10 having a screwing part 11 screwable to an exciting body, a support shaft part 20 fixable by screwing to the element mount surface 12a of a bottomed hole 12 formed in the housing 10, and a vibration detection part 30 comprising a PZT element 40 axially displaceably and axially inseparably installed to the support shaft part 20 and a weight 50 put on the PZT element 40. The PZT element 40 abuts on a circumferential part (corresponding to a center-of-gravity diameter ΦD) where the inside and outside masses of the weight 50 are mutually matched).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting knocking vibration of an internal combustion engine with a piezoelectric element.

[0002]

2. Description of the Related Art As an acceleration sensor, there is known an acceleration sensor in which a piezoelectric element having a polarization axis in the thickness direction and a weight are laminated and fixed to a vibrating body which is an object to be detected by a screwing member such as a bolt. .

In recent years, due to the increase in output of internal combustion engines, it has become necessary to detect knocking in a high rotation range. Therefore, it is desired that the acceleration sensor has a flat sensor output and a high output in the used frequency range.
On the other hand, from the viewpoint of increasing the sensor output, there is a so-called resonance type acceleration sensor that uses the resonance of the piezoelectric element and the diaphragm, but there is a problem that it can be applied only near the resonance frequency as a detectable frequency range. On the other hand, a so-called non-resonant type acceleration sensor has a small output, and thus a shield wire is indispensable.

As a countermeasure against this, there is a technique in which the resonance frequency of the piezoelectric element, the weight, and the housing holding the weight is increased by improving the holding shape of the housing (JP-A-9-508699).

According to Japanese Patent Publication No. 9-508699,
Disclosed is an acceleration sensor in which a vibration detection unit including an annular piezoelectric element and a weight stacked coaxially on the piezoelectric element is fitted into the outer periphery of a cylindrical base portion having a flange portion at the lower end. , Unnecessary unnecessary vibration caused by the contact surface of the flange portion fixed to the vibrating body is prevented.

[0006]

In the conventional configuration, it is assumed that the output is increased only near a specific frequency, or that the output obtained by the vibration detecting portion of the acceleration sensor is amplified by an amplifier to ensure a high output. The resonance frequency, which is a factor that hinders the realization, is only increased.

Therefore, consideration has not been sufficiently given to increase the sensor output in a flat manner with a simple structure.

The present invention has been made in consideration of such circumstances, and therefore, an object thereof is to provide an acceleration sensor capable of producing a flat and high sensor output with a simple structure.

[0009]

According to claim 1 of the present invention, a housing having a screwing portion that can be screwed into a vibrating body and a device mounting surface of a bottomed hole formed in the housing are screwed together. A support shaft portion that can be fixed, a piezoelectric element that is axially displaceable on the support shaft portion and that cannot be detached in the axial direction, and a vibration detection portion that is a weight that is stacked on the piezoelectric element are provided. Abutting on the circumference where the outer and outer masses match.

The sensor output can be increased by increasing the mass of the weight and increasing the mass, or by increasing the mass of the weight and reducing the pressure receiving area of the piezoelectric element. In that case, the laminated structure of the piezoelectric element that supports the weight tends to be unstable.

On the other hand, in the acceleration sensor of the present invention, since the pressure receiving surface of the piezoelectric element is arranged so as to abut on the circumferential portion where the mass inside and outside of the weight match, the geometrical center of the mass of the weight is arranged. The piezoelectric element can support the weight by the circumference of the static average circle or an annular pressure receiving surface having a predetermined width including the circumference. As a result, it is possible to suppress bending vibration of the weight caused by the vibration force applied to the center of gravity of the weight and the reaction force that the piezoelectric element resists via the pressure receiving surface, and therefore, it is possible to increase the upper limit frequency of the flat portion and increase the output. Compatibility is possible.

According to the second aspect of the present invention, the spacer is provided in the radial gap between the piezoelectric element and the support shaft portion.

As a result, since the pressure receiving surface of the piezoelectric element that abuts against the weight can be arranged coaxially with the weight, for example, when it is desired to reduce the pressure receiving area of the piezoelectric element and increase the sensor output, It is easy to maintain the state in which the pressure receiving area of the piezoelectric element is brought into contact with the circumferential portion.

According to claim 3 of the present invention, the thickness of the element mounting surface is in the range of 2 to 2.5 mm.

That is, when the thickness of the housing forming the element mounting surface is thin, the deformation associated with the bending of the housing is large, and when it is thick, the deformation associated with the expansion and contraction of the housing is large. Exists.

According to the fourth aspect of the present invention, the groove is formed on the outer peripheral side of the element mounting surface on which the piezoelectric element abuts.

As a result, of the housing forming the element mounting surface of the bottomed hole, the housing element mounting portion that directly contacts the piezoelectric element and the housing side wall portion forming the side wall of the bottomed hole form a groove. Since the connection is made at the housing rigidity lowering portion, the influence of the side wall portion which is deformed by the vibration force of the vibrating body due to the rigidity lowering portion is absorbed, and unnecessary vibration transmitted to the housing element mounting portion is eliminated. Will be alleviated. Therefore, unnecessary vibration of the housing element mounting portion that directly abuts the piezoelectric element is reduced, so that the upper limit frequency of the flat portion of the sensor output can be increased.

According to the fifth aspect of the present invention, the side wall portion forming the side wall of the bottomed hole is eliminated in the housing.

As a result, the deformation of the side wall portion, which is one of the factors of the unnecessary vibration of the housing on which the piezoelectric element is mounted, can be eliminated.

According to the sixth aspect of the present invention, the gap between the housing without the side wall and the outer periphery formed by the weight is made airtight with the resin material.

As a result, unnecessary vibration of the housing can be reduced and intrusion of water or the like into the piezoelectric element can be prevented.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the acceleration sensor of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a sectional view showing the structure of an acceleration sensor according to an embodiment of the present invention. Figure 2
2 is a diagram illustrating an arrangement configuration related to a pressure receiving surface of a piezoelectric element that supports a weight, which is an essential part of the present invention in FIG. 1.
FIG. 2A to FIG. 2C are schematic diagrams showing a state where the pressure receiving surface is inside the center of gravity diameter, abuts on the center of gravity diameter, and is outside the center of gravity diameter with respect to the center of gravity diameter of the weight. Figure 3
2A and 2B are graphs for explaining sensor output characteristics of the acceleration sensor shown in FIG. 1, in which (I) is a configuration of the weight and the piezoelectric element of the comparative example, and (II) is a characteristic of the sensor output characteristic of the configuration of the present embodiment. It is a curve.

As shown in FIG. 1, the acceleration sensor includes a housing 10 having a screwing portion 11 that can be screwed into an internal combustion engine as a vibrating body, and a bottomed hole 1 formed in the housing 10.
Support shaft portion 20 that can be screwed and fixed to the element mounting surface 12a of No. 2
And a vibration detecting section 30 which is mounted on the support shaft section 20 so as to be displaceable in the axial direction and not detachable in the axial direction.
Is a ring-shaped piezoelectric element (hereinafter, P
A ZT element) 40 and a weight 50 stacked on the piezoelectric element. The PZT element is polarized in the axial direction and detects the vibration acceleration of the vibrating body in the vertical direction, which is the vertical direction shown in FIG.

The weight 50 is a cylindrical body having a predetermined mass, and is made of PZT by the axial force of the supporting shaft portion 20 such as a bolt.
It is mounted together with the element 40 so as to be displaceable in the axial direction and not detachable in the axial direction.

The piezoelectric element 40 includes a weight 30 and a housing 1.
It is sandwiched between the element mounting surface 12a of 0 and the PZT.
Silver electrodes are baked on both main surfaces of the element 40. PZ
A base (not shown) of the terminal is sandwiched between the T element 40 and the element mounting surface 12a, and a ring-shaped resin film for electrical insulation is provided between the base and the element mounting surface 12a. An insulator (not shown) is interposed. Further, a base portion (not shown) of the terminal is sandwiched between the PZT element 40 and the weight 50, and an insulator made of a ring-shaped resin film for electrical insulation is provided between the base portion and the weight 50. (Not shown) is provided. Both terminals are embedded in a connector portion (not shown) of a resin mold (not shown) forming the ceiling of the bottomed hole 12, and the sensor of the PZT element 40 for detecting the exciting force of the vibrating body. It is arranged to transmit the output signal to the outside. The resin mold may be any resin-molded member as long as it can prevent moisture and the like from entering the vibration detection unit 30 housed in the bottomed hole 12.

The sensor output of the PZT element 40 changes in accordance with the stress applied to the PZT element, and the PZT element 40 that achieves both high output and flat output characteristics is achieved. The arrangement of the weight 50 will be described later.

The housing 10 together with the screwing portion 11 which can be screwed into the vibrating body and the supporting shaft portion 20 are included in the vibration detecting portion 3.
0, a base portion 13 having an element mounting surface 12a for sandwiching a PZT element 40 and a weight 50, and a bottomed hole 12
And a side wall portion 14 forming a side wall.

In the acceleration sensor having the above-mentioned structure, the base portion 13 which forms the element mounting surface 12a through the screwing portion 11 which is screwed into the internal combustion engine and which is vibrated by the combustion of the internal combustion engine as a vibrating body. Transmitted to. This element mounting surface 12a
When the vibration due to the vibrating body is transmitted to the PZT element 40, the PZT element 40 generates an electric charge according to the vibration (exciting force) applied to the vibration detecting unit 50, and the electric charge is generated by an external circuit connected through the terminal. It is output as a sensor output.

Here, the PZT which achieves both high output of the sensor output of the PZT element 40 and flattening of its output characteristics.
The arrangement of the element 40 and the weight 50 will be described below.

First, the sensor output of the PZT element 40 is P
In order to increase the output of the ZT element 40 according to the stress applied to the ZT element 40, generally, the means for increasing the physical size of the weight 50 to increase the mass and the mass of the weight 50 remain unchanged. The weight 50 of the PZT element 40
There is a means for reducing the pressure receiving area in contact with.

When the mass of the weight 50 is increased to increase the output, the physique around the acceleration sensor, particularly the housing 10 accommodating the vibration detecting portion 30, may increase. In recent years, there has been an increasing demand for high-density engine rooms from the viewpoint of improving vehicle habitability, the dead space in the engine room is decreasing, and the mounting space tends to be reduced. A reduction in vehicle weight is desired. Due to this social demand, it is not desirable to increase the output of the acceleration sensor by increasing the mass of the weight 50 and increasing the weight of the acceleration sensor.

On the other hand, when the pressure receiving area of the PZT element 40 is reduced to achieve high output, the acceleration sensor does not increase in size and weight, and at least the weight of the PZT element 40 is reduced by reducing the pressure receiving area. It is possible to reduce the weight of the acceleration sensor.

In the embodiment of the present invention, the PZT element 4 will be described below.
A case will be described where the pressure receiving area of 0 is reduced to achieve high output.

First, when the weight 50 is correspondingly increased or the pressure receiving area is reduced on the pressure receiving surface of the PZT element 40 to transmit the exciting force of the vibrating body, the contact state between the weight 50 and the PZT element 40 ( For example, depending on the surface roughness, flatness, etc.), the uniform distribution of the pressing load of the weight 50 that gives stress to the PZT element 40 may be deteriorated and unnecessary vibration may occur. On the other hand, the configuration in which the pressure receiving area of the present embodiment is made smaller than the configuration in which the weight 50 is increased is
Since the rigidity of the PZT element 40 decreases, the PZT element 40
Also, the contact state is easily corrected by the axial force of the support member 20 that fixes the weight 50 by screwing. In other words, the vibration detecting unit 30 is applied to the state where the laminated structure of the PZT element 40 supporting the weight 50 becomes unstable due to the contact state or the like.
The PZT element 40 having reduced rigidity by reducing the pressure receiving area due to the configuration in which the support shaft portion 20 is screwed and fixed.
Can improve its contact state and thus prevent unnecessary vibration.

Next, the exciting force F that causes the PZT element 40 to generate stress is determined by the mass m of the weight 50 and the vibration acceleration α (F = mα). Therefore, in the present embodiment, the weight 50 is provided by the pressure-receiving surface of the PZT element 40, which has a predetermined width including a circumference (hereinafter referred to as a center-of-gravity diameter) G in which the masses inside and outside the weight 50 match, or a circumference G. (See FIG. 1 and FIG. 2B).

FIG. 2 shows the vibration modes when the arrangement of the pressure receiving surface of the PZT element 40 is changed with respect to the center of gravity G.
As shown in FIG. 5, the weight 50 sandwiched between the PZT element 40 and the support shaft portion 20 has a fixed end at the sandwiched portion of the weight 50 and a free end at other outer peripheral portions. The deformation becomes larger and resonance is more likely to occur as the outer peripheral side is farther from the sandwiched central portion (see FIG. 2A).
On the other hand, when the outer diameter of the pressure receiving surface is increased (here, in detail, the pressure receiving surface of the PZT element 40 has the same pressure receiving area and the same thickness as the axial thickness), the outer periphery of the PZT element 40 is supported from the free end. Since it moves to the end, the deformation of the PZT element 40 can be reduced (see FIGS. 2B and 2C).
In particular, as shown in FIG. 2B, the center of gravity G of the weight 50 is
When the pressure receiving surface of the PZT is brought into contact with the upper side, the deformation of the vibration mode due to the exciting force applied to the weight 50 can be reduced. Therefore, the weight 50 and the PZT element 40 which are difficult to resonate should be arranged. You can

As shown in FIG. 1, the PZT element 40
It is desirable that a spacer 60 is provided in a radial gap between the support shaft portion 20 and the support shaft portion 20. Accordingly, it is possible to easily maintain the state in which the pressure receiving surface of the PZT element 40 is brought into contact with the gravity center diameter G of the weight 50 or the annular inner peripheral portion having a predetermined width including the gravity center diameter G.

FIG. 3 shows an experimental result of measuring the sensor output characteristic of the acceleration sensor of this embodiment. As shown in FIG. 3, compared with the output curve indicated by the broken line in the comparative example in which the outer circumference of the weight 50 in (I) is a free end, (I
The output curve shown by the solid line in this embodiment of I) can increase the resonance frequency (in FIG. 3, it is improved from about 20 kHz to about 25 kHz). Therefore, the upper limit frequency of the flat portion in the sensor output characteristic is set to 15 kHz of the comparative example.
Can be increased to 18 kHz.

Therefore, by reducing the pressure receiving area of the PZT element as compared with the conventional one, high output can be achieved, and
The upper limit frequency of the flat portion can be increased. Moreover, since a high output can be secured as compared with the conventional non-resonant type acceleration sensor, it is possible to provide an acceleration sensor that has a simple configuration and can output a flat sensor output.

Here, it is desirable that the housing 10 for holding the vibration detecting section 50 has the following features to reduce unnecessary vibration.

(Second Embodiment) In the second embodiment, as the shape of the housing 10 for reducing unnecessary vibration,
The thickness T of the base portion 13 forming the element mounting surface 12a is
It is configured to be in the range of 2 to 2.5 mm.

FIG. 4 shows the housing 10, particularly the base portion 13.
The experimental result of investigating the influence on the sensor output by changing the thickness T of the is shown. FIG. 4A is a graph showing the output of the flat portion of the sensor output characteristic, and FIG. 4B is 8 kHz.
It is a graph which shows the output increase rate of 15 kHz with respect to the output of z. As shown in FIG. 4 (a), the change in output is small due to the difference in thickness T, but as shown in FIG. 4 (b), the upper limit frequency of the flat portion can be increased, that is, the so-called flatness can be improved. There is a range of thickness. That is,
When the thickness T is in the range of 2 to 2.5 mm, the output increase rate can be reduced, and thus the flatness can be improved.

The thickness T of the housing 10 shown in FIG.
When the thickness T of (I) is thin, the deformation due to the bending of the housing 10 is large, and when the thickness T of (III) is large, the housing 10 expands and contracts as shown in the schematic diagram showing the vibration mode related to While the resulting deformation is large,
This is because in the intermediate range (II) of the specific thickness T, the housing 10 is dispersed by bending and expansion and contraction, and as a result, its deformation can be reduced.

(Modification) As a modification, as the shape of the housing 10 for reducing unnecessary vibration, the element mounting surface 12a is formed.
Among them, as shown in FIG. 5 (II), the groove portion 12b is formed on the outer periphery of the surface (specifically, the circle within the diameter ΦD) with which the PZT element 40 contacts.

Housing 10 fixed by screwing portion 11
Since the threaded portion 11 is a fixed end and the other portions are free ends, the outer peripheral side of the housing 10, especially the bottomed hole 12
The side wall portion 14 forming the side wall of the is greatly deformed. Therefore, in the configuration without the groove portion 12b shown in FIG.
The outer peripheral side of the element mounting surface 12a is affected by the deformation of the side wall portion 14 (see FIG. 5A-I).

On the other hand, in the structure having the groove portion 12b of the present embodiment, the gap between the element mounting portion (specifically, the inner peripheral side of ΦD of the base portion 13) directly contacting the PZT element 40 and the side wall portion 14 is provided. Are connected at the portion where the housing 12 is provided with the groove 12b and whose rigidity is reduced.
The effect of the deformation of No. 4 is absorbed and alleviated by the reduced rigidity portion of the groove 12a (see FIG. 5 (a-II)).
Therefore, even if part of the housing 10 (specifically, the side wall portion 14) resonates, so-called vibration coupling to the element mounting portion with which the PZT element 40 directly abuts can be suppressed.

5 (a-I) and FIG. 5 (a-I)
In I), it is a result of experimental measurement with a vibration force of 1 G and a frequency of 15 kHz.

Therefore, as shown in the sensor output characteristic of FIG. 5B, the groove portion 12b of the present embodiment of (II) is compared with the output curve shown by the broken line of the comparative example without the groove portion 12b of (I). In the configuration having the structure, the influence of the vibration coupling due to the resonance of the side wall portion 14 can be reduced, so that the flatness can be improved.

(Third Embodiment) As a third embodiment, the side wall portion 14 forming the side wall of the bottomed hole 12 is eliminated in the housing 10.

As a result, the deformation of the side wall portion 14, that is, the resonance, which is one of the factors causing the unnecessary vibration of the housing 10 in which the PZT element 40 is mounted, can be eliminated.

Moreover, since the mass of the housing 10 can be reduced by eliminating the side wall portion 14, the deformation of the base portion 13, that is, the element mounting portion can be further suppressed.

When the vibration detecting portion 30 needs to be airtight, the gap between the base portion 13 and the weight 50 on the outer periphery is filled with the resin material 70 or the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a view for explaining an arrangement configuration relating to a pressure receiving surface of a piezoelectric element that supports a weight, which is a main part of the present invention in FIG.
2 (a) to 2 (c), the pressure receiving surface is in contact with the center of gravity diameter of the weight, and the pressure receiving surface is in contact with the center of gravity diameter.
It is a schematic diagram which shows the state in which it exists outside the center-of-gravity diameter.

3A and 3B are graphs for explaining sensor output characteristics of the acceleration sensor shown in FIG. 1, in which (I) is a weight and a piezoelectric element arrangement of a comparative example, and (II) is a sensor output according to the arrangement of the present embodiment. It is a characteristic curve showing a characteristic.

FIG. 4 is a diagram for explaining the influence of the shape of the housing, which is the main part of the second embodiment, in particular the thickness, and FIG.
Is a sensor output characteristic, and FIG. 4B is a graph showing flatness.

5A and 5B are views for explaining an influence of a housing shape, which is a main part of a modified example, in particular, the presence or absence of a groove, and FIGS.
FIG. 5A is a graph in which the vibration state due to the exciting force applied to the mounting surface where the piezoelectric element directly abuts the housing is viewed in the radial direction. (B) is a graph showing a sensor output characteristic.

FIG. 6 is a sectional view showing a configuration of an acceleration sensor according to a third embodiment.

[Explanation of symbols]

10 Housing 11 Threaded Part 12 Bottomed Hole 12a Element Mounting Surface 12b Groove 13 Base Part 14 Sidewall 20 Support Shaft 30 Vibration Detecting Part 40 PZT Element (Piezoelectric Element) 50 Weight 60 Spacer 70 Resin Material ΦG Center of Gravity (Weight 50 (The circumference where the inside and outside masses match)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Ito             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Hisashi Matsuoka             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Kimio Uchida             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO (72) Inventor Satoshi Matsuura             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO F-term (reference) 3G084 DA04 DA20 FA25

Claims (6)

[Claims] 1. A housing having a screwing portion that can be screwed into a vibrating body, a support shaft portion that can be screwed and fixed to an element mounting surface of a bottomed hole formed in the housing, and the support shaft portion. A piezoelectric element mounted so as to be axially displaceable and axially non-separable, and a vibration detection unit composed of a weight stacked on the piezoelectric element, wherein the piezoelectric element has a circumference in which the inside and outside masses of the weight match. An acceleration sensor characterized by being in contact with a portion. 2. The acceleration sensor according to claim 1, wherein a spacer is provided in a radial gap between the piezoelectric element and the support shaft portion. 3. The thickness of the element mounting surface is 2 to 2.5 mm
It is in the range of Claim 1 or Claim 2
The acceleration sensor according to. 4. The groove portion is formed on the outer peripheral side of the surface on which the piezoelectric element contacts, of the element mounting surface, according to any one of claims 1 to 3. Acceleration sensor. 5. The acceleration sensor according to claim 1, wherein a side wall portion forming a side wall of the bottomed hole is eliminated in the housing. 6. The acceleration sensor according to claim 5, wherein an outer circumferential gap formed by the housing and the weight is airtight with a resin material.