JP2722939B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of an acceleration sensor mainly used in a vehicle airbag device.

[0002]

2. Description of the Related Art Some conventional acceleration sensors are configured as shown in FIGS. 5 and 6 by using a piezoelectric element as an acceleration detecting element.

That is, this piezoelectric acceleration sensor has a hybrid IC 2 including a piezoelectric element 21 constituting an acceleration detecting element and a processing circuit for a detection signal outputted from the piezoelectric element 21.
2, a metal base plate 23, and a shield case 24. Then, the piezoelectric element 21 and the hybrid IC
22 is mounted on the surface of the metal base plate 23 and sealed by the shield case 24. Also,
At this time, the piezoelectric element 21 is supported in a cantilever manner via a pedestal 25 disposed on the surface of the metal base plate 23, and acceleration in the vertical direction C orthogonal to the support surface acts thereon. As a result, the free end bends to output a detection signal corresponding to the magnitude of the acting acceleration.

Further, both surfaces of the piezoelectric element 21 and the hybrid IC 22 are individually connected via lead wires 26. In addition, the code | symbol 27 in a figure is
3 shows external connection pin terminals that penetrate along the thickness direction thereof and protrude to the outside while ensuring an insulating state with the metal base plate 23.

[0005]

In the conventional acceleration sensor, the piezoelectric element 21 is supported in a cantilever manner, and has a structure that bends and deforms in accordance with the applied acceleration. Therefore, when an excessive acceleration is applied, the free end portion is largely swung, which may result in breakage of the piezoelectric element 21 itself, and it is difficult to obtain good impact resistance. There was an inconvenience. In this conventional example, the piezoelectric element 21
And the hybrid IC 22 are connected by the lead wires 26, each of the lead wires 26 may be disconnected due to metal fatigue caused by vibration. In order to prevent the disconnection, it is conceivable to increase the wire diameter of the lead wire 26 to increase the strength. However, in such a case, a lead having a large mass due to vibration caused by the action of the acceleration is considered. The line 26 may cause resonance, which may adversely affect the acceleration detection operation of the piezoelectric element 21.

Further, in the conventional acceleration sensor for detecting acceleration in the vertical direction C orthogonal to the piezoelectric element 21 and its supporting surface, the piezoelectric element 21
The piezoelectric element 21 and the hybrid IC 2 need to adopt a strong configuration in which the support portion of the piezoelectric element 21 does not bend.
2 is mounted on the surface of the metal base plate 23, and the open surface of the shield case 24 is closed by the metal base plate 23. However, in the case of such a configuration, the weight of the metal base plate 23 which is heavy and expensive is used, so that not only does the overall shape of the acceleration sensor become large, but also the acceleration sensor itself becomes large. It must be firmly attached to the object to be measured, which eventually leads to an increase in cost.

The present invention has been made in view of such inconvenience, and does not require the use of a lead wire and a metal base plate. It is an object of the present invention to provide an acceleration sensor which can enhance the reliability, has high reliability, and can reduce its overall shape.

[0008]

An acceleration sensor according to the present invention comprises a hybrid IC substrate having a pair of signal extracting electrodes formed on a surface thereof in parallel, and an acceleration detecting element provided between the signal extracting electrodes. In this acceleration detecting element, each polarization direction is a hybrid I
A pair of piezoelectric elements which are oriented parallel to the surface of the C substrate and whose polarization directions are opposite to each other;
A weight (weight) is provided between them, and one surface of each of the piezoelectric elements parallel to the polarization direction is electrically connected to each other via the weight while being parallel to the polarization direction of each of the piezoelectric elements. The other surface is individually and electrically connected to each of the signal extraction electrodes. The hybrid IC board referred to herein is a hybrid IC board including a processing circuit for a detection signal output from the acceleration detecting element, which is integrated into an insulating board.

[0009] Alternatively, the acceleration detecting element includes a pair of piezoelectric elements in which each polarization direction is parallel to the surface of the hybrid IC substrate and each polarization direction is opposite to each other. The surfaces orthogonal to the polarization direction of each piezoelectric element are closely connected to each other and electrically connected, while the other surfaces orthogonal to the polarization direction of each piezoelectric element are individually electrically connected to each of the signal extraction electrodes. May be done.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing the entire configuration of an acceleration sensor according to this embodiment, and FIG. 2 is an enlarged perspective view showing an acceleration detecting element which is a main part thereof. Hybrid IC substrate 1 and acceleration detecting element 2
And the hybrid I covering only the acceleration detecting element 2
And a shield case 3 fixed on the surface of the C substrate 1. That is, this hybrid IC substrate 1
As shown in FIG. 1, a hybrid IC (not shown) including a processing circuit for a detection signal output from the acceleration detection element 2 is integrated into an insulating substrate 4 having a predetermined thickness. Surface of substrate 4 (upper side in the figure)
At least a pair of signal extraction electrodes 5 and 6 connected to the built-in hybrid IC are formed in parallel on the upper side. The acceleration detecting element 2 is provided between the signal extraction electrodes 5 and 6 formed on the surface of the hybrid IC substrate 1, while a plurality of external connection pin terminals 7 are provided on the hybrid IC substrate 1 itself. These pin terminals 7 penetrate the hybrid IC substrate 1 along the thickness direction thereof and are projected to the outside.

On the other hand, as shown in FIG. 2, the acceleration detecting element 2 has its polarization (axial) directions A ₁ and A ₂ both set to be parallel to the surface of the hybrid IC substrate 1.
In addition, a pair of piezoelectric elements 8 and 9 whose polarization directions A ₁ and A ₂ are opposite to each other and are opposite to each other are provided, and a weight 10 made of a conductive material bridged therebetween.
Is provided. One surface (upper surface in the figure) 8 parallel to the polarization directions A ₁ and A _{2 of} the piezoelectric elements 8 and 9, respectively.
a, 9a are electrically connected to each other via a weight 10, while the polarization directions A ₁ ,
Other surface parallel to the A ₂ (lower side in the figure) 8b, 9b are electrically connected individually with each of the hybrid IC signal extraction electrodes 5 and 6 in parallel formed on the surface of the substrate 1.

That is, the piezoelectric elements 8 and 9 and the signal extraction electrodes 5 and 6 are bonded with an adhesive (not shown).
On the other hand, the weight 10 formed by using a nickel alloy or the like is fixed on the piezoelectric elements 8 and 9 in a cross-linked manner by using a similar adhesive (not shown). Therefore, one surface 8a, 9a of each of these piezoelectric elements 8, 9 is
Is electrically conductive, which means that it is in an electrically short-circuit state. At this time, the polarization direction A of each of the piezoelectric elements 8 and 9 constituting the acceleration detecting element 2 is set.
₁ and A ₂ may be set in the opposite directions away from each other, or a block-shaped weight 10 may be formed by using a non-conductive ceramic material. Needless to say, a conductive layer may be formed for electrically connecting the surfaces 8a, 9a of the piezoelectric elements 8, 9 respectively.

Further, the shield case 3 is formed as a bottomed cylindrical shape by using a metal, a resin, or the like, and includes only a pair of piezoelectric elements 8 and 9 and a weight 10 constituting the acceleration detecting element 2. After being covered, it is fixed on the surface of the hybrid IC substrate 1 using an insulating adhesive (not shown) or the like. The shield case 3 is attached according to the conditions of use of the acceleration sensor and the like, and need not always be used.

In the acceleration sensor incorporating the acceleration detecting element 2 having such a configuration, when an acceleration acts on the piezoelectric elements 8 and 9 in a parallel direction A from outside, the weight 10 acts on the acceleration element. Since it will be swung along the direction A and will move along the direction parallel to the surface of the hybrid IC substrate 1,
A shear strain occurs in each of the piezoelectric elements 8 and 9 disposed between each of the signal extraction electrodes 5 and 6 formed on the hybrid IC substrate 1 and the weight 10, and the piezoelectric element Opposite charges are generated on both main surfaces 8 and 9, that is, on one surface 8 a, 9 a and the other surface 8 b, 9 b. At this time, the polarization directions A ₁ and A _{2 of} the piezoelectric elements 8 and 9 are opposite to each other, and the surfaces 8 a and 9 a that are the displacement-side main surfaces are electrically connected via the weight 10. If a positive charge is generated on the displacement-side main surface of one of the piezoelectric elements 8 (9), a negative charge is generated on the displacement-side main surface of the other piezoelectric element 9 (8). Charges will be generated, and these positive and negative charges will be canceled via the weight 10.

Since these piezoelectric elements 8 and 9 are individually and electrically connected to the signal extraction electrodes 5 and 6, respectively, the fixed-side main surfaces of the piezoelectric elements 8 and 9, that is, the other surfaces are provided. The electric charges generated in 8b and 9b are extracted through the signal extraction electrodes 5 and 6, respectively, whereby the direction and magnitude of the acceleration acting on the acceleration detecting element 2 are detected. In the present embodiment having the above-described configuration, the acceleration to be detected acts in parallel with the surface of the hybrid IC substrate 1, so that the degree to which the hybrid IC substrate 1 is deformed by the acceleration to be detected is small. become. Furthermore, even if the hybrid IC substrate 1 is deformed due to an acceleration component acting in a direction different from the above, the deformation is caused by the piezoelectric elements 8 and 8 when the acceleration is detected.
Since the distortion occurs in a direction different from the distortion direction 9, the acceleration detecting operation by the piezoelectric elements 8 and 9 is not significantly affected. Therefore, there is no need to particularly increase the rigidity of the hybrid IC substrate 1 or to firmly support it.

In the above description, the acceleration detecting element 2 has the configuration as shown in FIG. 2, but is not limited to this, and is shown in the modified examples of FIGS. 3 and 4, respectively. It goes without saying that such a configuration may be adopted.

That is, in the acceleration detecting element 2 in the first modified example shown in FIG. 3, both the polarization directions A ₁ and A ₂ are oriented parallel to the surface of the hybrid IC substrate 1, and The piezoelectric device includes a pair of piezoelectric elements 8 and 9 whose directions A ₁ and A ₂ are opposite to each other, and a conductive weight 10 that is bridged therebetween. The surfaces 8a and 9a of the piezoelectric elements 8 and 9 which are parallel to the polarization directions A ₁ and A ₂ are electrically connected to each other via a weight 10 sandwiched therebetween, while the piezoelectric elements 8 and 9 are electrically connected to each other. 9 Each polarization direction A ₁ , A ₂
The other surfaces 8b and 9b parallel to the electrodes 5b and 9b are connected to the signal extraction electrodes 5 through the support members 11 and 12 having a conductive shape.
6 are individually and electrically connected to each other. Here, each of the support members 11 and 12 is formed by using the same conductive material as the weight 10.

Therefore, in the acceleration sensor incorporating the acceleration detecting element 2, the piezoelectric elements 8, 9 are externally provided.
When the acceleration acts along the direction B orthogonal to the parallel direction A, the same acceleration detection operation as described above is performed.

Further, the acceleration detecting element 2 in the second modification shown in FIG. 4 has a pair of polarization directions A ₁ and A ₂ parallel to the surface of the hybrid IC substrate 1 and opposite to each other. Piezoelectric elements 8 and 9 are provided, and these piezoelectric elements 8 and 9 are formed such that respective surfaces 8c and 9c orthogonal to the polarization directions A ₁ and A ₂ are in close contact with each other and electrically connected. It is integrated. Then, the other surface 8 orthogonal to the polarization directions A ₁ and A _{2 of} the piezoelectric elements 8 and 9 respectively.
Each of d and 9d is individually and electrically connected to each of the signal extracting electrodes 5 and 6 via conductive support members 13 and 14 having a block shape. That is, the support member 1
Reference numerals 3 and 14 denote other surfaces 8d and 9 of the piezoelectric elements 8 and 9, respectively.
The support members 13 and 14 each have a U-shape in plan view in which the piezoelectric elements 8 and 9 integrated with each other by being in contact with both ends of the support member d are sandwiched and supported. It is fixed to the signal extraction electrodes 5 and 6 using an adhesive (not shown).

Therefore, in an acceleration sensor incorporating the acceleration detecting element 2 having such a configuration, when an acceleration is applied from the outside in the parallel direction A of the piezoelectric elements 8 and 9, that is, in the direction in which the piezoelectric elements 8 and 9 are in close contact with each other. The central portions of the piezoelectric elements 8 and 9 integrated with each other bend with the action of acceleration, and the same acceleration detection operation as described above is performed.

[0022]

As described above, according to the acceleration sensor of the present invention, the entire surface or at least both ends of the piezoelectric element subjected to the acceleration is directly or indirectly connected to the signal extraction electrode. Since the piezoelectric element is supported by the hybrid IC substrate, even if an excessive acceleration is applied, the piezoelectric element itself is not significantly bent and deformed, so that the piezoelectric element itself is not broken and has excellent impact resistance. A configuration is obtained. At this time, since it is not necessary to use the lead wire, various inconveniences caused by the use of the lead wire cannot occur.

Further, the polarization direction of each piezoelectric element is set in a direction parallel to the surface of the hybrid IC substrate, and the acceleration is detected by the piezoelectric element being distorted or bent in the direction of the acceleration. From
Slight deformation and deflection in the vertical direction parallel to the support surface can be tolerated, and the structure for supporting the piezoelectric element does not need to be as strong as in the prior art. As a result, it is not necessary to use a metal base plate as in the related art, and it is possible to reduce the overall shape of the acceleration detecting element while increasing the shock resistance of the acceleration detecting element while using a member having relatively low rigidity. Is obtained.

[Brief description of the drawings]

FIG. 1 is a partially broken perspective view showing the entire configuration of an acceleration sensor according to the present embodiment.

FIG. 2 is an enlarged perspective view showing an acceleration detecting element as a main part thereof.

FIG. 3 is a perspective view showing a first modification of the acceleration detection element.

FIG. 4 is a perspective view showing a second modification of the acceleration detection element.

FIG. 5 is a plan view showing an overall configuration of an acceleration sensor according to a conventional example.

FIG. 6 is a sectional view taken along line DD of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hybrid IC board 2 Acceleration detection element 5 Signal extraction electrode 6 Signal extraction electrode 8 Piezoelectric element 8a One surface of piezoelectric element 8b Other surface of piezoelectric element 9 Piezoelectric element 9a One surface of piezoelectric element 9b Piezoelectric element Other side 10 weight

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jiro Inoue 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-2-171659 (JP, A) JP-A-5-180864 (JP, A) JP-A-5-215766 (JP, A) JP-A-5-288768 (JP, A) JP-A-2-150568 (JP, A) U)

Claims (2)

(57) [Claims] A hybrid IC substrate (1) having a pair of signal extraction electrodes (5, 6) formed in parallel on the surface.
And an acceleration detection element (2) provided between the signal extraction electrodes (5, 6), wherein the acceleration detection element (2) has a polarization direction (A ₁ , A ₂ )
Are oriented parallel to the surface of the hybrid IC substrate (1), and the polarization directions (A ₁ , A ₂ ) are opposite to each other. And a polarization direction (A ₁ , A ₂ ) of each of the piezoelectric elements (8, 9).
Are parallel to each other (8a, 9a) are weights (10)
While the other surfaces (8b, 8b, 9) parallel to the polarization directions (A ₁ , A ₂ ) of the piezoelectric elements (8, 9) are connected.
9b) is an acceleration sensor which is individually and electrically connected to each of the signal extraction electrodes (5, 6). 2. The acceleration detecting element (2), wherein each of the polarization directions (A ₁ , A ₂ ) is oriented parallel to the surface of the hybrid IC substrate (1), and the polarization directions (A ₁ , A ₂₎ ) Are opposite to each other.
9), and the polarization direction (A ₁ , A ₂ ) of each piezoelectric element (8, 9)
The surfaces (8c, 9c) that are orthogonal to each other are in close contact and electrically connected to each other, while the other surfaces (8d, 9d) that are orthogonal to the polarization directions (A ₁ , A ₂ ) of the respective piezoelectric elements (8, 9). 2. The acceleration sensor according to claim 1, wherein each of the electrodes is electrically connected to each of the signal extraction electrodes.