JPH0712841A - Capacitive acceleration sensor and air bag system - Google Patents

Abstract

PURPOSE:To provide a capacitive acceleration sensor which can be fixed to a housing or a board with no influence of microstress on the accuracy or reliability thereof, and a highly reliable air bag system employing the capacitive acceleration sensor. CONSTITUTION:The beam 5 of an acceleration detecting element 2 is set in the longitudinal direction 62 at 90 deg.+ or -30 deg. with respect to the direction 61 of sensor fixing hole. When the acceleration detecting element 2 is secured in such direction, the beam 5 is scarcely subjected to microstress, the wiring 37 interconnecting the element 2 and an IC 32 is scarcely subjected to stress, and thereby the joints between the wiring 37 and the element 2 and between the wiring 37 and the IC 32 are not subjected to stress. Furthermore, since the wiring 37 is not stretched by the distortion at the time of fixing the acceleration sensor, the tension is sustained constant and thereby the stray capacitance having critical influence on the accuracy of capacitive acceleration sensor is sustained constant resuling in an acceleration sensor having invariable characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to acceleration detection, and more particularly to a capacitance type acceleration sensor suitable for detecting a collision of an automobile and an air bag system using the capacitance type acceleration sensor.

[0002]

2. Description of the Related Art A conventional electrostatic capacitance type acceleration sensor is known to utilize silicon fine processing technology.
As disclosed in Japanese Laid-Open Patent Publication No. 1-253657, application of a pulse width modulation electrostatic servo technique has been proposed.

Further, as a mounting structure of a strain gauge type acceleration sensor, there has been proposed one disclosed in Japanese Patent Laid-Open No. 2-275363.

[0004]

Since the performance of an acceleration sensor generally used in an automobile air bag system is an important factor related to human life, a highly accurate product is required.

Although various types of acceleration sensors are currently used, a large number of capacitance type acceleration sensors, which are advantageous in terms of accuracy and reliability, are being used.

Generally, the acceleration sensor has a structure in which it is fixed by one or more mounting screws. For this reason, in the case of an electrostatic capacitance type acceleration sensor which is particularly susceptible to distortion during mounting, a small stress is applied to the sensor by the mounting torque of the screw, which is one of the factors that impair the accuracy of the sensor.

However, the above-mentioned Japanese Patent Laid-Open No. 1-2536 has been used.
In the conventional technique described in Japanese Patent Publication No. 57-57, mounting of a sensor,
In particular, the influence of minute stress when the sensor is attached to the housing is not taken into consideration, and there is a problem in accuracy.

Further, in the prior art disclosed in Japanese Laid-Open Patent Publication No. 2-275363, no consideration is given to the influence of stray capacitance due to wiring or the like which is important for a capacitance type sensor.

An object of the present invention is to provide an electrostatic capacitance type acceleration sensor in which accuracy and reliability are not deteriorated due to the influence of minute stress when mounting the electrostatic capacitance type acceleration sensor on a housing or a substrate, and at the same time, the reliability is improved. It is to provide a high degree airbag system.

[0010]

In order to achieve the above-mentioned object, the present invention has a movable electrode that is displaced with respect to acceleration and at least one fixed electrode, and the movable electrode is formed by at least one beam. An acceleration that is supported and has an acceleration detection element that detects displacement of the movable electrode as a change in electrostatic capacitance, converts the change in electrostatic capacitance into an electric signal to detect acceleration, and is fixed by at least two mounting holes. In the sensor, a capacitance type acceleration sensor characterized in that the beam length direction and the two mounting hole directions are 90 ° ± 30 °, and the capacitance type acceleration sensor is used. Provide an airbag system.

[0011]

According to the present invention, a highly accurate electrostatic capacitance type acceleration sensor which is not affected by minute stress when mounted on a vehicle housing, a mounting toy, or the like, and the electrostatic capacitance type acceleration sensor are provided. The highly accurate and highly reliable airbag system used can be submitted.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A capacitance type acceleration sensor (hereinafter referred to as an acceleration sensor) and an airbag system according to an embodiment of the present invention will be described below. FIG. 1 shows a mounting structure of an acceleration sensor according to the present invention.

In the present invention, the length direction 62 of the beam 5 of the acceleration detecting element 2 is fixed so as to be perpendicular to the mounting hole direction 61 of the acceleration sensor. When the acceleration detecting element 2 is fixed in such a direction, almost no stress is applied to the wiring 37 for connecting to the IC 32, and therefore, the wiring 37 and the acceleration detecting element 2 and the wiring 37 and the IC 32.
No stress is applied to the connection part of.

Further, since the wiring 37 is not pulled by the strain, the tension does not change, and thus the stray capacitance that has an important effect on the accuracy of the electrostatic capacitance method does not change. Does not change.

FIG. 2 shows a sectional structure (cut by a straight line AA) of the acceleration sensor of the present invention shown in FIG. Fixed electrode 7,
The respective gaps between 8 and the movable electrode 6 are almost unchanged and constant. Therefore, it is unlikely to be affected by the minute strain that occurs when the acceleration sensor is tightened with screws or the like, and no error occurs.

FIG. 3 shows the relationship of the error with respect to the angle φ between the length direction 62 of the beam 5 and the mounting hole direction 61 of the acceleration detecting element 2 of the acceleration sensor. The error when the angle φ is 0 ° is 10
At 0%, the error becomes the smallest when the angle φ is 90 °, and the error becomes the largest when the angle φ is 0 °.
Also, the relationship of the error with respect to the angle φ is not proportional,
The error sharply decreases at 60 ° or more. In order to reduce the effect of strain due to screw tightening to 1/2 or less, the length direction 62 of the beam 5 of the acceleration detection element 2 and the mounting hole direction 6 of the acceleration sensor 6
It is advisable to set the angle φ of 1 to 90 ± 30 °. When the structure shown in FIGS. 1 and 2 is used and the structure shown in FIG. 3 is attached as described above, it is possible to reduce the influence of strain when the screw is tightened, and to improve accuracy. In addition, there is an effect that the possibility that the movable electrode 6 and the fixed electrodes 7 and 8 collide with each other to be destroyed is reduced.

FIG. 4 shows another embodiment of the present invention.

This is configured such that the mounting hole 102 is one and the acceleration sensor is mounted on the housing or the like by using one screw. Even in such a structure, since the acceleration sensor is fixed by the screw and the lead pin 34, distortion occurs in the direction of the straight line 101.

Therefore, by setting the angle φ between the lengthwise direction 62 of the beam 5 of the acceleration detecting element 2 and the fixing direction (straight line 101) of the acceleration sensor to 90 ± 30 °, the influence of strain can be reduced.

Further, in the case of such a structure, since the screw hole 102 mainly plays a role of fixing the acceleration sensor, there is a problem that it resonates in the direction of the straight line 101. In order to reduce this effect, the present embodiment has a great effect (the strain applied to the detection element 2 due to resonance can be minimized).

FIG. 5 shows the operating principle of the acceleration sensor used in the present invention.

This acceleration sensor comprises a signal application section 1, an acceleration detection element 2, a capacitance detection section 3 and an amplification section 4.

The acceleration detecting element 2 is further composed of a beam (silicon beam) 5, a movable electrode 6, and fixed electrodes 7 and 8.

The beam (silicon beam) 5 is formed by the fine processing technique of silicon, and may be composed of either a single beam or a plurality of beams, and the movable electrode 6 having the function of a weight is formed at the tip. Etching the silicon plate 9 from both sides,
The movable electrode 6 supported by the beam (silicon beam) 5 is integrally formed.

On the other hand, the pair of fixed electrodes 7 and 8 arranged so as to face the movable electrode 6 are made of a metal material such as aluminum and are formed on the glass plates 10 and 11 by vapor deposition or any other suitable method. . One end 9a of the silicon plate 9 serves as a spacer. When configuring such a detection unit, the fixed electrodes 7 and 8 provided on the glass plates 10 and 11 and the movable electrode 6 are aligned with each other, and the glass plates 10 and 11 are interposed via the spacers 9a and 9b. And the glass plates 10 and 11 and the spacers 9a and 9b are anodically bonded. In this way, the fixed electrodes 7 and 8 are arranged to face each other with the movable electrode 6 interposed, but an initial gap d0 (about several μm) is secured between the movable electrode 6 and each fixed electrode 7 and 8. To be done. The movable electrode 6 is displaced by receiving an inertial force due to the acceleration to be detected. When the movable electrode 6 is displaced, the electrostatic capacitance C1 between the movable electrode 6 and the fixed electrode 7,
And the electrostatic capacitance C2 between the movable electrode 6 and the fixed electrode 8 changes.

The capacitance detecting section 3 detects the difference ΔC between C1 and C2 by the rectangular wave AC voltage generated by the signal applying section 1, converts it into a voltage, and outputs it.

After the acceleration signal is converted into the voltage signal Vo by the capacitance detection unit 3, it is amplified and adjusted to a predetermined voltage value by the amplification unit 4, and a linear output voltage Vout proportional to the acceleration can be obtained. .

FIG. 6 shows a plan view of the silicon plate 9.
The cross-sectional view shown in FIG. 5 is a view taken along the line AA in FIG.

In this acceleration sensor, two beams (silicon beams) are formed to support the movable electrode 6.

FIG. 7 shows a mounting structure of a conventional acceleration sensor.

The acceleration detecting element 2 is fixed to a substrate 31 made of ceramic, epoxy or the like in the direction as shown in the drawing (lateral direction of paper) with an adhesive such as silicon. Similarly, the IC 32 in which the capacitance detection unit 3 and the amplification unit 4 are integrated is also fixed to the substrate 31.

The substrate 31 is fixed to a base 33 made of a metallic material such as copper or iron, or plastic by an adhesive or the like. The metal terminal 34 of the base 33 is glass 35
It has a structure that is hermetically sealed (hermetically sealed) by the like, and is electrically connected to the outside. Further, the base 33 is provided with two holes 36a and 36b for mounting the acceleration sensor.

In FIG. 8, the acceleration sensor shown in FIG.
A sectional view when cut by -A is shown.

A cap 41 made of metal or plastic is mounted on the base 33 by welding or adhesion.

FIG. 9 shows a cross section of a conventional acceleration sensor in a mounted state.

The acceleration sensor has mounting holes 36a and 36b.
It is attached to the housing 52 or the like by screws 51a, 51b (or pins) or the like.

At this time, when torque due to screw tightening is applied to both ends of the mounting hole due to roughness of flatness due to the limit of machining accuracy of the mounting surface of the base 33 or insufficient accuracy of flatness of the mating side (housing etc.). In addition, a slight warpage occurs in the base 33, the acceleration sensor is distorted, and the characteristics change.

FIG. 10 shows an enlarged view of the acceleration detecting element 2 and the IC 32 attached in the state of FIG.

When the base 33 is deformed in a convex shape due to the torque of tightening the screw, the acceleration detecting element 2 is deformed and is distorted as shown in FIG. In such a state, the gap between the fixed electrode 7 and the movable electrode 6 and the gap d0 between the fixed electrode 8 and the movable electrode 6 (several μm, even if the acceleration is not applied to the acceleration sensor). The capacitance ΔC changes due to the change of (very small), and an error occurs in the output.

Further, as shown in FIG. 10, stress is also applied to the wiring 37 electrically connecting the acceleration detecting element 2 and the IC 32, so that the wiring 37, the acceleration detecting element 2, and the wiring 37 are connected. Since stress is applied to the connecting portion between the IC 32 and the IC 32, the wire may be broken in the worst case.

Further, since the wiring 37 is pulled by the strain and the tension is changed, the stray capacitance, which has an important effect on the accuracy of the capacitance method, is changed, and the characteristics of the acceleration sensor may be changed.

FIG. 11 shows an embodiment of an airbag system using the acceleration sensor of the present invention.

The airbag system of the present embodiment comprises an acceleration sensor 101 of the present invention, a microcomputer 102 composed of a CPU 103 and a memory 104, a power supply section 105 for regulating or boosting the battery voltage, and a crash record.
DA 106, start-up circuit 107, fail-safe circuit 10
8. A control unit 114 including an alarm circuit 109, a seat belt operating circuit 110, etc., an alarm device 111, an airbag 112, and a seat belt 113.

The acceleration signal detected by the acceleration sensor 101 of the present invention is sent to the CPU 103 in the microcomputer 102.
To the air conditioner to determine whether to activate the airbag. Simultaneously with the processing, the latest speed signal is stored in the memory 104 composed of RAM or the like.

When the CPU 103 determines that the airbag should be operated, the output waveforms from the acceleration sensor before and after the collision are output to the crash recorder 1 such as the EEPROM.
06. EE the output waveform from the acceleration sensor
At the same time when the data is recorded in the crash recorder 106 such as a PROM, at the same time, an activation signal is sent from the CPU 103 to the activation circuit 107 for driving the airbag 112, and the airbag 112 is expanded.

When the impact is not enough to activate the airbag, the seat belt 113 is rewound so that the seat belt 113 is appropriately tightened by the seat belt operating circuit 110 to fix the occupant to the seat.

Further, since the airbag system is a safety device, its reliability is very important. Therefore, the failure of each component is constantly diagnosed by the microcomputer 102,
If a failure occurs, the content and time of the failure are recorded in the crash recorder 106. In addition, the fail-safe circuit 108 operates to fix the operations of the starting circuit 107 and the seat belt operating circuit 110 to the fail-safe mode, control the operations of the airbag 112 and the seat belt 113, and at the same time send a signal to the alarm circuit 109. A warning device such as a lamp or a buzzer is activated to notify an occupant of the failure.

With such a system configuration, there is an effect that the safety device can be controlled with high accuracy and optimally according to the degree of collision. Moreover, there is an effect that a highly reliable system can be constructed.

[0049]

According to the present invention, there is an effect that it is possible to reduce the influence of strain when tightening a screw and to detect acceleration with high accuracy.

There is also an effect that a highly accurate acceleration sensor can be realized without increasing the number of parts.

Further, since the possibility of disconnection of the wiring can be reduced, the reliability of the sensor can be improved, and at the same time, the system configuration using the acceleration sensor of the present invention enables the highly reliable and high precision. The airbag system of can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a mounting structure of an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of an acceleration detection element of the acceleration sensor of the present invention.

FIG. 3 is a diagram showing a relationship between a mounting angle and an error of the acceleration sensor of the present invention.

FIG. 4 is a diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing the operating principle of the acceleration sensor used in the present invention.

FIG. 6 is a diagram showing a plan view of a silicon portion including a movable electrode of a detection element.

FIG. 7 is a diagram showing a mounting structure of a conventional acceleration sensor.

8 is a diagram showing a cross-sectional structure of FIG.

FIG. 9 is a diagram showing a cross-sectional structure when a conventional acceleration sensor is mounted.

10 is a diagram showing a cross section of the acceleration detection element of FIG. 9 and a shape of an IC.

FIG. 11 is a diagram showing an embodiment of an airbag system using the acceleration sensor of the present invention.

[Simple explanation of symbols]

1-signal applying section, 2-acceleration detecting element, 3-capacitance detecting section, 4-amplifying section, 5-silicon beam, 6-movable electrode,
7, 8-fixed electrode, 9-silicon, 10, 11-glass, 31-substrate, 32-IC, 3-base, 34-lead pin, 35-glass, 36a, b-mounting hole, 37-
Wiring, 41-Cap, 51a, 51b-Screw, 52-
housing,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masahiro Kurita Inventor Masahiro Kurita 2520 Takaba, Takata, Ibaraki Prefecture Hitachi Ltd. Automotive Equipment Division (72) Inventor Tetsuo Matsukura 2520 Takaba, Katsuta, Ibaraki Hitachi Ltd. Mfg. Co., Ltd. Automotive Equipment Division (72) Inventor Yasuhiro Asano 2471, Kashima Yatsu, Katsuta-shi, Ibaraki Pref. 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Masayoshi Suzuki 2520, Takata, Katsuta-shi, Ibaraki Hitachi, Ltd. Factory Automotive Equipment Division

Claims (4)

[Claims] 1. A movable electrode that displaces with respect to acceleration and at least one fixed electrode, wherein the movable electrode is supported by at least one beam, and the displacement of the movable electrode is recognized as a change in capacitance. A capacitance type acceleration sensor having an acceleration detecting element for converting a change in the capacitance into an electric signal to detect an acceleration, and being fixed by at least one mounting hole; An electrostatic capacity type acceleration sensor, characterized in that the fixing direction of the electrostatic capacity type acceleration sensor is 90 ° ± 30 °. 2. A movable electrode that displaces with respect to acceleration and at least one fixed electrode, wherein the movable electrode is supported by at least one beam, and the displacement of the movable electrode is recognized as a change in electrostatic capacitance. In the capacitance type acceleration sensor having an acceleration detection element for converting the change of the capacitance into an electric signal to detect the acceleration, the capacitance type acceleration sensor fixed by at least two mounting holes, and An electrostatic capacitance type acceleration sensor characterized in that one mounting hole direction is 90 ° ± 30 °. 3. The capacitance type acceleration sensor according to claim 1 and 2, wherein the acceleration detecting element and an IC in which a control circuit unit for controlling the acceleration detection result is integrated are separated from each other. An electrostatic capacitance type acceleration sensor characterized by being composed of a chip. 4. An air bag system, which operates in the event of a collision of an automobile to protect human life, and is arranged so that a gap between the fixed electrode and the movable electrode of the acceleration detecting element is constant. Type acceleration sensor, arithmetic processing means for judging whether or not to actuate the airbag based on an acceleration signal input from the electrostatic capacitance type acceleration sensor, and the aforesaid based on a start signal from the arithmetic processing means. An airbag system having a starting means for operating an airbag.