Airbag system using three-dimensional acceleration sensor

• US 5,707,077 A
• Filed: 06/07/1995
• Issued: 01/13/1998
• Est. Priority Date: 11/18/1991
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Yokota, Yoshihiro, Hayashi, Masahide, Matsumoto, Masahiro, Koide, Akira
• Primary Examiner(s): Culbreth, Eric D.
• Application Number:
  US08/479,451
• Time in Patent Office: 951 Days
• Field of Search: 280/734, 280/735, 73/517 R, 73/517 B, 73/514.32, 361/280, 361/283.1, 361/283.2, 361/283.4, 361/282.4
• US Class Current: 280/735
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass

Abstract

A three-dimensional acceleration sensor capable of detecting a small acceleration value and even an acceleration value amounting up to 100 G occurring in the event of a collision has a diaphragm for linking a frame and a massive part, and diaphragms and beams for linking the massive part and a central part. These elements are formed by working a single crystalline silicon plate. Gaps between the massive part and opposing electrodes are changed by acceleration applied to the massive part. A circuit connected to terminals detects the changes in gaps as changes in capacitances and determines direction and level of the applied acceleration.

Claims

1. An airbag system comprising:

a three-dimensional acceleration sensor having a support on which a stationary electrode is arranged, a central part fixed to said support, a single massive part acting as a movable electrode and a link member for interconnecting said central part and said massive part;

said link member being comprised of a combination of diaphragms and beams which are operatively provided around said central part; and

means for starting an airbag on the basis of an output of an arithmetic output unit of said three-dimensional acceleration sensor, wherein means is provided for sensing changed electrical capacitance between the stationary electrode and the single massive part at four positions thereof, and means is further provided for detecting applied acceleration in response to changes in sensed electrical capacitance at the four positions by addition and subtraction of changes in electrical capacitance values.

2. The airbag system according to claim 1, wherein said central part has a square form and said beams are provided at respective sides of the square form.

3. The airbag system according to claim 1, wherein said detecting means comprises a circuit configured to decide the direction of applied acceleration by detecting changes in capacitance between said massive part and a plurality of opposing stationary electrodes.

4. The airbag according to claim 3, wherein wiring lines are etched on the support from the stationary electrodes and are configured to avoid disturbing balance of said massive part.

5. A airbag system according to claim 1, wherein a distance between an electrode portion of said massive part and said stationary electrode is larger than a distance between said support and said massive part.

6. The airbag system according to claim 5, wherein said detecting means comprises a circuit which decides the direction of applied acceleration by detecting changes in capacitances between said massive part and a plurality of opposing stationary electrodes.

7. The airbag system according to claim 6, wherein wiring lines are etched on the support from the stationary electrodes and are configured to avoid disturbing balance of said massive part.

8. The airbag system according to claim 1, wherein a frame surrounds said single massive part, and an additional diaphragm links said frame and said single massive part.

9. The airbag system according to claim 1, further comprising a frame surrounding said single massive part, a link member comprised of a diaphragm and linking said frame and said single massive part, said means for sensing changed electrical capacitance between the stationary electrode and the single massive part being at four positions of the single massive part, and means for detecting applied acceleration in response to changes in sensed electrical capacitance at the four positions by addition and substraction of changes in electrical capacitance values.

10. The airbag system according to claim 9, wherein a distance between an electrode and said massive part is larger than a distance between said support and said massive part.