# US 5,707,077 A · Airbag system using three-dimensional acceleration sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,707,077 A - Document ID: US5707077A - Status: Granted - Kind: A - Application number: 08/479,451 - Filed: 1995-06-07 - Granted: 1998-01-13 - Earliest claimed: 1991-11-18 - Assignees: Hitachi, Ltd. - Inventors: Yoshihiro Yokota; Akira Koide; Masahiro Matsumoto; Masahide Hayashi - Web page: https://patentgrep.com/patent/US5707077A ## CPC - G01P 15/125: by capacitive pick-up - G01P 15/18: in two or more dimensions - 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} - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) ## 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 ### Claim 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. ### Claim 2 (depends on 1) 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. ### Claim 3 (depends on 1) 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. ### Claim 4 (depends on 3) 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. ### Claim 5 (depends on 1) 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. ### Claim 6 (depends on 5) 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. ### Claim 7 (depends on 6) 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. ### Claim 8 (depends on 1) 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. ### Claim 9 (depends on 1) 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. ### Claim 10 (depends on 9) 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.