Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-09-01
2002-01-08
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C180S282000, C200S06145M, C073S514360
Reexamination Certificate
active
06336658
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an acceleration switch and a method of manufacturing the same.
Recently, many cars have been equipped with air bags. Generally, an air bag system comprises an air bag, an inflator and an ECU (electronic control unit). A sudden change in acceleration caused by a car collision is sensed by an acceleration sensor, which is a part of the ECU. An acceleration sensor for sensing a collision employs, for example, a semiconductor type acceleration sensor, in which a strain gauge is formed on a beam supporting a mass. When an applied acceleration is equal to or greater than a set value, the ECU actuates the inflator to inflate the air bag.
A mechanical acceleration switch
51
has been proposed in the prior art, which is shown schematically in FIG.
10
. The acceleration switch
51
comprises a switch body
52
, and two inertia weights
53
,
54
located in a space inside the switch body
52
. The first inertia weight
53
is spherical in shape, and has an eccentric shaft
59
positioned eccentrically relative to its center of gravity. The first inertia weight
53
is rotatably supported at its eccentric shaft by the switch body
52
. The first inertia weight
53
is connected to the second inertia weight
54
by a beam
55
. The second inertia weight
54
is smaller and lighter than the first inertia weight
53
. Also, a pair of terminals
56
,
57
provided with contacts at their distal ends are arranged in the vicinity of the second inertia weight
54
. These terminals
56
,
57
are electrically connected to an unillustrated printed circuit board, on which an acceleration sensor, switching elements and the like are mounted.
When the acceleration switch
51
is accelerated, a movable part composed of the first and second inertia weights
53
,
54
and the beam
55
is subjected to the force of inertia, which tends to move the movable part relative to the switch body
52
. If the acceleration is great enough, the force of inertia turns the heavy first inertia weight
53
as well as the second inertia weight
54
and the beam
55
about the eccentric shaft
59
. Then a push portion
58
provided on the beam
55
comes into contact with one of the terminals
56
, and the terminal
56
is pushed into contact with the terminal
57
. On the other hand, if the acceleration is relatively small, the first inertia weight
53
cannot revolve around the eccentric shaft
59
, and the push portion
58
does not contact the terminal
56
. Therefore, the terminal
56
does not contact the terminal
57
. In this manner, with the acceleration switch
51
, the terminals
56
,
57
contact each other only when an acceleration exceeding the set value is applied.
Acceleration sensors are being miniaturized, but miniaturization is presently thwarted by the acceleration switch
51
since the acceleration switch
51
is mechanical as shown in FIG.
10
. Accordingly, an ECU provided with a mechanical type acceleration switch
51
is comparatively bulky.
Also, if the acceleration switch
51
were made smaller, the sensitivity of the switch would likely decrease because the weights would not be large enough. Accordingly, there is a demand for smaller, more sensitive acceleration switches.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide an acceleration switch that is small and highly reliable. It is another object of the present invention to provide a method of reliably and simply manufacturing acceleration switches that are small and reliable.
To attain the objects described above, in the first aspect of the present invention, there is provided an acceleration switch adapted to be switched between the states of ON and OFF depending upon the magnitude of acceleration applied. The acceleration switch comprises a substrate and a semiconductor chip mounted on the substrate. The substrate includes a first contact formed thereon. The semiconductor chip includes a movable part adapted to move between an open position and a closed position depending upon the magnitude of acceleration applied. The movable part has a second contact. When the magnitude of the acceleration applied is less than a predetermined value, the movable part is located in the open position and the second contact is spaced from the first contact. When the magnitude of acceleration applied is equal to or greater than the predetermined value, the movable part is located in the closed position and the second contact comes into contact with the first contact.
In a second aspect of the present invention, there is provided a method of manufacturing an acceleration switch having a movable part adapted to move between states of ON and OFF depending upon the magnitude of acceleration applied. The method comprises the steps of forming an N-type silicon epitaxial growth layer on a silicon chip composed of a P-type single crystal, forming a first high concentration P-type silicon layer having a predetermined configuration in the N-type silicon epitaxial growth layer, forming a second high concentration P-type silicon layer having a predetermined configuration on the first high concentration P-type silicon layer in the N-type silicon epitaxial growth layer, reforming the first and second high concentration P-type silicon layers into porous silicon layers by subjecting them to anodic oxidation, and forming the movable part by removing the porous silicon layers by alkali etching.
In a third aspect of the present invention, an air bag system mounted on a car to protect on occupant of the car from the shock of a collision is provided. The system comprises an air bag, an inflator for inflating the air bag, and an ECU for instructing actuation of the inflator. The ECU comprises an acceleration switch for outputting an ON signal to the ECU when acceleration of the car reaches a predetermined value. The acceleration switch comprises a substrate and a semiconductor chip mounted on the substrate. The substrate has a first contact. The semiconductor chip includes a movable part adapted to move between an open position and a closed position depending upon the magnitude of acceleration applied. The movable part is provided with a second contact. When the magnitude of the acceleration applied is less than the predetermined value, the movable part is located in the open position and the second contact is spaced from the first contact. When the magnitude of the acceleration applied is equal to or greater than the predetermined value, the movable part is located in the closed position and the second contact comes into contact with the first contact.
Features of the present invention thought to be novel will be made apparent particularly in the appended claims. The present invention as well as its object and advantages will be understood from the description of embodiments, which are preferred at present, with reference to the accompanying drawings.
REFERENCES:
patent: 4706374 (1987-11-01), Murakami
patent: 4855544 (1989-08-01), Glenn
patent: 5138414 (1992-08-01), Shinohara
patent: 5157472 (1992-10-01), Takemura
patent: 5177331 (1993-01-01), Rich et al.
patent: 5342089 (1994-08-01), Fink et al.
patent: 5594172 (1997-01-01), Shinohara
patent: 5828138 (1998-10-01), McIver et al.
patent: 5905203 (1999-05-01), Flach et al.
patent: 6236005 (2001-05-01), Kvisteroey et al.
Itoigawa Koichi
Murate Makoto
Yoshida Yutaka
Dickson Paul N.
Kabushiki Kaisha Tokai Rika Denki Seisakusho
Sheridan & Ross P.C.
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