Acceleration switch

Details Acceleration switch Acceleration switch

2001-06-29

2003-07-01

Easthom, Karl D. (Department: 2832)

Electricity: circuit makers and breakers

Special application

Change of inclination or of rate of motion responsive

C200S06145M

Reexamination Certificate

active

06586691

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an acceleration switch, and more particularly, to an acceleration switch including a movable electrode that contacts a fixed electrode when subjected to acceleration that exceeds a predetermined value.
Many automobiles are presently equipped with air bag systems. A typical air bag system includes an air bag, an ignitor, and an electronic control unit (ECU). The ECU includes an acceleration sensor, which detects a sudden change in acceleration upon collision of the vehicle. The employment of a mechanical acceleration switch (i.e., safing sensor) has been proposed as such acceleration sensor.
FIGS. 1A
to
1
C schematically show the structure of a prior art acceleration switch
51
. The acceleration switch
51
includes a silicon chip
52
and a substrate
53
, which are connected to each other. As shown in
FIG. 1B
, the silicon chip
52
has a length of L
1
and a width of W
1
. Further, the silicon chip
52
has a hollow portion
52
a
in which a block-like inertia weight
54
is arranged.
A beam
55
is provided on each long side of the inertia weight
54
and extends from a position offset from the middle of the long side. The beams
55
connect the inertia weight
54
and the silicon chip
52
. The inertia weight
54
pivots about the beams
55
at a position offset from the center of gravity of the inertia weight
54
. Referring to
FIG. 1B
, the beams
55
each have a length of T
2
. Two movable electrodes
56
,
57
are arranged on the lower side of the inertia weight
54
, as viewed in FIG.
1
A. The movable electrodes
56
,
57
are located close to each other at the middle of the weight end that is farther from the beams
55
.
A hollow portion
53
a
is defined in the upper surface of the substrate
53
. A fixed electrode
58
is formed in the hollow portion
53
a
at a position corresponding to the movable electrodes
56
,
57
. The movable electrodes
56
,
57
are normally separated from the fixed electrode
58
.
When the acceleration switch
51
is subjected to acceleration, inertial force pivots the inertia weight
54
about the axis of the beams
55
in a downward direction (the direction indicated by arrow G in FIG.
1
A). When the acceleration becomes greater than or equal to a predetermined value, the inertia weight
54
pivots in a direction indicated by arrow F in
FIG. 1A
, and the movable electrodes
56
,
57
contact the fixed electrode
58
. When the value of acceleration is small, the movable electrodes
56
,
57
do not contact the fixed electrode
58
. Accordingly, the acceleration switch
51
is actuated only when the acceleration becomes greater than or equal to a predetermined value.
To actuate the acceleration switch
51
at a relatively small acceleration, the beams
55
may be thinned or elongated. However, the formation of thinner beams
55
has physical limitations and is thus not effective. Further, the formation of longer beams
55
limits miniaturization. For example, when the length of the beams
55
is changed to T
3
(T
2
<T
3
) as shown in
FIG. 2
, the width W
2
of the silicon chip
52
is increased by 2×T
3
−2×T
2
in comparison to when the width of the silicon chip
52
is W
1
(FIG.
1
B). This increases the area of the silicon chip
52
and enlarges the acceleration switch
51
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an acceleration switch having improved detection sensitivity while avoiding enlargement.
To achieve the above object, the present invention provides an acceleration switch including a switch body, a fixed electrode arranged in the switch body, and a movable weight arranged in the switch body. The movable weight is displaced when subjected to acceleration. The movable weight includes a movable electrode that contacts the fixed electrode when the movable weight is displaced, a recess formed in a side of the movable weight, and a beam connecting the movable weight and the switch body. The beam pivotally supports the movable weight and extends into the recess.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.


REFERENCES:
patent: 5828138 (1998-10-01), McIver et al.
patent: 6080944 (2000-06-01), Itoigawa et al.
patent: 6336658 (2002-01-01), Itoigawa et al.
patent: 3509054 (1986-04-01), None
patent: 3214531 (1991-09-01), None

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