Acceleration switch

Details Acceleration switch Acceleration switch

2002-11-26

2004-09-28

Scott, James R. (Department: 2832)

Electricity: circuit makers and breakers

Special application

Change of inclination or of rate of motion responsive

C200S06145M, C200S061490

Reexamination Certificate

active

06797899

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an acceleration switch, and more particularly, to an acceleration switch that includes a movable portion, which has a movable electrode, and a fixed electrode and that moves the movable portion when acceleration is applied so that the movable electrode contacts the fixed electrode.
Many automobiles are nowadays equipped with air bag systems. An air bag system generally 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 when the vehicle collides. A semiconductor acceleration sensor is used as such type of an acceleration sensor. The semiconductor acceleration sensor includes, for example, a strain gauge arranged on a beam, which supports a mass. The ECU activates the ignitor when determining that the applied acceleration is greater than or equal to a predetermined value. The thermal expansion of heated air instantaneously inflates a folded air bag.
The ECU may function erroneously when affected by electromagnetic waves generated by surrounding devices. Therefore, the employment of a mechanical acceleration switch (i.e., safing sensor) in addition to an electronic acceleration sensor has been proposed. The mechanical acceleration switch is less affected by the electromagnetic waves than the electronic 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 attached to each other. The silicon chip
52
has a hollow portion
52
a
, in which a generally rectangular parallelepiped inertial weight
54
is arranged. A beam
55
is provided on each long side of the inertial weight
54
at a position offset from the middle of the long side. The beams
55
connect the inertial weight
54
and the silicon chip
52
. The beams
55
support the inertial weight
54
at a position offset from the center (center of gravity) of the inertial weight
54
. Two movable electrodes
56
,
57
are arranged close to each other on the lower surface of the inertial weight
54
at a generally middle part of the distal end that is on the side 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 arranged in the hollow portion
53
a
at a position corresponding to the movable electrodes,
56
,
57
. The movable electrodes
56
,
57
are normally spaced from the fixed electrode
58
.
When acceleration is applied to the acceleration switch
51
, inertial force is applied to the inertial weight
54
such that the inertial weight
54
pivots about the beam
55
in a downward direction (the direction indicated by arrow G in FIG.
1
A). When the acceleration applied to the acceleration switch
51
becomes greater than or equal to a predetermined value, the inertial 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 acceleration is small, the inertial weight
54
does not pivot about the beam
55
. Thus, the fixed electrode
58
does not contact the movable electrode
56
. The acceleration switch
51
operates only when the applied acceleration is greater than or equal to the predetermined value.
When acceleration is applied to the acceleration switch
51
from a direction other than a predetermined detection direction, inertial force is applied to the inertial weight
54
from a direction indicated by arrow G in FIG.
2
A. In such case, the inertial weight
54
pivots in a twisted state, as shown in FIG.
2
A. In such state, an edge of the lower surface of the inertial weight
54
first contacts the substrate
53
, as shown in FIG.
2
B. This restricts the movement of the inertial weight
54
. The two movable electrodes
56
,
57
, which are on the same plane, may not contact the fixed electrode
58
. In other words, contact failure may occur in the acceleration switch
51
when acceleration is applied from a direction other than the predetermined detection direction.
BRIEF SUMMARY OF THE INVENTION
It is an objective of the present invention to provide an acceleration switch, which operation is guaranteed even when acceleration is applied to the acceleration switch from direction other than the a predetermined detection direction.
One perspective of the present invention provides an acceleration switch including a movable portion, which has a movable electrode, and a fixed electrode, in which movement of the movable portion in accordance with the application of acceleration causes the movable electrode to contact the fixed electrode. The acceleration switch has the movable portion, which includes an inertial weight moved in accordance with the application of acceleration, a beam portion for pivotably supporting the inertial weight, and a plurality of flexible plates arranged in the inertial weight, each of which has distal end, in which the movable electrode is located, and is flexed separately from one another.
In this structure, since the plurality of flexible plates, each provided with the movable electrode, flex separately, the movable electrodes move separately when the flexible plate are flexed. Therefore, even if only one of the movable electrodes contacts the fixed electrode when acceleration is applied to the acceleration switch from an unexpected direction, the other movable electrode moves separately from the former movable electrode and contacts the fixed electrode. Therefore, the activation of the acceleration switch is guaranteed even when acceleration is applied from an unexpected direction.


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patent: P2000-106070 (2000-04-01), None
patent: WO 01/92896 (2001-12-01), None

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