Electricity: circuit makers and breakers – Special application – Change of inclination or of rate of motion responsive
Reexamination Certificate
2001-08-17
2002-09-24
Scott, J. R. (Department: 2832)
Electricity: circuit makers and breakers
Special application
Change of inclination or of rate of motion responsive
Reexamination Certificate
active
06455791
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration detection device which detects acceleration of a moving body such as an automobile and sensitivity setting method therefor. In particular, the present invention relates to an acceleration detection device and sensitivity setting method therefor, which is used with a collision detection device which detects acceleration generated in the moving body during a collision and outputs an electric signal to an airbag activation device to operate an air bag.
2. Description of the Prior Art
FIG. 1
is a perspective view of a conventional acceleration detection device as shown in JP-A-9-211023 and shows the device with a part of a housing removed.
FIG. 2
is a sectional view of the acceleration detection device as shown in FIG.
1
. In the figures, reference numeral
1
denotes a mass body having a predetermined mass and being constituted by a first mass member
2
and a second mass member
4
.
3
is a moving contact which displaces with the mass body
1
.
5
is a slide shaft which passes through the mass body
1
to limit the moving direction of the mass body
1
and slidably supports the mass body
1
.
6
is a cylindrical compression coil spring which presses the mass body
1
in a predetermined direction (indicated by arrow A in FIG.
1
).
7
,
8
are fixed contacts which are arranged on an inner face of the housing
9
so as to be faced with each other and sandwich the slide shaft
5
, and which come into contact with the moving contact
3
when the mass body
1
is displaced at a fixed distance in an opposite direction to the above predetermined direction along the slide shaft
5
against the elastic force of the compression coil spring
6
.
9
is a housing which stores the mass body
1
, the moving contact
3
, the slide shaft
5
and the compression coil spring
6
.
10
is a cover which constitutes a case of the acceleration detection device by assembly with the housing
9
. One end of the compression coil spring
6
abuts with the mass body
1
and the other end abuts with the housing
9
. The cylindrical compression coil spring
6
has linear deflection-load characteristics in which a degree of deflection (the degree of displacement of the mass body
1
) is proportional to a load applied to the compression coil spring
6
.
The moving contact
3
is provided with two contacts
3
a
and positioning nails
3
b
. The moving contact
3
is sandwiched between the first mass member
2
and the second mass member
4
and is fixed to the mass body
1
. The tip portion of the contact
3
a
is formed in the shape of a letter R. The respective contacts
3
a
are formed in a straight cantilever with respect to the mass body
1
. The positioning nails
3
b
abut with the second mass member
4
, thereby to position the moving contact
3
and prevent rotation thereof.
The housing
9
is provided with a notch
9
a
for housing the contacts
3
a
of the moving contact
3
when not in contact with the fixed contacts
7
,
8
, a coil spring fixing portion
9
b
for fixing an end of the compression coil spring
6
, a stopper
9
c
for limiting the displacement of the mass body
1
, and a rotation stopper
9
d
for preventing the mass body
1
from rotating about the slide shaft
5
.
The first mass member
2
is provided with shock absorbing members
2
a
for absorbing the shock upon collision with the stopper
9
c
of the housing
9
, a tapered portion
2
b
for guiding the compression coil spring
6
when the first mass member
2
is coupled with the compression coil spring
6
and acting as a seat surface when joined, and a base
2
c
on which the shock absorbing members
2
a
and the tapered portion
2
b
are mounted. The shock absorbing member
2
a
is of a rubber-like material having a large shock absorbing capacity, for example, a thermoplastic elastomer and the shock absorbing member
2
a
is fixed to the base
2
c
by rotating from front to back through a hole provided in the base
2
c
or by burning onto the base
2
c.
The second mass member
4
is provided with a plate portion
4
a
which has a square cross section and limits the rotation of the mass body
1
by abutting with the rotation stopper
9
d
of the housing
9
, and a positioning portion
4
b
which abuts with the positioning nail
3
b
of the moving contact
3
.
In this type of acceleration detection device, an electric current flows between the fixed contacts
7
,
8
when the moving contact
3
is in contact with the fixed contacts
7
,
8
. In this way, it is possible to detect whether acceleration exceeds a predetermined value.
Furthermore, in this type of acceleration detection device, the sensitivity corresponding to a threshold value of a detectable acceleration is determined based on a spring constant of the compression coil spring
6
, an initial load which is a load applied to the compression coil spring
6
by the mass body
1
in an unloaded condition in which acceleration is not generated, the distance between the moving contacts
3
and the fixed contacts
7
,
8
in the unloaded condition, and the mass of the mass body
1
. The sensitivity of the acceleration detection device is set by regulating the pitch and/or the wire radius of the compression coil spring
6
, thereby regulating the spring constant and/or the initial load.
The operation of the conventional acceleration detection device when provided in a moving body such as an automobile will be described below.
When a moving body such as an automobile is running normally in an unloaded condition, the mass body
1
is urged towards the cover
10
by the elastic force of the compression coil spring
6
. As a result, the contacts
3
a
of the moving contact
3
are separated from the fixed contacts
7
,
8
, and does not make a contact with the fixed contacts
7
,
8
. Thus, an electrical connection does not exist between the moving contact
3
and the fixed contacts
7
,
8
. Therefore, the fixed contacts
7
,
8
are not electrically connected to each other and an electric current does not flow between them. This displays the fact that the moving body such as an automobile is traveling normally and has not undergone a collision.
When the moving body such as an automobile undergoes a collision and an acceleration (deceleration) is generated to the moving body, the mass body
1
slidably supported is displaced towards the stopper
9
c
against the elastic force of the compression coil spring
6
. At this time, the contacts
3
a
of the moving contact
3
come into contact with the fixed contacts
7
,
8
and slides in such a state. As a result, a continuous electrical connection exists between the fixed contacts
7
,
8
and the moving contact
3
. Thus, when the moving body such as an automobile collides and an acceleration is generated to the moving body, the fixed contacts
7
,
8
are electrically connected to each other and a current flows between them. This displays the fact that the moving body such as an automobile has undergone a collision.
Furthermore, when the moving body such as an automobile undergoes a strong collision and a large acceleration is generated as a result, the mass body
1
displaces to a position of the stopper
9
c
against the elastic force of the compression coil spring
6
and collides with the stopper
9
c
. As a result, the moving contact
3
vibrates, or the fixed contact
7
vibrates by transmission of the shock wave to the fixed contact
7
. Thus, the contact of the moving contact
3
with the fixed contacts
7
is momentarily released by the vibration and a so-called chattering is caused. The influence of the chattering is particularly conspicuous in the acceleration detection device as shown in
FIG. 1
in which the moving contact
3
is fixed to the mass body
1
. In order to avoid the influence of the chattering, the shock absorbing member
2
a
is provided on the first mass member
2
. In such a way, the collision energy generated by the collision of the mass body
1
with the stopper
9
c
can be damped and th
Murai Eiichiro
Yamashita Toshiyuki
LandOfFree
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