Shock detecting device

A hole 13 though which a firing pin 6a of a firing lever 6 is projected outside a housing 1 is formed in a wall 1c of the housing which is in parallel with a direction of an external shock applied to the housing 1. This structure ensures the rotational angle of the firing lever 6 and a biasing force of a spring 9 which urges the firing lever 6 can be used effectively as kinetic energy thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a shock detecting device, and in 
particular, to a shock detecting device for igniting an ignition element 
without using electric power. 
A shock detecting device is used as a sensor which is set to initiate an 
anti-shock safety device such as an air bag or a seat-belt tensioner. The 
conventional shock detecting device is disclosed, for example, in Japanese 
Patent Laid-open Print No. 249744/ 2nd year of Heisei (1990) which was 
published in 1990 without examination. In the conventional device, a 
weight is set to be rotated upon receipt of a shock whose magnitude is 
above a set value. Due to the resultant rotation of the weight, a firing 
lever is released from a cam portion of the weight which is biased by a 
spring, thereby rotating the firing lever. Thus, a firing pin formed 
integrally with the firing lever is extended outside a housing through a 
hole formed in a wall of the housing which is perpendicular to the 
direction of the application of the shock so that an ignition element such 
as a percussion element is struck. 
However, in the foregoing structure, since the firing pin is set to be 
extended in the opposite direction of the shock, the rotation of the 
firing lever is too small; and the biasing force of the spring is not 
effectively transformed into kinetic energy of the firing pin. 
SUMMARY OF THE INVENTION 
It is, therefore, a principal object of the present invention to provide a 
shock detecting device without the foregoing drawbacks. 
It is another object of the present invention to provide a shock detecting 
device in which a biasing force can be used effectively as the kinetic 
energy of a firing pin. 
In order to attain the foregoing objects, a shock detecting device in 
accordance with the present invention is comprised of a housing having a 
side wall for receiving an external shock and a bottom wall having a hole 
therethrough perpendicular to the side wall, a bracket accommodated within 
the housing and secured thereto, a weight having a first shaft coaxially 
therewith and supported on the bracket so as to be rotated when a second 
external shock exceeds a set value, a cam portion provided on the shaft, a 
firing lever accommodated within the housing and pivoted on the shaft 
which is connected to the housing so as to be parallel to the first shaft, 
a spring mounted on the second shaft and biasing the firing lever in one 
direction so as to engage the firing lever with the cam portion, a stopper 
pin provided on the weight and engaged with the bracket by the biasing 
force of the spring which is applied to the cam portion of the first 
shaft, and a firing pin provided on the firing lever and set to be rotated 
in one direction so as to be projected outside the housing through the 
hole upon release of the firing lever from the cam portion as a result of 
the external shock.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIGS. 1 and 2, a housing 1 of a shock detecting device 
according to the present invention includes a main body 1a in the form of 
a container whose top and portion is opened and a plate 1b for closing or 
covering the opening, within the inner space of the housing 1, a shock 
detecting mechanism 2 is accommodated. 
As shown in FIGS. 1 through 3, within the housing 1, there is installed a 
bracket 3 at an intermediate portion between the plate 1b and a bottom 
wall 1c of the housing 1. The bracket 3, which is formed from one metal 
sheet by bending, has a pair of opposed supporting portions 3a each of 
which is of an L-shape, a pair of opposed flange portions 3b each of which 
extends from an upper end of the corresponding supporting portion 3a with 
making an angle of 90 degrees relative thereto, and a connecting portion 
for connecting the upper end portions of both supporting portions 3a. The 
bracket 3 is secured or fixed at its supporting portions 3a to the bottom 
wall 1c. 
A weight 4 which is in the form of an annular member is secured coaxially 
to a geared portion 5a (see FIG. 3) of a shaft 5 so as to be movable 
therewith. The weight 4 is provided thereon with a stopper pin 4a which is 
in engagement with each flange portion 3b of the bracket 3 and this 
engagement sets an initial position of the weight 4 within the housing 1. 
It is noted that both ends of the shaft 5 are in sliding engagement with 
grooves 3a each of which is formed in the flange portion 3b. Thus, the 
weight is movable along grooves 3a and is also rotatable relative to the 
bracket 3. 
A firing lever 6 is rotatably mounted, via a bush or collar 8 (FIG. 3), on 
a pin 7 which is secured at its ends to the supporting portions 3a. As 
best shown in FIG. 4, a torsion spring 9 is arranged around the collar 8 
in such a manner that one end of the torsion spring 9 is secured to one of 
the supporting portions 3a and the other end is secured to the firing 
lever 6, thereby biasing the firing lever 6 continuously in the clockwise 
direction in FIG. 1. As shown in FIGS. 3 and 4, the pin 7 and the collar 8 
are formed with a stepped portion 7a and a stepped portion 8a, 
respectively, both of which are in opposition. The stepped portion 7a is 
used for supporting one end of the torsion spring 9 and the stepped 
portion 8a is used for supporting the other end of the torsion spring 9 
and the firing lever 6. 
A main portion 8b of the collar 8 is smaller than the stepped portion 8a in 
radius and a clearance is set to be defined between the main portion 8b 
and the torsion spring 9. As apparent from FIGS. 1 and 2, the firing lever 
6 is formed with a firing pin 6a, which is set to be projected outside 
housing 1 through a hole 13 formed in the bottom wall 13 upon rotation of 
the firing lever 6 as will be detailed. 
As illustrated in FIGS. 1 through 3, a pinion gear 10 is fixedly mounted on 
the shaft 5 near its one end portion and a rack gear 11 which is in mesh 
engagement with the pinion gear 10 is formed on one of the flange portion 
3b of the bracket 3. A cam portion 12 in a semi-circular shape in 
cross-section is formed on the shaft 5, which is detachably engaged with 
the firing lever 6, so as to be adjacent to the pinion gear 10. 
The structure as mentioned above is obtained after the following assembly 
processes. An engagement of the pinion gear 10 with the rack gear 11 is 
established under an initial condition that the stopper pin 4a is in 
abutment with the flange portion 3b after the mounting of the weight 4 on 
the shaft 5. Then, the firing lever 6 and the torsion spring 9 are 
supported on the collar 8, the resultant collar 8 is located between the 
supporting portions 3a, and thus located collar 8 is secured to the 
bracket 3 by the pin 7 secured to the supporting portion 3a after passing 
through the collar 8. Simultaneous to this fixing of the collar 8 to the 
bracket 3, an engagement of the firing lever 6 with the cam portion 12 of 
the shaft 5 is made. Thus, the bracket 3 in the form of a unit including 
the weight 4 and the firing lever 6 is formed. After this, the resultant 
bracket 3 is fixedly mounted to the housing 1, thereby competing the 
accommodation of the shock detecting mechanism 2 within the housing 1. 
As mentioned above, the firing lever 6, the pinion gear 10, the lack gear 
11 and the weight 4 are assembled in the bracket 3 as one unit independent 
from the housing 1. This serves for the effective assembly of the whole 
device. In addition, the bracket 3 per se is obtained from one metal 
sheet, which ensures the correct relationship between two any adjacent 
members without unexpected error. Thus, stable condition of the shock 
detecting device can be obtained. 
An operation of the foregoing structure or construction of the shock 
detecting device will be detailed hereinafter. 
Under the initial condition shown in FIG. 1, the cam portion 12 of the 
shaft 5 is in engagement with the firing lever 6, the weight 4 is in its 
initial state wherein the stopper pin 4a is in engagement with the flange 
portion 3b by the torsion spring 9, and the firing lever 6 is kept or held 
at its initial position by the foregoing engagement with the cam portion 
12 despite the application of the biasing force of the torsion spring 9 on 
the firing lever 6. 
Under the above-mentioned condition, when an external shock is applied to 
the housing 1 in a direction of an arrow indicated by "A" as shown in FIG. 
1 due to the collision of vehicles or collision of a vehicle with an 
object, the shock is detected by the weight 4. Then, as shown in FIG. 5, 
the weight 4 is moved along the rack gear 11 and each groove 3e by 
rotating in the clockwise direction against the biasing force of the 
torsion spring 9, resulting in the firing lever 6 being released from the 
cam portion 12. Thus, as shown in FIG. 6, the firing lever 6 is biased in 
the clockwise direction as a result of the biasing force of the torsion 
spring 9 which is being applied to the firing lever 6 and is brought into 
extension outside the housing 1 through the hole 13, thereby striking the 
percussion cap. 
In the foregoing embodiment, the holding of the weight under the initial 
condition and the rotation and the biasing of the firing lever 6 can be 
established by the common torsion spring 9. This enables the obtaining of 
large energy despite the narrow space for accommodating the source thereof 
and the decrease of components in number, thereby establishing the 
miniaturization of the shock detecting device itself. Furthermore, the 
weight is of larger diameter, by which a large moment of inertia can be 
obtained, thereby preventing the instantaneous detection of the shock 
during the vehicle's travel on a bad road. Thus, no danger of the 
unexpected initiation of the shock detecting device is established, which 
leads to the improvement of the device in reliability. 
In addition, since the projecting direction of the firing pin 6a is 
substantially perpendicular to the direction of the application of the 
shock, the rotating angle or the circumferential travel of the firing 
lever 6 can be set to be large, thereby enabling the effective use of the 
biasing force of the torsion spring 9 as the kinetic energy of the firing 
pin 6a. This means that the ignition of the percussion cap can't be 
initiated so long as the strike energy does not reach a set high value. In 
other words, high reliability in the ignition of the percussion cap can be 
obtained. 
Furthermore, due to the clearance between the collar 8 and the torsion 
spring 9, the frictional loss therebetween can be decreased, thereby 
stably holding the weight under the initial condition, and decreasing the 
loss of the kinetic energy of the firing pin 6a, thus improving the 
reliability of the ignition of the percussion cap. 
Although only one embodiment of the present invention has been disclosed 
and described, it is apparent that other embodiments and modifications of 
the present invention are possible without departing from the coverage of 
the attached claims.