JP2602615Y2 - Impact sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact sensor for reliably operating a reed switch for a certain period of time when a magnetic shielding member moving by impact releases a magnetic shield between a magnet and a reed switch.

[0002]

2. Description of the Related Art In order to reduce occupant fatal accidents due to a vehicle collision, there is an urgent need to introduce an airbag device that protects a driver sitting in a front seat or a driving assistant from the impact of a collision.
For example, in an airbag device 1 shown in FIG. 3, an airbag 2 is embedded in a center portion or a dashboard portion of a steering wheel of a vehicle, and when a collision occurs, an operating current is supplied to a detonating element 3 called a squib. , The airbag 2 is explosively deployed. The impact sensor 11 used for collision detection is of a mechanical contact type that closes a contact upon sensing an impact. The impact sensor 11 closes even when a relatively low gravitational acceleration is applied. The electronic switch 4 is connected in series with the shock sensor 11 with the detonating element 3 interposed therebetween, and is connected to the acceleration sensor 6 via the AD converter 5 so that the airbag 2 is not unnecessarily activated due to vibrations sometimes received from the road surface. Done C
The electronic switch 4 is closed when the PU 7 calculates an impact force exceeding a certain limit. Therefore,
The airbag 2 is not deployed only when the impact sensor 11 is closed, but is deployed only when both the impact sensor 11 and the electronic switch 4 are closed.

[0003] The shock sensor 11 does not close due to electromagnetic interference, unlike the electronic switch 4.
Although it is indispensable as a safety switch against the malfunction of the electronic switch 4, it must have a structure that reliably maintains the closed state until the electronic switch 4 is operated in the early stage of a collision. That is, the impact sensor 11 includes
It is required that the switch be reliably closed when a gravitational acceleration exceeding a certain value is detected, and that the closed state be maintained even if resonance or the like occurs until the electronic switch 4 is closed. . In particular, when the structural strength of the vehicle itself or the rigidity of the mounting location of the impact sensor 11 is insufficient, for example, as shown in FIG. 4, during the deceleration acting in the direction to close the impact sensor 11, the impact sensor 11 It should be noted that a resonance state in which an acceleration component acting in the direction of opening the gate is periodically superimposed is likely to occur, and the danger of chattering in which the shock sensor 11 repeatedly turns on and off in accordance with the resonance cycle increases.

FIGS. 5 and 6 are cross-sectional views showing the conventional shock sensor 11 used in the above-described airbag device, when it is opened and when it is closed. The illustrated impact sensor 11 encloses a reed switch 14 in an encapsulation tube 13 projecting from the center of a bottomed cylindrical holder 12, and further fits a coil spring 15 and an annular magnet 16 into the encapsulation tube 13. Finally, a cylindrical case 17 is attached to the holder 12. One end of the coil spring 15 is locked to the bottom surface of the holder 12,
The other end is locked by the magnet 16. Magnet 1
6 is normally in contact with the bottom of the case 17 and is out of the sensitive range of the reed switch 14, but when the impact sensor 11 receives an external impact, the cylindrical end surface of the holder 12 is compressed while the coil spring 15 is compressed. 18 to a position where it abuts and locks. The cylindrical end surface 18 is a stopper for locking the magnet 16 within the sensitive area of the reed switch 14, and the magnet 16 locked by this stopper closes the reed switch 14 by its magnetic force. Note that the sensitive area of the reed switch 14 is limited to a very narrow range in which the magnet 16 can be regarded as facing or directly facing the contact of the reed switch 14, so that the cylindrical end face 18 serving as a stopper has sufficient positioning. It must be manufactured with precision.

[0005]

The above-described conventional impact sensor 11 uses a magnet 16 when it hits a cylindrical end face 18.
So that it does not bounce out of the sensitive area
8 is raised by a projection 19 to provide a step in the vertical direction in the figure, and the magnet 1 abuts against the cylindrical end face 18.
By inclining 6, the inner wall of the opening of the loose fitting hole 16a is frictionally locked to the outer wall of the sealing tube 13. However, the loose fitting hole 16a of the magnet 16
Is generated between the outer wall of the sealing tube 13 and the outer wall of the sealing tube 13 because the entire periphery of the opening is not locked to the sealing tube 13 but only to two points near a point contact. The friction locking force was insignificant. For this reason, if the above-mentioned resonance in which the acceleration component is periodically superimposed during the deceleration occurs, the magnet 16 vibrates inside and outside the sensitive zone at a resonance cycle, and the electronic switch is generated due to chattering of the reed switch 14 and the like. Although the switch 4 was closed, the closing of the impact sensor 11 was delayed in some cases, and the airbag 2 could not be deployed properly.

In the conventional shock sensor 11, when the inner wall of the opening portion of the play hole 16a of the magnet 16 is frictionally locked to the outer wall of the sealed tube 13, two locking points for the sealed tube 13, that is, a play position. Since there is a distance difference of about the width of the magnet 16 between the distal opening and the distal opening of the fitting hole 16a, the impact transmitted to the reed switch 14 via the sealing tube 13 is the contact opening / closing direction (vertical direction in the figure). Easy to act on
This also contributed to the above-mentioned chattering, that is, breaking of the closed state. Further, Japanese Unexamined Patent Publication No.
No. 107266 “Magnetic acceleration sensor”
The center part is located between the switch and the contact part of the reed switch.
A fixed ring-shaped magnet and a shock
Sometimes release the magnetic field line shield from the magnetic field line shield position against the spring
Position and move the reed switch to the magnetic field line of the magnet.
With a ring-shaped shield member
An impact sensor is disclosed. However, this
The impact sensor is used in normal conditions where no impact is applied.
The shielding member, which is the magnetic shielding member, to the magnetic field line shielding position
There is no locking means, and it is shielded when impact is applied
The spring against the member should be
Since the shield member is only fixed,
The material is subject to impact in an unconstrained state where it can freely vibrate in both directions.
You will have to wait, and external
When a weak vibration is given, the shield member and the spring
If the vibration is close to the resonance frequency of the vibration system
Despite the absence of a strike, the shield is large
Displacement causes malfunction of reed switch
There was a problem that there were occasions.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a sealed tube in which a reed switch is sealed.
And a ring-shaped magnet fixed to the inner wall portion of the tubular body within the sensitive range of the reed switch,
It is loosely fitted in the enclosing pipe so as to be displaceable in the pipe axis direction, and is usually at a magnetic shielding position where it abuts and locks on the magnet, and shields a magnetic line of force between the magnet and the reed switch. A magnetic shielding member that is displaced to a magnetic shielding releasing position to release the shielding and responsively operates the reed switch by the magnetic field lines of the magnet, and a spring that biases the magnetic shielding member to the magnetic shielding position. It is characterized by having.

[0008] Further, according to the present invention, the magnetic shielding member comprises:
A small-diameter cylindrical portion for loosely inserting the hollow portion of the magnet,
The spring is loosely fitted to the inner wall of the tubular body, and one end of the tubular body is engaged with the locking surface of the spring.
Large-diameter, the other end of which is a contact locking surface with the magnet
Characterized in that it consists of a tubular part

[0009]

According to the present invention, a magnet is fixed within a sensitive area of a reed switch enclosed in a sealed tube, and a magnetic shielding member which is usually provided between the magnet and the reed switch and shields a magnetic field line is used to prevent impact. When it is received, it moves out of the shielded area against the spring to release the shield, and the reed switch is responsively operated by the magnetic force lines of the magnet, thereby reliably detecting the impact.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. 1 and 2 are cross-sectional views showing an embodiment of the impact sensor according to the present invention at the time of opening and at the time of closing, respectively.

An impact sensor 21 shown in FIG. 1 has an annular magnet 26 sandwiched between a holder 22 and a cylindrical case 27, and has a magnet 26 within a sensitive area of a reed switch 24 enclosed in an enclosure tube 23 serving as an outer shell. Is fixed. Further, a magnetic shielding member 30 composed of a magnetic ring that is loosely fitted into the sealing tube 23 is locked to the magnet 26 so that the lines of magnetic force reaching the reed switch 24 are shielded when no impact is applied. The magnetic shielding member 30 includes a small-diameter cylindrical portion 30a for loosely inserting the loose fitting hole 26a of the magnet 26 and a large-diameter cylindrical portion 30b for loosely fitting on the inner wall of the holder 22, and the end surface of the large-diameter cylindrical portion 30b and the bottom surface of the holder 22. And a coil spring 25 is fitted between them. In addition, since the magnetic shielding member 30 which is a movable body does not need to be locked at a specific position when receiving an impact, the movable distance of the magnetic shielding member 30 is sufficient in the embodiment. In this respect, it is significantly different from the conventional impact sensor 11 in which the magnet 26 is a movable body, in which the moving distance of the magnet 16 is limited in order to restrict the position of the magnet 16 in the sensitive area.

By the way, when no impact is applied, the magnetic shielding member 30 is pushed by the coil spring 25 to the magnetic shielding position where the large-diameter cylindrical portion 30b abuts on the end face of the magnet 26. There is . For this reason, the magnetic lines of force generated by the magnet 26 in the sensitive range of the reed switch 24 are shielded by the magnetic shielding member 30 and
, The reed switch 24 is open. That is, the magnetic shielding member 30 is in the shielding area to prevent the contact from closing.

Here, when an impact is applied to the impact sensor 21, the magnetic shielding member 30 which has been locked to the magnet 26 until then moves while compressing the coil spring 25, as shown in FIG.
As shown in (2), it reaches the magnetic shielding release position outside the shielding area.
As a result, the magnetic shielding between the magnet 26 and the reed switch 24 is released, and the contact of the reed switch 24 is closed by the magnetic force of the magnet 26. Magnetic shielding member 30
When the impact exceeds a certain limit, the coil spring 25 is compressed to the compression limit, but can move over a sufficient distance range before reaching the movement limit. Therefore, even if the magnetic shielding member 30 is repelled by the energy stored in the compressed coil spring 25, the magnetic shielding member 30 is again moved to the magnetic shielding position in the shielding area between the magnet 26 and the reed switch 24. It takes considerable time to return to. Even if the above-described resonance in which the acceleration component periodically overlaps during the deceleration occurs, the square root of k / M, which is the ratio between the weight M of the magnetic shielding member 30 and the spring constant k of the coil spring 25, is used. If the natural frequency of the magnetic shielding member 30 determined by is different from the resonance frequency, the magnetic shielding member 30 is hard to be pulled back into the shielding area,
Since the reed switch 24 can reliably maintain the closed state until the electronic switch 4 is closed, the airbag 2 can be properly deployed.

[0014] In this way, the shock sensor 21, shock waiting
Weak vibrations are given from the outside, and the vibrations are
A field close to the resonance frequency of the vibration system including the shielding member 30 and the spring
Even if it is, the magnetic shielding member 30 is greatly displaced.
No impact, and thus no actual shock
Nevertheless, if the reed switch 24 malfunctions
I never said. In addition, in order to move the magnetic shielding member 30 that magnetically shields between the reed switch 24 and the magnet 26 instead of moving the magnet 26, the reed switch 14 is moved like the case where the movable body is the magnet 16. never such range of movement of the magnet 16 or restricted by the size of the sensitive area, since the magnetic shielding member 30 is a movable body can be moved over a sufficient distance range, the magnetic shielding member 30 Move
In the direction, without providing a special stopper for the magnetic shielding member 30, the spring 25 compressed to the compression limit can be used as a stopper , so that, for example, during deceleration when the magnetic shielding member 30 is to be moved. Even if there is an acceleration component with the opposite direction of action and resonance occurs in which deceleration and acceleration alternately rise and fall with a fixed period, the conventional movable
As in the case of the magnet type, it is not possible for the magnet 16 that has moved into the sensitive area due to deceleration to repeatedly deviate out of the sensitive area due to swinging back due to resonance, or to cause chattering in which closing and opening continue in synchronization with the resonance cycle. Instead, the closed state can be maintained at least for the initially set fixed time against an impact exceeding a certain limit.

Further , the magnetic shielding member 30 is
6, a small-diameter cylindrical portion 30a into which the hollow portion is loosely inserted, and the holder 22
Of the spring 25, one end of which is a locking surface of the spring 25,
Is a large-diameter cylindrical portion 30 which is a contact locking surface with the magnet 26.
b, a magnetic shielding member made of a stepped cylindrical body
Just use 30 to secure contact with magnet 26
At the same time, and reattach the sealing tube of the reed switch 24 again.
Smooth displacement of the magnetic shielding member 30 as the guide
The magnetic shielding member 30, which moves while compressing the coil spring 25 when it receives an impact, can be smoothly vibrated at the natural frequency assumed at the time of design. On the other hand, the closed state can be surely maintained for a predetermined time set initially.

In each of the above embodiments, if only the shock sensor 21 continues to be closed without closing the electronic switch 4, the magnetic shielding member 30 may be damaged by vibration from the road surface or a shock when the vehicle rides on the road shoulder. It is highly probable that the state is kept locked outside the shielded area. In such a case, the abnormality of the impact sensor 21 can be displayed on an instrument panel or the like, and the user can be requested to perform an inspection.

[0017]

[Effect of the invention] As described above, this invention is enclosed
The reed switch enclosed in the pipe is housed in the cylindrical body,
An annular magnet is fixed to the inner wall portion of the tubular body within the sensitive range of the lead switch, and a magnetic shielding member, which is loosely fitted in the sealed tube so as to be displaceable in the tube axis direction, normally abuts and locks on the magnet. It is in the magnetic shielding position and shields the line of magnetic force between the magnet and the reed switch.When it receives an impact, it is displaced to the magnetic shielding release position against the spring to release the shielding, and the reed switch is released. Due to the structure that is sensitive to the magnetic field lines of the magnet, a weak vibration is given from the outside during the standby of the impact, and even if the vibration is close to the resonance frequency of the vibration system consisting of the magnetic shielding member and the spring, the magnetic shielding The member will not be displaced greatly,
Therefore, there is no possibility that the reed switch will malfunction even though no shock is actually applied,
Also, instead of moving the magnet, a magnetic shielding member that magnetically shields between the reed switch and the magnet is moved, so that the movable body is a magnet, depending on the size of the sensitive area of the reed switch, as in the case of a magnet. The moving range is not restricted, and the movable magnetic shielding member can be moved over a sufficient distance range. Therefore, the moving direction of the magnetic shielding member is Even if no special stopper is provided, it is possible to use the spring compressed to the compression limit as the stopper. For example, during the deceleration for moving the magnetic shielding member, an acceleration component whose operation direction is directly opposite is included, and the deceleration is reduced. Even if resonance occurs in which the speed and acceleration alternately rise and fall with a fixed period, the deceleration is the same as with the conventional movable magnet type. The magnet that has moved into the sensitive area does not repeatedly deviate out of the sensitive area by swinging back due to resonance, and does not generate chattering that keeps closing and opening synchronized with the resonance cycle, There is an excellent effect that the closed state can be maintained at least for the initially set certain time.

Further, the magnetic shielding member is provided for the magnet.
A small-diameter cylindrical portion into which a hollow portion is loosely inserted,
Fitting, one end is a locking surface of the spring, and the other end is the mag
It consists of a large-diameter cylindrical part that
Just use a magnetic shielding member consisting of a stepped cylindrical body
To secure the contact with the magnet,
The magnetic shield is guided by the reed switch enclosure.
Smooth can displacement at readily realized, the magnetic shield member to move while compressing the spring when impacted, it is possible to smoothly vibrate with a natural frequency which is assumed at the time of design
Therefore, there is an effect that the closed state can be reliably maintained for a predetermined time initially set against an impact exceeding a certain limit.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an opened state of an embodiment of the impact sensor of the present invention.

FIG. 2 is a cross-sectional view showing a closed state of the impact sensor shown in FIG.

FIG. 3 is a circuit configuration diagram illustrating an example of an airbag device.

FIG. 4 is a waveform diagram showing a time course of deceleration and acceleration in a resonance state.

FIG. 5 is a sectional view showing an open state of an example of a conventional impact sensor.

FIG. 6 is a sectional view showing a closed state of the impact sensor shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Impact sensor 22 Holder 23 Encapsulation tube 24 Reed switch 25 Coil spring 26 Annular magnet 27 Cylindrical case 30 Magnetic shielding member

Claims (2)

(57) [Scope of request for utility model registration] 1. An enclosure for enclosing a reed switch.
A tubular body, an annular magnet fixed to the inner wall portion of the tubular body within a sensitive range of the reed switch, and loosely displaceably fitted in the enclosing tube in the tube axis direction, and usually abutted on the magnet. It is in a magnetic shielding position to be locked and shields a magnetic field line between the magnet and the reed switch,
A magnetic shielding member that is displaced to a magnetic shielding release position when subjected to an impact to release the shielding and responsively operates the reed switch by the lines of magnetic force of the magnet; and biases the magnetic shielding member to the magnetic shielding position. An impact sensor comprising: a spring; 2. The magnetic shielding member according to claim 1, wherein :
A small-diameter cylindrical portion into which a hollow portion is loosely inserted,
Fitting, one end is a locking surface of the spring, and the other end is the mag
2. The impact sensor according to claim 1, wherein the impact sensor comprises a large-diameter cylindrical portion serving as an abutment locking surface to the net .