JPH08129027A - Impact sensor - Google Patents

Abstract

PURPOSE: To suppress the occurrence of chattering in order to realize the stable operation of an impact sensor and to continue the ON-time of a switch long while realizing cost reduction. CONSTITUTION: A lead switch 1 is housed in the cylindrical tube 2 formed at the central part of a sensor case 8 and the magnet 3 for driving the lead switch 1 is arranged along a part of the outer periphery of the tube 2. The impact sensor thus constituted has the spring 4 supporting the magnet 3, the back stopper 5 setting the initial position of the magnet 3 moved by an impact and the front stopper 7 determining the moving range of the magnet 3 from the back stopper 5. Especially, the front stopper 7 is formed of a resin material with Shore hardness A of about 30-70.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact sensor used for an automobile seat belt, an airbag, and the like, and more particularly to an impact sensor capable of detecting a sudden and large impact and operating.

[0002]

2. Description of the Related Art Conventionally, as such an impact sensor, a sensor using a reed switch and a magnet is known.
For example, there is one in which a sliding tube is arranged around a reed switch, and a ring-shaped magnet is supported by a spring on the outside thereof. In addition, this sensor has a back stopper that supports the magnet at the position where the reed switch is turned off, so that the magnet can move when a force exceeding a predetermined impact is applied from a direction parallel to the reed switch. ing. At that time, the magnet moves toward the front stopper and the reed switch is turned on. On the other hand, when the impact disappears,
The structure is such that the elasticity of the spring causes the magnet to return to its normal position.

In such an impact sensor, a relatively hard resin material having a Rockwell hardness of M90, such as non-magnetic metal, polyamide, or PBT, is used for the front stopper. Therefore, when an impact force of a predetermined amount or more is applied, the magnet collides with the front stopper, and the repulsive force moves the magnet in the direction of the back stopper to the region where the reed switch is turned off. Therefore, the contact of the reed switch is turned off, but the ON time of the contact is shortened or lengthened due to the resin material. Further, when the impact force continues at this time, the contact of the reed switch is turned on again, and chattering occurs. Further, when the magnet collides with the front stopper, the contact of the reed switch may cause chattering due to the vibration component of the collision.

As an impact sensor for preventing the occurrence of chattering, for example, a sensor as disclosed in Japanese Patent Laid-Open No. 3-110731 is known. This technique will be described using FIG. 5 below.

FIG. 5 is a sectional view of an impact sensor showing such a conventional example. As shown in FIG. 5, in this impact sensor, a case 8 provided with a sliding tube 2 is arranged around a reed switch 1 which leads a terminal 6 to the outside, and a magnet 3a is provided on the outside of the case 2 with a first magnet 3a. Inertial moving body 11
Is supported by the first spring 4A. The first inertial moving body 11 is integrated with the magnet 3a, and the first spring 4A is provided between the first inertial moving body 11 and the collision portion (surface) 10 of the case 8. Further, the second inertial moving body 12 is pressed against the collar portion of the magnet 3a by the second spring 4B.

Such a sensor has two inertial moving bodies 1.
1 and 12 and two springs 4A and 4B, and the first and second inertial moving bodies 11 and 12 having the magnet 3a move during a small collision to operate the reed switch 1, and immediately thereafter. Restore. Further, at the time of a large collision, the first inertial moving body 11 reaches the collision portion 10 and tries to repel, but is pressed by the second inertial moving body 12 and the repulsion is suppressed. Therefore, in the event of a major collision, the ON time of the contact of the reed switch 1 becomes long.

[0007]

In the above-mentioned conventional impact sensor, if it is attempted to realize with a simple structure, contact chattering occurs and the ON time of the contact varies, and this chattering is prevented to prevent contact. There is a drawback that the structure becomes complicated and the number of parts increases when trying to eliminate the variation in ON time.

Further, when the structure of the conventional impact sensor becomes complicated, there is a problem such that the inertial moving body is caught due to a difference in expansion coefficient of each piece in an ambient temperature change, especially in an environment of extremely cold -40 ° C. It has the drawback of increasing the probability of occurrence.

An object of the present invention is to prevent chattering of a reed switch due to such a difference in impact force, and
An object of the present invention is to provide a shock sensor that has a simplified structure, realizes a long ON time, has a small change even at a low temperature, and does not cause a problem.

[0010]

The impact sensor of the present invention comprises:
In a shock sensor in which a reed switch is housed in a cylindrical tube formed in the center of a sensor case, and a magnet for driving the reed switch is arranged along a part of the outer circumference of the tube, a spring supporting the magnet and , A back stopper that sets an initial position of the magnet that moves due to impact, and a front stopper that defines a moving range of the magnet from the back stopper, and the front stopper is a hardness Shore A3.
It is characterized by being formed of a resin material of about 0 to 70.

Further, in the shock sensor of the present invention, a protrusion for increasing the contact surface may be formed on the surface of the front stopper with which the magnet collides.

Further, in the impact sensor of the present invention, the front stopper is made of a resin material whose hardness does not change even at a low temperature, that is, the glass transition point is set to -40 ° C or lower.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view of an impact sensor showing one embodiment of the present invention. As shown in FIG. 1, in this embodiment, the reed switch 1 is housed in a cylindrical tube 2 formed in the center of a sensor case 8, and a ring-shaped magnet 3 for driving the reed switch 1 is provided on the outer circumference of the tube 2. The structure is arranged along a part of. The magnet 3 is supported by a spring 4 arranged outside the tube 2 and pressed against a back stopper 5 fixed to a case 8. The back stopper 5 sets the initial position of the magnet 3 that moves in the axial direction of the reed switch 1 due to an impact. A front stopper 7 made of a resin material is fixed to an end of the case 8 opposite to the back stopper 5. The front stopper 7 is provided to determine the moving range of the magnet 3 from the back stopper 5. To be Moreover, this front stopper 7
Has a hardness Shore A to absorb collision energy.
It is formed of a resin material of about 30 to 70, and the glass transition point of the resin material is set to -40 ° C or lower.

However, in the above-mentioned conventional example, when an excessive impact is applied, the magnet 3 collides with the front stopper at a high speed, or the inertial moving body 11 collides with the case colliding portion 10, and then the reed switch. Since it is bounced up to the contact OFF area of No. 1, the time when the switch is ON becomes short. Further, chattering occurs at the contact of the reed switch 1 due to the vibration component when the front stopper collides.

On the other hand, in this embodiment, when an excessive impact is applied to the sensor, that is, when the magnet 3 collides with the front stopper 7 at high speed, the resin material forming the front stopper 7 absorbs the collision energy. So
The repulsion amount of the magnet 3 is extremely small. as a result,
The magnet 3 is not rebounded to the contact OFF region of the reed switch 1, and the vibration component of collision is reduced. Further, since the vibration component of the collision is reduced, chattering of the contact of the reed switch 1 does not occur, so that the long ON
You will be able to continue your time.

FIG. 2 is a characteristic diagram of the front stopper hardness and the switch ON time in FIG. As shown in FIG. 2, the horizontal axis represents the ON time (about 4 ms) in the case of HRR90 and HRM90 used in the Rockwell hardness test of plastics, and hardness Shore A30 to 70 (Hs J
It is shown in comparison with the ON time (about 10 ms) in the case of ISA).

FIG. 3 is a distribution characteristic diagram of ON times of the switches in FIG. As shown in FIG. 3, the ON time of the switch in this embodiment is about 9 m in the case of a large impact.
s, about 11 ms for small impact,
The variation of the ON time due to the difference in the impact force is reduced, and the average ON time is about 10 ms. This is O
When represented by the normal distribution probability for N hours, the characteristic A shown by the solid line
become that way. The characteristic B shown by the dotted line is ON in the conventional example.
The time distribution characteristics are about 2 ms for a large shock and about 8 ms for a small shock, and the average ON time is about 4 ms. As described above, in this embodiment, the ON time is continued for a long time, while the fluctuation of the ON time due to the difference in impact force is reduced.

In this embodiment, the hardness of the front stopper 7 is defined because if it is too hard, it does not absorb the collision energy of the magnet 3 as in the conventional example, and if it is too soft. This is because the front stopper 7 may be over-compressed when the magnet 3 collides, and the magnet 3 may reach the contact OFF area on the front stopper 7 side. If the front stopper 7 is too soft, the magnet 3 will stick to the front stopper 7 and the back stopper 5 will remain even if the shock acceleration disappears.
Will not return to the initial position on the side.

Further, the glass transition point of the front stopper 7 is defined in this embodiment in order to prevent the hardness of the stopper 7 from becoming hard at a low temperature. That is, in order to prevent hardness change in the operating temperature range of the impact sensor or the one equipped with the sensor.

FIG. 4 is a sectional view of an impact sensor showing another embodiment of the present invention. As shown in FIG. 4, in this embodiment, the shape of the front stopper 7 is partially changed as compared with the above-described embodiment, and the front stopper 7 is made of a resin material having a hardness Shore A of about 30 to 70. The same applies to setting the glass transition point of the resin material to -40 ° C or lower. In this embodiment, the protrusion 9 having a concave-convex shape is formed on the magnet collision surface of the front stopper 7 so that the damping action is further increased as compared with the above-described embodiment.

[0021]

As described above, in the impact sensor of the present invention, the reed switch is housed in the cylindrical tube formed in the center of the sensor case, and the reed switch is mounted along a part of the outer circumference of the tube. A magnet for driving is arranged, a spring for supporting the magnet, a back stopper for setting an initial position of the magnet to be moved by impact, and a front stopper for defining a moving range of the magnet from the back stopper are provided. By forming the stopper with a resin material with hardness Shore A of about 30 to 70 and using a soft resin with little hardness change even at low temperatures, not only the occurrence of chattering is suppressed, but also the switch ON time depends on the difference in impact force. Has the effect of being able to continue for a long time.

In addition, since the present invention has the above-mentioned structure, the number of parts can be reduced and can be simplified, so that it is possible to realize a low price and to reduce the occurrence of problems such as a magnet being caught. .

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram of front stopper hardness and switch ON time in FIG.

FIG. 3 is a distribution characteristic diagram of the ON time of the switch in FIG. 1;

FIG. 4 is a sectional view of an impact sensor showing another embodiment of the present invention.

FIG. 5 is a cross-sectional view of an impact sensor showing an example of the related art.

[Explanation of symbols]

 1 Reed Switch 2 Cylindrical Tube 3 Magnet 4 Spring 5 Back Stopper 6 Terminal 7 Front Stopper 8 Sensor Case 9 Projection

Claims (3)

[Claims] 1. A shock sensor in which a reed switch is housed in a cylindrical tube formed in the center of a sensor case, and a magnet for driving the reed switch is arranged along a part of the outer circumference of the tube. A spring for supporting the magnet, a back stopper for setting an initial position of the magnet that moves due to impact, and a front stopper that defines a moving range of the magnet from the back stopper. An impact sensor characterized by being formed of a resin material of a certain degree. 2. The impact sensor according to claim 1, wherein the front stopper has a protrusion on a surface with which the magnet collides. 3. The shock sensor according to claim 1, wherein the glass transition point of the resin material of the front stopper is −40 ° C. or lower.