JPH08201422A - Acceleration detector - Google Patents

Abstract

PURPOSE: To maintain the TTC and increase the DWT by covering the surface of a ring-like magnet except its inner peripheral surface with a nonmagnetic material. CONSTITUTION: When acceleration G is abruptly applied to an acceleration detector, magnets 12 move toward retainers 15 from their initial positions in accordance with the magnitude of the acceleration G and stop at the positions where the forces generated from coil springs 13 balance with the weights of the magnets 12. However, even when such acceleration G that is stronger than a prescribed value and moves the magnets 12 beyond the positions of stoppers S is applied to the detector, the magnets 12 do not move beyond the stoppers S. When the acceleration is removed, in addition, the magnets 12 are returned to the initial positions by the resiliency of the springs 13. A nonmagnetic material 10 has a large specific gravity and, when the material 10 is attached to the magnets 10, the masses of the magnets 12 largely increase. When the masses of the magnets 12 increase, the TTC(time to contact) does not change much and the DWT(dwell time) can be prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration detector of a system which is mounted on a moving body such as an automobile and is required to detect acceleration of an occupant protection device at the time of a collision.

[0002]

2. Description of the Related Art FIG. 2 schematically shows a vertical sectional view of a conventional acceleration detector. In this structure, the reed switch 1 is housed inside the shaft 7 in the case 4. On the other hand, a ring-shaped magnet 2 for turning on the reed switch 1
Are installed on the outer periphery of the shaft 7. here,
Referring also to FIG. 3B for explaining the operation, the magnet 2 is initially fixed to the initial position X ₀ by the coil spring 3 (state of FIG. 2). By adding the acceleration G, it moves to the stopper position X _S. Although this is not shown in FIG. 2, the magnet 2 moves leftward to the stopper S at the end of the retainer 5 in the figure.

The movement stroke of the magnet 2 is from X ₀ to X _S
The reed switch 1 is in an ON state at an X _ON position between them, and the reed switch 1 is at an X _OFF position which is in the middle until the magnet 2 returns to the initial position X ₀ by releasing the acceleration G. The ON signal can be taken out from the signal terminal 6 until the state becomes the OFF state.

[0004]

In this acceleration detector, the characteristic with respect to impact is the time from the application of impact to the turning on of the reed switch TT as shown in FIG. 3 (a).
There are two characteristics: a C (Time To Contact) characteristic and a DWT (Dwell Time) characteristic which is the duration of the reed switch ON. Generally, the acceleration detector is required to have a short TTC and a long DWT.

A technical problem of the present invention is to provide an acceleration detector which maintains the TTC and lengthens the DWT.

[0006]

According to the present invention, a ring-shaped magnet having a portion other than the inner periphery thereof covered with a non-magnetic material is used as a mass system for detecting an impact, and thus a mass for detecting an impact is provided. The system becomes large. As a result, it is possible to provide an acceleration detector having a large DWT while keeping the shapes of the magnets substantially the same and maintaining TTC.

[0007]

The present invention is characterized in that the portion other than the inner peripheral surface of the ring-shaped magnet is covered with a non-magnetic material to increase the mass system for detecting impact. Due to this increase in mass system, TT
It is possible to obtain an acceleration detector having a particularly large DWT characteristic while maintaining the C characteristic.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The acceleration detector of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a vertical sectional view of an acceleration detector which is an embodiment of the present invention. Further, FIG. 3 schematically shows the behavior of the magnet with respect to impact. Inside the acceleration detector of the present invention, as shown in FIG. 1, a ring-shaped magnet 12 is provided on the inner wall surface of the case 14 in one direction, and the coil spring 1 is provided.
3 and the retainer 15. The portion of the magnet 12 other than the inner circumference facing the shaft is the non-magnetic body 1.
Covered by 0s. Also, the reed switch 11
Is fixed at a predetermined position inside the shaft 17.

When an acceleration G is suddenly applied to this detector from a predetermined direction (from the left in the figure), the magnet 12 moves from the initial position X ₀ toward the retainer 15 according to its size, and the coil spring is moved. It stops at the position commensurate with the generated force of 13. At this time, when the acceleration G of a predetermined value or more is applied so that the magnet 12 moves to the stopper S position X _S or more, the retainer 15 prevents the magnet 12 from moving more than the stopper position X _S. When the acceleration G is released, the magnet 12 is returned to the initial position X ₀ by the repulsive force of the coil spring 13.

In this process, from the reed switch ON position X _ON to the stopper position X _S and the stopper position X _S
The range from to the reed switch OFF position X _OFF is the section where the reed switch is ON.

As the non-magnetic material used in the present invention, it is desirable to use a material having a large specific gravity. When such a non-magnetic material is attached to the magnet, its mass is increased as compared with the conventional magnet alone.

FIG. 3 (b) is a schematic diagram showing the effect of the magnet mass on the stroke of the magnet when a shock is applied. Comparing the locus 21 of movement of the magnet when the mass of the magnet is small and the locus 22 of movement of the magnet when the mass of the magnet is large, the smaller the mass of the magnet, the faster the return to the initial position X _{0 of the} magnet. This is because the return of the magnet to the initial position depends on the size of the magnet mass that resists the repulsive force of the coil spring. Therefore, if the magnet mass is large, the TTC is hardly affected and the DWT can be lengthened.

FIG. 4 shows the magnet 12 and the non-magnetic body 10 shown in FIG.
An example of the combination of The non-magnetic body 10 is molded into a cup shape so that the outer diameter of the magnet 12 is just accommodated. However, the inner surface of the magnet 12 is not covered. Further, a plurality of tapered slits are provided above the cup of non-magnetic material. This is for covering the end surface of the magnet 12 when the magnet 12 and the non-magnetic body 10 are combined, and can be easily attached by bending the magnet 12 in the central direction after insertion. It is not preferable to cover a portion other than the inner peripheral surface of the magnet with a magnetic material, because the magnetic flux in the direction of operating the reed switch inside the magnet is reduced, and the operating speed of the reed switch is reduced.

[0015]

As described above, according to the present invention, by covering a portion other than the inner circumference of the ring-shaped magnet with a non-magnetic material,
It is possible to provide an acceleration detector that maintains TTC and lengthens DWT.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an acceleration detector according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional view of a conventional acceleration detector.

3A and 3B are explanatory views schematically showing the operating characteristics of the acceleration detector with respect to a shock, FIG. 3A shows the shock and the movement trajectory of the magnet, and FIG. 3B is a case where the magnet mass is increased. It shows in comparison with the case where the motion locus of is not increased.

FIG. 4 is an explanatory diagram showing an example of a non-magnetic body attached to a magnet. FIG. 4A is a diagram before mounting, and FIG. 4B is a diagram after mounting.

[Explanation of symbols]

1,11 Reed switch 2,12 Magnet 3,3 Coil spring 4,14 Case 5,15 Retainer 6 Signal terminal 7,17 Shaft 10 Non-magnetic material 21 Magnet movement locus when magnet mass is small 22 When magnet mass is large Movement locus of magnet G Acceleration X ₀ (magnet) initial position _XS (magnet) stopper position X _ON reed switch ON position X _OFF reed switch OFF position S stopper

Claims (1)

[Claims] 1. An acceleration detector configured by a reed switch, a magnet, and a coil spring, wherein the reed switch is operated by movement of the magnet in accordance with an acceleration applied in a detection direction. An acceleration detector characterized in that the parts other than the peripheral surface are covered with a non-magnetic material.