JP3204131B2 - 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 which can always output a stable closing signal without being affected by the magnitude of an applied impact.

[0002]

2. Description of the Related Art In-vehicle airbag devices for protecting occupants from the impact of a collision are often equipped with complicated electronic circuits in order to enhance the collision determination performance. When such electronic circuits malfunction due to the influence of electromagnetic noise or the like. In order to prevent accidental deployment of the airbag, a mechanical shock sensor called a safing sensor is often connected to an ignition circuit for a detonating element called a squib. FIG. 5 is a block diagram showing an example of a conventional airbag device. The airbag device 11 shown in FIG. 1 is configured such that when a collision occurs, the airbag control unit 12 applies an ignition current to the squib 25 to cause ignition, and the airbag 13 is deployed using the ignition energy at that time as a trigger. It has been.
The airbag control unit 12 has a built-in acceleration sensor 20, and an electric signal corresponding to the acceleration generated in the vehicle is transmitted from the acceleration sensor 20 to the CPU 22 via the AD converter 21.
Supplied to The CPU 22 makes a collision determination based on the acceleration signal converted into the digital signal, and
The transistor switch 23, which grounds one end of the squib 25, is turned on, and an ignition current is supplied to the squib 25.

The other end of the squib 25 is connected to a battery power supply + B via a mechanical shock sensor 24 called a safing sensor, and when the airbag 13 does not need to be deployed, for example, the CPU 22 Even if a malfunction occurs under the influence of electromagnetic noise and a conduction command is erroneously issued to the transistor switch 23, the shock detection sensor 24 functions as an erroneous explosion prevention means so that the ignition current is not supplied to the squib 25.

The impact sensor 24 has a sectional shape as shown in FIG. That is, the reed switch 3 is inserted into a hollow shaft 36 coaxially passing through a cylindrical housing 35.
The reed switch 32 is closed when the ring magnet 30 that is displaced in the housing 35 in the axial direction by receiving an impact reaches the sensitive area of the reed switch 32 against the coil spring 31. It has a configuration. The ring magnet 30 is normally locked on the left side wall of the housing 35 by the urging force of the coil spring 31. However, when a deceleration of a certain value or more occurs in the right direction in the figure, the coil spring acting on the ring magnet 30 31 becomes larger than the urging force of the ring magnet 30.
Starts moving rightward in the figure while compressing the coil spring 31. Ring magnet 30 is reed switch 3
2, the contact in the reed switch 32 is closed by the magnetic force generated by the ring magnet 30.

[0005]

The above-described conventional shock sensing sensor 24 is designed to be used when the deceleration is relatively small, that is, when a low G shock is applied as shown by a solid line in FIG. The switch 32 is closed when the deceleration becomes equal to or more than the trigger value Gt, as shown in FIG. However, this closed state is maintained until the deceleration falls below the trigger value Gt even if the deceleration falls after the peak value. For this reason, when the CPU 22 determines that the airbag 13 needs to be deployed and turns on the transistor switch 23 at time T2, the conduction time is completely included in the closing period of the reed switch 32, and accordingly, the squib 25 In this case, the ignition current is supplied for a time required for normal ignition initiation, for example, for about 5 msec. That is, when a low G impact is applied, the reed switch 3
A period during which the transistor 2 and the transistor switch 23 are closed at the same time is secured with a margin, and the squib 25 can be reliably fired and detonated.

On the other hand, when the deceleration is relatively large,
That is, when a high G impact is applied as indicated by a dotted line in FIG. 7A, the reed switch 32 closes when the deceleration becomes equal to or more than the trigger value Gt, as in the case of applying a low G impact, but the deceleration is Since the ring magnet 30 is large, the ring magnet 30 abuts against the right side wall of the housing 35, and moves back in the left direction in FIG. 6 by the reaction force at that time. As a result, despite the occurrence of deceleration exceeding the trigger value Gt, the reed switch 32
Once returns to the open state, then hits the left side wall of the housing 35, moves forward again, reaches the sensitive area of the reed switch 32, and closes the reed switch 32 again. Accordingly, during the period ΔT shown in FIG. 7C in which the ring magnet 30 is out of the sensitive range of the reed switch 32,
The closed state of the reed switch 32 is cut off. On the other hand, the CPU 22 that has determined that it is necessary to deploy the airbag early based on the magnitude of the impact closes the transistor switch 23 at the timing of time T2.
Since the closing state of the reed switch 32 is interrupted during the closing period of the transistor switch 23 shown in (E), the supply of the ignition current to the squib 25 is also interrupted during the interruption period, and the continuous ignition current is interrupted. There has been a problem that the squib 25 that is ignited by electric power exceeding a certain value may not be ignited, and the airbag may not be deployed.

Conventionally, in order to cope with this kind of problem, a special processing program is added to the collision determination processing of the CPU 22 so as to suppress the variation at the time T2 which defines the power supply timing to the transistor switch 23, Although the timing was optimized, the addition of this kind of special processing requires a CPU with a high-speed processing capability, which inevitably increases the manufacturing cost. Since a circuit for inputting the formed state to the CPU 22 is required, there is a problem that not only the cost reduction request but also the size reduction of the airbag control unit 12 may be reversed. In particular, since the disconnection timing and the disconnection period of the reed switch 32 in the closed state depend on the waveform of the deceleration applied to the vehicle, the timing of closing the transistor switch 23 depends on the strict opening / closing characteristics of the impact sensor 24. However, it must be accurately grasped in advance through experiments, simulations, and the like, which poses a problem that involves great difficulty.

The present invention has been made to solve the above-mentioned conventional problems, and provides an impact sensor which can always output a stable closing signal without being affected by the magnitude of an applied impact. It is intended for.

[0009]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a reed switch which is held in a housing and is closed by receiving a magnetic force, and a first spring which receives a shock and moves the inside of the housing. Axial displacement in the axial direction against
A ring magnet for closing the reed switch inside the first spring;
The ring magnet and the ring magnet pressed against
Pressed and held by both the second spring that is not interlocked with the net
If you receive a shock that does not exceed a certain limit,
Only the ring magnet moves in the axial direction without moving
The second position when it is displaced and receives an impact exceeding a certain limit .
Follow the ring magnet against the spring
A movable plate that moves forward in the forward direction and locks the ring magnet that is about to return by the reaction force abutting against the wall of the housing in the sensitive range to limit the return movement. It is characterized by the following.

Further, according to the present invention, the first spring is a first coil spring loosely fitted to the reed switch, and the second spring is a second coil spring loosely fitted to the second spring.
The coil spring is characterized in that:

[0011]

Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing one embodiment of the shock sensor of the present invention, FIG. 2 is a cross-sectional view showing a state of the shock sensor shown in FIG. 1 when a low G shock is applied, and FIG. High G of the shock sensor shown in
FIG. 4 is a cross-sectional view showing a state when a shock is applied, and FIG. 4 is a timing chart for explaining the operation of each part of the shock sensor shown in FIG.

In the shock sensor 10 shown in FIG. 1, a reed switch 5 is provided in a hollow shaft 9 which passes through the center of the inside of a housing 8 in the axial direction. The closing signal of the reed switch 5 is extracted to the outside by two reed terminals 6 and 7 penetrating the left and right side walls at both axial ends of the housing 8. A ring magnet 1, a first coil spring 2 for urging the ring magnet 1, a movable plate 3, and a second coil spring 4 for urging the movable plate 3 are fitted on the hollow shaft 9. The first coil spring 2 has the second coil spring 4 loosely inserted coaxially. Movable plate 3
Locks the ring magnet 1 so that when an impact exceeding a certain limit is received, the ring magnet 1 is rearwardly displaced in the axial direction against the second coil spring 4 so that the ring magnet 1 is moved backward. The ring magnet 1 is locked in the sensitive range of the reed switch 5 to limit the return movement.

A first end of which is locked to the ring magnet 1
The other end of the coil spring 2 is engaged with the deep bottom portion 8a of the right side wall of the housing 8, and the other end of the second coil spring 4 is engaged with the movable plate 3 at the other end. 8b. The shallow portion 8b is formed at a position closer to the reed switch 5 side than the deep portion 8a.
It also has the function of regulating within the sensitive range.

When a low-G impact is applied to the impact sensor 10 having the above-described structure, only the ring magnet 1 is displaced forward as shown in FIG. That is, the ring magnet 1 is displaced rightward away from the movable plate 3, but the ring magnet 1 is in a stationary state.
This includes the weight of the movable plate 3 and the second coil spring 4
Has been determined from the dynamic force balance condition. However, the ring magnet 1 has the same sensitivity characteristics as the conventional impact sensor 24. Therefore, when a low G impact is applied, the movable plate 3 is kept pressed against the left side wall of the housing 8, and only the ring magnet 1 moves forward while compressing the first coil spring 2, and the transistor switch 23 is pressed. Remains within the sensitive range of the reed switch 5 for a period sufficiently including the closing period of

On the other hand, when a high G impact is applied, each part of the impact sensor 10 behaves as shown in FIG. First, when the deceleration becomes equal to or more than the trigger value Gt (time T3 in FIG. 4), the ring magnet 1 moves forward while compressing the first coil spring 2 prior to the movable plate 3. When the deceleration becomes equal to or more than the trigger value Gu (time T4 in FIG. 4), the movable plate 3
, And moves forward while following the ring magnet 1. The ring magnet 1 that has been displaced forwardly before the movable plate 3 abuts on the shallow bottom portion 8b of the housing 8 and attempts to displace backward by the reaction force at that time. However, before the ring magnet 1 that has started the backward displacement leaves the sensitive zone of the reed switch 5, the ring magnet 1 is locked by the movable plate 3 that follows the ring magnet 1.

The movable plate 3 locks the ring magnet 1 within the sensitive range of the reed switch 1 over a time range exceeding the conventional cutting period ΔT, that is, a period from time T4 to time T7 in FIG. In the related art, the reed switch 5 maintains the closed state even during the interruption period (between times T5 and T6) in FIG. 4B in which the ring magnet 1 has been detached from the sensitive area of the reed switch 5. However, as shown in FIG. 4D, disconnection in the closed state is prevented. Therefore, the conduction period of the transistor switch 23, which is conducted by the CPU 22 in the airbag control unit 12, is completely included in the closing period of the reed switch 5, as shown in FIG. It is possible to reliably avoid the inconvenience that the disconnection of the reed switch 5 in the closed state as in the related art causes the airbag 13 to fail to deploy.

As described above, according to the shock sensor 10 described above, only the ring magnet 1 is displaced in the forward direction with respect to a shock equal to or less than a predetermined limit, and the reed switch is switched over for a necessary and sufficient period. 5 while staying within the sensing range, and can continue to output the closing signal during that time. When a shock exceeding a certain limit is applied, the ring magnet 1
The movable plate 3 that follows the ring magnet 1 blocks the inconvenience of being reflected back to the forward movement limit and moving back out of the sensitive area, so that the reed switch 5 is continuously operated for a required period of time. It can be kept closed. For this reason, like the airbag device 11 using the reed switch 5 as a safing sensor for preventing accidental explosion, the closed period of the reed switch 5 and the conduction period of the transistor switch 23 that is turned on by a command from the electronic circuit are set to the airbag. 1
3 can be overlapped over the period required for the ignition and detonation of the squib 25, which triggers the deployment of the squib 25, and the deployment of the airbag 13 can be ensured. It is possible to provide an economical and compact airbag control unit without adding a special program.

Further, the first spring is the first coil spring 2 loosely fitted to the reed switch 5, and the second spring is the second coil spring 4 loosely fitted to the first spring. The pair of coil springs 2 and 4 coaxially inserted allows the spring accommodating space to be made as compact as possible, and that the coil springs 2 and 4 do not interfere with each other, so that each of them can be securely positioned. And a compact and economical impact sensor 10 can be provided.

[0019]

As described above, according to the present invention,
A reed switch held in the housing and closed by receiving a magnetic force; and a ring for receiving an impact to reciprocate in the housing in the axial direction against a first spring to close the reed switch in the sensitive zone. The magnet and the ring magnet are locked, and when a shock exceeding a certain limit is received, the ring magnet is displaced forward in the axial direction following the ring magnet against the second spring, and the ring magnet that is about to return is moved. Since a movable plate that locks within the sensitive range and restricts the return movement is provided, only the ring magnet is displaced in the forward direction with respect to an impact less than a certain limit, as in the past, for a necessary and sufficient period. To stay within the sensitive range of the reed switch, and can continue to output the closing signal during that time.When an impact exceeding a certain limit is applied, the ring magnet is reflected to the forward limit. The inconvenience of returning to outside the service area is prevented by the movable plate that follows the ring magnet within the service area, so that the reed switch can be kept closed for a required period of time. Like an airbag device that uses a reed switch as a safing sensor to prevent accidental explosion, a detonating element that triggers the deployment of an airbag between the closing period of the reed switch and the conducting period of a transistor switch that is turned on by a command from an electronic circuit. Over the period required for the ignition of the
The deployment of the airbag can be ensured, so that there is no need to add a special program to the collision determination program or the like on the electronic circuit side, and an economical and small airbag control unit can be provided. And so on.

Also, the first spring is a first coil spring loosely fitted to the reed switch, and the second spring is a second coil spring loosely fitted to the first spring. By a pair of coil springs to be loosely inserted,
Since the spring housing space can be made as compact as possible, and since the coil springs do not interfere with each other, each can reliably perform the expected function. It has effects such as being able to be provided.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing a state of the shock sensor shown in FIG. 1 when a low G shock is applied.

FIG. 3 is a cross-sectional view illustrating a state of the shock sensor shown in FIG. 1 when a high G shock is applied.

FIG. 4 is a timing chart for explaining the operation of each part of the shock sensor shown in FIG. 1;

FIG. 5 is a block diagram illustrating an example of an airbag device.

FIG. 6 is a cross-sectional view illustrating an example of a conventional impact sensor.

FIG. 7 is a timing chart for explaining the operation of each part of the shock sensor shown in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ring magnet 2 1st spring (1st coil spring) 3 Movable plate 4 2nd spring (2nd coil spring) 5 Reed switch 8 Housing 8a Deep bottom 8b Shallow bottom 9 Hollow shaft 10 Impact sensor 11 Air Bag device 12 Airbag control unit 13 Airbag 20 Acceleration sensor 22 CPU 25 Squib

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-110731 (JP, A) JP-A-5-288773 (JP, A) JP-A-9-152446 (JP, A) 34374 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/135 B60R 21/32 H01H 35/14

Claims (2)

(57) [Claims] A reed switch which is held in a housing and is closed by receiving a magnetic force;
A ring magnet for closing the reed switch inside the first spring;
The ring magnet and the ring magnet pressed against
Pressed and held by both the second spring that is not interlocked with the net
If you receive a shock that does not exceed a certain limit,
Only the ring magnet moves in the axial direction without moving
The second position when it is displaced and receives an impact exceeding a certain limit .
Follow the ring magnet against the spring
A movable plate that moves forward in the forward direction and locks the ring magnet that is about to return by the reaction force abutting against the wall of the housing in the sensitive range to limit the return movement. An impact sensing sensor characterized by the following. 2. The first spring is a first coil spring loosely fitted to the reed switch, and the second spring is a second coil spring loosely fitted to the first spring. The impact sensor according to claim 1, wherein: