JPH0986337A - Air bag device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To try to lower cost by interposing a power supply release switching element between a power supply and a capacitor, switching the power supply over to an interruption state when collision is detected, and thereby making its capacity small in a device trying to back up the power supply by the use of electric charge accumulated in the capacitor. SOLUTION: When it is judged by a microcomputer 1 based on the output of an acceleration sensor 15 that collision has been caused, an ON signal is fed to transistors 4 and 14, and discharge current from a capacitor 5 is fed to squibs 3 and 13 through constant current circuits 2 and 12. By this constitution, an air bag is expanded so as to be developed for protecting occupants. Besides, the microcomputer 1 turns transistors 6 and 7 off, releases a battery 9, and allows the squibs 3 and 13 to be actuated only by energy charged in the capacitor 5. By this constitution, there is no fear of applying excessive energy to the constant current circuits 2 and 12 and the transistors 4 and 14, and each rated capacity for them can thereby be made small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air bag control circuit, which is a type of automobile safety device, and more particularly to an air bag control system that uses a charge stored in a capacitor as a power source for initiating an air bag inflation squib. Regarding the device.

[0002]

2. Description of the Related Art An air bag device is a device for inflating and protecting an occupant when an automobile receives a sudden acceleration in a deceleration direction due to a collision or the like, and usually detects an automobile collision by operating an acceleration sensor. Then, an electric current is supplied to the squib (also called an inflator) for inflating the airbag to cause an explosion, and the airbag is momentarily inflated. By the way, such a safety device is required to have a higher reliability than anything else, and this is no exception to the airbag device, and in particular, it is necessary to maintain sufficient reliability in guaranteeing the power supply from the power source.

Therefore, conventionally, as shown in FIG. 3, a capacitor 5 charged from a battery 9 for power supply through a diode 8 is provided, and the ignition switch 17 is closed, so that the capacitor 5 is charged. When a collision is detected, an air bag device is proposed in which, when a collision is detected, a discharge current due to the electric charge stored in the capacitor 5 is used to supply a current to the squibs 3 and 13 for inflating and expanding the air bag to cause an explosion. ing.

This conventional example is an example of a device equipped with two airbags, and includes a microcomputer (microcomputer) 1 and
An acceleration sensor 15 and a safing sensor 16 are provided, and when a signal from the acceleration sensor 15 causes the microcomputer 1 to determine that a collision has occurred, an ON signal is supplied to the transistors 4 and 14 that form the squib current switch element.
(A signal for making conductive), and further provided with constant current circuits 2 and 12, through which the discharge current from the capacitor 5 is supplied to the squibs 3 and 13, respectively. This ensures that an accurate airbag deployment time is always obtained.

Here, the safing sensor 16 is a mechanical switch whose circuit is closed when an acceleration in the deceleration direction exceeding a predetermined value is applied to the automobile. It is composed of mechanical contacts that are used to close when a ball-shaped object moves due to acceleration, and in combination with the judgment of the microcomputer 1 by the acceleration sensor 15, the detection mechanism is a dual system. After the safing sensor 16 operates,
On the premise of this, when the acceleration sensor 15 operates, it is provided to prevent malfunction by detecting a collision and to ensure that the airbag is activated only when a true collision occurs. There is something.

As the above-mentioned prior art, for example, a device according to the application of Japanese Patent Application No. 2-112178 (Actual Fairness 6-
No. 38771).

[0007]

In the above prior art, no consideration is given to the operating time of the constant current circuit and the squib current switch element, and it is necessary to increase the capacitance of these constant current circuit and switch element. As a result, there is a problem that the device becomes large.

That is, in the prior art, when the squib is operating, the current value is limited by the constant current circuit, but the time during which the squib is energized is determined by the performance of the safing sensor and is energized for a considerable time. So, for this reason, as mentioned above,
It is necessary to increase the capacity of the constant current circuit and the squib current switch element, which results in an increase in size of the device.

More specifically, the safing sensor is usually a switch having mechanical contacts as described above. Therefore, as shown in FIG. 4A, chattering of contacts and movement of an object are performed. Due to the hunting that accompanies the operation, the contact is not stable immediately after being activated. Therefore, in order to reliably operate the airbag, as shown in Fig. 4 (b), the safing This is because it is necessary to keep the squib current switch element on (conductive state) for a considerably long time so that the contact of the sensor can be closed for a certain time or longer.

It is an object of the present invention to provide an airbag device capable of reliably operating the airbag when necessary while enabling a sufficient size reduction.

[0011]

An object of the present invention is to provide an air bag of a type which is provided with a capacitor charged from a power source through a diode and supplies a current to a squib for inflating an air bag by discharging the capacitor when a collision is detected. In the apparatus, a power source disconnecting switch element is connected between the power source and the capacitor, and when a collision is detected, the switch element is controlled to be switched from on (conductive state) to off (cutoff state).

That is, according to the present invention, the above-mentioned problems of the prior art are caused by the fact that when a collision is detected, in addition to the discharge current of the capacitor, a current is also supplied from the power supply to the airbag inflating squib. After detecting the collision, disconnect the air bag inflation squib from the power supply,
It is designed so that the squib is detonated only by the energy due to the charge accumulated in the capacitor before the collision detection.

The squib may be provided with a constant current circuit in series. Further, a plurality of the power supply disconnecting switch elements may be provided in parallel. Furthermore, the terminal voltage of the capacitor may be monitored, and when an abnormality is detected, it may be displayed.

When a collision is detected, a current is supplied from the capacitor to the squib to inflate the airbag. At this time, the switch element for disconnecting the power source is turned off and the power source is disconnected from the squib. The energy supplied to the capacitor will be defined only by the amount of charge stored in the capacitor, regardless of the length of the on-time of the squib current switch element. Therefore, it is not necessary to increase the capacitance of the constant current circuit or the squib current switch element, and the size can be reduced.

As described above, in order to ensure that the current is supplied to the squib when the safing sensor operates, it is necessary to prolong the time when the safing sensor is reliably turned on. The squib current switch element must be on.

This is because, as shown in FIG. 4, even when the safing sensor operates, the contact has chattering or hunting. Therefore, the time required for surely initiating the squib can be ensured. In order to guarantee that the contacts are closed, the squib current switch element should be turned on for a long time of, for example, 200 msec after the collision is detected at time t ₀ until time t _1. Because it must be. Then, as a result,
When the energy applied to the transistors 4 and 14 in the related art is calculated, the result is as follows.

Now, let the resistance value of the squibs 3 and 13 be R
[Ω], the voltage of the power supply battery 9 is V _B [V], and the current value required to detonate the squibs 3 and 13 is I [A],
If the voltage applied to the transistors 4 and 14 is V _TR [V] and the time during which the current is flowing is T [seconds], the loss energy J _TR [J] of the transistors 4 and 14 can be expressed by the following equation. J _TR = (V _B −R · I) · IT · Here, looking at the actual value, V _B = 12
[V], R = 2 [Ω], I = 2 [A], T = 0.2
[Seconds], therefore J _TR = 3.2 [J], which is a considerably large value.

By the way, detonating the squibs 3, 13
It is known that the energy required to deploy the airbag is generally one tenth or less of this value. This is because, as mentioned above, since the safing sensor is usually a mechanical switch, it is not known at which point in time after the occurrence of a collision the reliable contact opening can be obtained. This is because it is necessary to turn on the transistor for a long time after that. Therefore, in the conventional technique, the capacity of the transistor is set to 10 times the capacity required to drive the squib.
I had no choice but to double it.

In the present invention, however, the power supply is disconnected at the time of collision detection, so that the energy supplied to the squib is stored in the capacitor regardless of the length of the on-time of the squib current switch element. Since this is determined only by the amount of energy, this charge is a value corresponding to the energy required to detonate the squib and deploy the airbag, that is, one-tenth or less of the energy in the above-described conventional technology. Can be a value of.

Therefore, according to the present invention, even if the squib current switch element has a long on-time, it is not necessary to increase the capacitance of the switch element or the constant current circuit, and the size can be reduced.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The airbag device according to the present invention will be described below in detail with reference to the illustrated embodiments. FIG.
3 is an embodiment of the present invention, in which the present invention is applied to an airbag device having two airbags as in the conventional example of FIG. 6, 7 are connected in parallel between the diode 8 and the capacitor 5, and further the light emitting diode 10 and the transistor 11 are connected.
The hardware is the same as that of the conventional example of FIG.

As a result, when the microcomputer 1 determines from the signal of the acceleration sensor 16 that a collision has occurred in the automobile, the microcomputer 1 controls the transistors 4 and 14 constituting the squib current switch element to be turned on, Assuming the operation of the safing sensor 16, current is supplied to the squibs 3, 13 so that the squibs 3, 1,
This is also the same as the fact that 3 is detonated and the airbag is deployed to give an operation of protecting the occupant.

The transistors 6 and 7 each constitute a switching element for disconnecting the power source, and are configured to be controlled by the microcomputer 1, respectively. Therefore, in the microcomputer 1, the ignition switch 17 is closed. Under the condition, the transistors 6 and 7 are controlled to be turned on, and thereafter, this on state is maintained, and when it is determined that a collision has occurred in the automobile by the signal of the acceleration sensor 15,
It is configured to control these transistors 6 and 7 from on to off.

The light emitting diode 10 is for displaying an abnormality, and is turned on when the transistor 11 is turned on to display the occurrence of the abnormality. Transistor 11 is a light emitting diode 1 for display
It is an element that controls the lighting of 0, and this is also controlled by the microcomputer 1. Therefore, the microcomputer 1
Similarly, on condition that the ignition switch 17 is closed, as shown in FIG. 2, after the time point t _IG when the ignition switch 17 is closed, the transistor 6,
The terminal voltage V _C of the capacitor 5 is taken in at a time point t ₂ after a predetermined time T _{M has} elapsed from the time point t _S when the 7 is turned on, and this voltage V _C is used as a predetermined judgment voltage V _REF (0 <V _REF <V _B : (The voltage of the battery 9), the transistor 11 is controlled to be turned on only when it is determined that V _C ≤V _REF , and V _C > V
_{When REF} is satisfied, the transistor 11 is kept off.

Next, the operation of this embodiment will be described.

When the engine key of the automobile is operated and the ignition switch 17 is closed, the microcomputer 1 first turns on only the transistors 6 and 7 and turns off the transistors 4 and 14 and the transistor 11 as described above. Leave it alone. As a result, the capacitor 5 is connected to the battery 9 via the ignition switch 17, the diode 8 and the transistors 6 and 7 controlled to be turned on.
, And the terminal voltage V _C thereof is made substantially equal to the voltage V _{B of the} battery 9.

Then, as shown in FIG. 2, the terminal voltage V _C of the capacitor 5 is taken in at time t ₂ , this voltage V _C is compared with a predetermined judgment voltage V _REF, and the judgment result is V _C ≤V
_At the time of _REF, an ON signal is supplied to the transistor 11 to turn on the light emitting diode 10 to display the occurrence of an abnormality, but when the determination result is V _C > V _REF , the state is kept as it is, and thereafter the acceleration sensor 15 From the acceleration sensor 15 is awaited.

At this time, if the light emitting diode 10 is turned on, this means that the terminal voltage V _C of the capacitor 5 is lower than the voltage V _{B of the} battery 9, as is apparent from FIG. Meaning, so at this time,
From battery 9 including transistors 6 and 7 to capacitor 5
Indicates that some abnormality has occurred in the circuit up to.

Because, as is apparent from FIG. 1, if the transistors 6 and 7 are normal, the terminal voltage V _C of the capacitor 5 rises to the voltage V _{B of the} battery 9 after they are turned on. However, it should be higher than the determination voltage V _REF . Therefore, according to this embodiment, the state of charge of the capacitor 5 is constantly monitored, and when an abnormality occurs, it is displayed, so that high reliability can be obtained.

If there is no abnormality after the ignition switch 17 is closed, as described above, the acceleration sensor 1
The process shifts to the monitoring of the signal from No. 5 and waits for the generation of the signal from the acceleration sensor 15. However, normally, this state is continued until the ignition switch 17 is turned off.

However, if, unfortunately, a collision occurs in the automobile in the meantime, a signal is input from the acceleration sensor 15 to the microcomputer 1 here. At this time, the safing sensor 16 is also turned on.

As a result, assuming that the microcomputer 1 determines that a collision has occurred, the microcomputer 1 then detects that the transistor 4,
14 is supplied with an ON signal, which causes the transistor 4,
14 is turned on, the constant current circuit 2, 1 from the capacitor 5
A discharge current from the capacitor 5 is supplied to the squibs 3 and 13 via 2 so that the squibs 3 and 13 are detonated and the airbag is inflated and deployed to protect the occupant.

At the same time, the microcomputer 1 stops the output of the ON signal supplied to the transistors 6 and 7, and turns these transistors 6 and 7 from ON to OFF. As a result, the battery 9 is disconnected from the capacitor 5 and the squibs 3 and 13, and the supply of current from the battery 9 is cut off. Therefore, the squibs 3 and 13 operate only with the charging energy stored in the capacitor 5. As a result, as described above, even if the on time of the transistors 4 and 14 is lengthened, there is no fear that extra energy will be applied to the constant current circuits 2 and 12 and the transistors 4 and 14. Therefore, according to this embodiment,
The rated capacities of the constant current circuits 2 and 12 and the transistors 4 and 14 can be suppressed small, and the miniaturization can be sufficiently achieved.

By the way, since the constant current circuits 2 and 12 are provided in the embodiment of FIG. 1, the airbag device having a plurality of squibs as shown in the figure is advantageous in terms of safety. This is because when the plurality of squibs 3 and 13 are provided with the constant current circuits 2 and 12, respectively, as in this embodiment, even when one of the plurality of squibs 3 and 13 is short-circuited, the operation is performed. This is because a normal operating current can be supplied to the other squib.

That is, if there is no constant current circuit, during operation, the discharge current from the capacitor 5 will flow only to the shorted squib, and no current will be supplied to the other squib. If there is a current circuit, even if one of the squibs is short-circuited, the current flowing through it is limited by the constant current circuit, so a current with a normal value can flow through the other squib. is there.

Further, in the above embodiment, the power supply disconnecting switch element is composed of two transistors 6 connected in parallel,
Even if one transistor becomes abnormal, the capacitor 5 can be charged by the other transistor, so that reliability is improved and high safety can be secured. it can.

[0037]

According to the present invention, in order to improve reliability,
In an airbag device that uses the charge stored in the capacitor to back up the power supply, it is possible to eliminate the need to increase the capacity of the switch element that controls the current for operating the squib, thus reducing the size of the device. And the cost can be easily reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an airbag device according to the present invention.

FIG. 2 is a timing diagram for explaining the operation of the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional example of an airbag device.

FIG. 4 is a timing diagram illustrating the operation of the safing sensor.

[Explanation of symbols]

1 Microcomputer (microcomputer) 2, 12 Constant current circuit 3, 13 Squib 4, 14 Transistor that constitutes a squib current switch element 5 Capacitor for power source backup 6, 7 Transistor that constitutes a switch element for disconnecting power source 8 Diode 9 For power source Battery 10 Light emitting diode for abnormal display 11 Transistor for abnormal display control

Claims (4)

[Claims] 1. An airbag device comprising a capacitor charged from a power source through a diode, and supplying a current to an airbag inflating squib by discharging the capacitor when a collision is detected. An air bag device, characterized in that a switching element for disconnecting a power source is connected between them, and when a collision is detected, the switching element for disconnecting the power source is controlled to switch from a conductive state to a cutoff state. 2. The airbag device according to claim 1, wherein a constant current circuit is connected in series with the airbag inflating squib. 3. The airbag device according to claim 1, wherein at least two switching elements for disconnecting the power source are provided in parallel. 4. The invention according to claim 3, further comprising means for monitoring the terminal voltage of the capacitor, wherein a predetermined warning display is executed when the terminal voltage becomes a predetermined value or less. Characteristic airbag device