JPH07156745A - Ignition driving judging circuit of air bag - Google Patents

Abstract

PURPOSE:To easily check the ignition ability and an ignition FET by connecting a safing switch to a squib, providing an ignition FET between first and second capacitances, and monitoring the voltage on the D+ terminal from the second capacitance by using a microcomputer. CONSTITUTION:A safing switch 32 connected to a squib 31 is closed in the collision, and one side of an ignition FET 33 is connected to the other side of the squib 31, and the other side is connected to an ignition power source. A microcomputer 34 connected to the ignition FET 33 closes the ignition FET 33 in the collision, and the squib 31 is energized and ignition is executed. Capacitances 35, 36 for back-up are provided, and when the ignition power source is lost, the circuit of the capacitance 35, the ignition FET 33, the capacitance 36, the squib 31, and the safing switch 32 is formed. The microcomputer 34 monitors the voltage VD at the middle point between the capacitance 36 and the resistor R24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag for protecting an occupant in the event of a vehicle collision, and more particularly to an improvement of a determination circuit for checking the inactivation of ignition drive of the airbag.

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field, an air bag is used to inflate a bag between an occupant and an instrument panel or a steering wheel at the time of collision of an automobile to mitigate obstacles caused by a secondary collision. The airbag is basically composed of a collision detection sensor, a gas generator, and a bag. When the sensor determines and detects the severity of a collision that requires an airbag,
The gas generator is energized. When the gas generator is ignited, for example, the bag is inflated within a few tens of milliseconds and the passenger can be restrained. An ignition drive determination circuit for an airbag used in such an airbag will be described in detail below.

FIG. 4 is a diagram showing a conventional ignition drive circuit for an airbag. As shown in the figure, the ignition drive circuit of the airbag has a squib 1 for igniting a gas generator to deploy the airbag. This squib 1 has an electrical resistance of 2.2 to 3.65 ohms. The safing switch (SS) 2 connected to the squib 1 via a diode D1 is composed of a mechanical switch that is normally opened and closed when a vehicle crashes, and a resistor connected in parallel with the mechanical switch. The safing switch 2 is connected to the ignition power source (not shown) of 6 to 16 V. The other side of the squib 1 is an ignition FET (Field Effect Transistor).
r) One of both ends of 3 is connected and the other is grounded.
The gate of the ignition FET 3 is connected to the port of the microcomputer 4 via a transistor or the like, and is normally opened electrically. The microcomputer 4 analyzes and estimates the collision based on the input of another sensor (not shown), and closes the ignition FET 3 based on this result. Therefore, when the car collides, the safing switch 2 and the ignition FET 3
Is closed and the squib 1 is energized to ignite the gas generator. However, it is necessary to double the ignition power source (form a doubler circuit) in order to improve the safety by anticipating that the power supply from the ignition power source cannot be obtained for some reason. Therefore, the ignition power supply is provided with backup capacitors 5 and 6. The capacitance 5 has a capacitance of C1 and is charged by the ignition power source through the resistor R1 to approximately the ignition power source voltage VFIR. Further, the capacitance 6 has a capacitance C2, and the resistors R4 and R
Charged via 5. When the ignition power supply is lost, an ignition current path such as capacitance 5, safing switch 2, capacitance 6, squib 1, and ignition FET 3 is formed as shown by the dotted line on the circuit. Capacitances 5 and 6 are E of the battery between D + and D-.
100 ms after the CU input terminal is disconnected, the electric charge that allows a current of 1.2 A or more to flow for 3 ms is accumulated.

Incidentally, the diode D1 between the squib 1 and the safing switch 2 is redundant so that the airbag can be deployed only by the ignition power source in the path indicated by the arrow solid line even when there is a failure that the capacitance 6 becomes open. It has sex.

[0005]

In order to check the ignition ability of the capacitance 5 in such an airbag ignition drive circuit, the microcomputer 4 is used.
In order to check the ignition capability of the doubler circuit and the operation of the ignition FET 3, the safing switch 1 is closed and the ignition FET 3 is closed, and the voltage VD + which will be described later at the intermediate point between the resistor R4 and the capacitance 6 is monitored. There must be. However, since the safing switch 2 is a mechanical sensor, its contact does not close unless a certain acceleration is applied. Therefore, normally, the voltage VD +
There is a problem that it is difficult to check.

Accordingly, the present invention has been made in view of the above problems.
An object of the present invention is to provide an airbag ignition drive determination circuit capable of checking a doubler circuit (ignition ability) and an ignition FET.

[0007]

In order to solve the above problems, the present invention provides a squib which is energized from an ignition power supply for deploying an airbag and a first backup power supply which is charged to the ignition power supply voltage. And a second capacitance for backup which is connected in series to the first capacitance and supplies a current to the squib when the ignition power source is lost. Between a safing switch connected to the ignition power source and a safing switch having a switch connected in parallel to the other and closed by an automobile collision, and a resistor connected in parallel to the switch, and the first capacitance and the second capacitance. And an ignition FET provided in the.
A microcomputer that periodically closes the ignition FET monitors the potential applied to the D + terminal from the second capacitance.

[0008]

According to the ignition drive determination circuit for an airbag of the present invention, an ignition F connected to the ignition power source and provided between the first capacitance and the second capacitance.
By periodically closing the ET, the voltage of the sum of the ignition power supply and the charging voltage of the second capacitance can be monitored. It is no longer necessary to simply short the contacts of the safing sensor to check the doubler circuit (ignition ability).

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an ignition drive determination circuit for an airbag according to an embodiment of the present invention. As shown in this figure, the safing switch 32 and the fire FET mainly differ from those of FIG. 4 in the configuration of the ignition drive determination circuit of the airbag.
The arrangement with 33 is the opposite of that of FIG.
The outline of the configuration of this figure will be described. In the airbag ignition drive determination circuit, the squib 31 for igniting the gas generator that deploys the airbag electrically has a resistance of 2.2 to 3.65 ohms. The safing switch 32 connected to the squib 31 is composed of a mechanical switch that is normally opened and closed when a vehicle crashes, and a resistor connected in parallel with the mechanical switch. The safing switch 32 has the other grounded. Diode D1 on the other side of squib 32
One of both ends of the ignition FET 33 is connected via 0, and the other is connected to an ignition power source of 6 to 16 V (not shown). The gate of the ignition FET 33 is connected to the port of the microcomputer 34 and is normally opened electrically. The microcomputer 34 analyzes and estimates the collision based on the input of another sensor (semiconductor G sensor) not shown, and closes the ignition FET 33 based on this result. Therefore, when the car collides, the safing switch 2 and the ignition FET
33 is closed and the squib 31 is energized to ignite the gas generator. However, it is necessary to duplicate the ignition power source in order to improve safety in anticipation that the power supply from the ignition power source cannot be obtained for some reason.
Therefore, the ignition power supply is provided with backup capacitors 35 and 36. The capacitance 35 has a capacitance of C1 and is charged by the ignition power source through the resistor R23 to approximately the ignition power source voltage VFIR. Further, the capacitance 36 has a capacitance of C2, and resistors R24 and R25
Is charged through. When the ignition power source is lost, the capacitance 35, the ignition FE, as shown by the dotted line on the circuit,
An ignition current path such as T33, capacitance 36, squib 31, and safing switch 32 is formed.
In order to monitor the voltage VD + at the intermediate point between the capacitance 36 and the resistor R24, the microcomputer 34 connects a voltage dividing resistor to the intermediate point and inputs the divided voltage.
Here, the value of the resistor R24 is set to 680Ω and the value of the resistor 25 is set to 1 kΩ.

Further, the diode D10 between the squib 31 and the safing switch 32 enables the airbag to be deployed only by the ignition power source by the path indicated by the arrow solid line even when there is a failure that the capacitance 36 becomes open. It has redundancy. In this figure, the transistors and the like connected to the gate of the ignition FET 3 as shown in FIG. 4 are omitted for simplification of description.

FIG. 2 is a diagram of FIG. 1 when the ignition is turned on.
It is a figure which shows the charging voltage of the capacitance 36 of FIG. As shown in the figure, when the ignition is turned on, the voltage on the positive and negative sides of the capacitance 36 becomes a voltage value of about 0.6 VFIR volt in which the ignition voltage VFIR volt is divided by the resistors 24 and 25. The positive side then rises to VFIR volts and the negative side falls to 0 volts.

FIG. 3 is a diagram showing the relationship of the positive side voltage VD + of the capacitance 36 with respect to the ignition signal from the microcomputer 34. As shown in this figure (a), the ignition signal (5 volt) is periodically sent from the microcomputer 34.
Is output to the gate of the ignition FET 33. With this output, a current flows as shown by the dotted line in FIG. In this case, the voltage on the positive side of the capacitance 36 changes from VD + (FET OFF) to VD + (F
ET ON). This VD + (FETON)
Is approximately expressed by the following equation.

VD + (FET ON) = VFIR + 2 × {(VD + (FET OFF) −0.6VFIR} (1) The second half of the equation (1) is approximately the charging voltage of the capacitance 36. As described above, if the safing switch 2 is not turned on between the capacitances 5 and 6, there is a voltage drop due to the resistance of the safing switch 2. Therefore, the above voltage cannot be easily expressed as in the equation (1). By arranging the switching switch 31 and the ignition FET 33, the initial purpose can be achieved without applying acceleration to the safing switch 31.

The microcomputer 34 has a margin,
When the voltage of the following formula is VD + (FET ON) ≦ 0.8 × [VFIR + 2 × {(VD + (FET OFF) −0.6VFIR}] (2), either the ignition FET 33 or the ignition capability (doubler circuit) is input. Is determined to be abnormal.

If the ignition power source abnormality occurs due to some reason while the vehicle is running, the capacitance 35 supplies the same voltage as the ignition power source instead. Another advantage of the present invention is that in the conventional case of FIG. 4, the microcomputer 4 needs a port therefor to monitor the charging voltage of the capacitance 5, whereas as in the case of FIG. One of the reasons is that the port is no longer needed.

[0016]

As described above, according to the present invention, the ignition FET connected to the ignition power source and provided between the first capacitance and the second capacitance for backup is periodically closed. The voltage of the sum of the voltage of the ignition power source and the charging voltage of the second capacitance can be easily monitored, and the ignition capability (doubler circuit) and the ignition FET can be easily checked. That is, the ignition ability can be monitored without simply short-circuiting the contacts of the safing sensor as in the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing an ignition drive determination circuit for an airbag according to an embodiment of the present invention.

FIG. 2 is a diagram showing a charging voltage state of a capacitance 36 in FIG. 1 when an ignition is turned on.

FIG. 3 is a diagram showing a relationship between a positive side voltage VD + of a capacitance 36 with respect to an ignition signal from a microcomputer 34.

FIG. 4 is a diagram showing a conventional ignition drive circuit for an airbag.

[Explanation of symbols]

 31 ... Squib 32 ... Safing switch 33 ... Ignition FET 34 ... Microcomputer 35, 36 ... Capacitance

Claims (1)

[Claims] 1. A squib (31) energized from an ignition power source for deploying an airbag, and a backup capacitance (35) charged to the ignition power source voltage.
And a backup capacitance (36) connected in series with the capacitance (35) and energizing the squib (31) when the ignition power source is lost from the backup capacitance (36). A safing switch (32) having a switch connected to (31) and grounded at the other end to be closed by a collision of an automobile; and a safing switch (32) having a resistor connected in parallel with the switch;
5) and an ignition FET (33) provided between the capacitance (36) and a microcomputer (34) for periodically closing the ignition FET (33) and monitoring a potential applied to D + from the capacitance (36). ) And an ignition drive determination circuit for an air bag.