JPH10282137A - Crew-protecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce costs and to diagnose an interface circuit constantly by connecting the grounding side terminal of a resistor for dividing the voltage of an interface circuit to the failure diagnosis signal output terminal of a CPU. SOLUTION: A small amount of diagnosis current is supplied to squibs 10 and 11 by operating a constant-current circuit 16, a voltage value that is generated at an input terminal point B of an interface circuit 15 at that time is divided by resistors 15b and 15c, and the voltage at a point C is supplied to an input terminal A of a CPU 14. When a voltage value is within a specific range, the CPU 14 judges that the interface circuit 15 operates normally. However, when the value is outside the specific range, an area between the terminals A and C may be disconnected. At this time, a diagnosis signal output terminal O of the CPU 14 is set to a high level and the voltage of the connection point C between the resistors 15b and 15c is switched to a high level. When the high- level signal is inputted to the terminal A, the CPU 14 judges that an area between the signal lines A and C is normal and judges that the interface circuit 15 failed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an occupant protection device for an airbag which protects, for example, an occupant of a vehicle from a collision accident.

[0002]

2. Description of the Related Art An occupant protection device of this type will be described with reference to a vehicle occupant protection device shown in FIG. In FIG. 2, reference numerals 1 and 2 denote transistors 3 described below.
Is turned on by the control of the squibs 10, 1
A switching transistor (TR) 3 for transmitting and supplying a developing current to 1 is a driving transistor that turns on the transistors 1 and 2 when an ignition signal is received from a microcomputer (hereinafter referred to as CPU) 14.
Also, when 4 and 5 are turned on under the control of the CPU 14,
It is a switching transistor for supplying a diagnostic current sufficiently smaller than a deployment current when the airbag is deployed to the squibs 10 and 11. Note that 73 and 74 are diagnostic power supplies. Reference numerals 10 and 11 denote squibs, and these squibs 10 and 11 deploy the airbag when a deployment current passes. The squib 10 is for a driver's seat airbag, and the squib 11 is for a passenger seat.

Further, reference numeral 12 denotes an acceleration sensor for detecting a collision of a vehicle, and reference numeral 13 denotes a mechanical acceleration switch (or SS (Sa)).
fing Sensor). The mechanical acceleration switch 13 is turned on when receiving an acceleration equal to or more than a predetermined value generated at the time of a collision. The mechanical acceleration switch 13 is connected in series to each of the squibs 10 and 11.

[0004] Then, reference numeral 15 denotes a mechanical acceleration switch 13.
Is an interface circuit connected so as to apply a predetermined voltage to the input side. This interface circuit 15
Is for detecting the change in the voltage applied to the input side of the mechanical acceleration switch 13, that is, the non-grounded side, and supplying it to the CPU 14, whereby the CPU 14 recognizes the on / off state of the mechanical acceleration switch 13. Therefore, the interface circuit 15 has one end connected to the power supply 70 and the other end connected to the mechanical acceleration switch 13 and the backflow prevention diode 4.
A pull-up resistor 15a connected to the connection point between the cathodes 5 and 46, voltage dividing resistors 15b and 15c for dividing the voltage at the connection point, and switching and grounding the connection point as necessary. And the biasing resistors 15e and 15f of the switching transistor 15d. Note that the CPU 14 has a collision determination function and a diagnosis function, and when the diagnosis function is operating, supplies a high-level signal from the output terminal O of the CPU 14 to the switching transistor 15d to control the switching transistor 15d to be turned on. Is forcibly grounded (or reduced to a low voltage value) as necessary. However, since a low level signal is normally supplied, a low level signal is supplied from the interface circuit 15 to the CPU 14 at this time. Then, the CPU 14 determines that the mechanical acceleration switch 13 is on. Also,
The CPU 14 includes transistors 4, 5, transistor 3,
The on / off of the constant current circuit 16 is controlled to diagnose a failure of each part of the ignition system of the device.

When the CPU 14 determines that a collision has occurred to deploy the airbag based on the detection signal from the acceleration sensor 12 while the collision determination function is operating, the CPU 14 outputs an airbag ignition signal. And squib 1
A development current is supplied to 0 and 11.

Reference numerals 71 and 72 denote backup capacitors (C), reference numerals 50 to 65 denote resistors (R), and reference numerals 80 and 81 denote voltage detection circuits 31 to 31 each comprising a differential amplifier for inputting a voltage between terminals of the squibs 10 and 11. 36, 45, 46
Is a diode (D) for preventing current from flowing backward. That is, when each of the diodes 39 and 41 has an open fault, it cannot be detected by diagnosis.

Reference numeral 16 denotes a constant current circuit. The constant current circuit 16 is connected to the diodes 45 and 46 when the transistor 6 is turned off and the transistor 7 is turned on for diagnosis by the CPU 14. The constant current is drawn from the Reference numeral 75 denotes a power supply for the constant current circuit 16.

Next, the operation will be described. First, the operation at the time of collision will be described. When the vehicle collides with an impact sufficient to deploy the airbag, the acceleration sensor 1
2 outputs a detection signal indicating the acceleration at that time to the CPU 14. The mechanical acceleration switch 13 is turned on by the collision.

Then, the CPU 14 outputs an ignition signal to the driving transistor 3 to turn on the transistors 1 and 2. As a result, deployment currents from the backup capacitors 71 and 72, which are deployment current power supplies, are sent to the corresponding squibs 10 and 11, and the squibs 10 and 11 that have received the deployment current deploy the airbag.

Next, the operation of the circuit diagnostic processing will be described.
When diagnosing a short circuit between the squibs 10 and 11,
The CPU 14 first turns on one of the transistors 4 and 5 and the transistor 7 of the constant current circuit 16, and a constant current of an insufficient level for ignition flows through the one squib 10.

Then, a voltage detecting circuit 80 corresponding to the squib 10 measures a voltage difference generated between both ends of the squib 10, and the voltage difference is supplied to the CPU 14 and compared with a reference value. Is also small, a short circuit fault between the lines of the squib 10 is detected. If the voltage is supplied from the voltage detection circuits 80 and 81 to the CPU 14 without turning on the transistor 7, the CPU 1
4 judges that the mechanical acceleration switch 13 has a short-circuit failure. The squib 11 is diagnosed by turning on the other transistor 5 and the transistor 7 and performing the same operation as described above.

When diagnosing the interface circuit 15, the CPU 14 determines that the mechanical acceleration switch 13 is normal, and then turns on / off the transistor 15d to reduce the voltage supplied from the interface circuit 15 at that time. Monitor. Thereby, the CPU 14 makes a diagnosis based on whether or not a predetermined voltage corresponding to the non-ground side voltage of the mechanical acceleration switch 13 is input from the interface circuit 15 to the CPU 14.

[0013]

However, in such an occupant protection device, the interface circuit 15 is not provided.
However, there is a problem that the cost is increased because the device is composed of five resistors and one switching transistor.
If the mechanical acceleration switch 13 is short-circuited, the voltage of the non-ground terminal of the mechanical acceleration switch 13, that is, the voltage at the point B of the interface circuit 15 is always at the 0 level. There was a problem that a diagnosis could not be made.

The present invention has been made in view of such a problem, and the interface circuit is composed of three resistors to reduce the cost. Further, even if the mechanical acceleration switch is short-circuited, the interface circuit can be used. The purpose is to enable diagnosis.

[0015]

An occupant protection system according to the present invention is provided with an acceleration switch connected in series to a squib and supplied with power, a voltage value generated between terminals of the acceleration switch, and a voltage input terminal. An interface circuit for forcibly lowering a terminal to a low voltage; a collision determination function for determining a magnitude of a collision based on an acceleration signal from an acceleration sensor and generating a signal for supplying an ignition current to the squib; A microcomputer having a diagnostic function of inputting a voltage generated between terminals of the acceleration switch from an interface circuit and generating a diagnostic signal for performing a failure diagnosis of the acceleration switch based on the voltage value; In the protection device, the interface circuit may connect a voltage input terminal of the acceleration switch to the microcomputer. A first resistor inserted into a signal line connected to the first resistor, a second resistor that pulls up an input side of the first resistor to a power supply, and one end connected to the output side of the first resistor, And a third resistor connected to the diagnostic signal output terminal of the microcomputer.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, the present invention will be described with reference to FIG. Although the configuration will be described with reference to FIG. 1, components having the same configuration as that described in FIG. 2 or equivalent components will be denoted by the same reference numerals and description thereof will be omitted, and only different configurations will be described below. .

That is, in FIG. 1, the switching transistor 15d and the bias resistors 15e and 15f constituting the interface circuit 15 in FIG.
In addition, the ground terminal of the resistor 15c is connected to a terminal O of the CPU 14 from which a failure diagnosis signal is output.

Next, the signal line between the input terminal B of the interface circuit 15 and the input terminal A of the CPU 14 and diagnosis of the interface circuit 15 will be described.

(1) Diagnosis of the interface circuit 15 Since the terminal O of the CPU 14 to which the diagnostic signal is output is always at a low level, the terminal C of the resistor 15c connected to the CPU 14 is grounded. Here, the constant current circuit 16 is operated to supply a small diagnostic current to the squibs 10 and 11, and the voltage value generated at the input terminal B of the interface circuit 15 at that time is represented by the resistances 15b and 15c.
And the voltage at point C is
If the voltage value at that time is within a predetermined range, the CPU 14
5 is determined to be normal. However, when the voltage value of the input terminal A does not fall within the predetermined range, the signal line between the points A and C may be disconnected. If the intervening signal line is normal, it is determined that the interface circuit 15 has failed.

(2) Diagnosis of signal line between A and C At this time, since the diagnostic signal output terminal O of the CPU 14 is set to the high level, the voltage at the connection point C between the resistors 15b and 15c is set to the high level. Switch. When the high-level signal is input to the input terminal A, the CPU 14
Determines that the signal lines A and C are normal.

[0021]

As described above, according to the present invention, diagnosis can be performed with a simple configuration, and the effects of reducing costs can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional circuit.

[Explanation of symbols]

 1, 2, 3 Transistor (switch means) 4, 5 Transistor (diagnosis switch means) 10, 11, Squib 12 G sensor (acceleration sensor) 13 Mechanical acceleration switch (acceleration sensor) 15 Interface circuit 45, 46 Diode

Claims (1)

[Claims] 1. An acceleration switch connected in series to a squib and supplied with power, an interface circuit for inputting a voltage value generated between terminals of the acceleration switch and forcibly lowering the voltage input terminal to a low voltage. A collision judging function of judging the magnitude of a collision based on an acceleration signal from an acceleration sensor to generate a signal for supplying an ignition current to the squib, and a voltage generated between terminals of the acceleration switch from the interface circuit. And a microcomputer having a diagnostic function of generating a diagnostic signal for performing a failure diagnosis of the acceleration switch based on the voltage value of the acceleration switch. A first resistor having a voltage input terminal inserted into a signal line connecting the microcomputer; A resistor, a second resistor that pulls up the input side of the first resistor to a power supply, and one end connected to the output side of the first resistor, and the other end connected to a diagnostic signal output terminal of the microcomputer. An occupant protection device comprising a third resistor.