JP2000009781A - Failure detection device for occupant protecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a failure detection device for an occupant protecting device, capable of accurately detecting a power source short-circuiting of a squib ignition circuit and a GND short-circuiting. SOLUTION: This failure detection device is constituted, such that a first resistance R1 and a second resistance R2 are connected in series at an upstream side and a downstream side of a squib 40, and constant current circuits 37, 38 are connected in parallel to these resistances R1, R2, respectively. Then, for example, in the case where an electric wiring at the upstream side of the squib 40 is subjected to short-circuiting to generate a leak resistance, a terminal voltage of the squib 40 is raised, based on the leak resistance. The resistance of the second resistance R2 connected to the downstream side is made apparently small, to decrease the terminal voltage of the squib 40 by turning on the constant current circuit 38 at the downstream side of the squib 40. Short- circuiting in the upstream of the squib can be accurately detected by comparing the terminal voltage of the squib 40 with a threshold for detecting short- circuiting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure detection device for an occupant protection device having a failure detection function, and more particularly, to a failure detection device for an occupant protection device for detecting a failure of a starting means with high accuracy.

[0002]

2. Description of the Related Art Generally, a squib of an air bag (a low-resistance ignition filament) and a power supply circuit must always be checked by an air bag computer for disconnection, short-circuit, and abnormality in the resistance value of the squib. FIG. 10 shows a failure detection device of the above-mentioned occupant protection device according to the prior art.
In a configuration in which the squib 101 is connected in series, a minute current I is supplied to the squib 101, and a squib resistance value is detected using a terminal voltage of the squib 101 due to the small current I.

When the power supply is short-circuited on the upstream side of the squib 101, as shown in FIG. 11A, a leak resistance R _{+ is applied} between the upstream end of the squib 101 and the positive electrode side of a power supply circuit (power supply voltage Vc) (not shown). Occurs, and the voltage V1 at the end of the squib rises under the influence of the leak resistance R ₊ . for that reason,
If the change in the voltage V1 at the end of the squib is large, it is determined that the short circuit has occurred, and the driver is warned of the occurrence. Conversely, when the ground short-circuit (hereinafter abbreviated as “GND short”) on the downstream side of the squib 101, as shown in FIG.
01 the leak resistance R that occur between the GND side of the upstream end and not shown of the power supply circuit (power supply voltage Vc) _- voltage V1 of the end of the squib to the influence of drops. And the voltage V
When the change in 1 is large, the driver is warned, as in the case of the power short-circuit.

As described above, when either the upstream side or the downstream side of the squib is short-circuited, a leak resistance R + and a leak resistance R- are generated, and the terminal voltage V1 of the squib is thereby reduced. Changes in
A short failure can be determined. However, it is known that the value of the leak resistance differs depending on the mode of the short circuit. Generally, when a short circuit is caused by water or dust between wirings, the value of the leak resistance is high. In this case, although a short circuit has occurred, it is not necessary to detect a short circuit failure.

[0004] This will be described with reference to the graph of FIG. For example, when the resistance 100 and the resistance 102 in FIG. 11A are each 10 kΩ, the leakage resistance R + is about 500 kΩ as shown in FIG.
1 starts to increase from Vc / 2, and the leak resistance R + is approximately 1 k
In the case of Ω, the voltage V1 rises to 9Vc / 10, which is almost equal to the power supply voltage Vc. Also, the voltage V1 increases,
The voltage change rate decreases as the value approaches the power supply voltage Vc. When the value of the leak resistance R +, which is considered to be an actual power supply short-circuit fault, is 1 kΩ or less,
For example, the threshold value of the terminal voltage V1 corresponding to the leak resistance 500Ω must be set to a value close to the power supply voltage Vc. However, as described above, when the terminal voltage V1 approaches the power supply voltage Vc, the change with respect to the leak resistance R + is small.
A short-circuit failure of the power supply cannot be accurately determined.
In particular, when the voltage V1 output from the squib fluctuates due to the environment around the squib and its failure detection device, the voltage V1 for judging the power supply short circuit varies. For this reason, there is a problem that the determination of a power supply short-circuit failure or the like is not accurate.

In particular, at present, in order to reduce the cost of the airbag device, the resistors R1 and R
2 is being built into an IC as in the present embodiment. In this case, it is necessary to set the resistance values of the resistors R1 and R2 to be relatively high in consideration of space restrictions when the IC is built in the IC and heat generation due to electric power. However, the resistors R1 and R2
Is high, the rise of the squib terminal voltage V1 at the time of a power supply short-circuit failure is large, and the above problem occurs remarkably.

In the case of a GND short-circuit failure, the voltage V1 drops to near the GND voltage 0V. Then, as in the case of the power supply short-circuit failure, the terminal voltage V1 becomes G
In the vicinity of the ND voltage 0 V, there is a problem that the GND short-circuit failure cannot be determined with high accuracy because the change with respect to the leak resistance R− is small.

An object of the present invention is to provide a failure detection device for an occupant protection device having high detection accuracy.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a starter of an occupant protection device connected in series to a power supply circuit and a terminal voltage of the starter are measured. A terminal voltage measuring unit, a first resistor connected in series upstream of the starting unit, a second resistor connected serially downstream of the starting unit, and a first resistor or a second resistor connected in series to the starting unit. A voltage drop changing means for changing a voltage drop of at least one of the resistors, and a failure detecting means for detecting a connection failure of the activation means based on the terminal voltage measured by the terminal voltage measuring means after the voltage drop is changed. A failure detection device for an occupant protection device, comprising:

With the above configuration, the terminal voltage measuring means measures a voltage corresponding to the resistance values of the first resistor and the second resistor as the terminal voltage of the starting means. When detecting a failure, the terminal voltage after the voltage drop is changed by the voltage drop changing means is detected. When the voltage drop of the first resistor is reduced, the terminal voltage increases, and the connection failure of the activation unit is determined in a range where the rate of change of the terminal voltage is large. A connection failure can be accurately detected. In addition, when the voltage drop of the second resistor is reduced, the terminal voltage decreases and the connection failure of the activation unit is determined in a range where the rate of change of the terminal voltage is large. The connection failure on the side can be accurately detected.

Further, according to the invention of claim 2, a plurality of starting means each connected in series to the power supply circuit, and a resistor arranged so as to be connected in series upstream or downstream of the starting means, Connected between the activation means and the resistor,
A connection switching unit that realizes both a connection state between the resistor and one of the activation units and a connection state between the resistor and another activation unit different from the one activation unit; A failure detecting means for detecting a failure of the activation means based on a potential difference between both ends of the activation means connected to the resistor by connection switching means.

With the above configuration, the connection switching means is connected between the plurality of starting means and the resistor, and is connected to the power supply circuit. When the connection switching unit connects the resistor and the first activation unit, the failure detection unit detects the failure of the first activation unit. Further, when the connection switching unit realizes a connection state between the resistor and another activation unit different from the first activation unit, the failure detection unit detects a failure of the other activation unit. Therefore,
Since the failure detection of a plurality of activation means can be performed by one resistor, the number of resistors connected in series to the activation means can be reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a failure detection device 10 for an airbag device according to an embodiment mounted on a vehicle.

As shown in FIG. 1, a failure detection device 10 for an airbag device determines the deployment of an airbag (not shown) for protecting an occupant (such as a driver's airbag), and operates according to the present invention. The following are provided in addition to the microcomputer 12 that supervises the situation described above.

The air bag device failure detecting device 10 includes, as a control system, an acceleration sensor 14 for detecting acceleration applied to the vehicle, and an EEPROM for storing data transferred from the microcomputer 12 and holding the data even after the power is turned off.
M and the nonvolatile memory 16 and the microcomputer 1
2 for connection. The microcomputer 12 is C
A PU, ROM, and RAM are configured as logical operation circuits, and input / output with the acceleration sensor 14 and the like is performed by input / output ports I / O connected to each other via a common bus.

Further, a failure detection device 10 for an airbag device is provided.
Are a battery power supply 20 as an ignition system, a diode circuit 22 for rectifying a power supply current supplied from the battery power supply 20 to obtain an ignition power supply, and a DC-DC converter 24 for converting the voltage of the ignition power supply. And a backup power supply 26 containing a large-capacity capacitor, and a safing sensor 32, and a squib 40
The IC 45 has a built-in circuit for diagnosing a failure. The IC 45 is connected to the output terminal of the DC-DC converter 24 and the IC
Is connected to the GND side of the battery power supply and the output connector (-B) of the IC. The input connector (+ B) of the IC 45 is provided with the IC 4
The power supply voltage Vc of the circuit in 5 is applied.

The IC 45 includes first and second ignition transistors 33 and 34, first and second resistors R1, R2,
And second constant current circuits 37 and 38.
A first ignition transistor 33 is connected between the input connector (+ B) of the IC 45 and a connector (+ D) to which the upstream end of the squib 40 is connected, and the first ignition transistor 33 further includes a first ignition transistor 33. The resistor R1 and the first constant current circuit 37 are connected in parallel. A first switching element 41, for example, an FET, is connected in series to the constant current circuit 37.
When 1 is ON, the squib 40 from the first constant current circuit 37
Is supplied with a constant current. On the other hand, a second ignition transistor 34 is connected between the connector (-D) to which the downstream end of the squib 40 is connected and the output connector (-B) of the IC. Resistance R
The second and second constant current circuits 38 are respectively connected in parallel. A second switching element 42, for example, an FET, is connected in series to the constant current circuit 38. When the second switching element 42 is turned on, a constant current is taken from the squib 40 into the second constant current circuit 38. It is. still,
The first and second switching elements 41 and 42 are connected to the microcomputer 12 and are turned on in response to a control signal from the microcomputer 12.

The safing sensor 32 is normally off, but when the vehicle is decelerated in the front-rear direction, it is turned off.
N is a mechanical acceleration sensor that emits an N signal, and the set acceleration (first reference acceleration GS1) is the acceleration sensor 14
Second reference acceleration GS2 (ignition transistor 33,
The acceleration is set to be smaller than the acceleration at which an ignition signal is issued at 34. The bases of the ignition transistors 33 and 34 are connected to the microcomputer 12, and are turned on in response to a control signal from the microcomputer 12.
Therefore, the safing sensor 32 and the ignition transistor 3
When both 3 and 34 are turned on, the squib 40 is supplied with an ignition current.

The backup power supply 26 supplies the ignition current to the squib 40 by discharging the electric charge stored in the capacitor even when the power supply from the battery power supply 20 is cut off due to the disconnection of the wiring or the like at the time of collision. I do. When the ignition switch 44 is turned on, the diode circuit 22 receives supply of a power supply current from the battery power supply 20.

In addition, a failure detection device 1 for an airbag device
0 is provided with an airbag warning light 43, and when the microcomputer 12 detects an abnormality of the failure detection device 10 of the airbag device, the airbag warning light 43 is turned on to warn the user of the abnormality.

The microcomputer 12 includes an upstream end (+ D) and a downstream end (-D) of the safing sensor 32 of the ignition system and the squib 40 as well as the acceleration sensor 14 of the control system involved in the deployment of the airbag. D) It is also connected to the ignition transistors 33 and 34. And
The failure detection device 10 of the airbag device is constantly monitored for a failure, for example, whether there is an open or short circuit in an electrical wiring or a conduction failure of these devices, and if there is a failure, the air is detected as described above. Back warning light 43
Lights up.

Next, the power supply short-circuit and GND short-diagnosis processing of the squib of the present embodiment having the above-described configuration will be described with reference to FIGS. FIG. 2 is a diagram showing a circuit configuration used for the squib power supply short & GND short diagnosis, and FIG. 3 is a flowchart showing the squib power supply short & GND short diagnosis processing. FIG. 4 shows an equivalent circuit of a failure detection device for an airbag device in which a leak resistance R + when a power supply is short-circuited is taken into consideration. Note that the interrupt timing and priority of the processing described below are adjusted in advance.

When the power supply short & GND short diagnosis process is started, as shown in the flowchart of FIG. 3, first, in step 1 (hereinafter, referred to as "S1"), the squib 40 is connected to the DC-DC converter. 24
From the upstream end of the squib 40 (+
The voltage V1 of D) is taken into the microcomputer 12. Next, in S2, it is determined whether or not the voltage V1 is higher than the threshold voltage V _{th +.}
Then, it is determined whether or not the voltage V1 is smaller than the threshold voltage _{Vth-. If} it is determined that the voltage is _higher than the threshold voltage _Vth- , the electric wiring is determined to be normal, and the airbag warning lamp 43 is turned off in S9. For example, when the electrical wiring is normal,
When the resistance value R1 of the first resistor is equal to the resistance value R2 of the second resistor, the voltage V1 of the following equation is taken. Note that the resistance value of the squib (usually about several Ω) is sufficiently smaller than the resistance values R1 and R2 and can be ignored.

[0023]

(Equation 1)

Next, at S2, the voltage V1 is changed to the threshold voltage V _{th +}
If it is determined that it is larger than the threshold, it is determined that there is a possibility of an abnormality in the electric wiring, and in S3, the input connector (+) of the IC is determined.
In FIG. 4, a signal for operating the second constant current circuit 38 is output from the microcomputer 12 to the second switching element 42, and the DC- DC converter 2
4 supplies the current supplied to the squib 40 to the constant current circuit 38.
It is taken in. Therefore, a current much larger than the current flowing through the second resistor R2 is taken into the constant current circuit 38, so that the voltage value V1 on the upstream side of the squib falls. As a result, the resistance value of the second resistor R2 is apparently reduced.

Here, the relationship between the threshold value for judging the power supply short-circuit and the resistance value R + of the leak resistance will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the upstream side voltage V1 of the squib and the resistance value R + of the power supply side leakage resistance.
1 is shown on the vertical axis and the resistance value R + is shown on the horizontal axis.

As shown in FIG. 5, the upstream voltage V1 of the squib 40 changes according to the resistance value R + of the leak resistance. And the resistance value R + is the first and second resistance R
1, R2 (in this embodiment, R1 = R2). When the first and second resistors are built in the IC as in this case, their resistance values are relatively large in consideration of space limitations in the IC and heat generation due to electric power. Will be. Therefore, as shown by the dotted line in FIG. 5, the upstream side voltage V1 of the squib starts to increase at about 500 kΩ where the leak resistance R + is relatively large, and when the leak resistance R + is about 1 kΩ, the voltage V1 becomes about 9 kΩ.
Vc / 10, which is almost equal to the power supply voltage Vc. Further, as the voltage V1 increases and becomes closer to the power supply voltage Vc, the rate of change decreases. Then, the value of the leak resistance R + that causes an actual power supply short-circuit fault is 500Ω or less, and the threshold value of the terminal voltage V1 corresponding to the leak resistance as the threshold value must be set to a value close to the power supply voltage Vc. However, as described above, the change in leak resistance R + decreases as terminal voltage V1 approaches power supply voltage Vc. Therefore, even if the threshold value of the terminal voltage V1 is set to a value close to the power supply voltage Vc, when the terminal voltage V1 decreases due to environmental conditions, the change range of the leak resistance R + with respect to the voltage change becomes wide, and the power supply short-circuit failure occurs. It is not possible to judge accurately.

Therefore, in S2, V1 is set to the threshold voltage V _{th +}
Only in the case where it exceeds the value, in S3, a signal for turning on the second switching element 42 is output from the microcomputer 12 to operate the second constant current circuit 38.
Then, the small current I supplied from the battery power supply 20 to the squib 40 is taken into the second constant current circuit 38, so that the resistance value of the second resistor R2 is apparently reduced.
Therefore, as shown by the solid line in FIG. 5, the terminal voltage V1 is reduced. Then, in S4, the reduced terminal voltage V1 is changed to the threshold voltage V corresponding to the threshold of the leak resistance in a region where the rate of change of the terminal voltage V1 with respect to the leak resistance is large.
_In comparison with _{th +} , a power supply short-circuit failure is determined. That is, the squib upstream side voltage V1 becomes the threshold voltage V
It is determined whether or not it is greater than _{th +} . Note that this threshold voltage V _{th +} is a leak resistance R + for determining an actual short-circuit failure.
Is determined by the threshold value. If the voltage is equal to or higher than the threshold voltage V _{th +} , the determination is YES, and it is determined in S5 that the power supply is short-circuited. In S5, the airbag warning lamp 43 is turned on.

That is, in the present invention, the microcomputer 12 outputs a current for turning on the second switching element 42 connected between the downstream terminal of the squib 40 and the ground terminal. The switching element 42
Is turned on, the switching element 42 conducts, and the constant current circuit 3 connected in series with the switching element 42.
8, the current supplied to the squib 40 is taken. As a result, the current flowing through the second resistor R2 becomes small, and by suppressing the voltage drop generated at the resistor R2 to a small value, the resistance value on the downstream side of the squib 40 is apparently reduced. Therefore, the terminal voltage V1 of the squib 40
, The threshold value of the terminal voltage corresponding to the leak resistance R + for determining the short-circuit failure can be set at an intermediate value between 1/2 Vc and the power supply voltage Vc.
The power supply short-circuit failure can be determined in a range where the terminal voltage change rate is large, and the accuracy of the power supply short-circuit failure determination is increased.

In step S4, the terminal voltage V1 is changed to the threshold voltage V
If it is equal to or lower than _{th +,} it is determined in S6 whether or not the terminal voltage V1 is equal to the threshold voltage _Vth-.
It is determined whether or not there is a GND short failure. Note that the case where the connector (-B) on the downstream side of the squib 40, that is, the ground side connector (-B) is short-circuited, is substantially the same as the case where the power supply of the squib 40 is short-circuited.

A short circuit downstream of the squib 40, that is, G
In the case of the ND short, contrary to the power short, the terminal voltage V1 falls from the normal voltage (1 / 2Vc). If the voltage V1 is smaller than the threshold voltage _Vth- in S6, it is determined that there is a possibility that the electric wiring is abnormal,
At 7, a signal for operating the first constant current circuit 37 is output from the microcomputer 12 to the first switching element 41. The DC-DC converter 2 is an equivalent circuit shown in FIG. 6 that takes into account the leak resistance R- connecting the input connector (-D) of the IC 45 and the downstream side of the squib.
The current supplied from 4 is taken into the constant current circuit 37. Therefore, a current much larger than the current flowing through the first resistor R1 is taken into the constant current circuit 37, so that the voltage value V1 on the squib upstream side increases. As a result, the first
The resistance value of the resistor R1 is apparently reduced.

Next, the relationship between the threshold value for judging the power supply short-circuit and the resistance value R- of the leak resistance will be described with reference to FIG. FIG. 7 is a graph showing the relationship between the upstream side voltage V1 of the squib and the resistance value R− of the power supply side leakage resistance.
Is shown on the vertical axis, and the resistance value R− is shown on the horizontal axis. As shown by the dotted line in FIG. 7, the upstream voltage V1 of the squib 40 starts to decrease from a relatively large value of the leak resistance R-, and the leak resistance R-
Is approximately 1 kΩ, the voltage V1 is almost the GND voltage 0V
To a value close to. Then, the change rate of the voltage V1 decreases as the value approaches 0V. Therefore, as shown by the solid line in FIG. 7, by reducing the terminal voltage V1, the terminal voltage V1 is reduced to ＶVc in S8.
In the range where the rate of change between the voltage and the GND voltage 0V is large, a threshold voltage V _th- for determining a short-circuit failure is compared,
A GND short failure is determined. If it is an actual GND short failure, the airbag warning lamp is turned on by the control signal of the computer 12 in S5, and if it is not the GND short failure, the airbag warning lamp is turned off in S9.

In this embodiment, a first constant current circuit 37 and a second constant current circuit 38 are connected in parallel to the first and second resistors, respectively, for example, when the power supply of the squib 40 is short-circuited. Then, the second constant current circuit 38 is operated to apparently reduce the resistance value between the downstream end of the squib 40 and the connector (-B) on the GND side, thereby increasing the failure detection accuracy. . However, the present invention is not limited to the present embodiment in which the constant current circuit is connected. By connecting resistors in parallel to the first and second resistors 35 and 36, the squib upstream end and the power supply connector (+ B) are connected. The same effect can be obtained by apparently reducing the resistance between the squib 40 and the GND side connector (-B).

Also, as in the present case, by operating the constant current circuit only when the squib upstream side voltage V1 is equal to or higher than the threshold voltage _{Vth +} or the threshold voltage _Vth- , noise generated at the time of diagnosis is minimized. can do. However, the resistance values of the first resistor R1 and the second resistor R2 can be apparently reduced by always operating the constant current circuit without being limited to this embodiment.
It is possible to accurately detect a short circuit failure of the airbag device.

In the first embodiment, the case where the present invention is applied to an airbag has been described. However, the present invention is not limited to this embodiment and may be applied to a seat belt pretensioner.

In the present embodiment, the squib 40
Corresponds to “starting means” in the claims, the microcomputer 12 serves as “terminal voltage measuring means”, the constant current circuits 37 and 38 serve as “voltage drop changing means”, and the squib upstream side voltage V1 exceeds the threshold Vth. The routine (S5) for determining whether or not there is a function corresponds to "failure detecting means".

Next, a failure detection device for an occupant protection device according to a second embodiment of the present invention will be described with reference to FIG. Since the control system and the ignition system of the second embodiment are almost the same as those of the first embodiment, only a brief description will be given here, and only different parts in the ignition system of the occupant protection device will be described. This will be described in detail. However, in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and overlapping description will be omitted.

The ignition system of the present embodiment has a battery power source 2
0, a diode circuit 22 for rectifying a power supply current supplied from the battery power supply 20 to obtain an ignition power supply,
An IC 50 having a DC-DC converter 24 for converting the voltage of the ignition power supply and a backup power supply 26 containing a large-capacity capacitor, and including first and second changeover switches 51 and 52 in its circuit. Across the first
The current supply resistor 53 and the second current supply resistor 54 are connected in series. The IC 50 has an output terminal of the first current supply resistor 53 and an input connector (+ B) of the IC 50.
However, the input terminal of the second current supply resistor 54 and the output connector (-B) of the IC 50 are connected to each other.

A first switch 51 is connected to the input connector (+ B) of the IC 50. A second switch 52 is connected to the output connector (-B) of the IC 50. Then, the plurality of squibs 55, 55 are sandwiched between the first switch 51 and the second switch 52.
By switching the first switch 51 and the second switch 52, the squibs 55, 56, 57, 58 are respectively connected to the first current supply resistor 53 and the second current supply Is connected in series with the use resistor 54. However, each of the squibs 55, 56, 57, 58
As in the first embodiment, a safing sensor is connected in series similarly to the first embodiment, and an ignition transistor corresponding to each squib is provided between the squib and the first switch 51 in the IC. , And a first resistor is connected in parallel to the ignition transistor, but the description thereof and the description of the drawings are omitted here. The squibs 55, 56, 57, and 58 here operate a driver airbag, a passenger seat airbag, a driver pretensioner, and a passenger seat pretensioner, respectively. The microcomputer 12 is connected to the switches 51 and 52, and the contacts of the switches 51 and 52 are switched by a signal from the microcomputer 12.

The microcomputer 12 includes not only an acceleration sensor 14 of a control system involved in the deployment of an air bag, but also a safing sensor (not shown) of an ignition system and upstream end portions of squibs 55, 56, 57, and 58. (+ D) and the downstream end (-D) are also connected to an ignition transistor (not shown). The occupant protection device 10 is constantly monitored for a failure, for example, whether there is an open / short circuit in the electrical wiring or a continuity failure of these devices, and if there is a failure, an airbag warning is issued as described above. The lamp 43 is turned on.

Next, each fault monitoring process will be described. However, this time, the explanation of the open circuit of the electric wiring of the acceleration sensor, the safing sensor, and the ignition transistor
The method of checking for a short circuit is omitted, and only the open / short fault monitoring method of the squib will be described in detail. FIG. 9 is a flowchart showing a plurality of squib failure monitoring processes, and the processes are executed by interruption every predetermined time. When this process is started, first, in S21, the first switch 51 and the second switch 52 are switched and connected to the first squib 55. Then, in S22, a current is supplied from the DC-DC converter 24 to the first squib 55, and the voltage generated at both ends of the squib 55 at that time is read into the microcomputer 12. The current I flowing through the squib 55 is a voltage Vc (input connector voltage of the IC) obtained by boosting the ignition power supply voltage by the DC-DC converter 24 as the first current.
And by dividing by the sum of the resistance values R1 and R2 of the second squib current supply resistors 53 and 54,
In this case, the resistance value of the squib 28 (normally several ohms)
Is negligible because it is sufficiently smaller than the resistance values R1 and R2.

Next, in S23, the microcomputer 1
ΔV generated at both ends of the squib 55 taken in
, The resistance value of the squib 55 is detected. And S
24, whether or not the squib end-to-end voltage ΔV is smaller than a threshold voltage ΔV _th1 for determining a squib short; or
It is determined whether or not it is greater than a threshold voltage ΔV _th2 for determining squib open. If the squib voltage V is not within the range of the threshold voltage, it is determined that the squib is abnormal.
Lights up. In S23, if the squib end-to-end voltage ΔV falls within the range of the threshold voltage, the first squib 55
Is normal, and in S24, the first and second switches 51 and 52 are switched, and the first current supply resistor 53 and the second current supply resistor 54 are connected in series with the second squib 56. Connected. Then, in S25, the same processing as the above-described first squib failure monitoring processing is performed on the second squib 56. If it is determined that the second squib is abnormal, the airbag warning lamp 43 is turned on in S31. If it is determined that the first and second switches 5 and 5 are normal, the process proceeds to step S26.
1 and 52 are switched, the first current supply resistor 53 and the second current supply resistor 54 are connected to the third squib 57, and a squib failure monitoring process is performed on the third squib 57 in S27. Will be Therefore, if it is determined that the third squib 57 is abnormal, the airbag warning lamp 43 is turned on in S31. If determined to be normal, the first and second switches 5
1 and 52 are switched, the first current supply resistor 53 and the second current supply resistor 54 are connected to the fourth squib 58, and the squib failure monitoring process is performed on the fourth squib 58 in S29. Done. Therefore, if it is determined that the fourth squib 58 is abnormal, in S31,
If the airbag warning lamp 43 is turned on and is determined to be normal, all the squibs 55, 56, 57 and 58 are determined to be normal, and the airbag warning lamp 43 is turned off in S30. You. Thus, the processing of this routine ends.

With the above configuration, the first and second squibs 55, 56, 57, 58
Are switched, and the respective squibs 55, 56, 57, 58 are connected in series with the first and second current supply resistors 53, 54, and a squib failure monitoring process is performed each time. Therefore, the plurality of squibs 55,
It is possible to detect a short / open failure of 56, 57, 58. Generally, in order to detect a squib short / open, it is necessary to use highly accurate resistors for the first and second squib current supply resistors 53 and 54 which determine the voltage to be supplied to the squib. However, the cost of the resistor itself is high, and many occupant protection devices are mounted on the vehicle.
Using the second resistor leads to an increase in cost. Further, since the resistance value varies depending on each resistor, it is difficult to accurately detect a short / open failure of the squib. Therefore, with the above-described configuration, a plurality of squib failure monitoring processes can be performed by using only one set of resistors, so that the cost can be significantly reduced and the accuracy of the squib short / open failure detection can be improved. Can be done.

Note that, in the present embodiment, the first and second
Corresponds to a "connection switching means" in the claims, and a routine in which the squib voltage V.sub.V is compared with a threshold value for determining a squib failure (S23, S25, S27, S27).
29) correspond to “failure detection means”.

As described above in detail, in the failure detecting device for an occupant protection device according to the first aspect, when the voltage drop of the resistor is changed by the voltage drop changing device, the terminal voltage of the starting device changes. Since the connection failure of the starting unit can be detected in a range where the rate of change of the terminal voltage is large, the connection failure of the starting unit can be detected with high accuracy. Further, in the failure detection device for the occupant protection device according to the second aspect, the connection switching means can set the connection state of the resistor to one of the activation means and the connection state of the resistor to another activation means. Becomes Therefore, the failure detection of the starting unit in each connection state can be performed by one resistor, so that the number of resistors to be connected in series to the starting unit can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an occupant protection device mounted on a vehicle.

FIG. 2 is a diagram showing a circuit configuration used for a squib power supply short & GND short diagnosis.

FIG. 3 is a flowchart showing a squib power supply short & GND short diagnosis process.

FIG. 4 is a diagram showing an equivalent circuit when a power supply is short-circuited.

FIG. 5 is a graph showing a relationship between an upstream voltage V1 of the squib and a power supply side leak resistance R +.

FIG. 6 is a diagram showing an equivalent circuit when a GND short occurs.

FIG. 7 is a graph showing a relationship between a squib upstream voltage V1 and a GND-side leak resistance R−.

FIG. 8 is a diagram illustrating an occupant protection device according to a second embodiment.

FIG. 9 is a flowchart illustrating a plurality of squib failure monitoring processes.

FIG. 10 is a diagram showing a failure detection device for an occupant protection device according to the related art.

FIG. 11A is a diagram illustrating a case where a power supply is short-circuited in the failure detection device according to the related art. FIG. 4B is a diagram illustrating a case where a GND short circuit occurs in the failure detection device of the related art.

FIG. 12 shows an upstream side voltage V of the squib according to the related art.
6 is a graph showing the relationship between the power supply side leakage resistance R + 1 and R +.

[Description of Signs] 10, occupant protection device 12, microcomputer 2
0, battery power supply 24, DC-DC converter 3
7, first constant current circuit 38, second constant current circuit 40, squib 41, first switching element 4
2, the second switching element 43, the airbag warning light 53, the first current supply resistor 54, the second current supply resistor 55, the first squib 56, the second squib 57, and the third squib 58 , The fourth squib R
1, the first resistor R2, the second resistor

Claims (2)

[Claims] 1. An occupant protection device starting means connected in series to a power supply circuit, a terminal voltage measuring means for measuring a terminal voltage of the activating means, and a first means connected in series upstream of the starting means. A resistor, a second resistor connected in series downstream of the activating means, and a first resistor or a second resistor of the activating means.
Voltage change means for changing the voltage drop of at least one of the resistors, and failure detection means for detecting a connection failure of the activation means based on the terminal voltage measured by the terminal voltage measurement means after the voltage drop is changed. A failure detection device for an occupant protection device. 2. A plurality of starting means respectively connected to a power supply circuit, a resistor arranged so as to be connected in series upstream or downstream of the starting means, and between the starting means and the resistor. A connection switching unit that is connected and realizes both a connection state between the resistor and one of the activation units and a connection state between the resistor and another activation unit different from the first activation unit. And a failure detecting means for detecting a failure of the activating means based on a potential difference between both ends of the activating means connected to the resistor by the connection switching means.