JP2729345B2 - Abnormality diagnosis device for squib abnormality detection circuit - Google Patents

Abstract

PURPOSE:To provide an abnormality diagnosis apparatus for squib abnormality diagnosis circuit which can make diagnosis of the normality/abnormality of first and second abnormality detection circuits. CONSTITUTION:Between a plus-side of a power source voltage VD and one end of a squib 20 there is provided a first abnormality detection circuit 12 composed of a resistor R4 and a transistor TRH and connected with a safing sensor 14 and intended for detecting the abnormality of the squib and there are provided a second abnormality detection circuit composed of a resistor R3 and a transistor T so as to detect the abnormality of the squib 20 and connected with a second resistor R2 and a resistor R1, the second abnormality detection circuit 13 having a point of connection B which is connected to a microcomputer 17 through an operational amplifier 15 and an A/D converter 16, the microcomputer being connected to the transistor TRH and the transistor TRL.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing an abnormality in a squib abnormality detecting circuit for diagnosing whether or not there is an abnormality in a squib abnormality detecting circuit constituting an airbag diagnosis system.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram schematically showing a squib abnormality detecting circuit mainly used at present.
5, 50 squib abnormality detection circuit, 20 denotes a squib, plus end side of the squib 20 is connected to the supply voltage V _D via the current limiting resistor R _4, the negative terminal of the squib 20 The side is grounded via a switching transistor _TR50 . Moses the current limiting resistor R ₄ is constituted by a resistor R ₅ and a switch S1 - Fingusensa 14 are connected in parallel, the connection point A and the connection point C is connected to operational amplifier 51, operational amplifier 51 It is connected to a microcomputer (not shown) via an A / D converter (not shown). In addition,
A control signal related to switching is input from a microcomputer (not shown) to the base of the switching transistor _TR50 .

In the circuit configured as described above, detection of whether the squib 20 is normal (= squib 20
Measurements of the resistance value R _S) is carried out as follows. The switching transistor T _R50 is turned on, a test current flows through the squib 20, and a potential difference ΔV is generated at both ends of the squib 20. Next, the potential of the connection point A is monitored, and the magnitude I of the test current is calculated. Then, the squib 20 is determined from the potential difference ΔV and the magnitude I of the test current.
Of the resistance R _s (= ΔV / I).

However, the resistance value R of the squib 20 is
_{The S} detection method has the following problems. The airbag device is usually mounted in a steering wheel, and the wire harness to the squib 20 is twisted between the high side and the low side of the wire harness that supplies current to the cushion. For this reason, there is a possibility that the wire harness to the squib 20 rarely short-circuits with the wire harness that supplies the current to the cushion. When the wire harness to the squib 20 is rarely short-circuited, the value of the test current flowing through the squib 20 changes slightly, but the resistance value R _S of the squib 20 can be measured accurately. A problem arises in that it is no longer possible.

For example, when a test current of about 25 mA is supplied to the squib 20, if the high-side wire harness of the squib 20 is short-circuited by + B rare via the high-side wire harness of the horn, the high horn of the horn is high. Current flows into the plus end of the squib 20 from the side wire harness, and the current flowing through the squib 20 becomes 50
mA. At this time, the potential on the plus end side (= connection point A) of the squib 20 increases, and the potential difference ΔV between both ends of the squib 20 also increases. On the other hand, when the wire harness on the low side of the squib 20 is short-circuited to GND via the wire harness on the low side of the horn, a current flows out from the minus end of the squib 20 and the current flowing through the squib 20 is about 10 mA. become. At this time, the potential at the connection point A decreases, and the potential difference ΔV also decreases.

As described above, when a rare short circuit occurs in the wire harness to the squib 20, the value of the current flowing through the squib 20 changes, and the potential of the connection point A and the squib 20
Is varied. Therefore, the squib 2 is monitored by monitoring the potential of the connection point A and the potential difference ΔV.
In the case of the squib abnormality detection circuit (FIG. 5) which obtains a resistance value of 0, if a rare short occurs in the wire harness to the squib 20, the potential of the connection point A fluctuated by the rare short and the squib 20 Since the resistance value R _S of the squib 20 is calculated based on the potential difference ΔV between both ends, there is a problem that the resistance value R _S of the squib 20 is erroneously detected.

As described above, the conventional squib abnormality detection circuit 50 shown in FIG. 5 has the above-mentioned problems. Therefore, it is possible to determine whether a rare short wire harness to the squib 20 when measuring the resistance value R _S of the squib 20 occurs, the resistance value R _S precisely detected, the squib 20 is normal or The inventor has previously proposed a squib abnormality detection circuit 60 (FIG. 6) obtained by improving the circuit shown in FIG. 5 so that the circuit can accurately determine the abnormality.

<Improvement Example> The difference between the squib abnormality detection circuit 60 shown in FIG. 6 and the squib abnormality detection circuit 50 shown in FIG. 5 is that the switching between the current limiting resistor R ₄ and the connection point A is performed. A first abnormality detection circuit 12 is configured with a transistor T _RH interposed, and a second abnormality detection circuit 13 in which a switching transistor T _RL and a current limiting resistor R ₃ are connected in series is a switching transistor T _RH.
It is connected in parallel to _R50 , and the other configuration is the same. In the squib abnormality detection circuit 60, the potential of the connection point A on the plus end side of the squib 20 and the potential of the connection point C on the minus end side, and the potential difference ΔV between both ends of the squib 20 can be monitored. ing.

The squib abnormality detection circuit configured as described above
In the road 60, the resistance value R of the squib 20_S The detection of
It is performed as follows. First, the microcomputer
(Not shown) by the switching transistor T _RHAnd
And switching transistor T_RLIs turned on. About
And the power supply voltage V_D From the current limiting resistor R_Four ー Switchon
G transistor T_RH-Squib 20-Current limiting resistor R
_Three -Switching transistor T_RLSquib 2 on the route
A test current is supplied to zero. And by the test current
Based on the resulting potential difference ΔV between both ends of the squib 20,
Resistance value R of Eve 20_S Is detected.

Next, if the squib abnormality detection circuit 60 is used, it can be determined whether or not a rare short circuit has occurred in the wire harness to the squib 20.
That the resistance value R _{S of} 0 can be accurately detected,
A brief description will be given. [When + B rare short occurs] When the high side wire harness to the squib 20 is + B rare short,
The potentials at the connection points A and C both rise. At this time, the potential of the connection point C is monitored and the current limiting resistor R ₃
The flowing current I _L is calculated (potential V _C at the connection point C
Then, I _L = V _C / R ₃ ). Then, based on the potential difference ΔV across of the current I _L and the squib 20,
The + B rare short cancels the detection error due to the current flowing into the plus end of the squib 20.

[When GND rare short circuit]
The wire harness on the low side to Eve 20 is GND rare
The potentials of the connection points A and C are both lowered.
Descend. At this time, the potential of the connection point A is monitored to control the current.
Limiting resistor R_Four Current I flowing through_H Is calculated (connection point A
Potential of V _A Then I_H = (V_D -V_A ) / R_Four When
Become). And the current I_H And both ends of the squib 20
Squib with GND rare short based on the position difference ΔV
The detection error due to the current flowing from the minus end of
Canceled. As described above, squib abnormality detection
If the circuit 60 is used, the wire harness to the squib 20
Can determine whether rare shots have occurred.
The resistance value R of the squib 20_S Can be accurately detected
it can.

[0012]

However, the switching transistor T _RH constituting the first abnormality detecting circuit 12 and / or the switching transistor T _RL constituting the second abnormality detecting circuit 13 of the squib abnormality detecting circuit 60 are normal. Otherwise, the above-described effect in the squib abnormality detection circuit 60 cannot be obtained. That is, the squib abnormality detection circuit 60 includes the first abnormality detection circuit 1.
If the second and / or second abnormality detection circuit 13 is out of order, there is a problem that the squib 20 is erroneously detected as abnormal even though the squib 20 is normal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a squib abnormality capable of diagnosing whether the first abnormality detection circuit and the second abnormality detection circuit constituting the squib abnormality detection circuit have an abnormality. An object of the present invention is to provide an abnormality diagnosis device for a detection circuit.

[0014]

In order to achieve the above object, an abnormality diagnosis apparatus for a squib abnormality detection circuit according to the present invention comprises a resistor and a transistor between a positive side of a power supply voltage and one end of the squib. A first abnormality detecting circuit for detecting abnormality of the squib is provided, and a second abnormality detecting circuit for detecting abnormality of the squib is provided between the other end of the squib and the ground, the resistance being configured by a resistor and a transistor. A detection circuit is interposed, a safing sensor including a switch and a resistor is connected in parallel to the first abnormality detection circuit, and a second resistor is connected in parallel to the second abnormality detection circuit. An end of the squib and a connection point B between the second abnormality detection circuit and the second resistor are connected to a microcomputer via monitoring means for monitoring the potential of the one end and the connection point B. It is, in the microcomputer is characterized in that it is connected to the transistors constituting the transistor and the second abnormality detection circuit constituting the first abnormality detection circuit.

[0015]

In the abnormality diagnosis device for a squib abnormality detection circuit according to the above configuration, the potential VB at the connection point _B and one end of the squib (= the connection point A between the one end of the squib and the first abnormality detection circuit). ) and the potential V _a of is monitored by the monitor means. The determination as to whether the switching transistor of the first abnormality detection circuit and / or the switching transistor of the second abnormality detection circuit is abnormal or normal is performed as follows.

In a state where both of the switching transistors are turned off, or in a state where only one of the switching transistors is turned on, the potential VA of the connection point A obtained by actually monitoring and the potential V _A of the connection point B are obtained. Potential V _B
Are compared with each other in a predetermined magnitude relationship. If both the transistors are normal, the first resistance, the second resistance, the resistance configuring the safing sensor, the resistance configuring the first abnormality detection circuit, and the second abnormality The theoretical value of the potential _{VA at} the connection point A, which can be obtained by dividing the power supply voltage with a resistor constituting a detection circuit, and the magnitude of the monitored potential _VA are compared. Based on the result, it is determined whether the switching transistors are normal or abnormal.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a squib abnormality detecting circuit according to an embodiment of the present invention; Note that components having the same functions as those of the conventional example are denoted by the same reference numerals.

FIG. 1 is a circuit diagram schematically showing an abnormality diagnosis apparatus 10 for a squib abnormality detection circuit according to an embodiment. In FIG. 1, reference numeral 12 denotes a switching transistor T
₅ shows a first abnormality detection circuit composed of _RH and a current limiting resistor R ₄ , wherein the emitter of the switching transistor is connected to the power supply voltage V _D , and the collector is a connection point via the current limiting resistor R _4. A is connected. The connection point A is connected to the plus side of the squib 20 and the squib 2
The negative side of 0 is grounded via the second abnormality detection circuit 13, the connection point B and the first resistor R _1. Second abnormality detection circuit 13 is constituted by a resistor R ₃ and the switching transistor T _RL current limiting, current limiting resistor R
₃ of one end of which is connected to the negative side of the squib 20, the other end is connected to the collector of the switching transistor T _RL, the emitter of the switching transistor T _RL is connected to the connection point B.

Further, the first abnormality detection circuit 12 is connected to the safing sensor 14 composed of a resistor R ₅ and the switch S1 in parallel, the second parallel to the second abnormality detection circuit 13 the resistor R ₂ is connected. The connection points A and B are connected to an operational amplifier 15, and the operational amplifier 15 is connected to a microcomputer 17 via an A / D converter 16. The microcomputer 17 is connected to the base of the switching transistor T _RH constituting the first abnormality detection circuit 12 and the base of the switching transistor T _RL constituting the second abnormality detection circuit, respectively. Although not shown in FIG. 1, the potentials at both ends of the squib 20 are also input to the microcomputer 17 via an operational amplifier (not shown) and an A / D converter (not shown), and need not be described. You can do it.

The operation of the abnormality diagnosing device 10 for a squib abnormality detecting circuit having the above-described configuration will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the microcomputer 17 relating to a process of diagnosing an abnormality of the first abnormality detection circuit 12 and the second abnormality detection circuit 13. FIGS. _{when RH} and the switching transistor T _RL is turned on and off, an equivalent circuit showing a path through which a current to be supplied to the squib 20 from the power supply voltage V _D flows.

First, the equivalent circuits shown in FIGS. 3 and 4 will be described. FIG. 3A shows a case where both the switching transistor T _RH and the switching transistor T _RL are turned off. The resistance value R _S of the squib 20 is usually about 2 to 3Ω, which is considerably smaller than the resistance values of R _{1 to} R ₅ . Therefore, in the case of FIG. 3A, although the value actually includes the resistance value R _{S of the} squib and becomes slightly larger than the value represented by the following equation, the potential V of the connection point A is actually increased.
_Aa may be considered as V _Aa = p · V _D ‥‥. Here, p = (R ₁ + R ₂ ) / (R ₁ + R ₂ + R ₅ ).

FIG. 3B shows a switching transistor T
_{The case where RH} is turned off and the switching transistor _TRL is turned on is shown. Similarly to the above, in the case of FIG. 3B, the potential V _Ab of the connection point A is V _Ab = m · V _D ‥‥
Becomes Here, m = (R ₁ + R ₂₃ ) / (R ₁ + R
₂₃ + R ₅ ) and R ₂₃ = R ₂ · R ₃ / (R ₂ + R ₃ ).

FIG. 4A shows a switching transistor T
_This shows a case where _RH is turned on and the switching transistor _TRL is turned off. Similarly to the above, in the case of FIG. 4A, the potential V _Ac of the connection point A is V _Ac = r · V _D ‥‥
Becomes Here, r = (R ₁ + R ₂ ) / (R ₁ + R
₂ + R ₄₅ ) and R ₄₅ = R ₄ · R ₅ / (R ₄ + R ₅ ).

FIG. 4B shows the switching transistor T
_The case where both _RH and the switching transistor _TRL are turned on is shown. Similarly to the above, in the case of FIG. 4B, the potential V _Ad of the connection point A is V _Ad = V _D · (R ₁ +
The _{R 23) / (R 1 +} R 23 + R 45) ‥‥.

Next, based on the flowchart shown in FIG.
And the first abnormality detection circuit 12 and / or the second abnormality
Micro to diagnose whether there is abnormality in the detection circuit 13
The abnormality diagnosis processing in the computer 17 will be described. Ma
First, in step 1, the microcomputer 17
Switching transistor T_RHAnd switching transistors
Star T_RLSwitching signal to turn off both
Is forced. As can be seen from the equivalent circuits shown in FIGS.
And the potential V at the connection point A_A Is lowest in Figure 3
Theoretical value V in (b)_AbIs the case. In step 2
Is actually monitored under the condition set in step 1.
Potential V at connection point A_A Is the logic shown in FIG.
Theoretical value V_Ab(= MV_D Is lower than
That is, V_A <V_AbIs determined. V_A 
<V _AbIf so, the process proceeds to step 3 where the squib 20 is G
ND short circuit or safing sensor 14
It is determined that it may be open. one
In step 2, V_A ≧ V_AbWas determined to be
If so, go to step 4.

In step 4, it is determined whether or not the potential V _A at the connection point _A and the potential V _{B at the} connection point B, which can be actually obtained by monitoring, satisfy the relationship _VA <n · V _B. . Here, n = (R ₁ + R ₂ ) / R ₁ . By the way, in the case of FIG. 3A, V _Aa = n · V _Ba , and FIG.
In the case of (b), V _Ab = V _Bb · (R ₁ + R ₂₃ ) / R ₁ . Therefore, in the state of step 1, if the switching transistor _TRL is not short-circuited, _VA = n
· While the V _B, if the switching transistor T _RL is _{short, V A = V B · (} R 1 + R 23) / R
It becomes ₁ . Here, R ₂ > R ₂₃ and n> (R ₁ +
R ₂₃ ) / R ₁ , the switching transistor T
_{When RL} is short-circuited, the value obtained by multiplying the potential V _B of the connection point B actually obtained by monitoring by n = (R ₁ + R ₂ ) / R ₁ is obtained by actually monitoring. Connection point A
Is always higher than the potential V _A. Therefore, step 4
If it is determined that the above relationship is YES in step 5, it is determined in step 5 that the switching transistor _TRL is short-circuited, and if it is determined that the relationship is NO, the process proceeds to step 6.

In step 6, the potential V at the connection point A is_A Is V
_A > PV_D To determine if the relationship
Is done. The squib abnormality detection circuit has an abnormality
If there is not always, as shown in FIG.
In the state, the potential V of the connection point A_A Is almost pV_D 
 Becomes Therefore, in step 6, V_A > PV _D 
If it is determined that the
Connection point A is directly connected to the power supply.
State or the switching traffic
Transistor T_RHIs short-circuited and the connection point A and the power supply voltage V_D When
The resistance interposed between R₄₅(<R_Five ) And the connection point
It is considered that the potential of A has risen. On the other hand, in step 6
If no, proceed to step 8 and switch
Ching transistor T_RLInput an ON signal.

In step 9, the potential V _{A of the} connection point _A becomes
A determination is made as to whether a V _A> q · V _B. However,
q = (R ₁ + R ₂₃ ) / R ₁ . In step 9, a determination process is performed from the viewpoint opposite to the determination process in step 4. That is, if the switching transistor T _RL is not open, _VA = q · V _B , but if the switching transistor T _RL is open, _VA = n · V _B. As described above, q <n
Since it is, the value obtained by multiplying the q to V _B when the switching transistor T _RL is open, in fact is necessarily smaller than the potential V _A at the connection point A obtained by monitoring at that time . Therefore, in step 9,
When it is determined that V _A> q · V _B is Step 1
If it is determined that the switching transistor T _RL is open at 0, and it is determined that _VA ≦ q · V _B , the process proceeds to step 11.

In step 11, an ON signal is input to the switching transistor T _RH , and an OFF signal is input to the switching transistor T _RL . Whether the step 12, V _A <r · V _D is determined. If the switching transistor T _RH is normal, the equivalent circuit at this time is as shown in FIG. 4A, and the potential VA at the connection point _A is _VA = r · V _D. However, if the open switching transistor T _RH, the equivalent circuit at this time becomes as shown in FIG. 3 (a), V _A =
p · V _D. Here, since r> p, V _B when the switching transistor T _RH is open
Value obtained by multiplying r in fact always greater than the potential V _A at the connection point A obtained by monitoring at that time to.
Therefore, if the determination in step 12 is affirmative, the process proceeds to step 13 where the switching transistor T _RH is considered to be open. On the other hand, if the determination in step 12 is no, the process proceeds to step 14. Then, the open / short detection processing of the squib 20 is started.

As described above, if the abnormality diagnosing device 10 for the squib abnormality detecting circuit according to the embodiment is used, the first abnormality detecting circuit 12 is configured before the process of detecting the open / short abnormality of the squib 20 is performed. It is possible to diagnose whether or not the switching transistor T _RH and the switching transistor T _RL constituting the second abnormality detection circuit are abnormal.

[0031]

As described above in detail, by using the abnormality diagnosis apparatus for a squib abnormality detection circuit according to the present invention, the switching transistor constituting the first abnormality detection circuit is performed before performing the processing for detecting the abnormality of the squib. And it can be diagnosed whether or not there is any abnormality in the switching transistor constituting the second abnormality detection circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing an embodiment of an abnormality diagnosis device for a squib abnormality detection circuit according to the present invention.

FIG. 2 is a flowchart showing an operation relating to abnormality diagnosis processing of the microcomputer.

FIG. 3 and

FIGS. 4A and 4B are equivalent circuits showing a path of a current flowing according to the ON / OFF state of a switching transistor.

FIG. 5 is a circuit diagram schematically showing a conventional squib abnormality detection circuit.

FIG. 6 is a circuit configuration diagram schematically showing an improved example obtained by improving the conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 squib abnormality detection circuit abnormality diagnosis device 12 first abnormality detection circuit 13 second abnormality detection circuit 14 safing sensor 15 operational amplifier (monitor) 16 A / D converter (monitor) 17 microcomputer 20 squib R _1st 1 resistance R ₂ second resistance

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location G01R 31/00 (56) References JP-A-6-171455 (JP, A) JP-A-6-74987 (JP) JP-A-6-72281 (JP, A) JP-A-6-72279 (JP, A) JP-A-5-319201 (JP, A) JP-A-5-278560 (JP, A) 5-262201 (JP, A) JP-A-5-178163 (JP, A) JP-A-4-266550 (JP, A) JP-A-4-185552 (JP, A) JP-A-1-306343 (JP, A A)

Claims (1)

(57) [Claims] 1. A squib having a first abnormality detection circuit which is comprised of a resistor and a transistor between a positive side of the power supply voltage and one end of the squib, and detects an abnormality of the squib. A second detecting means for detecting an abnormality of the squib, comprising a resistor and a transistor between the ground and the ground;
An abnormality detection circuit and a first resistor are interposed. A safing sensor including a switch and a resistor is connected in parallel to the first abnormality detection circuit, and a safing sensor is connected in parallel to the second abnormality detection circuit. And a connection point B between the one end of the squib and the second abnormality detection circuit and the second resistance is connected via a monitor means for monitoring the potential of the one end and the connection point B. A microcomputer connected to a transistor constituting the first abnormality detection circuit and a transistor constituting the second abnormality detection circuit; apparatus.