JPH068120U - Failure diagnosis circuit for vehicle occupant protection device - Google Patents

Abstract

(57) [Summary] (Correction) [Purpose] It is possible to provide a highly reliable and safe vehicle occupant protection device failure diagnosis circuit that can diagnose the state of the ignition circuit with a minute current. [Structure] Micro-constant currents of different magnitudes are supplied to the ignition circuit 13, potential differences corresponding to these micro-constant currents of different magnitudes are detected, and the ignition circuit abnormality identification circuit 2 is detected.
When 0, the failure diagnosis of the ignition circuit is performed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a failure diagnosing circuit for a vehicle occupant protection device, and more particularly to a vehicle occupant protection device capable of identifying whether the ignition circuit of the vehicle occupant protection device is normal or abnormal by passing a small current through the ignition circuit. This is related to the device failure diagnosis circuit.

[0002]

[Prior art]

 2. Description of the Related Art A conventional failure diagnosis circuit for a vehicle occupant protection device is, for example, that shown in FIG. In this figure, 51 is a power supply battery, 52 is an ignition switch, and 53 is an ignition power supply circuit equipped with a step-up DC-DC converter. 54 is an acceleration sensor, 55 is a high-pass filter, 56 is an integrator, 57 is a threshold circuit, and 58 is an amplifier. The high-pass filter 55, the integrator 56, the threshold circuit 57, and the amplifier 58 constitute an operation determination circuit 59. There is. Reference numeral 60 is a diagnostic voltage dividing resistor, 61 is an acceleration switch, 62 is a resistor connected in parallel to the acceleration switch 61, and 63 is a firing circuit for igniting explosive powder for inflating an airbag.

Reference numeral 64 is a constant current circuit for supplying a constant current of 100 mA to the ignition circuit 63, and 64 a is a switch circuit for operating the constant current circuit 64. Reference numeral 65 denotes a differential amplifier circuit, the inverting input terminal of which is connected to the power source side terminal of the ignition circuit 63 via a resistor, and the non-inverting input terminal of which is connected to the ground side terminal of the ignition circuit 63 via a resistor. Has been done. The differential amplifier circuit 65 detects a potential difference between both terminals of the ignition circuit 63 and amplifies and outputs it.

Reference numeral 66 is a comparator, the non-inverting input terminal of which is connected to the plus side terminal of the reference voltage source 67 and is supplied with the reference voltage Vref. On the other hand, the inverting input terminal of the comparator 66 is connected to the output terminal of the differential amplifier circuit 65. In the vehicle occupant protection device failure diagnosis circuit, the ratio of the offset amount in the signal output from the differential amplifier circuit 65 is suppressed to a small value, and the ignition circuit 63 is disconnected from the normal state or only disconnected. A relatively large constant current of 100 mA is passed through the ignition circuit 63 in order to enable the differential amplifier circuit 65 to output a signal of a sufficient magnitude to distinguish it from a faulty state.

Next, the operation will be described. When a shock acceleration is applied to the vehicle body due to a collision accident, the acceleration sensor 54 and the acceleration switch 61 detect this. As a result, the acceleration switch 61 is turned on, and an electric signal corresponding to the impact acceleration applied from the acceleration sensor 54 is output to the operation determination circuit 59. This electric signal is supplied to the base terminal of the output transistor of the amplifier 58 via the high pass filter 55, the integrator 56, and the threshold circuit 57. As a result, the output transistor of the amplifier 58 is turned on, so that a sufficient current is supplied from the ignition power supply circuit 53 to the ignition circuit 63. As a result, the ignition circuit 63 ignites the explosive and inflates the airbag.

On the other hand, when no shock acceleration is applied to the vehicle body, the output transistors of the acceleration switch 61 and the amplifier 58 are in the off state. When the switch circuit 64a is closed to diagnose the state of the ignition circuit 63, a constant current of 100 mA is supplied from the ignition power supply circuit 53 to the ignition circuit 63. The ignition circuit 63 does not operate depending on this current value. When the constant current flows through the ignition circuit 63, a potential difference occurs between both terminals of the ignition circuit 63 depending on the state where the ignition circuit 63 is broken or is about to be broken.

The differential amplifier circuit 65 amplifies this potential difference and outputs a signal corresponding to this potential difference to the comparator 66. The comparator 66 compares the signal output from the differential amplifier circuit 65 with the reference voltage Vref output from the reference voltage source 67, and if the signal output from the differential amplifier circuit 65 exceeds the reference voltage Vref, the ignition circuit 63 fails. Output a signal. Therefore, for example, if the ignition circuit 63 is defective or broken, the potential difference across the ignition circuit 63 becomes larger than that in the normal case, or rises to the power supply voltage supplied. As a result, the output signal of the differential amplifier circuit 65 becomes large, the magnitude of the signal supplied to the inverting input terminal of the comparator 66 exceeds the reference voltage Vref, and the comparator 66 outputs a failure signal.

[0008]

[Problems to be solved by the device]

 In the above-described vehicle occupant protection device failure diagnosis circuit, the current supplied to the ignition circuit 63 for diagnosing the state of the ignition circuit 63 is a constant current of 100 mA, and the ignition circuit 63 operates depending on this current value. However, since this current value is a comparatively large value with respect to the operating current of the ignition circuit 63, the ignition circuit 63 will be activated if this current value temporarily increases. There is a problem.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to diagnose normality and failure of an ignition circuit by a minute current, and also to provide highly reliable safety. Another object of the present invention is to provide a failure diagnosis circuit for a vehicle occupant protection device.

[0010]

[Means for Solving the Problems]

 According to the failure diagnosing circuit for a vehicle occupant protection device of the present invention, a switch circuit and an ignition circuit are connected in series between both terminals of the battery, and the ignition circuit is activated by turning on the switch circuit. In a vehicle occupant protection device that operates a vehicle occupant protection device, a constant current circuit that supplies a small constant current of different magnitude to the ignition circuit and a potential difference between both terminals of the ignition circuit are detected and output. A first differential amplifier circuit, and a first sample that samples and holds the output signals output from the first differential amplifier circuit in synchronization with the timings when the minute constant currents of different magnitudes are supplied to the ignition circuit. The hold circuit and the second sample and hold circuit, and the output of the first differential amplifier circuit sample-held by the first sample and hold circuit and the sample and hold circuit by the second sample and hold circuit. The second differential amplifier circuit for detecting the difference between the held output of the first differential amplifier circuit and the output signal output from the second differential amplifier circuit, and comparing the output signal with a reference value to determine whether the ignition circuit is normal or abnormal. And a control circuit for controlling the constant current circuit, the first sample-hold circuit, and the second sample-hold circuit.

[0011]

[Action]

 In the vehicle occupant protection device fault diagnosis circuit according to the present invention, minute electric currents of different magnitudes are applied to the ignition circuit, and the potential difference generated between the terminals of the ignition circuit is detected. The detected potential difference between both terminals of the ignition circuit is sampled and held by a sample hold circuit in synchronization with the timing at which the current is supplied to the ignition circuit. Further, the difference between the sampled and held potential differences is obtained, this difference is compared with a reference value, and based on this result, the normal or abnormal state of the ignition circuit is identified and diagnosed. Therefore, the state of the ignition circuit can be diagnosed by the minute current, and a highly reliable and safe failure diagnosis circuit for the vehicle occupant protection device can be obtained.

[0012]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an electric circuit diagram showing the configuration of an embodiment of a failure diagnosing circuit for a vehicle occupant protection system according to the present invention. In this figure, 1 is a power supply battery, 2 is an ignition switch, and 3 is an ignition power supply circuit including a step-up DC-DC converter. Reference numeral 4 is an acceleration sensor, 5 is a high-pass filter, 6 is an integrator, 7 is a threshold circuit, and 8 is an amplifier. The high-pass filter 5, the integrator 6, the threshold circuit 7, and the amplifier 8 constitute an operation determination circuit 9. There is.

Reference numeral 10 is a diagnostic voltage dividing resistor, 11 is an acceleration switch, 12 is a resistor connected in parallel with the acceleration switch 11, and 13 is a firing circuit for igniting explosive powder for inflating an air bag. A constant current circuit unit 14 is connected between the ignition circuit 13 and the ground. The constant current circuit unit 14 includes a first constant current circuit 14a, a second constant current circuit 14b, and a changeover switch circuit 14c. The first constant current circuit 14a can pass a constant current of 10 mA. On the other hand, the second constant current circuit 14b can flow a constant current of 20 mA.

The changeover switch circuit 14c is switched to the first constant current circuit 14a side or the second constant current circuit 14b side by the changeover signal SS, and 10 mA or 20 mA for performing a diagnostic check such as disconnection of the ignition circuit 13 or the like. Is a circuit for supplying a minute constant current of the above to the ignition circuit 13. Reference numeral 15 is a first differential amplifier circuit, which detects and amplifies a potential difference generated between both terminals of the ignition circuit 13 when the minute constant current of 10 mA or 20 mA flows in the ignition circuit, and outputs it.

Reference numeral 16 denotes a first sample-hold circuit, which samples and holds the signal output from the first differential amplifier circuit 15 at the timing when the sample pulse signal SP1 is supplied. A second sample-hold circuit 17 samples the signal output from the first differential amplifier circuit 15 at the timing when the sample pulse signal SP2 is supplied. Reference numeral 18 is a control circuit. This control circuit controls the switching signal SS supplied to the changeover switch circuit 14c, the sample pulse signal SP1 supplied to the first sample hold circuit 16 and the sample pulse signal SP2 supplied to the second sample hold circuit 17. Output. The sample pulse signal SP1 output from the control circuit 18 is output in synchronization with the period during which the changeover switch circuit 14c is switched to the first constant current circuit 14a side by the changeover signal SS, while the sample pulse signal SP1 is output. SP2 is output in synchronization with the period in which the changeover switch circuit 14c is changed over to the second constant current circuit 14b side by the changeover signal SS.

Reference numeral 19 is a second differential amplifier circuit. The second differential amplifier circuit 19 detects and increases the difference between the output signals of the first differential amplifier circuit 15 sampled and held by the first sample and hold circuit 16 and the second sample and hold circuit 17, respectively. Width and output. Reference numeral 20 is a comparator. The output signal of the second differential amplifier circuit 19 is supplied to the inverting input terminal of the comparator 20. On the other hand, the non-reflective input terminal is supplied with the reference voltage Vref from the reference voltage source 21.

Next, the operation of the failure diagnosis circuit of the vehicle occupant protection system of this embodiment will be described. In order to diagnose the failure of the vehicle occupant protection device, the control circuit 18 switches the switching signal SS, the sample pulse signal SP1 and the sample pulse signal SP2 to the switching switch circuit 14c, the first sample hold circuit 16 and the second sample hold circuit 1, respectively. Output to 7. As a result, the changeover switch circuit 14c is switched to the first constant current circuit 14a side or the second constant current circuit 14b side at a predetermined cycle by the changeover signal SS, and a small constant current of 10 mA or 20 mA flows through the ignition circuit 13. A potential difference occurs between both terminals of the ignition circuit 13 according to the magnitude of the current flowing through the ignition circuit 13.

The first differential amplifier circuit 15 detects this potential difference and outputs it to the first sample hold circuit 16 and the second sample hold circuit 17. The first sample and hold circuit 16 samples and holds the output signal of the first differential amplifier circuit 15 when the changeover switch circuit 14c is switched to the side of the first constant current circuit 14a, while the second sample and hold circuit 17 is provided. Holds the output signal of the first differential amplifier circuit 15 when the changeover switch circuit 14c is switched to the second constant current circuit 14b side. In this case, the output signal of the first differential amplifier circuit 15 sample-held by the first sample-hold circuit 16 corresponds to the potential difference between both terminals of the ignition circuit when a current of 10 mA flows through the ignition circuit 13. On the other hand, the output signal of the first differential amplifier circuit 15 sampled and held by the second sample and hold circuit 17 corresponds to the potential difference between both terminals of the ignition circuit when a current of 20 mA flows through the ignition circuit 13. Therefore, these differences are twice as large as in the case where one kind of current is passed through the ignition circuit 13. Therefore, the amplification degree of the first differential amplifier circuit 15 can be set smaller accordingly, and the offset amount output from the first differential amplifier circuit 15 becomes smaller. Further, since the difference between the output signals of the first differential amplifier circuit 15 sample-held by the first sample-hold circuit 16 and the second sample-hold circuit 17 is obtained, the outputs of the first differential amplifier circuit 15 are obtained. The offset amount contained in the signal is canceled out, which improves the reliability of the failure diagnosis circuit of the vehicle occupant protection device.

Further, when the ignition circuit 13 is normal, a constant potential difference is generated between both terminals of the ignition circuit 13 with respect to a constant current of 10 mA or 20 mA flowing in the ignition circuit 13. Based on this, the normality of the ignition circuit 13 is identified. On the other hand, when the ignition circuit 13 is broken, the difference between the output signals of the first differential amplifier circuit 15 sampled and held by the first sample and hold circuit 16 and the second sample and hold circuit 17 becomes zero. The comparator 20 identifies the abnormality of the ignition circuit 13.

In this embodiment, a current of 10 mA or 20 mA is passed through the ignition circuit 13 to cause a difference in the potential difference between both terminals of the ignition circuit 13 due to the respective currents. It is possible to suppress the current flowing through the ignition circuit 13 that can be used for diagnosis, and prevent malfunction of the ignition circuit.

[0021]

[Effect of device]

 As described above, according to the present invention, it is possible to diagnose normality or failure of the ignition circuit with a small amount of current, so that the malfunction of the ignition circuit due to the current flowing through the ignition circuit during the failure diagnosis can be performed. A fault diagnosis circuit for a vehicle occupant protection device that can be prevented and is highly reliable and safe is obtained.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing the configuration of an embodiment of a failure diagnosing circuit of a vehicle occupant protection system according to the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a failure diagnosis circuit of a conventional vehicle occupant protection device.

[Explanation of symbols]

 1 Power Supply Battery (Battery) 8 Amplifier (Switch Circuit) 11 Acceleration Switch (Switch Circuit) 13 Ignition Circuit 14 Constant Current Circuit Unit (Constant Current Circuit) 15 First Differential Amplifier Circuit 16 First Sample Hold Circuit 17 Second Sample Hold Circuit 18 Control circuit 19 Second differential amplifier circuit 20 Comparator (ignition circuit abnormality discrimination circuit)

Claims (1)

[Scope of utility model registration request] 1. A switch circuit between both terminals of a battery,
In a vehicle occupant protection device for activating an occupant protection device for a vehicle, wherein the ignition circuit is connected in series and the switch circuit is turned on to operate the vehicle occupant protection device, a small constant current having a different magnitude in the ignition circuit. A constant current circuit for supplying a constant current circuit, a first differential amplifier circuit for detecting and outputting a potential difference between both terminals of the ignition circuit, and a timing at which the minute constant currents of different magnitudes are respectively supplied to the ignition circuit. A first sample-hold circuit and a second sample-hold circuit, which synchronously sample and hold the output signals output from the first differential amplifier circuit, respectively.
A second sample-hold circuit, and a second detecting a difference between the output of the first differential amplifier circuit sample-held by the first sample-hold circuit and the output of the first differential amplifier circuit sample-held by the second sample-hold circuit. An ignition circuit abnormality identification circuit that compares the output signals output from the differential amplification circuit and the second differential amplification circuit with a reference value to identify normality or abnormality of the ignition circuit, the constant current circuit, and the first sample hold. And a control circuit for controlling the second sample and hold circuit, a failure diagnostic circuit for a vehicle occupant protection device.