JPH0930363A - Occupant protection device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diagnose the capacity of a backup capacitor by allowing a control means to send a signal for suspending operations to a DC/DC converter when its capacity diagnosis function is in operation, thereby suspending its boosting function, and feeding a discharge indication signal to a switching transistor thereafter. SOLUTION: When an ignition switch is turned on, a back-up capacitor 4 is thereby charged through a rash preventing resistor 2d. While electricity is being charged, periodic pulses are fed to a DC/DC converter 2 out of the output terminal P1 of a control circuit 13, and boosting operation is thereby started. The back-up capacitor 4 is charged by the boosted voltage of the DC/DC converter 2, and its charging voltage is fed to the control circuit 13 through a diagnosing resistor 10, a resister dividing circuit 12. When charging voltage is made higher, the output terminal P1 is made low in level so as to allow the boosting operation to be suspended, on the other hand, the control circuit 13 allows a discharge indication signal to be fed to a switching transistor 11 out of its output terminal P3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle occupant protection device such as an airbag for protecting an occupant of a vehicle from a collision accident.

[0002]

2. Description of the Related Art A vehicle occupant protection system of this type will be described with reference to a vehicle occupant protection system shown in FIG. 3, that is, Japanese Utility Model Publication No. 6-8935. In FIG. 3, reference numeral 20 is a vehicle-mounted battery, 21 is a DC / DC converter that boosts and outputs the output voltage of the battery 20,
The input terminal is connected to the battery 20 through the first backflow prevention diode 22 and the ignition switch 24 in series. 23 is a second backflow prevention diode,
The anode is connected to the battery 20 via the ignition switch 24, and the cathode is connected to the output terminal of the DC / DC converter 21 by a third backflow prevention diode 25.
Connected through. Reference numeral 26 denotes a backup capacitor which is connected to a connection point X between the second and third backflow prevention diodes 23 and 25 via an inrush current prevention resistor R1.

[0003] A discharge diode 27 has its cathode connected to the output terminal of the DC / DC converter 21 via the third backflow prevention diode 25. Thereby, the backup capacitor 26 is charged by the output voltage V0 of the DC / DC converter 21. or,
This output voltage V0 is supplied to the processing circuit (diagnostic circuit) 28 as a power supply monitor input. One end of the backup capacitor 26 is connected to the collector of the switching transistor Tr1 via a resistor R2, and this transistor T1
A control signal is supplied from the processing circuit 28 to the base of r1.

The terminal voltage of the backup capacitor 26 is divided by resistors R3 and R4, and the divided voltage at point A in FIG. 3 is applied to one input terminal of each of comparators 29 and 30. The output voltage V0 is equal to the resistances R5, R6, R7.
The divided voltage V1 is applied to the other input terminal of the comparator 29 as a reference voltage, and the other voltage V2 (V2 <V1) is applied to the other input terminal of the comparator 30 as a reference voltage. Has been. The output B of the comparator 30 and the output C of the comparator 29 are supplied to the processing circuit 28 and used to check the capacitance C1 of the backup capacitor 26.

When the ignition switch 24 is turned on, an output voltage V0 is obtained from the DC / DC converter 21, and this output voltage V0 charges the backup capacitor 26 with a predetermined time constant through the resistor R1. As a result, the terminal voltage of the backup capacitor 26 has a charging waveform as shown in FIG. 4, and the output waveform at the point A rises as the backup capacitor 26 is charged. At the same time, reference voltages V1 and V2 are applied to the other input terminals of the comparators 29 and 30, respectively. As a result, first, when the output waveform at the point A reaches V2, the output waveform at the point B of the comparator 30 becomes high level at the point a. Then, when the output waveform at point A reaches V1 at point b,
The output waveform C point of the comparator 29 becomes high level.

As a result, the control signal is sent from the processing circuit 28 to the base of the transistor Tr1 and the transistor Tr1 is turned on. Therefore, the electric charge of the backup capacitor 26 is discharged through the resistor R2 and the transistor Tr1, and the output waveform at the point A drops. And FIG.
When it becomes V1 at point c, the output waveform at point C is inverted to a low level, and when it becomes V2 at point d, the output waveform at point B is also inverted to a low level. The processing circuit 28 measures the discharge time t from the point c to the point d, calculates based on this time t, and calculates the capacity of the backup capacitor 26.

Further, V2 is selected to be a value larger than the voltage required for expanding the airbag. If the capacitance C1 obtained by this calculation falls within a predetermined allowable range, the processing circuit 28 regards the transistor Tr1 as off and ends the check. After this, the backup capacitor 26 is charged again to prepare for deployment of the airbag. If the capacity C1 does not fall within the predetermined allowable range due to the deterioration of the backup capacitor 26, an alarm is issued.

[0008]

However, in such a vehicle occupant protection device, since the backup capacitor is discharged to perform the capacity diagnosis when the DC / DC converter is in operation, Since the DC / DC converter is charged through the resistor R1 during discharging, the accuracy of measuring the size of the capacity of the backup capacitor becomes poor. Also, the discharge resistor R
2. There is a possibility that an error may occur because the variations of the reference resistors R3 and R4 are measured as they are. Further, since the backup capacitor is always charged, it is necessary to increase the capacity of the resistor R2 and the transistor Tr1.

The present invention has been made in view of such a problem, and an object thereof is to make it possible to accurately and stably perform capacity diagnosis of a backup capacitor.

[0010]

A vehicle occupant protection system according to the present invention is a DC for boosting an output voltage of an on-vehicle battery.
/ DC converter, a backup capacitor charged by the DC / DC converter, and a resistor are connected in series to form a time constant circuit together with the resistor and a forced discharge path for the charge charged in the backup capacitor. A transistor, a collision determination function that outputs an ignition signal when the size of the collision is determined based on the acceleration signal detected by the acceleration sensor and a serious collision is determined, and a discharge instruction signal is supplied to the switching transistor. , A control means having a capacity diagnostic function of causing a charge charge charged in the backup capacitor to flow in the time constant circuit and diagnosing a capacity abnormality of the backup capacitor based on the discharge curve, a detonator, and the DC /
In a vehicle occupant protection device including a switch means which is connected in series with the detonator to an output terminal of a DC converter and receives an ignition signal from the control means and is turned on, the control means operates its capacity diagnostic function. Sometimes the DC / D
A signal for stopping the operation of the C converter is supplied to stop the boosting function, and then a discharge instruction signal is supplied to the switching transistor to diagnose the capacity of the backup capacitor.

[0011]

According to the vehicle occupant protection system of the present invention, when the capacity of the backup capacitor is diagnosed, the operation of the DC / DC converter is stopped and then discharged through the forced discharge path, and the discharge curve obtained at that time is obtained. Based on the above, the capacity diagnosis function of the control means determines whether the backup capacitor is normal or abnormal, so that the measurement accuracy can be improved, and the resistance and the transistor having a small capacity can be used.

[0012]

Embodiment An embodiment according to the present invention will be described with reference to FIG. Reference numeral 1 is an on-vehicle battery, 2 is a DC / DC converter, and a coil 2a, a first backflow prevention diode 2b, an inrush current prevention resistor 2d, and a connection point between the coil 2a and the first backflow prevention diode 2b are connected in series. Has a transistor 2c whose on / off control is performed by supplying a periodic pulse to the base from an output terminal P1 of a control circuit (microcomputer) 13 described later. The inrush current prevention resistor 2d of the DC / DC converter 2 is connected to the vehicle-mounted battery 1 through a second backflow prevention diode 3,
The output voltage of the on-vehicle battery 1 is boosted by turning on and off the current flowing through the coil 2a based on the periodic pulse from the control circuit 13. The boosted voltage is supplied to the backup capacitor 4 connected to the output terminal of the DC / DC converter 2,
Since the amount of current input to the / DC converter 2 is limited by the inrush current prevention resistor 2d, it is possible to prevent a charging current of a magnitude that deteriorates the backup capacitor 4 from flowing.

Reference numeral 5 is a third backflow preventing diode, the anode of which is connected to the on-vehicle battery 1 and the cathode of which is connected to the cathode of a discharging diode 6 described later. A switching transistor 7 has an emitter connected to a connection point between the cathode of the third backflow preventing diode 5 and the cathode of the discharging diode 6, and its collector is connected to one end of a series circuit including a detonator 8 and a mechanical acceleration switch 9. While being connected, the other end of the series circuit is grounded. The base of the switching transistor 7 is connected to the output terminal P2 of the control circuit 13 described later.

A diagnostic resistor 10 has a high resistance value and is connected between the emitter and collector of the switching transistor 7. A switching transistor 11 forms a forced discharge path for the backup capacitor 4 together with the resistor R. When a high level discharge instruction signal is supplied from an output terminal P3 of the control circuit 13 described later, the switching transistor 11 is turned on to form a discharge path. .

Reference numeral 12 denotes a resistance voltage dividing circuit, which divides the charging voltage of the backup capacitor 4 appearing at the point A, that is, the cathode side of the discharging diode 6, by the resistance voltage dividing circuit 12 and the diagnostic resistor 10.

Reference numeral 13 is a control circuit having a collision judgment function and a diagnosis function, which inputs an acceleration signal output from an acceleration sensor (not shown) from the input terminal X to judge the magnitude of the collision and sets the output terminal P2 to low. The level is set to turn on the switching transistor 7. In addition, this control circuit 1
3 is supplied with a periodic pulse from the output terminal P1 to the transistor 2c when the power is turned on (IGN-SW in FIG. 2), and the transistor 2c is periodically turned on and off to drive the DC / DC converter. 2, the charging voltage is input to the control circuit 13 via the resistance voltage dividing circuit 12, and the charging waveform is V2 in FIG.
(At a voltage value of about 70% of full charge, the resistance voltage divider circuit 12
Input terminal), the output terminal P1 is set to a low level at time T3 to stop the boosting operation, and the control circuit 1
3 outputs a high-level discharge instruction signal to the switching transistor 11 from the output terminal P3 to turn it on and start the time counting operation. Further, when the charging voltage of the backup capacitor 4 drops to V1 (<V2), the control circuit 13 periodically switches the output terminal P1 to the high level and the low level at the time T4, and stops the timing operation. , The time required to reach the voltage V1 from the voltage V2 is measured, and if the measured time falls within a predetermined allowable range, it is determined to be normal, and otherwise, it is determined to be abnormal and an alarm signal is output.

Next, the operation of the above structure will be described with reference to FIG. When the ignition switch is turned on at time T1, power is supplied from the vehicle-mounted battery 1 to the DC / DC converter 2, and the backup capacitor 4 is charged via the inrush current prevention resistor 2d. Control circuit 13 during the charging
A periodic pulse is supplied to the DC / DC converter 2 from the output terminal P1 of the above, and the boosting operation is started (time T2 in FIG. 4).

As a result, the backup capacitor 4 is D
The C / DC converter 2 is charged by the boosted voltage, and the charging voltage (voltage at the point A) is
It is supplied to the control circuit 13 via the resistance voltage dividing circuit 12.
When the charging voltage further rises to V2, the output terminal P1 is set to the low level to stop the boosting operation, while the control circuit 13 outputs the discharging instruction signal (Tr.
2 between time T3 and T4) switching transistor 1
Feed to 1. As a result, the control circuit 13 starts the timekeeping operation, stops the timekeeping operation when it detects that the discharge voltage has dropped to V1, and determines that the time is normal when the time is within the predetermined range. (Indicated by a solid line from time T3 to time T4 in the charging waveform of FIG. 2), the periodic pulse is again output from the output terminal P1 (T of FIG. 2).
It is indicated by a periodic pulse after time T4 of r2).

When it does not fall within the predetermined allowable range (indicated by the broken line from time T3 to time T4 in the charging waveform of FIG. 2), the periodic pulse is output again (of the charging waveform of FIG. 2). Of these, an alarm signal (indicated by a broken line after time T4) (a high level state after time T4 in the alarm of FIG. 2) is output to an alarm unit (not shown) together with the alarm signal.

Incidentally, the control circuit 13 inputs the acceleration signal detected by the acceleration sensor (not shown) from the terminal A, and when it is judged from the change state of the acceleration signal that the acceleration signal is caused by a serious collision. Turns the output terminal P2 to a low level and causes the charge charged in the backup capacitor 4 to flow into the detonator 8 through the switching transistor 7 and the acceleration switch 9 to operate the airbag or the like.

[0021]

As described above, according to the present invention, since the operation of the DC / DC converter is stopped at the time of diagnosis, the accuracy of the capacitance measurement of the backup capacitor can be improved and the discharge path is formed. Even if the resistance and the transistor have a small capacitance, the cost can be reduced. Further, in the related art, a capacitor having a large capacitance has been used in relation to the measurement accuracy, but since the accuracy is improved, it is not necessary to use a large capacitor, so that the effect of reducing the cost is exhibited.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of waveforms in FIG.

FIG. 3 is an explanatory diagram of a conventional circuit.

FIG. 4 is an explanatory diagram of waveforms in FIG.

[Explanation of symbols]

 2 DC / DC converter 3, 5 Backflow prevention diode 4 Backup capacitor 6 Discharge diode 7, 11 Switching transistor 8 Detonator 9 Acceleration switch 12 Resistance voltage divider circuit 13 Control circuit

Claims (1)

[Claims] 1. A DC for boosting the output voltage of an on-vehicle battery
/ DC converter, a backup capacitor charged by the DC / DC converter, and a resistor are connected in series to form a time constant circuit together with the resistor and a forced discharge path for the charge charged in the backup capacitor. A transistor, a collision determination function that outputs an ignition signal when the size of the collision is determined based on the acceleration signal detected by the acceleration sensor and a serious collision is determined, and a discharge instruction signal is supplied to the switching transistor. , A control means having a capacity diagnostic function of causing a charge charge charged in the backup capacitor to flow in the time constant circuit and diagnosing a capacity abnormality of the backup capacitor based on the discharge curve, a detonator, and the DC /
In a vehicle occupant protection device including a switch means which is connected in series with the detonator to an output terminal of a DC converter and receives an ignition signal from the control means and is turned on, the control means operates its capacity diagnostic function. Sometimes the DC / D
A vehicle occupant characterized by supplying a signal for stopping its operation to the C converter to stop the boosting function, and then supplying a discharge instruction signal to the switching transistor to diagnose the capacity of the backup capacitor. Protective device.