JPS61241231A - Backup device for on-board battery for vehicle - Google Patents

Abstract

PURPOSE:To prevent the lowering of capacitance of a main capacitor connected in parallel to an on-board battery for source power back-up, from being erroneously detected, by comparing the terminal voltage of the main capacitor with that of an auxiliary capacitor having an integrating time constant different from that of the main capacitor. CONSTITUTION:A charge and discharge circuit 22 for a large capacity main capacitor Cm which is a back-up power source for a detonator 2 in a gas inflation type cushion, is connected in parallel with a comparating reference charge and discharge circuit 23 having an integrating time constant slightly larger than that of the first mentioned circuit 22. Further the charge and discharge characteristic curves of both charge and discharge circuits 22, 23 are compared with each other by a comparator circuit 24 for detecting the lowering of capacitance of the main capacitor Cm. A charge resistor Rm in the above-mentioned charge and discharge circuit 22 is connected in parallel with a discharge diode Dm, and a resistor Rs for an auxiliary capacitor Cs in the charge and discharge circuit 23 is connected in parallel with a discharge circuit composed a resistor r3 and a diode Ds connected in series to the resistor r3. Further, the output of the comparator circuit 24 energizes an alarm circuit 26.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an on-vehicle power backup device that automatically detects a decrease in the capacity of a main capacitor for power backup at the time of engine startup.

[Conventional technology]

2. Description of the Related Art In order to protect occupants, such as passengers, from the impact of a collision, a passenger car equipped with an occupant protection device has been proposed in which a gas-inflatable cushion is provided near the driver's seat or other seats. in general,
This food's occupant protection device.

It has a gas generator that contains a current-activated explosive, and the shock at the time of a collision detonates the gas generator to generate gas, which inflates a cushion between the passenger and the single compartment to provide cushioning. has been done.

The detonator is equipped with a detonator called a squeezo, which ignites when a current exceeds a certain level.

Even if the on-board power supply does not operate effectively in the event of a collision.

To enable electricity to flow, a large capacity capacitor that is charged when the engine starts is usually used as a power backup.

The vehicle-mounted power backup device 1 shown in FIG.

In order to ensure reliable operation of the detonator 2, a power backup capacitor C0 with a capacity drop alarm circuit 3 is provided. The detonator 2 has a resistor switch So, which is closed by a collision shock, at both ends of a detonator 4b in a gas generator 4 equipped with a gas-expandable cushion 4a. Shock sensors 5, 6, and 7 are connected in parallel to the in-vehicle 1! when the engine start switch S is closed. Source 8
The current supplied flows through the resistor in the detonator 2 and the detonator 4b via the engine start switch S.

The current flows into the ground via the diode D1, but since this current is extremely small, it does not reach the point where the detonator 4b ignites.

1iIE11@Backup capacitor co is between the engine start switch 8K and diode DI.

It is provided in parallel with the detonator 2, and charging and discharging are performed through a parallel connection circuit of a resistor island and a diode D.

The capacitance reduction alarm circuit 3 is configured to detect a reduction in the capacitance of the capacitor C from the magnitude of the differential time constant during charging of the capacitor C0 for power backup, and is connected to the negative terminal of the capacitor C0.

A circuit for monitoring terminal voltage changes during charging.

Furthermore, a circuit for determining a monitoring period is connected to the positive terminal.

Now, if you close the engine start switch S1.

Capacitor C. is charged by the current flowing through resistor R3, but the voltage at the negative terminal decreases as charging progresses. At this time, the voltage change on the negative terminal is 1. The inverting input terminal and non-inverting input terminal are gate circuits 9 and 1, respectively.
This is checked by a comparator circuit 11 connected to the negative terminal via 0. Gate circuits 9 and 10 are closed by gate pulses of different duration, which are the outputs of comparator circuits 12 and 13, respectively. Further, a charging/discharging circuit 14 serving as a reference for comparison is connected between the gate circuit 10 and the non-inverting input terminal of the comparator circuit 11, and when the capacitor C1 in this charging/discharging circuit 14 is discharged, The constant is.

This is set to be slightly smaller than the differential time constant when charging the power supply backup capacitor C0.

First, as the engine start switch 8m is closed, the power supply voltage from the on-vehicle power supply 8 rises as shown in the fourth position.

The output of the comparison circuit 15 for engine start detection is kept at a high level for a certain period of time corresponding to the time constant of the integration circuit [6] in the previous stage. During the period when the output of the comparator circuit 15 is at a high level, the transistors Q□e Qla connected to the inverting input terminals of the comparator circuits 12 and 13 are conductive, and then the output of the comparator circuit 15 is at a low level, and the transistor Q Capacitor CI in parallel with □, Q□! *Until C1m is charged to a constant voltage, the comparator circuits 12 and 13 are operated as shown in FIG. 4(B).

The pulse shown in (C) is output. These gate pulses have a shorter pulse width in the comparator circuit 13 than in the comparator circuit 12, so the charging/discharging circuit between the gate circuit 10 and the comparator circuit 11 is charged for a long time after the engine is started. , transition to discharge. The time constant of capacitor C1 during this discharge is smaller than the differential time constant of capacitor C0 for X source backup, so if the capacitance of capacitor co satisfies the rated capacity, the output of comparator circuit 11 will be As shown in FIG. 4(F), only when the capacitance of the capacitor C0 drops below the rated capacity is the comparator circuit 1
The output of 1 is high level tonal.

The output of the comparator circuit 11 is the output of a comparator circuit 12 for gate pulse generation and a comparator circuit 17 that outputs a high-level signal when the negative terminal voltage of the capacitor C0 for power backup falls below a certain voltage. Together with each output, it is supplied to an AND gate circuit 18, and the output of the AND gate circuit 18 is outputted via a buffer amplifier circuit 19 as a capacity drop alarm output.

[Problem that the invention seeks to solve]

In the above-mentioned conventional vehicle-mounted power backup device 1, when the power supply voltage fluctuates in a pulse-like manner due to a transient cause as shown in the fourth diagram, the time differential with respect to this fluctuation is shown by the dashed line in the figure. Like, power backup capacitor co
Therefore, the input voltage of the non-inverting input terminal of the comparator circuit 11 temporarily exceeds the input voltage of the inverting input terminal, and the voltage of the capacitor C0 decreases. Even though this is not the case, the output of the specific diaphragm circuit 11 is at a high level, resulting in a false alarm and causing unnecessary confusion.

c.Means for solving problems] This invention solves the above problems.

Current is supplied from the on-vehicle power supply via the closed engine start switch, and the main capacitor for power supply backup, which charges and discharges with a predetermined time constant at the rated capacity, is connected in parallel to this main capacitor, and the predetermined Charging time constant is larger than the charging time constant and discharge time constant is smaller than the charging time constant.
a comparison circuit that compares a terminal voltage of a sub-capacitor that discharges and the terminal voltage of the sub-capacitor and the main capacitor during a certain period after starting the engine, and outputs an output when the terminal voltage of the sub-capacitor exceeds the terminal voltage of the main capacitor; The gist of this is that it consists of an alarm circuit that receives the output of this comparison circuit and issues an alarm to indicate if there is a decrease in the capacity of the main capacitor.

[Effect]

This invention uses a comparison circuit to detect the difference in terminal voltage between a main capacitor for power backup connected in parallel to the vehicle power supply and a sub capacitor that has a different integration time constant from the main capacitor. When the speed decreases, a warning is issued based on the output of the comparison (b) road.

〔Example〕

Embodiment Iζ of the present invention will be described below with reference to FIGS. 1 and 2. 1 and 2 are a circuit configuration diagram and a signal waveform diagram of the circuit valleys, respectively, showing an embodiment of the vehicle-mounted power backup device of the present invention.

In FIG. 1, the same components as in FIG. 3 are given the same reference numerals.

7%1 In the figure, the on-vehicle power supply backup device 21 is connected in parallel to the charging/discharging circuit 22 of the large-capacity main capacitor Cm, which is the backup power source, and has an integral time constant slightly larger than that of the light/discharging circuit 22. Charging/discharging circuit 23 for comparison reference
The structure is such that a decrease in the capacitance of the main capacitor Cm is detected by connecting the two light/discharge circuits and comparing the charge/achievement curves of the two light/discharge circuits using a comparison circuit.

In this embodiment, a discharging diode Dm is connected in parallel to the charging resistor of the charging/discharging circuit 22.

Further, a series connection circuit of a resistor ra and a diode Ds is connected in parallel to the charging resistor R3 of the sub-capacitor C5 in the charging/discharging circuit for discharging. Naturally, when the main capacitor Cm has a rated capacity, the charging time constant of the main capacitor Cm is smaller than that of the sub capacitor Ca, and the discharging time constant of the main capacitor Cm is smaller than that of the sub capacitor C8. It is also set to be large.

The 1 inverting input terminal and the non-inverting input terminal of the comparator circuit 24 are
The terminal voltages of the main capacitor C1rl and the sub capacitor C3 are respectively applied, and the output of the comparator circuit 24 is as follows.

W
The signal is supplied to the information circuit 26. The W information circuit 26 is.

It consists of a transistor Q that is turned on by the output of the NOR gate circuit 25, and a lamp 26a that is energized when the transistor Q1 is turned on. In addition, the NOR gate circuit 25
An inverter circuit 27 is connected to the other input terminal of the inverter circuit 27, which is connected to a transistor Q that becomes conductive when the terminal voltage of the capacitor Ct, which is charged when the on-vehicle power supply 8 starts up, reaches a certain level, thereby cutting off the supply of the power supply voltage VCC. is connected.

Here, when the capacity of the main capacitor Cm is full of the rated capacity, the charging speed after the engine start switch Si is closed is as shown in Figure s2 fc), tD), and the charging/discharging rate is
Although the t circuit 22 is faster than the photo-discharge circuit.

When the capacitance of the main capacitor Cm decreases by a predetermined value from the normal value, the relationship between the charging speeds is reversed.

The NOR gate circuit 25 is opened by the high level output of the comparator circuit 24 shown in FIG.
Along with the operation, the lamp 26a lights up to notify that an abnormality has occurred.

By the way, when gt of the main capacitor Cm satisfies the rated capacity, the power supply voltage from the on-vehicle power supply 8 is.

Even if there is a pulse-like fluctuation as shown in the second illustration due to a temporary cause, the charging curves of the charging/discharging circuits 22 and 23 will show a similar phase of change without crossing. This means that the light/discharge circuit 22 has a smaller light RL time constant than the charge/discharge circuit.

This is because there is an inverse relationship with respect to the discharge time constant, and unlike the conventional vehicle-mounted power supply backup device 1, an alarm notifying of capacity reduction is not issued erroneously.

In this way, the on-vehicle power supply backup device 21 has a difference in terminal voltage between the main capacitor Cm for power backup connected in parallel to the on-vehicle power supply 8 and the sub-capacitor C3, which has a charging/discharging time constant different from the main capacitor (4). is detected by the comparator circuit 24, and when the charging speed decreases as the capacity of the main capacitor Cm decreases, the alarm circuit 26 issues an alarm based on the output of the comparator circuit 24, so that the engine start switch S1 is closed. When the main capacitor Cm starts charging as the main capacitor Cm starts charging, it is possible to check the difference in the integration time constant between the main capacitor Cm and the sub-capacitor C3 by comparing the charging curves. Even if Cm, C, and the charging curves of the two capacitors change in a similar manner, it is possible to reliably prevent the inconvenience of false alarms being issued based on the intersection of the charging curves of the two capacitors.

〔Effect of the invention〕

As explained above, according to the present invention, the main capacitor for power backup connected in parallel to the on-vehicle power supply,
A comparator circuit detects the difference in terminal voltage of the sub capacitor, which has a different charging/discharging time constant from the main capacitor, and issues an alarm based on the output of the comparator circuit when the charging speed decreases as the capacitance of the main capacitor decreases. Because of this configuration, when the main capacitor starts charging with the closing of the engine start switch, it is possible to check the difference in the integral time constant between the main capacitor and the sub capacitor by comparing the charging curves, and also to check the difference in the integral time constant between the main capacitor and the sub capacitor by comparing the charging curves. Even if the voltage of the onboard power supply fluctuates during operation, the charging curves of the 0-car capacitors change similarly, so it is possible to reliably prevent the inconvenience of false alarms being issued based on the intersection of the 0-car charging curves. It has excellent effects.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit configuration diagrams and signal waveform diagrams of various parts of the circuit, respectively, showing an embodiment of the vehicle-mounted power backup device of the present invention, and Figures 3.4 are examples of conventional vehicle-mounted power source backup devices. FIG. 2 is a circuit configuration diagram and a signal waveform diagram of each part of the circuit. 8... Vehicle-mounted power supply, 21... Vehicle-mounted power supply backup device. 22, 23...Charging/discharging circuit, 24...Comparison circuit, 26...Alarm circuit, Cm...Main capacitor, C3
... Sub-capacitor. SL...Engine start switch.

Claims (1)

[Claims] Current is supplied from the on-vehicle power supply via the closed engine start switch, and a main capacitor for power supply backup that charges and discharges with a predetermined time constant at the rated capacity is connected in parallel to this main capacitor, and the predetermined A sub-capacitor that charges and discharges with a charging time constant that is larger than the time constant and a discharging time constant that is smaller than the time constant, and the terminal voltages of this sub-capacitor and the main capacitor are compared during a certain period after the engine starts, and the terminal voltage of the sub-capacitor is compared. An on-vehicle power supply backup device consisting of a comparison circuit that outputs an output when the terminal voltage exceeds the terminal voltage of the main capacitor, and an alarm circuit that receives the output of this comparison circuit and issues an alarm that the capacity of the main capacitor has decreased.