JP2741462B2 - Ignition control device for vehicle safety device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition control device for a vehicle safety device, and more particularly to an ignition control device for a vehicle safety device capable of controlling the ON time of a safety device ignition circuit.

[0002]

2. Description of the Related Art There is known a system that detects acceleration of a vehicle or the like based on an output signal of an acceleration sensor, determines a collision from the detected signal, and operates a safety device. In this system, the ignition means (squib) is ignited based on the collision judgment to rapidly inflate the airbag or to activate a seat belt pretensioning device.

[0003] For example, the device described in Japanese Patent Application Laid-Open No. 3-208749 is configured as follows. 4, when the evaluation circuit 10 detects that a collision has occurred, the evaluation circuit 10 outputs a trigger signal to the ignition circuit 20. The trigger signal is input to a one-shot circuit 21 which is a component of the ignition circuit 20, and the output of the one-shot circuit turns on the field-effect transistor 22 to activate the squib 30 connected to the field-effect transistor 22. I try to ignite. When the squib 30 is ignited, the airbag 40 is inflated.

[0004]

The above-mentioned conventional apparatus has the following problems. In order to ignite the squib, it is necessary to turn on the field effect transistor for a predetermined time and supply sufficient electric energy to the squib. That is, the turn-on time of the field effect transistor is set so that sufficient energy necessary for ignition of the squib is obtained.

Since the turn-on time is set with a sufficient margin, the turn-on time tends to be longer than necessary. If the turn-on time, that is, the current supply time to the squib is long, circuit components that are durable against temperature rise are required, and the capacity of a capacitor provided as an auxiliary power supply also needs to be increased. As a result, there are problems that the size of the apparatus is increased and that unnecessarily expensive parts must be used.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide an ignition control device for a vehicle safety device that can set a required minimum squib ignition time.

[0007]

Means for Solving the Problems The above problems are solved,
The present invention for achieving the object achieves a semiconductor scan when a collision is recognized based on a detection signal input from an acceleration sensor .
A switch is turned on to output an energization instruction to the squib, and after the energization instruction, the energization instruction is stopped when the temperature of the semiconductor switch representing the energy supplied to the squib exceeds a predetermined value. There is a characteristic in that.

[0008]

According to the present invention having the above characteristics, the supply of current is continued based on the energy input to the squib until the total amount of energy reaches a predetermined value. Since the squib is ignited by the total amount of energy supplied to the squib, the control of the optimum current supply time can be performed by detecting the input energy.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an ignition control device according to one embodiment of the present invention. In FIG. 1, a drive circuit 1 is provided with an activation element for activating a safety device such as an airbag (not shown), that is, a squib 2. In the event of a collision,
A mechanical switch and a semiconductor switch, which will be described later, operate to supply current to the squib 2, and as a result, the squib 2 ignites and the safety device is activated.

A squib 2 has a P-channel FE at one end.
The source of T3 is connected, and the other end is an N-channel FET4.
Drain is connected. These two FETs 3, 4
Is a semiconductor switch for supplying a current to the squib 2. A mechanical switch 5 is connected between the drain of the FET 3 and the power supply, and a current measuring resistor 6 is connected between the source of the FET 4 and the ground. Further, the drive circuit 1 is provided with a capacitor 7 for storing power as an auxiliary power supply. One of the outputs of the CPU 9 is inverted by the inverter 8 and supplied to the base of the FET 3,
The other is supplied to the gate of the FET4.

As the mechanical switch 5, a switch configured as follows can be used. For example, it is possible to use one having a ball or roller-shaped moving body and an open contact, and configured to close the open contact when the moving body is deflected by acceleration. An example of a mechanical switch configured to close a contact by a ball is disclosed in Japanese Patent Application No. 3-339466.

Further, FET3 as a semiconductor switch,
4 operates based on the output signal of the G sensor 10 which detects acceleration and converts it into an electric signal. As the G sensor 10, for example, a piezoresistive element can be used. The output signal of the G sensor 10 is supplied to the CPU 9 and the CPU 9
Is compared with a preset comparison value. When a collision is determined based on the comparison result, the CPU 9 outputs a collision determination signal. This collision determination signal is output from the FET3,
4 is supplied to the gate of FET 4, and as a result, the FETs 3 and 4 are turned on.

When the contacts of the mechanical switch 5 are closed and the FETs 3 and 4 are turned on, current is supplied to the squib 2 from a power supply or an auxiliary power supply, that is, a capacitor 7.

In this embodiment, in the above configuration, the current supply time, that is, the ON time of the collision determination signal output from the CPU 9 is controlled. For this control, the CPU 9 receives the potentials Vs1 and Vs2 at both ends of the squib 2 and the potential Vi at the junction between the FET 4 and the resistor 6. Hereinafter, the on-time control of the collision determination signal will be described in detail.

FIG. 2 is a block diagram showing the main functions of the ignition control device according to the present embodiment. The same reference numerals as in FIG. 1 denote the same or equivalent parts. In the figure, an output signal of a G sensor 10 is input to a comparison unit 11. In the comparison unit 11,
The threshold value stored in the threshold value storage unit 12 for collision determination is compared with the output signal of the G sensor 10. The result of the comparison is input to the collision determination unit 13. The collision determination unit 13 determines whether or not a collision has occurred based on the signal from the comparison unit 11, and outputs a collision determination signal to the semiconductor switches, that is, the FETs 3 and 4 when the collision determination is obtained.

On the other hand, the energy calculator 14 calculates the total energy supplied to the squib 2. The total energy is determined as follows. First, the voltage Vs applied to the squib 2 based on the potentials Vs1, Vs2, and Vi read from the drive circuit 1, that is, (Vs1-Vs
2) and calculate the current Is, that is, (Vi ÷ R).
The symbol R indicates the resistance value of the resistor 6. And the voltage V
The integrated amount of energy W obtained by multiplying s and current Is with time is calculated.

The energy determination unit 15 compares a threshold value stored in the energy threshold value storage unit 16 with the output of the energy calculation unit 14. When the total energy amount calculated by the energy calculation unit 14 exceeds the threshold value, the energy determination unit 15
To output a collision determination signal output stop command. As a result, the collision determination signal output to the squib 2 is stopped.

3A and 3B are timing charts of the above operation. FIG. 3A shows the output waveform of the G sensor 10, FIG. 3B shows the on / off state of the collision determination signal, and FIG. 3 shows changes in total energy.

As described above, in this embodiment, current is supplied to the squib 2 when the output of the G sensor 10 exceeds a predetermined value, and the total energy amount given by this current supply is When the predetermined amount is exceeded, the semiconductor switch is turned off and the current supply is stopped.

In the present embodiment, the energy is calculated based on the magnitude and duration of the current and the voltage. However, the present invention is not limited to this, and represents the energy supplied to the squib 2. You may make it control by another parameter. Due to the application of the energy, the temperature of not only the squib 2 but also other components increases. Therefore, a temperature measuring element such as a thermistor may be bonded to the FET 4, for example, and the output of the collision determination signal may be stopped when the temperature detected by the thermistor exceeds a predetermined value. Represent energy
Function when the parameter to be set is the temperature of FET4,
Explaining with reference to FIG. 2, the energy calculating unit 14
Temperature measurement element as a parameter representing energy
Detects the temperature. On the other hand, energy threshold memory
The temperature threshold as a representative value of the energy amount is recorded in the section 16.
Remembered. In the energy determination unit 15,
The temperature of FET4 which is a representative value of the energy amount is a temperature threshold.
The temperature of the FET4 is detected by detecting whether the value
Stops semiconductor switch on operation when threshold is exceeded
The output signal is output.

The temperature rise of the FET 4 may be measured by means other than the thermistor. For example, power consumption may be calculated based on the voltage and current applied to the FET 4, and the temperature rise may be calculated from the product of the power consumption W and the thermal resistance (° C / W) of the FET 4.

The semiconductor switches connected to both ends of the squib 2 are not limited to FETs, but may be other transistors.

[0023]

As is clear from the above description, according to the present invention, the temperature of the semiconductor switch exceeds the predetermined value.
Can be shut off when Semiconductor switch
The temperature is rising due to the total amount of energy provided
In this case, the temperature of the semiconductor switch is equal to the total amount of the energy.
It reflects exactly the minimum necessary for squib ignition.
When power is supplied to the squib,
Can be shut off. Therefore, as a component for constituting the drive circuit of the squib, a component whose specification with respect to temperature is minimized can be used.

As a result, there is no need to provide a heat radiating plate for preventing a rise in temperature or use a large component, and the entire control device can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a hardware configuration of an ignition control device.

FIG. 2 is a block diagram showing functions of a main part of the ignition control device.

FIG. 3 is a timing chart showing an operation of the ignition control device.

FIG. 4 is a block diagram showing a configuration of a conventional safety device.

[Explanation of symbols]

2: Squib, 3, 4: FET, 5: mechanical switch, 7: auxiliary power supply

Claims (2)

(57) [Claims] An ignition of a vehicle safety device configured to supply an ignition current to a squib by turning on a semiconductor switch with a collision determination signal obtained based on a detection signal input from an acceleration sensor. In the control device, energy detecting means for detecting a representative value of the amount of energy supplied to the squib based on the temperature of the semiconductor switch; determining means for detecting whether or not the representative value of the energy amount exceeds a predetermined value; The semiconductor switch is interrupted by a signal output from the determining means when the representative value of the energy amount exceeds a predetermined value.
Ignition control device for a vehicle safety device, characterized in that configured in so that to cross. 2. The semiconductor switch is connected in series with the semiconductor switch,
Configured to close contacts in response to vehicle acceleration
The ignition control device for a vehicle safety device according to claim 1 , further comprising a mechanical switch .