JPH05319201A - Driving circuit for crew protecting device for vehicle - Google Patents

Abstract

PURPOSE:To perform reliable detection of short-circuit of a G switch in constitution wherein a constant current circuit using a mechanical type G switch and an FET, a squib, and an ignition transistor are arranged in series to a power source. CONSTITUTION:The voltage of a connection point between a G switch 34 and constant current circuits C and D is inputted to a CPU 43 and when the voltage is a value approximately equal to a source voltage level, it is decided that the G switch 34 is in a short-circuit state. In which case, when squib lines (b) and (c) are short-circuited with the source line (a), a current route running from the source line (a) through the parasitic diodes 21 and 27 of the FET 20 and 26 of the constant current circuits C and D, respectively, is about to form. However, formation of the current route is blocked by means of reverse- current preventing diodes 32 and 33 and the voltage of a connection point is prevented from attaining a value approximately equal to a source voltage. Thus, when the squib lines (b) and (c) are brought into short-circuit with the source line (a), it is prevented from erroneously deciding that the G switch 34 is short-circuited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a vehicle occupant protection device such as an air bag.

[0002]

2. Description of the Related Art Conventionally, as a device of this type, as shown in FIG. 4, a constant current circuit A is provided for squibs 1 and 2 for deploying and operating an airbag (not shown) for a driver's seat and a passenger's seat.
Ignition switch (actually, an ignition transistor as described later) that operates on the basis of acceleration signals from G switches 3 and 4 that operate at low G and a G sensor (not shown) provided with B.
There is a device in which a constant current is supplied to the squibs 1 and 2 when the 5 is turned on to operate the airbags corresponding to the constant currents.

Although not shown, the voltages at both ends of the squibs 1 and 2 and the voltages at the connection points of the constant current circuits A and B and the G switches 3 and 4 are detected to disconnect the squibs 1 and 2.
It has a diagnostic function to detect a short circuit and a short circuit of the G switches 3 and 4.

Reference numeral 5 is a vehicle battery, 6 is an ignition switch, and 7 is a backup capacitor. Also, as shown in the constant current circuits A and B,
Transistors 8 and 9 are provided in the starting current supply path of the squibs 1 and 2. Further, since the squibs 1 and 2 are provided in a place (airbag installation place) different from the drive circuits such as the constant current circuits A and B, the squibs b and c are provided.
Are formed. In addition, a is a power supply line.

[0005]

However, it is conceivable to use FETs having a low on-resistance and a low drive current for the transistors 8 and 9 of the constant current circuits A and B described above.

Further, it is preferable in terms of cost to use the G switches 3 and 4 in common rather than to individually provide the squibs 1 and 2. Therefore, it is conceivable that a common G switch is provided in the power supply line of the vehicle-mounted battery, and a constant current circuit using an FET is connected in parallel via this G switch (for this configuration, refer to the configuration of FIG. 1 described later). In this case, since the G switch is provided on the power supply line a side, the short circuit of the G switch is detected depending on whether or not the voltage at the connection point between the constant current circuit and the G switch has reached the power supply voltage level.

However, in this case, the FE
Since there is a parasitic diode at T, when an attempt is made to detect the short circuit of the G switch, when the squib lines b and c and the power supply line a are short-circuited, a current path is formed from the power supply line a through the parasitic diode of the FET. As a result, the voltage at the connection point between the constant current circuit and the G switch becomes a value close to the power supply voltage, which causes a problem that the G switch is erroneously determined to be short-circuited.

Such a problem is not limited to the constant current circuit using the FET between the G switch and the squib, but the same problem occurs in other circuit configurations using the FET. Therefore, as described above, the present invention aims to prevent erroneous short circuit detection by the parasitic diode of the FET.

[0009]

Therefore, the present invention is provided between an ignition device for operating an occupant protection device and a power supply line from an on-vehicle power supply and the ignition device, and detects a first acceleration state of a vehicle. Switch means for switch operation, second switch means provided between the ignition device and ground for detecting a second acceleration state of the vehicle, and switch operation, and the first and second switch means. On the basis of the voltage at the connection point between the first switch means and the current supply means, and the current supply means including an FET that supplies a starting current to the ignition device via the first switch means. Short-circuit detection means for detecting short-circuit of the first switch means; and a line from the current supply means to the ignition device short-circuits with the power supply line from the power supply line. It is characterized in that a current blocking means by the current path through the ET parasitic diode to prevent the voltage of the connection point is changed.

[0010]

With the above structure, the short circuit of the first switch means is detected based on the voltage at the connection point between the first switch means and the current supply means.

Here, when the line from the current supply means to the ignition device is short-circuited with the power supply line, a current path from the power supply line through the parasitic diode of the FET is about to be formed. However, the current blocking means prevents the voltage at the connection point from changing due to the formation of such a current path. Therefore, when the line from the current supply means to the ignition device is short-circuited with the power supply line, the first
It is possible to prevent short circuit detection of the switch means.

[0012]

The present invention will be described below with reference to the embodiments shown in the drawings. In the embodiment shown in FIG. 1, two squibs (for driver's seat and passenger's seat) are used as an ignition device, and constant current circuits C, D (current supply means) are provided to appropriately distribute the current to each squib. ) Is provided. The configuration of the constant current circuits C and D is basically the same as that shown in FIG. 4, but the P-channel M is used instead of the transistors 8 and 9.
OS-FETs 20 and 26 are provided. In this constant current circuit C, since the gate voltage of the FET 20 is set to a low level by the resistors 23 and 24,
0 is always on, but squib 1 described later
At the time of startup of the
When 0 is controlled and the drain current of the FET 20 increases, the voltage across the resistor 25 rises, and the transistor 22 controls the gate voltage of the FET 20 so that no more current flows. As a result, a constant current will flow through the squib 1. Transistor 2 for constant current circuit D
8. The gate voltage of the FET 26 is controlled by the resistors 29 to 31 to operate so as to supply a constant current to the squib 2.
Here, the resistors 25 and 31 have a very small value in order to increase the starting current to the squibs 1 and 2. The FETs 20 and 26 have parasitic diodes 21 and 27, respectively, as shown in the figure.

Between the constant current circuits C and D and the power supply line a, a mechanical G which is turned on at a low G (for example, about 2 G).
A switch 34 (first switch means) is commonly provided, and a resistor 35 for diagnosis is provided in parallel with the G switch 34. The G switch 34 is an ignition transistor 40, 41 (second switch means) described later.
Is provided as a safety mechanism for preventing the squibs 1 and 2 from erroneously igniting when they malfunction due to noise or the like. Therefore, it is set to close in the low G state before the collision determination based on the signal from the G sensor 42 described later.

Further, resistors 36 to 39 for supplying a monitor current to the squibs 1 and 2 are provided, and a predetermined voltage is generated between the squibs 1 and 2 by the supply of the monitor current. Therefore, by checking this voltage, disconnection or short circuit of the squibs 1 and 2 can be detected.

Ignition transistors 40 and 41 (second switch means) for driving the squibs 1 and 2 to be ignited are provided between the squibs 1 and 2 and the CPU 4 which will be described later.
It is turned on by the ignition signal from 3.

Further, a semiconductor type G sensor 42 is provided for detecting the collision state of the vehicle, and an acceleration signal corresponding to the acceleration generated in the vehicle is generated. This G sensor 4
The acceleration signal from 2 is input to the CPU 43, and it is determined whether or not the vehicle is in a collision state by a calculation process described later.

The voltage across the G switch 34 and the voltage across each of the squibs 1 and 2 are also input to the CPU 43 via the A / D converter 44 and used by the CPU 43 for a diagnostic function described later. Reference numeral 45 is a resistor for applying a voltage at a connection point between the G switch 34 and the constant current circuits C and D.

Numerals 46 and 47 are resistors and diodes for charging and discharging the backup capacitor 7, and numeral 48 is a 5V power source for converting the battery voltage of the vehicle-mounted battery 5 to supply power to the CPU 43.

Further, the CPU 43 has a diagnostic function which will be described later, and when any abnormality is detected, the lamp drive circuit 50 is detected.
The alarm lamp 49 is driven to light. Further, backflow prevention diodes 32 and 33 are provided between the constant current circuits C and D and the squib line, respectively, and when the squib lines b and c are short-circuited with the power line a, the current from the power line a is shorted. Through the parasitic diodes 21 and 27 of the FETs 20 and 26 to the connection point side of the G switch 34 and the constant current circuits C and D, and prevent the voltage thereof from becoming a value near the power supply voltage level.

The operation of the above structure will be described. First, when the ignition switch 6 is turned on, the power from the vehicle-mounted battery 5 is supplied to the circuits of the respective parts to activate them.

The CPU 43 receives the 5V voltage from the 5V power source 48, enters the operating state, and executes the arithmetic processing shown in FIG. First, in step 101, the voltage across the G switch 34, that is, the battery voltage and the connection point voltage between the G switch 34 and the constant current circuits C and D are input, and based on this, the G switch 34 is short-circuited. Determine if there is. If the G switch 34 is not short-circuited, the connection point voltage becomes a predetermined voltage level divided by the resistors 35 and 45, but if the G switch 34 is short-circuited, the divided voltage becomes the power supply voltage level. Because,
It is possible to determine the short circuit of the G switch 34.

When it is determined that the G switch 34 is not short-circuited, the routine proceeds to step 103, where the squib 1,
Input the voltage at both ends of 2. Based on the voltage across each of them, it is determined in step 104 whether the squib is short-circuited or disconnected.

When it is determined that the squib is not short-circuited or disconnected, in step 105 the G sensor 4
The acceleration signal from No. 2 is input, and the acceleration signal is integrated in step 106. This integration processing is for removing the influence of noise or the like.

According to the value obtained by this integration processing, step 10
At 7, it is determined whether the vehicle is in a collision state. If it is determined that the vehicle is in a collision state, a signal for driving the ignition transistors 40 and 41 to turn on is generated. By the time the collision of the vehicle is determined, the G switch 34 is in the ON state as described above. Therefore, when the ignition transistors 40 and 41 are turned on, the power source from the vehicle-mounted battery 5 (the auxiliary power source from the backup capacitor 7 if the battery line is disconnected) is turned on by the G switch 34.
Is supplied to the constant current circuits C and D, and the constant currents for starting are supplied to the respective squibs 1 and 2. By supplying the constant current, the squibs 1 and 2 are ignited and the airbag (not shown) is deployed.

On the other hand, in step 102, the G switch 34
If the short circuit of the squib or the disconnection of the squib or the short circuit is determined in step 104,
At step 09, the alarm lamp 49 is turned on, and at step 110, the ignition transistors 40 and 41 are kept off. As a result, it is possible to inform the driver of the abnormality of the airbag device and prevent erroneous ignition of the squibs 1 and 2.

The short circuit of the G switch 34 is determined based on the voltage at the connection point between the G switch 34 and the constant current circuits C and D. In this case, the backflow prevention diode 3 is used.
Without S 33 and S 33, if either squib line b or c is short-circuited with power line a, FE will be fed from power line a.
A current path is formed via the parasitic diodes 21 and 27 of T20 and T26. Here, since the resistors 25 and 31 are set to extremely small values as described above, the connection point voltage becomes a value close to the power supply voltage level due to the formation of the current path, and therefore it is erroneously determined that the G switch 34 is short-circuited. Will be done. On the other hand, as described above, by providing the backflow preventing diodes 32 and 33, the formation of the current path as described above is eliminated, and erroneous short circuit detection of the G switch 34 is prevented.

Further, when one squib (for example, squib 1) is opened, two monitor currents concentrate on the squib 2 without the backflow prevention diode. Therefore, in an extreme case, there is a possibility of erroneous ignition. However, by providing the backflow prevention diodes 32 and 33, these erroneous ignitions can be prevented.

Further, the backflow prevention diodes 32 and 33 are provided.
By providing the squib lines b and c in a state where the squib lines b and c are short-circuited with the power supply line a, even if the ignition transistors 40 and 41 are erroneously turned on due to noise or the like, the starting current due to the erroneous operation is generated. It prevents the squib from flowing to the other driving circuit side via the parasitic diode of the FET and causing the squib to erroneously ignite. For example, the squib line b of the squib 1 is short-circuited with the power supply line a, and in this state, if the ignition transistors 40 and 41 are erroneously turned on by noise or the like, the squib 1 will ignite. However, due to the backflow prevention diode 32,
The starting current of the squib 1 is prevented from flowing to the constant current circuit D side, and erroneous ignition of the squib 2 which is not short-circuited is prevented.

In the above embodiment, the ignition transistor 40, when the disconnection or short circuit of the squibs 1 and 2 is detected, or when the G switch 34 is short circuited.
Although the one in which the OFF state of 41 is maintained is shown, in order to ensure that the squibs 1 and 2 are not ignited in that case, the inhibit transistor 51 shown in FIG.
0 may be provided for each. That is, when the above abnormality is detected, the inhibition transistor 51 is turned off to turn on the FE.
Set the gate voltage of T20 and 26 to high level, and FET2
0 and 26 are forcibly turned off.

Further, in the above embodiment, the constant current circuits C and D are provided and the FETs 20 and 26 are provided therein, but when one squib is targeted instead of two or more squibs. Does not require a constant current circuit,
In this case, the prohibition circuit for the diagnosis as shown in FIG. 3 can be constructed by FET and provided in the squib starting current path. Also in this case, if a backflow prevention diode is provided for the parasitic diode of the FET in the same manner as described above, it is possible to reliably detect the short circuit of the G switch.

Further, in the above embodiment, the current blocking means is provided with the backflow prevention diode, but a switch element or a unidirectional buffer may be used instead.

Further, in the above-mentioned embodiment, the occupant protection device for activating the air bag is shown, but it may be applied to the control of the preloader for the seat belt, and it may be applied to the control of the combination of the air bag and the preloader. You may make it apply.

[0033]

As described above, in the present invention, when the line reaching the ignition device is short-circuited with the power supply line, the first switch means is provided for the current path through the parasitic diode of the FET in the current supply means. Since the current blocking means for blocking the change in the voltage at the connection point between the current supply means and the current supply means is provided, in such a case, it is possible to prevent an erroneous short circuit detection of the first switch means. There is.

[Brief description of drawings]

FIG. 1 is an electrical connection diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a calculation process of a CPU in FIG.

FIG. 3 is a partial configuration diagram showing another embodiment.

FIG. 4 is an electrical connection diagram showing a conventional configuration.

[Explanation of symbols]

 1, 2 Squib 20, 26 FET 32, 33 Reverse current prevention diode 34 G switch 40, 41 Ignition transistor

Claims (1)

[Claims] 1. An ignition device for activating an occupant protection device, and a first switch means provided between a power supply line from an on-vehicle power supply and the ignition device for detecting a first acceleration state of a vehicle and performing a switch operation. Second switch means provided between the ignition device and the ground for detecting a second acceleration state of the vehicle to perform a switch operation, and the first switch when the first and second switch means operate. A short circuit of the first switch means based on a voltage at a connection point of the first switch means and the current supply means, the current supply means having an FET for supplying a starting current to the ignition device via the means. And a short-circuit detecting means for performing the above, and a line from the current supplying means to the ignition device is short-circuited with the power supply line via the parasitic diode of the FET from the power supply line. Driving circuit of the vehicle occupant protection apparatus and a current blocking means for preventing the voltage of the connection point is changed by the flow path.