Air bag controller

Expansion enable/disable information expressing enable or disable of the expansion of an air bag at an assistant driver's seat is input from a cut-off switch, and the expansion enable/disable information is once retained in a register in a CPU. If an acceleration detected by a G-sensor and applied to a motor vehicle exceeds 2G for example, then any change in the expansion enable/disable information retained in the register of the CPU is inhibited by the CPU itself; and thus a change of the expansion enable/disable information retained in the register is inhibited even though the expansion enable/disable information input to the cut-off switch has been changed by the force majeure during the collision of the motor vehicle. Thus, any erroneous expansion of the air bag by the acceleration can be prevented during collision as long as the expansion inhibit state is continuing.

The contents of Application No. TOKUGANHEI 8-295212, with a filing date of 
Nov. 7, 1996 in Japan, are hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an air bag controller, and more 
particularly to an air bag controller which enables or prohibits the 
expansion of an air bag module only by a simple operation. 
2. Description of the Prior Art 
Motor vehicles equipped with air bag modules are being manufactured in 
recent years to secure the safety for passengers at the time of a 
collision of a motor vehicle. 
In the motor vehicle equipped with such an air bag module at the assistant 
driver's seat, an exclusive key switch is provided for canceling the 
operation of the air bag module at the assistant driver's seat, and the 
expansion of the air bag module at the assistant driver's seat is 
prohibited by directly disconnecting, with the key switch, a harness which 
supplies an ignition current required for the expansion of the air bag 
module at the assistant driver's seat. 
However, in the conventional air bag controller, the harness, connected to 
a squib in the air bag module for the assistant driver's seat, is directly 
disconnected using the key switch. Therefore even though the key switch 
has been set to a state for prohibiting the expansion of the air bag 
module at the assistant driver's seat, for example, chattering or the like 
occurs resulting in the key switch making contact and being set to a state 
permitting expansion of the air bag. 
It is also required that the key switch is provided with a switch contact 
having a high reliability for applying an ignition current to the squib. 
SUMMARY OF THE INVENTION 
The present invention is conceived to overcome the bove mentioned problems 
and its object is to provide an air bag controller capable of preventing 
erroneous expansion of the bag during a collision of the motor vehicle and 
capable of contributing to the enhancement of the reliability. 
To achieve the object described above, according to the present invention 
there is provided an air bag controller capable of detecting the collision 
of the motor vehicle and controlling the certain expansion of the air bag 
module provided at the assistant driver's seat comprising: an operation 
input means for generating an expansion enable/disable information 
expressing the enable or disable of the expansion of the air bag module at 
the assistant driver's seat, an information holding means for holding the 
expansion enable/disable information, an acceleration detection means for 
detecting an acceleration applied to the motor vehicle, an information 
change prohibiting means for prohibiting any change in expansion 
enable/disable information held in the information holding means if the 
acceleration detected by the acceleration detection means has exceeded a 
predetermined value, and an expansion control means for controlling the 
expansion of the air bag module at the assistant driver's seat based on 
the expansion enable/disable information held in the information holding 
means if the acceleration detected by the acceleration detection means has 
exceeded the predetermined value. 
According to the present invention, the expansion enable/disable 
information expressing the enable or disable of the expansion of air bag 
for the assistant driver's seat is input from the operation input means, 
and the expansion enable/disable information thus input is retained in 
information holding means. If an acceleration applied to a motor vehicle 
and detected by acceleration detection means exceeds a predetermined 
value, any change in expansion retained in the information holding means 
is prohibited by information change inhibit means; therefore, even though 
the expansion enable/disable information input to the operation input 
means has been changed by force majeure at the time of a car collision, 
the change in the expansion enable/disable information retained in the 
information holding means will be prohibited; and because of this, even 
though a change in switch condition such as chattering occurs by the 
impact during a car collision, any change in the switch condition can be 
ignored and, as a result, wasteful expansion in error of air bag for the 
assistant driver's seat can be prevented. Also, the expansion of the air 
bag for the assistant driver's seat can be definitively approved or 
prohibited only by a simple operation and this feature is able to 
contribute to the enhancement of the reliability of the air bag 
controller. 
In a preferred embodiment of the present invention, if the acceleration 
applied to a motor vehicle has exceeded the predetermined value, then the 
information change inhibit means prohibits any change in the expansion 
enable/disable information retained in the information holding means at 
least for a predetermined duration required for expanding the air bag 
module. 
In the preferred embodiment of the present invention, the information 
holding means comprises a memory of a microprocessor. 
To achieve the object described above, according to the present invention 
there is provided an air bag controller for controlling a certain 
expansion of an air bag module provided for an assistant driver's seat by 
detecting a collision of a motor vehicle, comprising: an operation input 
circuit for generating expansion enable/disable information expressing the 
enable or disable of the expansion of the air bag module at the assistant 
driver's seat; an information holding unit for holding the expansion 
enable/disable information; an acceleration detection unit for detecting 
an acceleration applied to the motor vehicle; an information change 
inhibit unit for inhibiting any change in expansion enable/disable 
information held in the information holding unit if an acceleration 
detected by the acceleration detection unit has exceeded a predetermined 
value; and an expansion control circuit for controlling the expansion of 
the air bag module at the assistant driver's seat based on the expansion 
enable/disable information held in the information holding unit if the 
acceleration detected by the acceleration detection unit has exceeded the 
predetermined value. 
In the preferred embodiment of the present invention, the information 
change inhibit unit is intended to inhibit the change of the expansion 
enable/disable information held in the information holding unit for a 
predetermined duration required at least for expanding the air bag module 
if the acceleration applied to the motor vehicle has exceeded the 
predetermined value. 
In the preferred embodiment of the present invention, the information 
holding unit comprises a memory of a microprocessor. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described hereinafter with reference to 
the accompanying drawings showing preferred embodiments. 
FIG. 1 illustrates the system configuration of the air bag controller 
related to the preferred embodiment of the present invention. 
In FIG. 1, a battery 3 for supplying electric power to an on-board 
electronic equipment may be installed in an engine room for instance. An 
ignition switch 5 intended to be closed for supplying an electric power 
from the battery 3 to the equipment is equipped in a lower portion of a 
steering wheel. 
As shown in FIG. 1, the air bag controller 1 comprises a control section 11 
which controls the expansion of an air bag module for an assistant 
driver's seat, a switch section 7 which generates expansion enable/disable 
information expressing whether the expansion of the air bag module for 
assistant driver's seat is to be prohibited or approved, and a cable 9 
connecting the control section 11 to the switch section 7. 
The switch section 7 comprises a cut-off switch 71 which instructs the 
enable or disable of the expansion of the air bag module for assistant 
driver's seat, an LED 72 which informs that the expansion of air bag 
module for the assistant driver's seat is in the state of enable, and a 
current limiting resistor R1 which limits a lighting current flowing to 
the LED 72. 
The control section 11 comprises a power supply circuit 13 which stabilizes 
an electric power supplied from the battery 3 through the ignition switch 
5 and supplies the stabilized electric power to a CPU 15 and a squib 19 
for the assistant driver's seat. The CPU 15 includes ROM and RAM and is 
intended to control the equipment in conformity with the stored control 
program and control data. The control section 11 also comprises a G-sensor 
17 for detecting an acceleration value applied to a motor vehicle, pull-up 
resistors R2 and R3 for converting the state of the cut-off switch 71 
transmitted through the cable 9 to the input level of the CPU 15, a drive 
transistor TR1 for energizing the LED 72 inside the switch section 7, a 
assistant driver's seat drive transistor TR2 for ON/OFF controlling the 
power supply to the assistant driver's seat squib 19, a safety sensor SS 
which conducts when a set limit is exceeded during a collision of the 
motor vehicle, and a capacitor C for supplying the output of the power 
supply circuit 13, after accumulating the power for a predetermined 
duration, to the squib 19 at the assistant driver's seat. 
Also, the squib 19 at the assistant driver's seat for expanding the air bag 
is to be built in the air bag module for the assistant driver's seat 
provided inside the upper left portion of an instrument panel. Also, the 
control section 11 is to be located at a convenient place for detecting 
the collision of the motor vehicle, such as inside a cabinet body (not 
shown in the drawings) mounted at a floor tunnel portion of the car body. 
Moreover, the switch section 7 is to be mounted in an instrument panel in 
front of the driver's seat. 
Next, the operation of air bag controller 1 will be explained by using a 
flowchart shown in FIG. 2. 
Firstly, in step S10, the state of cut-off switch 71 is input as signal A 
and signal B. Also, signal A and signal B expressing the state of cut-off 
switch 71 are connected to pull-up resistors R2 and R3 through the cable 9 
as shown in FIG. 1. Therefore, if the fixed contact C of the cut-off 
switch 71 is connected to a switch-over contact A and a switch-over 
contact B is in open state, then the input voltage V.sub.A at CPU 15 is at 
low level and the input voltage V.sub.B is at high level. On the other 
hand, the fixed contact C of the cut-off switch 71 is connected to the 
switch-over contact B; and if the switch-over contact A is in the open 
state, then the input voltage V.sub.A at the CPU 15 is at high level, and 
the input voltage V.sub.B is at low level. 
Next, in step S20, the CPU 15 judges whether the cut-off switch 71 is in 
the state of expansion enable state expressing the expansion enable as one 
of expansion enable/disable information of the air bag module for 
assistant driver's seat. That is, whether the state of signal A is 
V.sub.A =High 
and the state of signal B is 
V.sub.B =Low 
is judged. Here, if expansion enable state occurs, the operation proceeds 
to step S30; but if expansion enable state does not occur, that is, in the 
case of expansion inhibit state, the operation proceeds to step S40. 
In step S30, if the state of cut-off switch 71 is in the expansion enable 
state expressing the expansion of the air bag module for assistant 
driver's seat, then an actuation enable flag expressing the approval for 
expansion actuation of the air bag module for assistant driver's seat is 
set to "1". The actuation enable flag is constituted by a register in the 
CPU 15. 
The output of this actuation enable flag is connected to the base of a 
transistor TR2 for driving the assistant driver's seat and, therefore, if 
the actuation enable flag is set to "1", then the transistor TR2 for 
driving the assistant driver's seat is set to ON state. At the same time, 
the base of the drive transistor TR1 is set to high level, ON control is 
performed, and the LED inside the switch section 7 is lighted; and then 
the driver and passengers are informed of the air bag module for the 
assistant driver's seat which has been set to the expansion possible 
state. 
On the other hand, in step S40, if the cut-off switch 71 is in expansion 
inhibit state expressing no enable for expansion, then this actuation 
enable flag is cleared to "0". If the actuation enable flag has been 
cleared to "0", the transistor TR2 for driving assistant driver's seat is 
set to OFF state. At the same time, the base of the drive transistor TR1 
is set to low level, OFF control is performed, and the LED inside the 
switch section 7 is turned off, and the driver and passengers are informed 
of the air bag module for assistant driver's seat which has been set to 
expansion impossible state. 
Next, in step S50, the CPU 15 inputs a current acceleration value from 
G-sensor 17. 
Next, in step S60, the CPU 15 judges whether the input acceleration value 
is higher than 2G, for example. Here, if the acceleration value is higher 
than 2G, then one's own car is in the state of car collision and thus step 
S70 occurs. On the other hand, if the acceleration value is less than 2G, 
the one's own car has not entered the collision state and thus the 
operation returns to the step S10 and the processing of steps S10 to S60 
is repeated. 
Next, in step S70, one's own car is already in a collision state and thus 
the actuation enable flag set in step S30 or S40 is frozen to a change 
inhibit state. That is, the freezing to change inhibit state can be 
achieved by setting a register to rewrite inhibit state in the CPU 15 
constituting the actuation enable flag. 
Here, the change inhibit state for the actuation enable flag should be held 
for a predetermined duration required for the expansion of air bag module. 
Therefore, even though there is a change in contact state of the cut-off 
switch 71 due to the impact during collision of one's own car, the change 
in contact state of the cut-off switch 71 can be ignored because the 
actuation enable flag has been frozen to the change inhibit state. 
In consequence, if a child seat is placed or there in no passenger in the 
assistant driver's seat, and the cutoff switch 71 has been set to the 
expansion inhibit state, then the expansion of the air bag module at 
assistant driver's seat can be prohibited definitely and wasteful 
erroneous expansion of the air bag module at the assistant driver's seat 
can be prevented. 
On the other hand, if there is a passenger in the assistant driver's seat 
and the cut-off switch 71 has been set to the expansion enable state, then 
the expansion of the air bag module at assistant driver's seat has been 
permitted, and the drive transistor TR2 at assistant driver's seat is 
controlled to ON state and becomes conductive when the safety sensor SS 
has detected the collision of the motor vehicle in this state. 
As a result, a current flows to a circuit from the power supply circuit 13 
to assistant driver's seat drive transistor TR2 in ON state, assistant 
driver's seat squib 19, safety sensor SS and ground for expanding the air 
bag module at assistant driver's seat. Moreover, the assistant driver's 
seat squib 19 is heated suddenly and the air bag module at assistant 
driver's seat is expanded. 
Next, at the step S80, the CPU 15 inputs a current acceleration value from 
G-sensor 17. 
Next, at the step S90, the CPU 15 judges whether the input acceleration 
value is higher than 2G for example. Here, if the acceleration value is 
higher than 2G, then one's own car continues to be in a collision state, 
and thus the operation proceeds to the step S80. On the other hand, when 
the acceleration value is less than 2G, the one's own car is from 
collision state to stop state or in running state at a low acceleration, 
therefore, at the step S100, a register in the CPU 15 constituting the 
actuation enable flag is set to a rewrite enable state, the change inhibit 
state is canceled, and the operation returns to the step S10 and repeats 
the processing. 
As described above, the expansion enable/disable information expressing the 
enable/disable of the expansion of the air bag module at assistant 
driver's seat is input from the cut-off switch 71, and the expansion 
enable/disable information is once held in a register of the CPU 15. If 
the acceleration applied to the motor vehicle detected by the G-sensor 17 
exceeds 2G, for example, any change in the expansion enable/disable 
information retained in a register of the CPU 15 is prohibited by the CPU 
15; thus, even though the expansion enable/disable information input to 
the cut-off switch 71 has changed by the force majeure, any change in the 
expansion enable/disable information retained in the register will be 
prohibited; for example, even though a change such as chattering in the 
switch state occurs in the cutoff switch 71 by the impact during a 
collision, the contents retained in the register of the CPU 15 are not 
subjected to change; and the change in the state of the cut-off switch 71 
can be neglected at the base of assistant driver's seat drive transistor 
TR2 and, as a result, wasteful erroneous expansion of the air bag module 
for assistant driver's seat can be prevented. Also, the expansion of the 
air bag module at assistant driver's seat can be definitively permitted or 
prohibited only by a simple operation and thus this system is able to 
contribute to the enhancement of the air bag controller. 
It should be understood that many modifications and adaptations of the 
invention will become apparent to those skilled in the art and it is 
intended to encompass such obvious modifications and changes in the scope 
of the claims appended hereto.