Air bag system

In an air bag system according to the invention, there is employed a control device which can control the internal pressure of an air bag after expanded in such a manner that a buffer distance, for which the air bag after expanded can be compressed when it is contacted with an occupant, can be kept constant regardless of an increase or a decrease in the weight or the like of the occupant. In operation, the control device firstly takes out the acceleration data of the occupant corresponding to the degree of a collision in accordance with a signal from an acceleration sensor. Next, in accordance with the thus taken-out acceleration, a distance from the air bag before expanded to the head and bosom portion of the occupant obtained based on a signal from a distance sensor, and the weight of the occupant head and bosom portion obtained based on a signal from a weight sensor, the control device calculates a proper value of the internal pressure of the air bag according to a velocity/distance/power balancing condition equation, and controls a gas generation device in such a manner it can produce a generated gas pressure corresponding to the thus calculated proper value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an air bag system which is disposed in a 
vehicle and, in a vehicle collision, is used to restrain the head and 
bosom portion of an occupant with an air bag expanded and, in particular, 
to an air bag system which can adjust the internal pressure of the air bag 
to thereby expand the same according to the degree of the vehicle 
collision as well as according to the weight and sitting position of the 
occupant. 
2. Description of the Related Art 
Conventionally, as an air bag system which is used to restrain an occupant 
with an air bag expanded, there is known a system which adjusts the 
internal pressure of an air bag to thereby be able to expand the same 
according to the sitting position of the occupant, the degree of vehicle 
collision, and the like. In this type of air bag system, the degrees of 
collision, the sitting position of the occupant and the like are 
classified into stages according to predetermined boundary values, and the 
internal pressure of the air bag is adjusted according to the stages. 
That is, there are set boundary values which are respectively used to 
check, for example, whether, as the sitting position of the occupant, a 
distance from the air bag folded to the occupant is less than 40 cm or 
not, or whether the acceleration in the collision is less than 70 Km/H or 
not, or whether the weight of the occupant is less than 50 Kg or not, or 
the like. And, the internal pressure of the air bag is adjusted in stages 
in accordance with whether the above-mentioned parameters exceed their 
respective boundary values or not. 
However, in the above conventional air bag system, when the parameters are 
adjacent to these boundary values, for example, when the internal pressure 
of the air bag is adjusted in stages as low or high according to whether 
the weight of the occupant is less than 50 Kg or not, if the weight of the 
occupant is 49 Kg, then the occupant is restrained by the air bag expanded 
with a low level of internal pressure; and, if the weight of the occupant 
is 50 Kg, then the occupant is restrained by the air bag expanded with a 
high level of internal pressure. In this case, in spite of the fact that 
the weight difference is only 1 Kg, the occupant of 49 Kg is restrained 
with the low level air bag internal pressure. That is, in the conventional 
air bag system, there is still left room for improvement in restraining 
the occupant with the air bag properly. 
SUMMARY OF THE INVENTION 
The present invention aims at eliminating the drawbacks found in the 
above-mentioned conventional air bag system. Accordingly, it is an object 
of the invention to provide an air bag system which does not classify the 
sitting position and weight of the occupant as well as the degree of the 
collision but adjusts the internal pressure of the air bag in accordance 
with an increase or a decrease in the values of these parameters to 
thereby be able to expand the air bag properly. 
In particular, an air bag system according to the invention comprises: (1) 
an air bag including a vent hole, (2) a gas generation device which 
generates gas for expansion to thereby expand an air bag, (3) a distance 
sensor for measuring a distance from the air bag to the head and bosom 
portion of an occupant, (4) a weight sensor for measuring the weight of 
the occupant, (5) an acceleration sensor for measuring the acceleration of 
a vehicle, and (6) a control device for controlling the internal pressure 
of the air bag when it is to be expanded, wherein (A) the protrusion 
distance of the air bag when the expansion thereof is completed, (B) a 
contact area between the expanded air bag and occupant, and (C) a buffer 
distance for which the expanded air bag is compressed when it is contacted 
with the occupant are previously input into the control device as constant 
values, and further (D) the acceleration function of the occupant 
according to the degree of a vehicle collision is also previously input 
into the control device, and also wherein the control device calculates a 
proper value of the air bag internal pressure according to a 
speed/distance/power balancing condition equation based on the behavior of 
the air bag and occupant in the vehicle collision, using the acceleration 
of the occupant calculated from the (D) acceleration function based on a 
signal from the acceleration sensor, a distance from the air bag before it 
is expanded to the head and bosom portion of the occupant based on a 
signal from the distance sensor, the weight of the head and bosom portion 
of the occupant based on a signal from the weight sensor, and the (A) to 
(C) constant values previously input into the control device. 
In the air bag system according to the invention, the control device, using 
the acceleration of the occupant taken out from the previously input data 
based on the signal from the acceleration sensor, the distance from the 
air bag before it is expanded to the head and bosom portion of the 
occupant based on the signal from the distance sensor, the weight of the 
head and bosom portion of the occupant based on the signal from the weight 
sensor, and the previously input constant value of the air bag protrusion 
distance, contact area and buffer distance, calculates the proper air bag 
internal pressure value according to the above-mentioned 
speed/distance/power balancing condition equation based on the behavior of 
the air bag and occupant in the vehicle collision, and controls the gas 
generation device such that the gas generation device can generate a 
generated gas pressure corresponding to the thus calculated internal 
pressure value. 
That is, in the air bag system according to the invention, unlike the 
conventional air bag system in which the sitting position and weight of 
the occupant or the degree of the shock are classified in stages according 
to the boundary values to thereby adjust the internal pressure of the air 
bag according to such classification, in order to be able to keep constant 
a buffer distance for which the air bag is compressed when it restrains 
the head and bosom portion of the occupant, the increased or decreased 
values of the sitting position and weight of the occupant or the degree of 
the collision shock are substituted into the above-mentioned given 
balancing condition equation to thereby calculate a proper value of the 
internal pressure of the air bag, and the gas generation device is 
controlled according to the thus calculated internal pressure value. That 
is, the sitting position and weight of the occupant as well as the degree 
of the collision shock are not classified in stages but, according to the 
increase or decrease of these values, the air bag internal pressure can be 
adjusted properly and thus the air bag can be expanded properly. 
Also, according to the air bag system of the invention, regardless of an 
increase or a decrease in the sitting position and weight of the occupant 
or in the degree of the collision shock; the buffer distance for which the 
air bag is compressed when the air bag restrains the head and bosom 
portion of the occupant can be kept constant and, therefore, if the buffer 
distance is set for the maximum value of the air bag used, then the air 
bag expanded is able to restrain the occupant over the longest distance in 
the then condition whether the sitting position and weight of the occupant 
or the degree of the collision shock increase or decrease, so that a 
reaction given from the air bag and acting on the occupant can be 
restricted as much as possible in the then condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, description will be given below of a first embodiment of an air bag 
system according to the invention with reference to the accompanying 
drawings. 
An air bag system 10 according to the first embodiment of the invention, as 
shown in FIG. 1, comprises an air bag 11, a gas generation device 12, a 
distance sensor 13, a weight sensor 14, an acceleration sensor 15, and a 
control device 19. 
The air bag 11, which is formed in a bag shape, is stored in the 
instrumental panel of a passenger's seat of a vehicle in such a manner 
that it is folded. And, the air bag 11 includes a vent hole 11a which 
allows expansion gas to escape into the open air so that, when the air bag 
11 is expanded, the internal pressure of the air bag 11 can be kept 
constant until the air bag 11 is contacted with an occupant M and is 
thereby compressed. 
Also, the instrumental panel 1 includes a cover 1a which can be opened and, 
when the air bag 11 is expanded, the cover 1a is pushed open by the 
expanding air bag 11, thereby causing the air bag 11 to project toward the 
occupant M. 
The gas generation device 12 comprises two gas generating elements 12a and 
12b which respectively generate expansion gas when gas generating agents 
are set on fire due to the ignition of an igniter device: in particular, 
the gas generation device 12 is structured such that it can increase the 
pressure of the expansion gas to be supplied to the air bag 11 by 
approaching together the ignition timings of the two gas generating 
elements 12a and 12b; and, on the other hand, by staggering the above 
ignition timings greatly from each other, it can lower the pressure of the 
expansion gas to be supplied to the air bag 11. That is, as shown in FIG. 
2, if the ignition timings of the two gas generating elements 12a and 12b 
are staggered in the unit of 1/1000 sec., then the pressure of the 
generated expansion gas becomes lower accordingly and, during this 
staggering operation, if the expansion of the air bag 11 is completed to 
thereby cause the occupant M to be contacted with the air bag 11, then the 
internal pressure of the air bag 11 can be adjusted. By the way, even when 
the ignition timings are staggered, if the two gas generating elements 12a 
and 12b are ignited, then, finally, as shown in FIG. 2, the pressure of 
the generated expansion gas of the gas generation device 12 itself 
approaches a constant value; but, because there is formed in the air bag 
11 the vent hole 11a for causing the expansion gas to escape to the open 
air so that the internal pressure of the air bag 11 can be kept constant, 
the adjustment of the internal pressure of the air bag 11 after completion 
of the gas expansion can be achieved by adjusting the ignition timings of 
the two gas generating elements 12a and 12b. 
And, the distance sensor 13 is disposed at a given position of the 
instrumental panel 1 and is used to measure a distance L.sub.1 from the 
air bag 11 stored in the instrumental panel 1 to the head and bosom 
portion H of the occupant M. The distance sensor 13 is constituted by 
well-known optical sensor and ultrasonic sensor respectively using light 
and ultrasonic waves, an infrared sensor using infrared rays, and the 
like. 
The weight sensor 14 includes a pressure sensor and is disposed in a bag 
body 6 which is embedded in a seat portion 4 of a seat 3, in which the 
occupant M is to be seated, and is sealed with air. And, due to an 
increase in the internal pressure of the bag body 6 when the occupant M 
sits on the seat portion 4, the weight sensor 14 measures the weight of 
the occupant M. 
The acceleration sensor 15 is disposed in the front portion of a vehicle or 
the like and includes an acceleration meter of a well-known distortion 
gauge type, a piezo-gauge type, or the like. 
The control device 19, which comprises a microcomputer and the like, is 
disposed at a given position in the vehicle and is also connected 
electrically to the gas generation device 12, distance sensor 13, weight 
sensor 14 and acceleration sensor 15. And, on inputting therein signals 
from the distance sensor 13, weight sensor 14 and acceleration sensor 15, 
the control device 19 operates them and controls the operation of the gas 
generating elements 12a and 12b of the gas generation device 12. 
Also, the control device 19 is structured such that it can input therein 
signals from a child seat confirmation sensor 16, which is used to detect 
whether a child seat is disposed or not, and from a seat belt confirmation 
sensor 17 which is used to detect whether a seat belt is mounted or not. 
The sensor 16 includes two lead switches 16a and 16b disposed, for 
example, in a back portion 5 of the seat 3 and, on sensing one of the 
magnetic forces of two magnets separately provided on the front and rear 
sides of the child seat, a corresponding one of the lead switches 16a and 
16b is turned on to thereby be able to detect whether the child seat is 
mounted in a forwardly facing position (that is, a child is to be seated 
forwardly) or in a backwardly facing position (a child is to be seated 
backwardly). On the other hand, the sensor 17 comprises, for example, a 
photoelectric switch disposed in a buckle 7 and, if the light is cut off 
within the buckle 7 when the metal fittings of the seat belt are mounted 
into the buckle 7, then the sensor 17 is able to detect that the seat belt 
is mounted. 
Further, in the memory of the control device 19, previously, there are 
recorded the followings: that is, the acceleration function data of the 
occupant in a vehicle collision corresponding to the elapsed time from the 
time of collision (t.sub.0) to a time (t.sub.2) exceeding the boundary 
value (a.sub.s) of the acceleration that requires the restraint of the 
occupant; the protrusion distance (L.sub.2) of the air bag 11 after the 
expansion thereof is completed; a contact area (S) between the air bag 11 
expanded and the occupant M; a buffer distance (L.sub.m) for which the 
expanded air bag 11 is compressed when it is contacted with the occupant 
M; and, time data necessary for expansion when the expansion of the air 
bag 11 is completed with various internal pressures. 
Now, description will be given below of the basic concept of the control 
operation to be executed by the present control device 19 (see FIG. 3): 
At first, if a vehicle running at a constant velocity is collided head-on, 
then the vehicle is suddenly decelerated so that there is generated a 
backward acceleration a.sub.0 in the vehicle. At the collision time 
(t.sub.0), when the road surface is used as a yardstick, the occupant M 
not restrained is still moving at the constant velocity. However, with the 
room of the vehicle used as a yardstick, an apparent acceleration a.sub.0 
is generated forwardly in the occupant M and thus, from this moment, the 
occupant M starts to move forwardly in the vehicle room while increasing 
his or her velocity. 
And, at the time (t.sub.1) when the acceleration a.sub.0 exceeds the 
previously set boundary value a.sub.s of the acceleration requiring the 
restraint of the occupant, the gas generation device 12 is ignited (in the 
present embodiment, actually, at the time (t.sub.1) when the acceleration 
a.sub.0 exceeds the boundary value a.sub.s of the acceleration, the 
control device 19 performs a predetermined operation to determine the 
proper internal pressure value of the air bag 11 and the gas generation 
device 12 is ignited in accordance with the thus determined air bag 
internal pressure value. In this case, however, since the operation by the 
control device 19 is executed in an instant when compared with the 
behavior of the occupant M, the expansion of the air bag 11 and the like, 
there can be provided a similar condition to the case in which the gas 
generation device 12 is ignited at the time (t.sub.1) when the 
acceleration a.sub.0 exceeds the boundary value a.sub.s of the 
acceleration). 
After then, the air bag 11 completes its expansion and, at a given time 
(t.sub.2), the occupant M is contacted with the air bag 11. At the time 
(t.sub.2), the acceleration a.sub.0 is coming to an end, whereas a new 
acceleration a.sub.1 due to the reaction F.sub.1 of the air bag 11 is 
applied to the occupant M. And, the occupant M, while losing his or her 
moving velocity gradually, advances by a buffer distance L.sub.m and stops 
there. Unless the air bag 11 reaches its bottom (that is, unless the air 
bag 11 exhausts the expansion gas to be thereby compressed and thus the 
occupant M is caused to touch peripheral equipment), the longer the buffer 
distance L.sub.m is, the smaller shock is given to the occupant and, for 
this reason, the buffer distance L.sub.m may preferably be set as longest 
as possible regardless of the kinetic energy of the occupant M. 
Therefore, the buffer distance L.sub.m may be previously set according to 
the bag shape of the air bag 11, and the internal pressure value of the 
air bag 11 may be adjusted in such a manner that the occupant M can be 
made to stop at the position of the buffer distance L.sub.m. 
Also, since the air bag 11 includes the vent hole 11a which is capable of 
exhausting the expansion gas, the air bag 11 in contact with the occupant 
M is compressed in a condition that it keeps constantly the internal 
pressure thereof obtained at the time of completion of the expansion while 
exhausting the excess amount of the expansion gas from the vent hole 11a. 
Due to this, the pressure of the generated gas, which is obtained when the 
ignition timings of the gas generation device 12 are adjusted, provides 
the internal pressure of the air bag 11 which is maintained until the 
occupant M is made to stop. 
And, when calculating the internal pressure value of the air bag 11, the 
operating conditions of the gas generation device 12 must be decided at 
the time t.sub.1 when the gas generation device 12 is operated, that is, 
at the time t.sub.1 when the acceleration a.sub.0 measured by the 
acceleration sensor 15 exceeds the boundary value a.sub.s , while the 
forward acceleration a.sub.X of the occupant during the time t.sub.1 
.about.t.sub.3 must be estimated. 
However, due to the fact that the front frame and the like of the vehicle 
in collision are deformed while absorbing shock energy, the acceleration 
a.sub.0 provides a function which varies with time and, in fact, the 
acceleration a.sub.0 can be expressed by a.sub.X (t). And, the 
acceleration a.sub.X (t) expressed as the time function varies from 
vehicle to vehicle and also in every running velocity. Therefore, as shown 
in FIG. 4, it is necessary to prepare a large pieces of acceleration 
function data obtained by conducting an actual vehicle collision test in 
which a vehicle carrying thereon the air bag system 10 is made to collide 
at various running velocities, or by conducting a collision test through 
simulation. By the way, a.sub.A (t) expresses an acceleration when the 
vehicle is made to collide head-on at a fast running velocity, while 
a.sub.B (t) expresses an acceleration when the vehicle is made to collide 
head-on at a slow running velocity. And, according to the elapsed time 
from t.sub.0 to the time t.sub.1 when the acceleration value a.sub.0 based 
on a signal from the acceleration sensor 15 exceeds the boundary value 
a.sub.s , if the elapsed time is short, then the degree of the collision 
is large and thus there is employed the function data of a given line 
graph on the acceleration a.sub.A (t) side; and, if the elapsed time is 
long, then the degree of the collision is small and thus there is employed 
the function data of a given line graph on the acceleration a.sub.B (t) 
side. These function data on the acceleration a.sub.X (t) can be applied 
similarly to an actual vehicle, provided the vehicle is of the same type 
and, therefore, may be previously recorded in large number in the memory 
of the control device 19. 
And, referring to the operation of the air bag system 10 according to the 
present embodiment, at first, if a vehicle collides, then the control 
device 19 performs a computational processing on an electrical signal from 
the acceleration sensor 15 and, if the acceleration value a.sub.0 exceeds 
the acceleration boundary value a.sub.s which requires the restraint of 
the occupant M, then detects the collision of the vehicle and controls the 
air bag system 10 in such a manner as shown in FIG. 5. 
Firstly, in Step 100, it detects in accordance with presence or absence of 
a signal from the child seat confirmation sensor 16 whether the child seat 
is mounted or not and, if it is found that the child seat is mounted, then 
the processing advances to Step 101, whereas if not mounted, then the 
processing goes to Step 103. 
In Step 101, it is judged from a signal from either of the lead switches 
16a and 16b of the child seat confirmation sensor 16 whether the child 
seat is mounted in a forwardly facing manner or in a backwardly facing 
manner and, if it is found that the child seat is mounted in a forwardly 
facing manner, then the processing goes to Step 102 and the operation of 
the gas generation device 12 is controlled in such a manner that the air 
bag 11 can be developed in a weak mode. In this weak mode development, the 
control device 19 allows only the gas generating element 12a of the gas 
generation device 12 to be ignited, so that the air bag 11 is expanded by 
only the expansion gas from the gas generating element 12a. On the other 
hand, if it is found that the child seat is mounted in a backwardly facing 
manner, then, in order not to expand the air bag 11, the processing does 
not advance to Step 102 but the control of the control device 19 is 
terminated. 
In Step 103, when the child seat is not mounted on the seat 3, it is judged 
from a signal from the weight sensor 14 whether the occupant is seated on 
the seat 3 or not and, if it is found that the occupant M is not seated on 
the seat 3, then the control of the control device 19 is terminated in 
order not to expand the air bag 11. On the other hand, if the occupant M 
is seated on the seat 3, then the processing goes to Step 104. 
In Step 104, it is checked from a signal from the seat belt confirmation 
sensor 17 whether the occupant M wears the seat belt or not. If it is 
found that the occupant M wears the seat belt, then the processing goes to 
Step 102, where the operation of the gas generation device 12 is 
controlled in such a manner that the air bag 11 can be developed into the 
weak mode. On the other hand, if the occupant M does not wear the seat 
belt, then the processing advances to Step 105 in which the internal 
pressure of the air bag 11 is calculated. 
And, in Step 105, at first, there is computed a time which has passed from 
the time to when the vehicle collided, that is, the contact time t.sub.2 
when the occupant M starts to touch the air bag 11 with the expansion 
thereof completed. 
In this computation equation, according to the distance L.sub.1 from the 
air bag 11 before expanded to the occupant head and bosom portion H based 
on the signal from the distance sensor 13, the occupant M acceleration 
a.sub.X (t) expressed as function data employed according to the elapsed 
time when the acceleration value a.sub.0 measured based on the signal from 
the acceleration sensor 15 exceeds the acceleration boundary value a.sub.s 
from the collision time t.sub.0, and the protrusion distance L.sub.2 of 
the air bag 11 with the expansion thereof completed, there is firstly 
calculated a distance L.sub.3 which is necessary for the occupant head and 
bosom portion H to touch the air bag 11 with the expansion thereof 
completed. 
That is, 
EQU L.sub.3 =L.sub.1 -L.sub.2 (1) 
And, since the distance L.sub.3 is equal to a value obtained when the 
acceleration a.sub.X (t) from the vehicle collision time t.sub.0 to the 
contact time t.sub.2 is integrated twice, there is obtained the following 
equation (2): 
##EQU1## 
Then, t.sub.2 can be calculated from the above equations (1) and (2). 
By the way, since L.sub.1 is previously measured from the signal from the 
distance sensor 13 and L.sub.2 is previously recorded in the memory of the 
control device 19 according to the bag shape of the air bag 11, these 
values may be substituted in the above equations. Further, the collision 
time t.sub.0 is also previously recorded in the control device 19 which 
has input therein the signal from the acceleration sensor 15 and, 
therefore, the thus recorded value may be substituted in the above 
equations. 
After the contact time t.sub.2 is calculated, the advance velocity 
(V.sub.1) of the occupant M into the air bag 11 is found from the contact 
time (t.sub.2) and the occupant M acceleration (ax (t)) employed from the 
function data. 
That is, the advance velocity (V.sub.1) is a value obtained by integrating 
the occupant M acceleration (ax (t)) from the vehicle collision time 
t.sub.0 to the contact time t.sub.2, as shown below: 
##EQU2## 
Accordingly, V.sub.1 is calculated according to this equation (3). 
Next, the weight m of the occupant M head and bosom portion H is calculated 
in accordance with a signal from the weight sensor 14. In particular, the 
weight of the occupant M can be measured in accordance with the signal 
from the weight sensor 14 and the approximately 30% of the occupant M 
weight is equal to the weight m of the occupant head and bosom portion H. 
Thus, in the present embodiment, the value of the weight of the occupant M 
is multiplied by 0.3 to thereby calculate the weight m of the occupant 
head and bosom portion H. 
Also, because it can be assumed that the contact area (S) between the air 
bag 11 and occupant head and bosom portion H varies little among 
individuals even if they are respectively heavy or light in weight, in the 
present embodiment, it is set that S=0.13 m.sup.2. 
By the way, the numeric value used to multiply the weight value and the 
contact area S, which are respectively employed to calculate the weight m 
of the head and bosom portion H, can be changed properly according to 
cases. 
Now, description will be given below of the relationship among the 
deceleration (a.sub.1 (t)) of the air bag 11 acting on the occupant M, a 
stop time (t.sub.3) when the occupant M stops at the buffer distance 
(L.sub.m), and the internal pressure (P) of the air bag 11. 
At first, the buffer distance (L.sub.m ) may be found in such a manner that 
a value (distance), which is obtained when the deceleration (a.sub.1 (t)) 
causing generation of the reaction F.sub.1 of the air bag 11 acting on the 
occupant M from the contact time t.sub.2 to the stop time t.sub.3 is 
integrated twice, is subtracted from the advanced distance of the occupant 
M from the contact time t.sub.2 to the stop time t.sub.3. This can be 
expressed by the following equation (4): 
##EQU3## 
Also, since the advance velocity (V.sub.1) becomes zero from the contact 
time t.sub.2 to the stop time t.sub.3, the advance velocity (V.sub.1) 
balances oppositely in direction with the integrated value (velocity) of 
the deceleration a.sub.1 (t) which causes generation of the reaction 
F.sub.1 of the air bag 11 acting on the occupant M. This can be expressed 
in the following equation (5): 
##EQU4## 
Further, referring to a power balancing condition equation from the contact 
time t.sub.2 to the stop time t.sub.3, since the occupant M having the 
weight m of the head and bosom portion H thereof moves at the acceleration 
ax (t) and receives the internal pressure P of the air bag 11 in the 
contact area S in the opposite direction to the moving direction thereof, 
while the air bag 11 applies the oppositely-going deceleration a.sub.1 (t) 
to the occupant M having the weight m, the power balancing condition 
equation can be expressed by the following equation: 
EQU ma.sub.X (t)-PS=ma.sub.1 (t) 
That is, it can be expressed by the following equation: 
EQU a.sub.1 (t)=a.sub.X (t)-PS/m(where, t.sub.2 .ltoreq.t.ltoreq.t.sub.3)(6) 
And, while the deceleration (a.sub.1 (t)) of the air bag 11 acting on the 
occupant M, the stop time (t.sub.3) when the occupant M stops at the 
buffer distance (L.sub.m), and the internal pressure (P) of the air bag 11 
are unknowns, simultaneous equations consisting of the 
velocity/distance/power balancing condition equations (4).about.(6) based 
on the air bag 11 and occupant M in the collision time are operated to 
thereby calculate the internal pressure value (P) of the air bag 11. 
After the internal pressure value (P) of the air bag 11 is calculated, the 
processing goes to Step 106. In Step 106, when the occupant M is seated in 
the extremely front portion of the seat, it is necessary to prevent the 
occupant M from touching the air bag 11 being expanded and, therefore, the 
following condition equation (7) is operated. 
That is, whether the condition of 
EQU t.sub.2 .ltoreq.t.sub.1 +.DELTA.t.sub.b (7) 
is satisfied or not is operated. Here, t.sub.2 is the contact time between 
the air bag 11 and the occupant head and bosom portion H and is already 
calculated in Step 105, while t.sub.1 is the time when the acceleration 
value a.sub.0 previously measured in accordance with the signal from the 
acceleration sensor 15 exceeds the boundary value a.sub.s , and it is also 
previously known. Also, .DELTA.t.sub.b is a time necessary until the 
expansion of the air bag 11 is completed. In particular, since the time 
data obtained when the expansion of the air bag 11 is completed with 
various internal pressures are previously recorded in the memory of the 
control device 19, in accordance with the internal pressure value (P) 
calculated in Step 105, the time necessary for expansion with this 
internal pressure is taken out from the memory and the thus taken-out time 
value is then applied as .DELTA.t.sub.b. 
If the condition equation of the equation (7) is satisfied, then the 
occupant M is to touch the air bag 11 being expanded and, in order to 
prevent such touch, the processing goes to the weak mode development of 
Step 102. On the other hand, if the condition equation of the equation (7) 
is not satisfied, then the occupant M is to touch the air bag 11 with the 
expansion thereof completed and thus the expansion development of the air 
bag 11 is in time for touch with the occupant M, so that the processing 
goes to Step 107. 
In Step 107, while the mutual ignition timings of the gas generating 
elements 12a and 12b of the gas generation device 12 are being adjusted in 
such a manner that the internal pressure of the air bag 11 can provide the 
internal pressure value P of the air bag 11 calculated in Step 105, the 
gas generating elements 12a and 12b are ignited, thereby terminating the 
control of the control device. 
And, if the gas generation device 12 is ignited, then the air bag 11 opens 
the cover 1a due to the expansion gas discharged from the gas generation 
device 12 and expands until it turns into its expansion completed shape. 
After then, the air bag 11 receives the head and bosom portion H of the 
occupant M and is thus compressed by an amount corresponding to the buffer 
distance L.sub.m while exhausting the expansion gas from the vent hole 
11a, thereby stopping the movement of the occupant M. 
In the air bag system 10 according to the present embodiment, as has been 
described heretofore, unlike the conventional air bag system in which the 
sitting position and weight of the occupant or the degree of the shock are 
classified in stages according to the boundary values to thereby adjust 
the internal pressure of the air bag 11, in order to be able to keep 
constant the buffer distance L.sub.m of the air bag 11 for which the air 
bag 11 is compressed when it restrains the head and bosom portion H of the 
occupant, the increased or decreased values of the sitting position and 
weight of the occupant or the degree of the shock are substituted into a 
given balancing condition equation to thereby calculate the internal 
pressure value P of the air bag 11, and the gas generation device 12 is 
controlled according to the thus calculated internal pressure value P. 
That is, the sitting position and weight of the occupant as well as the 
degree of the shock are not classified in stages but, according to the 
increase or decrease of these values, the air bag internal pressure can be 
adjusted properly and thus the air bag 11 can be expanded properly. 
Also, in the air bag system 10 according to the present embodiment, 
regardless of an increase or a decrease in the sitting position and weight 
of the occupant M or in the degree of the shock, the buffer distance 
L.sub.m of the air bag 11, for which it is compressed when the air bag 
restrains the head and bosom portion H of the occupant M, can be kept 
constant and, therefore, if the buffer distance L.sub.m is set for the 
maximum value of the air bag 11 used, then even if the sitting position 
and weight of the occupant M or the degree of the shock increase or 
decrease, the air bag 11 expanded is able to restrain the occupant M over 
the longest distance in the then condition, so that the reaction F.sub.1 
given from the air bag 11 and acting on the occupant M can be restricted 
as much as possible in the then condition. 
By the way, in the illustrated embodiment, the adjustment of the generated 
gas pressure of the gas generation device 12 is achieved by means of the 
ignition timing adjustment of the two gas generating elements 12a and 12b. 
However, alternatively, as shown in FIG. 6, a single gas generating 
element (device) may be used, in the flow path of the expansion gas to the 
air bag 11, there may be disposed an electromagnetic type of flow rate 
control valve 20 which is capable of releasing the expansion gas into the 
open air in such a manner that the release amount of the expansion gas 
into the open air can be adjusted, and the control device 19 may be 
structured such that it can control the flow rate control valve. Here, in 
FIG. 6, the parts used in common with those in FIG. 1 are omitted. 
Further, to obtain the generated gas pressure in the ignition time, there 
may be prepared two or more kinds of gas generating elements (devices) 
such as small-sized, medium-sized, and large-sized gas generating 
elements, and they may be ignited at the same time individually or in 
proper combination thereof. For example, when the generated gas pressure 
is obtained by use of three kinds of, that is, small-sized, medium-sized, 
and large-sized gas generating elements, as shown in FIG. 7, there can be 
produced seven stages of generated gas pressure, while the control device 
19 may control and ignite one or more given gas generating elements in 
such a manner that the generated gas pressure can be near to the 
calculated internal pressure P of the air bag 11. 
By the way, when the generated gas pressure is adjusted by adjusting the 
ignition timing or by adjusting the flow rate of the flow rate control 
valve according to the illustrated embodiment, the generated gas pressure 
can be adjusted finely in an analog manner and, therefore, the internal 
pressure of the air bag 11 can also be adjusted finely in an analog 
manner, so that the occupant M can be restrained finely in an analog 
manner and continuously, that is, in the most suitable manner according to 
the sitting position and the weight of the occupant M or according to the 
increasing or decreasing value of the degree of the shock. Of course, when 
there are prepared two or more kinds of gas generating elements having 
different generated gas pressures in the ignition time, if the number of 
gas generating elements to be prepared is increased, then a similar effect 
to the above can be provided, while at least three pieces of gas 
generating elements may be prepared for this purpose. 
In the illustrated embodiment, description has been given of a case in 
which the present air bag system is applied to the passenger's seat but, 
of course, the present invention can also be applied to a driver's seat.