Occupant protective system

An occupant protective system for an automotive vehicle having a driver's seat and an assistant driver's seat. A magnitude of detected deceleration is compared with first and second threshold values, the second threshold value being greater than the first threshold value. If the magnitude of detected deceleration exceeds the second threshold value, both of a first air bag provided for the driver's seat and a second air bag provided for the assistant driver's seat are caused to be inflated even when the assistant driver's seat is not occupied, whereas if the magnitude of detected deceleration exceeds the first threshold value but does not exceed the second threshold value, the first air bag for the driver's seat alone is caused to be inflated when the assistant driver's seat is not occupied.

BACKGROUND OF THE INVENTION 
This invention relates to an occupant protective system for automotive 
vehicles, and more particularly to an occupant protective system adapted 
to protect occupants even when the shock upon crash of an automotive 
vehicle is very large. 
As an occupant protective system of this kind, a system is conventionally 
known, which has air bag devices provided for the driver's seat and the 
assistant driver's seat of an automotive vehicle, respectively, each of 
the air bag devices comprising an acceleration sensor for detecting shock 
upon crash of the vehicle, an inflator (gas generator) which generates a 
gas in response to a signal indicative of the detected acceleration 
supplied from the acceleration sensor, and an air bag which is inflated by 
the gas. 
According to this known system, when the vehicle receives shock upon crash 
thereof, for example, the signal indicative of the detected acceleration 
is supplied to the inflator, and a squib in the inflator is ignited to 
generate a nitrogen gas to thereby inflate the air bag, whereby the 
occupant is protected from hitting against the steering wheel or the 
windshield. 
However, in this occupant protective system, the air bag device provided 
for the assistant driver's seat is adapted not to operate if there is no 
occupant in the assistant driver's seat when the vehicle receives shock 
upon crash thereof etc. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide an occupant protective system 
for an automotive vehicle, which is capable of operating an air bag 
provided for the assistant driver's seat even when there is no occupant 
seated in the assistant driver's seat if the shock upon crash of the 
vehicle etc. is very large, to thereby more safely protect the occupant in 
the driver's seat. 
To attain the above object, the invention provides an occupant protective 
system for an automotive vehicle having a driver's seat and an assistant 
driver's seat which includes a first air bag provided for the driver's 
seat of the vehicle, a second air bag provided for the assistant driver's 
seat, and deceleration detecting means for detecting a magnitude of 
deceleration exerted on the vehicle, occupant detecting means for 
detecting whether or not there is an occupant seated on the assistant 
driver's seat. The occupant protective system further includes actuator 
means responsive to an output from the occupant detecting means for 
causing at least the first air bag to be inflated to absorb shock, when 
the magnitude of deceleration detected by the deceleration detecting means 
exceeds a predetermined value. 
The actuator means of the occupant protective system according to the 
invention is includes 
comparison means for comparing the magnitude of deceleration detected by 
the deceleration detecting means with first and second threshold values 
forming the predetermined value, the second threshold value being greater 
than the first threshold value. 
The actuator means of the occupant protective system further includes 
selecting means responsive to outputs from the comparison means and the 
occupant detecting means for causing both of the first and second air bags 
to be inflated even when no occupant is seated on the assistant driver's 
seat, if the magnitude of deceleration detected exceeds the second 
threshold value, and for causing the first air bag alone to be inflated 
when no occupant is seated on the assistant driver's seat, if the 
magnitude of deceleration detected exceeds the first threshold value and 
does not exceed the second threshold value. 
Preferably, the comparison means comprises a first comparator for comparing 
the magnitude of deceleration detected with the first threshold value, and 
a second comparator for comparing the magnitude of deceleration detected 
with the second threshold value, and the selecting means comprises an AND 
circuit having one input supplied with an output from the first comparator 
and another input supplied with an output from the occupant detecting 
means, and an OR circuit having one input supplied with an output from the 
second comparator and another input supplied with an output from the AND 
circuit. 
More preferably, the occupant detecting means has a switch provided at the 
assistant driver's seat for detecting an occupant seated thereon. 
The term "deceleration" used throughout the present specification means 
both its proper meaning, i.e. deceleration and acceleration, since a 
deceleration sensor used in the system of the invention many also be used 
as an acceleration sensor depending upon the direction in which it is 
mounted, the design of a signal processing circuit of the actuator system, 
etc. 
The above and other objects, features, and advantages of the invention will 
become more apparent from the ensuing detailed description taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION 
The invention will now be described in detail with reference to the 
drawings showing an embodiment thereof. 
FIG. 1 shows the arrangement of an actuator system of an occupant 
protective system according to the embodiment. In the figure, there is 
shown an actuator system of the occupant protective system for an air bag 
of same provided for the assistant driver's seat. The following 
description will refer to this actuator system alone, and drawings and 
description of an actuator system for an air bag provided for the driver's 
seat are omitted. The actuator system of the occupant protective system 
mainly comprises a deceleration sensor I for detecting deceleration acting 
on the vehicle, a deceleration signal-processing circuit 2 for evaluating 
a signal indicative of the detected deceleration supplied from the 
deceleration sensor 1, a squib 3 responsive to output from the 
deceleration signal-processing circuit 2 for actuating an air bag 6 and a 
power source 4 for feeding electricity to the squib 3. 
Connected to the deceleration signal-processing circuit 2 is an occupant 
detecting device 5 having a seat switch 5a formed e.g. of a piezo-electric 
element. The occupant detecting device 5 generates a signal when an 
occupant is seated in the assistant driver's seat. The deceleration 
signal-processing circuit 2 includes an amplifier 2a the input side of 
which is connected to the deceleration sensor 1, and the output side is 
connected to comparators 2d, 2e via a low-pass filter 2b and an 
integrating circuit 2c. The comparator 2d is directly connected to an OR 
circuit 2f, whereas the comparator 2e is connected to the OR circuit 2f 
via an AND circuit 2g. Further, also connected to the input side of the 
AND circuit 2g is the occupant detecting device 5. The OR circuit 2f is 
connected to the base of a transistor 2h, and the squib 3 is connected to 
the collector of same. A first threshold voltage V.sub.TH1 is supplied to 
an inverting input terminal of the comparator 2 e, while a second 
threshold voltage V.sub.TH2 higher than the first threshold voltage 
V.sub.TH1 is supplied to an inverting input terminal of the comparator 2d. 
The comparator 2e generates a high level output when voltage higher than 
the first threshold voltage V.sub.TH1 is supplied thereto from the 
integrating circuit 2c, while the comparator 2d generates a high level 
output when voltage higher than the second threshold voltage V.sub.TH2 is 
supplied thereto from same. 
The integrating circuit 2c integrates the signal indicative of the detected 
deceleration supplied thereto from the deceleration sensor 1 via the 
amplifier 2a and the low-pass filter 2b, and supplies voltage higher than 
a predetermined value to the comparators 2d, 2e only when shock having a 
predetermined or larger magnitude acts on the deceleration sensor 1 over a 
predetermined time period. 
The operation of the thus constructed occupant protective system according 
to the invention will be described with reference to the timing chart 
shown in FIG. 2. The symbols A, B, C, D, and E appearing in FIGS. 1 and 2 
indicate levels of outputs from the comparator 2e, the comparator 2d, the 
occupant detecting device 5, the AND circuit 2g, and the OR circuit 2f, 
respectively. 
If deceleration having a magnitude equal to or higher than a predetermined 
value is exerted on the deceleration sensor 1, the sensor 1 generates and 
supplies a signal indicative of the detected deceleration to the 
deceleration signal-processing circuit 2. The signal is amplified by the 
amplifier 2a, and has its high frequency components removed by the 
low-pass filter 2b. Then, the signal is integrated by the integrating 
circuit 2c, which supplies output voltage to the comparators 2d, 2e. 
When the output voltage from the integrating circuit 2c assumes a value 
higher than the first threshold value V.sub.TH1 and equal to or lower than 
the second threshold value V.sub.TH2, the comparator 2d does not generate 
a high level output (as indicated by B of FIG. 2). On the other hand the 
other comparator 2e operates in response to output from the integrating 
circuit 2c to generate a high level output (as indicated by A of same). On 
this occasion, if the assistant driver's seat is occupied, the seat switch 
5a is closed, so that a high level signal indicative of detection of the 
occupant is supplied from the occupant detecting device 5 to the AND 
circuit 2g (as indicated by C f same). Accordingly, the AND circuit 2g 
generates a high level output (as indicated by D of same), which is 
supplied to the OR circuit 2f. Then the OR circuit 2f generates a high 
level output (as indicated by E of same), which is supplied to the 
transistor 2h to turn it on, whereby electric current is supplied from the 
power source 4 to the squib 3. The squib 3 is heated to force nitrogen gas 
into the air bag 6, so that the air bag 6 is inflated to prevent the 
occupant from hitting against the windshield (t.sub.1 to t.sub.2 in FIG. 
2). 
In contrast, when there is no occupant seated on the assistant driver's 
seat in the above case, the signal indicative of detection of the occupant 
is not supplied to the AND circuit 2g, and hence the output from the AND 
circuit 2g remains low. Accordingly, the transistor 2h is not turned on, 
so that the squib 3 is not heated and hence the air bag is not inflated. 
On this occasion, the air bag for the driver's seat is inflated by the 
other actuator system, to thereby prevent the driver from hitting against 
the steering wheel etc. 
Next, when the output voltage from the integrating circuit 2c exceeds the 
second threshold value V.sub.TH2, the both comparators 2d, 2e operate, and 
the comparator 2d supplies a high level output to the OR circuit 2f (as 
indicated by B of FIG. 2, at t.sub.4 to t.sub.5. At the same time, the 
high level output from the comparator 2e is supplied to the AND circuit 2g 
(as indicated by A of FIG. 2, at t.sub.3 to t.sub.6), the output from 
which is dependent on whether the signal indicative of detection of the 
occupant is supplied thereto from the occupant detecting device 5. 
However, as mentioned as above, the high level output from the comparator 
2d is supplied to the OR circuit 2f, which in turn supplies the high level 
output to the base of the transistor 2h, so that the transistor 2h is 
turned on irrespective of the level of output from the AND circuit 2g, to 
thereby actuate the squib 3 to inflate the air bag. 
In other words, when shock having a magnitude larger than the larger 
threshold value acts on the vehicle, the air bag for the assistant 
driver's seat is inflated as well as the air bag for the driver's seat, 
irrespective of whether or not there is an occupant seated on the 
assistant driver's seat. The air bag for the assistant driver's seat is 
designed such that it covers the whole area of the windshield when it is 
inflated, so that the occupant on the driver's seat is more safely 
protected. 
Although, in the above described embodiment, an electric deceleration 
sensor is used as the deceleration sensor, this is not limitative, but two 
mechanical deceleration/acceleration sensors may be used, which operate 
upon occurrence of shocks having two different magnitudes corresponding 
respectively to two threshold values of voltage supplied to the 
comparators 2e, 2d. Even the use of each mechanical sensors can provide 
the same effects as provided by the above described embodiment.