Inflatable air bag safety device for motor vehicles

An improved inflatable passenger side air bag safety device for motor vehicles for detecting the presence or absence of a passenger positioned on or in front of a particular passenger vehicle seat. The safety device comprises a control unit for the intelligent triggering of the propellant charge for the air bag when a triggering event is detected, such as an impending collision, and the presence of a passenger is also detected. The control unit receives signals from a pair of switches, electrically connected in parallel to one another, including a first seat switch for detecting the presence or absence of a sitting passenger and a second foot switch for detecting the presence or absence of a standing, kneeling, or sitting passenger in the region in front of the vehicle seat. In the preferred embodiment both switches are flat, contact type switches, each having a broad surface area and are activated when subjected to the weight of a passenger from above. An acceleration sensor is also connected to the control unit for signaling the event of an impending collision. In an alternate embodiment the foot switch is a condenser-type switch in the form of a metallic screen interwoven within the floor carpet and detects fluctuations in the magnetic and electric fields corresponding to the presence or absence of a passenger positioned over the floor carpet. The air bag associated with the vehicle seat is caused to be activated during a triggering event if either of the seats switch and/or foot switch are activated by a passenger.

FIELD 
The invention relates in general to an improved safety device for 
triggering a passenger side air bag. More particularly, the invention 
relates to an improved passenger side air bag safety device wherein two 
sensors are provided to detect the presence of the passenger, including a 
first sensor located in the passenger seat for detecting the presence or 
absence of a seated passenger and a second sensor located under the floor 
carpet adjacent the passenger's foot area to detect the presence of a 
passenger who might be standing, kneeling or sitting on the floor board 
area in front of the passenger seat. Both sensors are electrically 
connected in parallel to a control unit which also receives a signal from 
an acceleration sensor which detects an impending collision. The control 
unit triggers the passenger side inflatable air bag when it has received a 
signal from the acceleration sensor and a definite signal from the seat 
and/or foot sensor. 
BACKGROUND 
It is known in the prior art to provide a driver's side inflatable air bag 
and place it within the steering wheel underneath an impact plate. It is 
also known from the prior art to provide an inflatable air bag for the 
other passenger seats, and in particular, the front passenger seat, 
whereby the passenger side air bag is inflated by ignition of a propellant 
charge, which is triggered by a signal detected by a known acceleration 
sensor whenever there is a heavy impact experienced. 
A disadvantage which arises with current state of the art passenger side 
air bags is the triggering of an air bag when the passenger seat is not 
occupied. A needlessly inflated air bag creates a sudden pressure wave 
within the passenger compartment, which may be harmful to the driver and 
other passengers. Furthermore, when a passenger side air bag is inflated 
in the absence of a passenger to be protected, considerable and 
unnecessary repair or replacement costs result in order to restore the 
system. This is especially true if the passenger side air bag has been 
integrated with other vehicle parts, (e.g., as the dashboard) and the 
parts are torn off or broken at pre-determined breaking points. Thus, it 
becomes very costly to repair the car interior after the inflatable air 
bag has been used. In the event of a minor accident with a modest repair 
cost, a needless triggering of a passenger side air bag may make the cost 
of repair so high that it may be more economical to consider the vehicle 
as totalled. 
The prior art is replete with methods to control the triggering of a 
passenger side air bag so that it is inflated only when the passenger may 
benefit from its use. It is known from DE-OS 21 34 590 and DE-OS 37 02 825 
how to arrange a seat contact switch exposed on the passenger seat so that 
the switch responds mechanically to the weight of a seated passenger in 
order to detect the presence or absence of a passenger on that particular 
seat. Each seat contact switch is connected to a control unit which 
controls the triggering of each air bag such that the air bag for a 
particular passenger is only triggered when that passenger has been 
detected on the seat by the appropriate seat contact switch. 
A safety device having a seat contact switch of the above type is also 
known from DE-OS 25 16 185. This known safety device discloses a seat 
contact switch which is used to detect an empty seat, whereby the 
associated air bag is still triggered, but is only partially inflated, 
thus posing a lesser risk of sudden-pressure and related safety problems 
associated with the needless inflation of an unused air bag. 
From the above described prior art safety systems, it becomes evident that 
two operating conditions must be simultaneously satisfied for the useful 
activation of the passenger side air bag. First, there must exist an 
appropriate level of severity of an accident such that the acceleration 
sensor will send a signal which has exceeded a pre-set threshold value to 
the control unit which controls the triggering of the passenger side air 
bag. And second, a passenger must physically occupy the particular 
passenger seat in order to activate the seat contact switch and send the 
signal corresponding to "seat occupied condition" to the control unit so 
that it knows that all conditions are satisfied to inflate the air bag. 
A common disadvantage with the above described methods exists since, in 
many instances, the seat contact switch does not respond to the presence 
of a passenger when that passenger is standing (such is often the case 
with children), kneeling on the floor, or sitting in a forward portion of 
his seat. When the seat switch does not respond, the air bag is not 
triggered by an impact, thus rendering the protective system ineffective. 
DE-PS 38 05 887 teaches to provide a seat contact switch which is 
mechanically activated by the body weight of a sitting person whereby the 
seat switch may detect the body weight of a person as he shifts his weight 
over a broad area of the seat surface. The seat contact switch comprises a 
sandwich-type switch mat, having a pair of spaced contact layers which are 
separated by an elastically deformable, electrically insulating 
intermediate layer. This intermediate layer, being electrically conductive 
in the vertical direction, completes the circuit between the two contact 
layers as it is elastically deformed (compressed) when under the influence 
of the body weight of a seated person. 
Seat switches of non-contact operation are also known in the prior art and 
are disclosed in DE-OS 36 35 644 wherein the seat switches comprise a 
condenser having two electrodes opposite to each other on the seat, such 
that an electrical field is set up between them. The capacity of the 
condenser changes with respect the presence or absence of a person on the 
seat. By sensing this capacity change, it is possible to detect the 
presence or absence of a person on the seat 
It is also known from DE-OS 38 09 074 how to determine various sitting 
positions or the position of the center of gravity of the seated 
passenger, such as in a forward bending position, by placing several known 
pressure sensors in a pre-selected arrangement on the seat. This German 
patent document also teaches how to activate and inflate an associated air 
bag in accordance with the particular sitting position of the seated 
passenger. 
In another known device for recognizing whether a vehicle seat is occupied 
or not, a distance measuring sensor is used instead of a seat switch to 
detect the presence of a passenger. This type of distance measuring sensor 
is typically provided on the dashboard and uses a radar-type method 
wherein a pulse is emitted in a direction towards the seated passenger 
and/or seat back. The pulse and echo are then reflected back either by the 
seat back (if the seat is empty) or by the stomach or chest region of the 
passenger (if the seat is occupied). The distance between the dashboard 
and the seat back or passenger is calculated from the pulse-echo travel 
time process and thus, the presence or absence of a person in the vehicle 
seat can be determined. This information is then used to determine whether 
or not the air bag for the passenger seat should be activated. This method 
requires the use of additional sensors to determine the particular 
position of a seat to account for horizontal fore-aft adjustment and 
angular tilt of the seat back. While this type of pulse-echo travel time 
process makes it possible to determine whether the region in front of the 
seat is occupied by a standing, kneeling, or sitting person, (while the 
traditional seat sensor would indicate the seat as empty), it is very 
costly to implement in view of the large manufacturing and installation 
expenses associated with the many seat location sensors involved. 
Thus, there is a significant need in the art to provide a simple and low 
cost safety device for passenger side inflatable air bags to detect a 
passenger irrespective of whether the passenger is seated or positioned in 
front of the passenger seat. There is also a need in the art for an 
improved safety detection device which is able to distinguish between the 
presence of a passenger from luggage or other objects placed in front of 
or on the passenger seat, so that the inadvertent activation of the 
passenger side air bag is not caused to occur. 
THE INVENTION 
Objects 
It is among the objects of the invention to provide a safety device for 
passenger side inflatable air bags which is able to detect the presence or 
absence of a passenger seated on or positioned in front of the passenger 
seat; 
It is another object of the invention to provide an improved safety device 
for passenger side inflatable air bag whereby two sensors are connected in 
parallel, including a first sensor associated with the passenger seat and 
second sensor associated with the floor mat area in front of the passenger 
seat and in which either sensor will detect the presence of a passenger 
independently of the other sensor; 
It is another object of the invention to provide an improved safety device 
for passenger side inflatable air bags, whereby the safety device is 
simple to operate and can be implemented for low cost; 
It is yet another object of the invention to provide an improved safety 
device for passenger side inflatable air bags which includes means for 
distinguishing between the presence of a passenger to be protected and 
luggage or other objects stored in the passenger area such that 
inadvertent activation of the associated passenger side inflatable air bag 
is not caused to occur. 
And still other objects will be evident from the following specification, 
drawing, and claims.

SUMMARY 
The objects of the invention are achieved by providing a second switch in 
the safety circuit for a conventional air bag safety mechanism of the type 
containing a delay sensor, such as an acceleration sensor, for detecting 
the direction and magnitude of a collision of the vehicle as identifying a 
triggering incident for the air bag, and a first seat switch for detecting 
the presence or absence of a passenger seated on a vehicle seat located in 
front of the inflatable air bag. The second switch is in the form of a 
foot switch located on the floor in front of the vehicle seat and thus 
makes possible the detection of a passenger who may be standing, kneeling, 
or sitting in the floor region in front of the vehicle seat. Thus, the 
presence of a passenger is detected irrespective of whether the seat 
switch fails to positively detect the presence of a passenger partially on 
or completely off the vehicle seat, and this signal is sent to the control 
unit to inflate the air bag when an accident is occurring. 
According to the invention, two conditions must be satisfied before the 
propellant charge associated with the air bag is ignited and the air bag 
is inflated. The first condition is the detection of the triggering event 
by the acceleration sensor and the second condition is the presence of a 
passenger by either the foot and/or seat switch. According to the 
invention, both the foot switch and seat switch are electrically connected 
in parallel, thus either activation of the foot switch, or seat switch, or 
both switches simultaneously will result in satisfying the second 
condition for activating the inflatable air bag. 
In a preferred embodiment, the foot switch is the form of a flat, 
sheet-like or mat-like element in order to provide a broad survey area in 
front of the vehicle seat. This flat, sheet-like element may either be 
arranged under the floor carpet or integrated into the floor carpet, 
depending on the particular type of switch which is to be used. For 
example, in a preferred embodiment the foot switch may be a simple 
electro-mechanical contact-type switch which is activated by detecting the 
presence of the weight of a passenger thereover. This physical-type 
contact switch may also be provided with known force and/or pressure 
measuring devices which provide a broader range of contact response other 
than a simple on/off response. In particular, it may make an evaluation of 
force and/or pressure distribution patterns to make accurate distinctions 
between persons and other articles stored on the floor carpet, such as 
luggage. 
An alternate embodiment of the foot switch includes a pair of electrodes 
connected to a metal screen or metal loops which may be worked into the 
floor carpet, thus forming a condenser element which can determine the 
presence or absence of a person through changes in the magnetic or 
electric fields over the floor carpet. The floor carpet is preferably 
removable, such as by pulling up sideways, so that easy and quick 
replacement of this type of non-contact foot switch is made possible. 
The control unit is also programmable with software to provide an override 
feature for the safety device of this invention for the conditions when 
the presence of a passenger is not positively detected by either the seat 
switch or foot switch so that the air bag will always be inflated when a 
triggering incident is detected by the acceleration sensor. 
The air bag safety device of this invention is particularly well-suited for 
protection of small children who may be standing, kneeling, or sitting in 
the floor board region between the dashboard and the front passenger seat, 
but is also easily implemented for use in protecting rear-seated 
passengers as well. 
DETAILED DESCRIPTION OF THE BEST MODE 
The following detailed description illustrates the invention by way of 
example, not by way of limitation of the principles of the invention. This 
description will clearly enable one skilled in the art to make and use the 
invention, and describes several embodiments, adaptations, variations, 
alternatives and uses of the invention, including what I presently believe 
is the best mode of carrying out the invention. 
The Figure is a schematic view of the interior 1 of a motor vehicle wherein 
a passenger seat 2 is shown to be fastened to the vehicle floorboard 3 and 
positioned with respect to the dashboard 4 in the conventional manner. The 
dashboard 4 is also provided with an inflatable air bag (not shown) which 
is adapted to break out from the dashboard to inflate within the interior 
1 in a manner to provide a recoil-free air cushion for a forward moving 
passenger during a collision of the appropriate severity. 
The seat cushion 5 of the passenger seat 2 is also provided with a seat 
switch 6 for detecting the presence or absence of a passenger seated 
thereon. The seat switch 6 is preferably of a known flat matlike contact 
switch of the type shown in DE-PS 38 05 887 wherein two contact layers are 
separated by an intermediate elastically deformable, electrically 
conductive layer, which contact switch is mechanically activated when the 
body weight of the seated passenger compresses the intermediate layer and 
completes a conductive pathway for the switching circuit. This type of 
contact switch permits the detection of a seated passenger over a wide 
survey area of the seat cushion surface 5 and is especially useful in 
detecting a passenger who may be shifting his position in the seat or 
leaning forward. It is understood that a simple physical contact switch or 
a condenser-type switch may also be used with equally good results. The 
seat switch 6 is part of the electric circuit comprising the control unit 
13 and lower foot switch 10 and is connected to the control unit 13 via 
lead wires 7 and 8. 
The foot switch 10 is preferably disposed under the floor carpet 9 in the 
area in front of the passenger seat 2 and is connected to the control 
circuit 13 via lead wires 11 and 12. The foot switch 10 and seat switch 6 
are connected in parallel to the control unit 13. Other elements of the 
electric circuit which are not shown include an acceleration sensor for 
the detection of a collision of the appropriate severity, and the physical 
connections to the triggering mechanism (i.e., propellant charge) of the 
inflatable air bag which is activated upon the appropriate signal 
generated by the control unit when all conditions for operation have been 
met. These other elements are well known in the art and are merely 
included in this discussion for completeness. The safety device of this 
invention operates as follows: 
Condition One 
A first condition for the activation of the air bag requires that a certain 
force of impact of the vehicle or sudden deceleration be detected by the 
acceleration sensor, whereby the sensor sends a signal to the control unit 
13 that the air bag should be triggered. Triggering of the air bag results 
from the ignition of a propellant charge associated with the inflatable 
air bag to begin the inflation process. The control unit is program driven 
and is also monitoring the operational states of the floor switch 10 and 
the seat switch 6. 
Condition Two 
The second condition which must be satisfied before the air bag is 
activated is that either one or both of the switches are closed, i.e. 
either seat switch 6 or foot switch 10 are closed. This indicates that the 
presence of a passenger is detected in the region adjacent the dashboard 
area. That is, the passenger may be either seated, (i.e., seat switch 6 is 
closed) or may be kneeling, standing, or otherwise positioned on the floor 
carpet 9 in front of the seat cushion 5 (i.e., foot switch 10 is closed). 
In either case, the control unit 13 is signalled that a passenger is 
present and this information is sent to the triggering device (not shown) 
for the inflatable air bag so that the air bag is inflated in time to 
protect the passenger in the event a collision of the appropriate severity 
is detected by the acceleration sensor according to condition one. 
While the Figure shows the safety device for the inflatable air bag of this 
invention in use for a front seated passenger, it is understood that the 
principles of this invention are applicable to all passengers within a 
vehicle including the rear seated passengers, irrespective of whether they 
are seated or positioned in the floor board area adjacent to the rear seat 
cushions. Thus, this invention is particularly well-suited to protect 
small children who may be predisposed to standing or kneeling in the 
floorboard areas adjacent the rear passenger seats. 
In a preferred embodiment of the invention the foot contact switch is in 
the form of a flat, sheet-like or mat-like element so that the detection 
of a passenger over a broad area is achieved. Known mat-type contact 
switches which are activated by the weight of the passenger may be used 
for this purpose. The mat-type foot contact switch 10 may be arranged 
underneath the floor carpet or even formed into the floor carpet if 
desired. 
It is also preferable to incorporate known force and/or pressure measuring 
devices in combination with the floor contact switch to permit more 
precise switch response. In accordance with this type of foot contact 
switch, the control unit 13 may be provided with appropriate software to 
evaluate force and pressure distribution patterns associated with this 
type of foot contact switch and fore/pressure measuring device to 
facilitate distinctions between the presence of a passenger kneeling, 
standing or sitting on the floor carpet 9 and other articles such as 
luggage which may be stored on the floor carpet 9 for which it is not 
necessary to inflate the air bag. In this way it becomes possible to 
deactivate the air bag should only luggage be detected by the floor 
contact switch 10. 
A first alternate embodiment for the foot switch may include the 
elastically deformable contact switch as disclosed in DE-PS 38 05 887. The 
switch may be located under the floor carpet or formed into the floor 
carpet. In a second alternate embodiment, the schematically shown foot 
switch 10 may take the form of a switch working on the non-contact 
principle such as the switch disclosed in DE-OS 36 35 644. In this 
embodiment the foot switches are preferably in the form of metal screens 
or metal loops which are integrated into the floor carpet to permit a 
determination as to the presence or absence of a person through changes 
measured in the magnetic or electric field set up by this switch. It is 
preferable to interweave these metallic screens or loops into the floor 
carpet so that it may be pulled up sideways for periodic removal and 
replacement. 
An override feature to the safety device of this invention may be 
implemented so that the passenger side air bag will always be inflated 
should either the foot or seat switches fail to definitely detect the 
presence of a passenger when a triggering incident is present by an 
external accident of the appropriate severity. This override feature can 
be insured through known means, for example, such as with appropriate 
software provided to the control unit 13. Alternately the override may be 
the reverse, to not trigger in the presence only of luggage on the floor 
and/or seat. 
It should be understood that various modifications within the scope of this 
invention can be made by one of ordinary skill in the art without 
departing from the spirit thereof. I therefore wish my invention to be 
defined by the scope of the appended claims in view of the specification 
as broadly as the prior art will permit.