Trigger system for a vehicular passenger restraint system

To facilitate assembly and provide for high-level output from a deceleration sensor which provides, inherently, only very low level output, an evaluation circuit, such as an amplifier structure, is connected immediately adjacent the deceleration sensor on a common metal plate, interconnected thereby by bonding wires, the common plate having connecting pins (18) passing therethrough for connection to a standard plug-and-socket connector; the evaluation circuit and the deceleration sensor are enclosed within a common sealed housing, so that both the deceleration sensor (12, 12') as well as the evaluation circuit (16, 17) are sealed against ambient influences, preferably retained within a high-viscosity fluid, such as insulating oil. All elements can be located on one side of the housing, in which a standard T5 transistor housing is suitable; or the deceleration sensor may be located on the other side of the metal plate (10) from the evaluation circuit, in which case a plastic housing can be used, only the deceleration sensor being secured to the metal plate by a metal housing cap, sealed to the metal plate.

Reference to related application, assigned to the assignee of the present 
invention, the disclosure of which is hereby incorporated by reference: 
U.S. Ser. No. 631,933, filed July 19, 1984, MATTES et al now U.S. Pat. No. 
4,614,876. 
The present invention relates to passenger restraint systems for automotive 
vehicles, and more particularly to the construction of a combined 
deceleration sensor and evaluation circuit therefor. 
BACKGROUND 
The literature reference referred to above describes a triggering 
arrangement for a passenger restraint system which, selectively, may be 
either a seat-and-lapbelt or other belt tensioning device, or, for 
example, an airbag. The literature describes such a system in which an 
accelerometer, or, more accurately, a deceleration sensor, senses 
deceleration of the vehicle of a magnitude representative of a collision 
or an impending collision, and provides an output signal to an evaluation 
circuit. The output signal then provides a triggering or firing signal to 
an electrical firing circuit which, for example by means of an explosive 
pellet or similar chemical reaction, causes immediate inflation of an 
airbag, or locking and/or tightening of a belting arrangement. The 
electrical portion of the system operates practically instantaneously; the 
chemical portion can operate later, and the separation between electrical 
operation and other operation is provided since, in case of a collision, 
electrical power may be interrupted by destruction of the electrical 
battery in the vehicle, or conductors and wires connected thereto. 
The signal levels supplied by the accelerometer, and processed within the 
evaluation circuit may be very low. It has previously been proposed--see 
U.S. Pat. No. 4,164,263, Heintz et al (to which German Patent Disclosure 
Document DE-OS No. 26 55 604 corresponds)--to locate the electrical 
portion of the evaluation circuit, including, if desired, the 
accelerometer in a separate restraint housing. This housing must be made 
specially, and introducing the respective elements therein is an expensive 
manufacturing and assembly operation, particularly since the accelerometer 
itself must be secured in a separate accelerometer housing or in a partial 
housing structure within the overall restraint housing element. 
THE INVENTION 
It is an object to so construct the triggering system or assembly of the 
passenger restraint system that it can be easily assembled within a 
housing which can be tight with respect to ambient changes, such as 
humidity, air pressure, and further is highly resistant to contamination, 
to thus provide a hermetically sealed overall structure. 
Briefly, at least one deceleration sensing element, and forming part of the 
deceleration sensing arrangement, since more than one deceleration sensor 
may be provided, is secured to a metal plate. A support carrier is 
provided, supporting the evaluation circuit, the support carrier in turn 
being secured to the metal plate. The evaluation circuit itself includes 
an integrated electronic circuit component. The metal plate is connected 
to a housing cap in an airtight structure, either forming a closing plate 
or being surrounded thereby if the various components within the housing 
structure are located on two sides of the metal plate. The support 
carrier, the metal plate, and the housing cap are all secured together 
into one structural integral unit, the housing cap retaining the metal 
plate in position. The metal plate may, simultaneously, function as a 
structural support element, securable to the vehicle for sensing of 
deceleration, and thus of sufficient strength to withstand deceleration 
resulting from an impact, while also acting as a cooling plate for the 
electrical components and as an overall support structure. 
The arrangement has the advantage that all the components can be simply and 
cheaply assembled, while being reliably attached to a plate which is of 
sufficient strength so that it can be applied to the vehicle and form this 
potentially life-saving sensing element. The housing structure, for 
example, may be a hat-shaped device, so that the overall element can be 
included within a standard transistor housing, for example the "T5" 
housing. The housing may, however, also surround the metal plate, the 
terminal elements passing through the metal plate. The metal plate, with 
the electrical and electronic components thereon, can be manufactured as a 
subassembly, the metal plate with all the components then being tightly 
secured in the housing, which is closed by the cover cap. The cover cap 
and the metal plate define a single, sealed chamber therebetween. The 
decelaration sensing arrangement as well as the evaluation circuit are 
thus retained in a single sealed chamber. 
In accordance with a preferred feature of the invention, current supply and 
signal supply terminals are passed through the metal plate, so that all 
terminal connections can be formed in one manufacturing step during 
manufacture of the metal plate, and separate termination elements, and 
their assembly costs can be eliminated. The respective electronic and 
electrical elements, and the current supply pins or leads themselves, can 
be connected similarly to the connection of integrated circuits, for 
example by bonding wires, with standarized bond connections. The 
externally extending connections, for example, can be in the form of 
connecting pins, so that the overall structure will fit into a standard 
multi-terminal electronic socket. 
The deceleration sensors, for example, may be piezoelectric strips. Such 
strips can easily be secured to a metal plate, which is deformed in the 
region of the acceptance of the strip by providing locating projections or 
locating bumps, so that the piezo-electric strip can be oriented on the 
metal plate during assembly. Electrical terminals to the piezo-electric 
strip then are connected over a ceramic socket or a metal socket for one 
terminal; the second terminal to the piezoelectric strip can be in the 
form of a small soldering area or solder plate, which retains a bonding 
plate connected to a standard bonding wire. The bonding plate and the 
soldering plate are then connected in well-known manner, the bonding 
plate, for example, being located on an insulating portion of a ceramic 
socket. This arrangement substantially simplifies the assembly and results 
in low manufacturing costs.

DETAILED DESCRIPTION 
A metal plate 10 (FIGS. 1, 2) forms, combined, a structural support and 
cooling element for various types of electronic components of the sensor. 
The metal plate 10 also forms a ground or chassis connection, and is 
adapted to be securely connected to a structural component of a motor 
vehicle. The metal plate 10 also forms a holding element for a base 11 for 
a piezoelectric deceleration sensor 12. The base 11 may be deformed from 
the major surface of the metal plate, and may include, for example, 
another metal plate or a ceramic plate, soldered or bonded to the top 
surface of metal plate 10, or integral with the metal plate 10 by a punch 
depression from below, resulting in a projection at the top side of the 
metal plate 10. The piezoelectric deceleration sensing element 12 is 
either soldered or bonded or adhered to the base 11. The deceleration 
sensor, preferably, is a dual piezoelectric strip, of well known 
construction extending essentially parallel to the metal plate 10. The 
base 11 forms one terminal, for example the ground terminal, for one of 
the electrodes of the deceleration sensor 12. The other electrode of the 
decleration sensor 12 has a solder plate 13 secured thereto, over which a 
bonding plate 14 is attached, for example by soldering or electrically 
conductive bonding. For precise positioning of the piezoelectric strip, at 
least three projecting bumps 15 are formed on the base 11. These bumps may 
be formed directly as projections from the base structure 11 during 
manufacture of the base structure 11, for example in a single punching 
operation from the bottom side of the metal plate 10 within a suitable 
die. 
A support carrier 16 for our evaluation circuit 17 is attached to the metal 
plate 10 in surface-to-surface engagement by a suitable adhesive, the 
metal plate 10 being formed with additional locating projections 15' to 
provide for proper positioning of the evaluation circuit support carrier 
16. Evaluation circuit 17 can be a standard integrated circuit of suitable 
amplifier construction to receive the signals from the deceleration sensor 
12. The evaluation circuit 17 itself is formed by an integrated circuit. 
Five connecting terminals 18 are carried through the metal plate 12, being 
insulated therefrom, by a standard insulating connecting pin arrangement. 
All the connecting pins, for example, are commonly embedded in an 
insulator 19, which is secured as a single element in the metal plate 10. 
The connecting pins 18, of course, can be individually passed through the 
metal plate 10 in insulated relation. Preferably, the insulated pins 18 
are part of a standard electronic plug-and-socket connection. 
The electrical connection of the evaluation circuit carrier 16 with the 
deceleration sensor 12 is provided by the metal plate 10, which forms the 
common ground or chassis or reference terminal. Connection to the pins 18 
as well as to the acceleration sensor is by bonding wires by well-known 
bond wire connection technology. 
In manufacture, the respective elements are secured to the metal plate 10, 
as noted by adhesion, soldering, and the like; then, the interconnections 
are made by connecting the bonding wires. A hat-shaped cover or cap 20 is 
then placed over the entire assembly, the interior is sealed, and the 
cover 20 is secured to the metal plate 10, for example by soldering, 
welding or other bonding or adhesion steps. The acceleration sensor as 
well as the evaluation circuit are thus combined into a single housing, 
totally sealed together, and shielded from external influences and noise 
signals. The top cover 20 likewise is of metal or of a metallized 
material, so that the deceleration sensor and evaluation circuit are all 
retained within a totally shielded enclosure. 
The metal plate 10 then can be secured in a suitable location, suitably 
oriented on a motor vehicle, for example by passing attachment screws or 
rivets through attachment holes 21, 22 (FIG. 1). FIG. 2 shows the top 
cover 20 in broken lines, so that the internal parts on plate 10 can be 
seen. 
The deceleration sensor 12 can be attached to the metal plate in various 
ways. For example, and referring to FIG. 3: A U-shaped base 30, of 
insulating material, preferably ceramic, is secured to the metal plate 10. 
It is attached to the metal plate by an adhesive or by a ceramic-to-metal 
bond, such as a solder or molten bond. The base 30 secures the 
piezo-electric strip 12 between the legs of the U. For electrical 
connection to the two sides of the deceleration sensor strip 12, socket 30 
is formed with two bores 31, 32, each, extending respectively to the upper 
and lower surfaces of the ceramic base 30. The deceleration sensing 
element 12 is then embedded in solder or a conductive plastic adhesive 
which extends also through the bores 31, 32; the electrically conductive 
fill within the bores 32 then effects electrical connection to the base 
plate 10; the conductive fill within the bores 31 effects electrical 
connection to the bonding plate 14. The bond plate 14 and/or the bottom 
plate 10 may be formed with projecting prongs extending into the openings 
31, 32, respectively, to improve the reliability of electrical connection 
through the fill within the openings 31, 32. 
The base for the deceleration sensor 12 can be in accordance with any other 
well-known construction; for example, an L-shaped base can be provided in 
which a solder and/or bonding plate 14 is directly attached to the top 
surface of the piezoelectric sensing element 12, the bottom thereof being 
connected similarly to the U-shaped construction shown in FIG. 3. 
Embodiment of FIGS. 4 and 5: The evaluation circuit 16 and the deceleration 
sensor 12' are again secured to the metal plate 10 but, in contrast to the 
embodiments of FIGS. 1-3, on respectively opposite sides. The deceleration 
sensor 12' is encapsulated in its own housing, which includes two 
connecting pins 23, 24 which extend through bores in the metal plate 10 to 
the top side thereof--on which the evaluation circuit is located. A second 
deceleration sensor 24 which, for example, may be a mercury switch, is 
included on the top side of the metal plate 10. It can be used, as 
disclosed in the referenced literature, to test the function of the 
deceleration sensor 12'. Metal plate 10 and the elements secured thereto 
are then included within a plastic housing 26 which, for example, may be 
constructed as a two-part element which is secured around the metal plate 
10 by an adhesive, or plastic-welded thereof. The housing 26 is formed on 
one side with a hollow recess 27 which, simultaneously, forms a receiving 
pocket for plug connections for the connecting pins 18, of which only two 
are shown in FIG. 4. 
The manufacturing sequence is to first pre-assemble all the elements on the 
metal plate, then place the metal plate within the plastic housing, with 
the top cover removed. This can be done effectively automatically. 
Connection of the bonding wires to the respective connecting pins, as well 
as internally, is then carried out, and thereafter a cover 28 is placed 
over the plastic housing for airtight closing thereof. The plastic housing 
can be open at the bottom, since the deceleration sensor 12' is retained 
within its own airtight casing, secured to the metal plate 10. The plastic 
housing is extended at the bottom of the metal plate 10 to provide for 
mechanical protection of the deceleration sensor 12'. 
The airtight housing prevents any spurious creep or sneak current paths, 
and thus attenuation of the very weak signals, which might, otherwise, 
occur for example by air humidity, formation of vapor condensation, and 
the like. In accordance with a preferred feature of the invention, the 
housing is filled with a highly viscous medium, for example oil. This oil 
filling can be used, both for insulation as well as for damping of the 
deceleration sensor. Various types of deceleration sensors may be used, 
and oil filling is particularly desirable if the deceleration sensor is 
not a piezo-electric element, but rather a bending-mass or bending-spring 
element which, preferably, should be damped. 
Various changes and modifications may be made, and various filling 
substances may be used, for example entirely or only partly filling the 
internal housing. The internal housing may be formed with a subdivision, 
for example for potting one portion thereof, and filling the remainder 
with oil, to form a damping fluid. 
In the embodiment of FIGS. 4 and 5, the housing portion surrounding the 
deceleration sensor 12', thus, preferably is a metal housing sealed to the 
metal plate 10 to provide for shielding of the deceleration sensor and to 
airtightly surround the deceleration sensor. The evaluation circuit which, 
preferably, is an amplifier, is adequately shielded by its integrated 
circuit structure and tight association with the metal plate 10 so that 
the surrounding airtight housing portion can then be made of plastic.