Communications: electrical – Land vehicle alarms or indicators – Of collision or contact with external object
Reexamination Certificate
1996-03-04
2001-01-16
Pope, Daryl (Department: 2736)
Communications: electrical
Land vehicle alarms or indicators
Of collision or contact with external object
C340S429000, C340S903000, C280S735000, C280S734000, C180S268000, C701S301000
Reexamination Certificate
active
06175299
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to techniques for processing analog signals, and more specifically to systems for processing analog accelerometer signals for determining airbag deployment.
BACKGROUND OF THE INVENTION
Airbag systems are commonly used in automotive applications to provide protection for the vehicle operator and/or passenger in the event of a vehicular collision. A popular technique for implementing an airbag system includes detecting vehicular acceleration via an accelerometer and then evaluating the resulting acceleration signal to determine whether an impact of sufficient severity has occurred to require the airbag to deploy.
Most acceleration-based airbag systems utilize a microprocessor to evaluate the acceleration signal. As is known in the art, such microprocessor use permits evaluation algorithms to be easily implemented in software. In so doing, the input analog acceleration signal is converted to a digital word, and all subsequent signal processing by the microprocessor is implemented digitally.
An example of one known microprocessor-based system for evaluating an acceleration signal is shown in
FIG. 1
as system
10
. Referring to
FIG. 1
, system
10
includes an accelerometer
12
which may be a micro-machined piezoresistive sensor whose differential analog output voltage (S+−S−=V
IN
) is proportional to the applied acceleration. The differential acceleration signals S+ and S− are applied to signal conditioning circuitry
14
via signal lines
16
and
18
, respectively. The signal conditioning circuitry typically includes a gain stage and temperature compensation circuitry, and provides a conditioned acceleration signal V
OUT
at output
20
. A microprocessor
24
is provided to evaluate V
OUT
and includes an input
22
connected to output
20
via signal path
26
. Microprocessor
24
receives the conditioned analog acceleration signal V
OUT
, converts the analog signal to a digital signal, and implements a software algorithm to evaluate the digital signal and determine whether the airbag should be deployed. Microprocessor
24
then controls airbag deployment circuitry via signal path
28
.
Software algorithms for evaluating acceleration signals to determine airbag deployment may be implemented in a number of ways. A conventional approach is to use a time-dependent algorithm wherein the algorithm begins when a predefined level of acceleration is exceeded. With the time-dependent approach, the digital acceleration signal is digitally integrated within microprocessor
24
, and the resulting predetermined velocity curve is evaluated against a predetermined curve to determine if a deploy event has occurred. Referring to
FIG. 2
, this approach is shown graphically.
FIG. 2
shows a plot of velocity versus time wherein curve
30
represents the maximum velocity allowed before a deploy is required, and curve
40
represents a velocity below which a deploy event should not occur and below which system
10
is reset. The break points and relative slopes of curves
30
and
40
can be adjusted by software to optimize system
10
for various vehicular applications. Additional breakpoints and slopes can be added, so long as there is sufficient memory in microprocessor
24
to store such data.
The foregoing microprocessor-based system and implementation thereof has a number of drawbacks. First, system
10
is designed around a process optimized for digital circuits, which requirements are inconsistent with the requirements for processing of analog signals such as those provided by analog accelerometer
12
. Second, microprocessors are typically large and complicated integrated circuits, resulting in significant cost and area penalties for the circuit and system designers. Third, variations in the accuracy of accelerometer
12
, along with the finite resolution of the data converter of microprocessor
24
, requires curves
30
and
40
of
FIG. 2
to be some minimum distance apart. This limits the accuracy of the algorithm and may delay a deployment of the airbag beyond the time when deployment should actually occur. Moreover, the finite resolution of the data converter of microprocessor
24
introduces error into the algorithm which can be cumulative, and in some cases unacceptable. Fourth, most low cost microprocessors process data at a relatively slow rate. This limits the number of break points and slopes which can be used in a time-dependent algorithm, which may then result in missing important information which occurs at too rapid a rate for the digital system to handle (known in the art as aliasing).
To avoid the foregoing drawbacks of a microprocessor-based acceleration signal evaluating system, it is desirable to implement an analog signal processing system for evaluating the analog acceleration signal. However, implementation of a time-dependent analog algorithm is a difficult task and very area intensive in the design of integrated circuitry to accomplish such an algorithm. What is therefore needed is an analog signal processing system implementing a time-independent algorithm to thereby eliminate or minimize the resolution constraints associated with data converters, and significantly reduce timing uncertainty and aliasing problems. An added benefit of implementing a time-independent algorithm is that it avoids secondary events, such as hitting a curb, for example, having any effect on the analog deployment algorithm.
SUMMARY OF THE INVENTION
The forgoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, an analog signal processing system for determining an airbag deployment signal from an analog acceleration signal comprises means for converting the analog acceleration signal to a first analog velocity signal, means for providing a first deployment signal if the first analog velocity signal exceeds a first analog reference signal, and means responsive to said first deployment signal for generating the airbag deployment signal.
In accordance with another aspect of the present invention, an analog signal processing system for determining an airbag deployment signal from an analog acceleration signal comprises a first analog signal processing circuit having a first analog reference signal associated therewith corresponding to a first velocity level, wherein the first circuit receives the analog acceleration signal and provides a first analog velocity signal corresponding thereto. The first circuit further provides a first output signal if the first analog velocity signal exceeds the first analog reference signal, and otherwise provides a second output signal. A logic circuit receives the first and second output signals and performs a logic operation thereon to provide the airbag deployment signal.
In accordance with yet another aspect of the present invention, a time independent method of determining an airbag deployment signal from an analog acceleration comprises the steps of: converting the analog acceleration signal to a first analog velocity signal; comparing the first analog velocity signal to a first analog reference signal corresponding to a first velocity and providing a first output signal if the first analog velocity signal exceeds the first analog reference signal and otherwise providing a second output signal; and performing a logic operation upon the first and second output signals and providing the airbag deployment signal therefrom.
One object of the present invention is to provide an analog signal processing system for determining airbag deployment conditions, wherein the system does not require or include a digital computer or similar digital signal processing arrangement.
Another object of the present invention is to provide a time-independent method of processing analog acceleration signals to determine airbag deployment conditions.
REFERENCES:
patent: 5285187 (1994-02-01), Hirao et al.
patent: 5436838 (1995-07-01), Miyamori
patent: 5445413 (1995-08-01), Rudolf et al.
patent: 5657831 (19
Kosiak Walter Kirk
Liu Jiyao
Manlove Gregory Jon
Ravas Richard Joseph
Delco Electronics Corporation
Funke Jimmy L.
Pope Daryl
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