Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-07-23
2003-06-24
Beaulieu, Yonel (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S046000, C280S728100
Reexamination Certificate
active
06584387
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems for determining if a vehicle seat is occupied by a person and, if so, insuring that the air bag will protect the person during a collision as well as possible.
BACKGROUND OF THE INVENTION
An air bag comprises an inflatable bag and means for inflating the bag. Air bags are highly desired life saving devices that have performed well in many accidents and saved many lives. However, the bag must be inflated in a very brief time such as {fraction (1/30)} of a second which requires rapid movement of the bag from a stored and compacted state to a fully inflated state. The rapid deployment of the bag involves great force. A deploying bag can injure a person during the early phases of deployment if the person is very close to where the airbag is stored. Another hazardous circumstances is when the occupant is a baby in a rear-facing baby seat. It is also desired to inhibit deployment if there is no person in the seat. Much effort has gone into developing systems for characterizing the occupant and ascertaining the occupant position to meet this need. Proposed systems attempt to ascertain the distance from the inflator to the occupant and systems using sonic and optical ranging for that purpose are well known. These systems are deficient in that they cannot reliably distinguish between an occupant and other things such as road maps, beverage cups, packages and voluminous clothing which cause indications that the occupant is near the inflator. Known prior art systems operate to measure the distance from the inflator to the occupant, presumably because that is the physical variable most easily related to the potential for injury.
Many vehicles include an accelerometer located in the passenger compartment for sensing the deceleration of a crash. These accelerometers are incorporated in sensing and diagnostic modules or “SDMs” which are decision making centers for the vehicle occupant protection system. The output of the accelerometer may be integrated by an analog circuit or a microprocessor in the SDM to compute a difference between the velocity the vehicle was traveling before a crash and the velocity of the passenger compartment during the crash. The integral of the accelerometer output may be integrated again to obtain the second integral of the deceleration which is the displacement of a free body from its initial position relative to the vehicle. An occupant not wearing a seat belt is, to a good approximation, a free body. Therefore, this calculation provides the distance an unbelted occupant has moved from his or her initial position at any time during the crash. Vehicles typically include seat belt latched sensors for indicating seat belt usage.
Ultrasonic distance measurement based on measuring a time period beginning when sound is generated by a sound emitter and ending when an echo from a object at the distance to be measured is received by a receiver located at a point near the sound emitter is well known and has been used for many years in such as focusing systems for cameras. Using ultrasonic distance measurement to measure the distance from the back of a vehicle seat to the back of a seat occupant works well at larger distances that provide time for vibrations excited during the sound transmission to subside and leave the receiver responsive to low intensity sound.
Position and angle sensors are in commercial production for sensing the position of a seat on its track and the angle the seat is reclined.
Capacitive proximity sensors have been well known for many years and have many successful applications. In addition to measuring capacitance, the Q of the capacitance may be measured to provide additional information about the nature of the material being detected. Some materials including materials containing water tend to significantly reduce the Q of the sensed capacitance.
Ignoring the self inductance of the lead wires, a capacitor is conventionally viewed as a pure capacitor having capacitive reactance
X
C
=
1
2
·
π
·
f
(
frequency
)
·
C
(
capacitance
)
in series with an energy dissipating resistance R
C
and the combination has an impedance
Z={square root over (R
2
2
+X
C
2
)}
The Power Factor (PF) is defined as the ratio of the effective series resistance R
C
to the impedance Z and is usually expressed as a percentage.
The Dissipation Factor (DF) is the ratio of the effective series resistance R
C
to capacitive reactance X
C
and is usually expressed as a percentage. The DF and PF are essentially equal when the PF is 10 percent or less.
The Quality Factor (Q) is a figure of merit and is the reciprocal of the dissipation factor DF, Q=X
C
/R
C
.
Circuits for measuring capacitance and the Q of a capacitor are well known and are incorporated in many commercially available measuring instruments.
The concept of the impedance of a capacitor leads to measuring the capacitance of a capacitor by applying an alternating current voltage to the capacitor and measuring the displacement current through the capacitor. The impedance Z is equal to the applied voltage divided by the current, Z=V(voltage)/I(displacement current). The current leads the voltage by a phase angle (phi).
If the Q of the capacitor is large, R
C
can be ignored, Z and X
C
are approximately equal, and the capacitance is obtained directly from the displacement current and the frequency and voltage of the applied alternating current
C
(
capacitance
)
=
I
(
displacement
current
)
2
·
π
·
f
(
frequency
)
·
V
(
voltage
)
For smaller Q or greater precision, the capacitive reactance X
C
, the resistance R
C
, and the capacitance are calculated from:
X
C
=Z
·sin(phi)
R
C
=Z
·cos(phi)
C
=
1
2
·
π
·
f
(
frequency
)
·
X
C
The page 322 of the book
Electrical Instruments and Measurements
by Walter Kidwell and published in 1969 by McGraw-Hill, Inc. states that “Capacitance can be measured in a number of ways”. It further states “Generally, there are two practical ways of measuring capacitance:
“1. Absolute measurements in terms of other electrical units.”
“2. Comparison methods, where the unknown capacitor is compared with a known standard which has been previously calibrated.”
“Bridge methods are in the latter category, and it is to these methods that we shall confine our discussion on the following pages.”
The aforementioned book then proceeds to illustrate a Wien Bridge”, a “Generalized capacitance bridge”, a “Five terminal bridge network”, a simplified method of connecting a three terminal network, a “Schering bridge”, a “shielded Schering bridge”, and a bridge having a “Wagner ground”.
All of the capacitance bridges share the common feature of presenting an alternating current signal to the series combination of an unknown capacitor and a first known element(s) of the bridge. Other elements of the bridge with known properties form a second voltage divider producing a signal for comparison with the signal at the junction between the unknown capacitor and the first known element of the bridge. When the bridge is balanced, the amplitudes and phases of currents in all of the elements of the bridge can be calculated relative to the amplitude and phase of the alternating current signal. Therefore, the illustrated capacitance bridges operate by a process that determines the amplitude and phase shift of the current in the capacitor.
The following two paragraphs illustrate by using the examples of the Wien bridge and the Schering bridge cases of capacitance measurement accomplished by applying a signal to a first plate of a capacitor and observing the signal at the other plate of the capacitor.
FIG. 3
illustrates a Wien bridge. It is reproduced from
FIGS. 10-15
of the aforementioned book
Electrical Instruments and Measurements
. Pages 322 through 329 of this book describe methods for measuring capacitance. In
FIG. 3
the parallel combination of C
d
and R
d
represent respectively the lossless and lossy p
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