Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-03-25
2001-03-13
Wu, Daniel J. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C330S146000
Reexamination Certificate
active
06201480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for measuring a seat weight including a weight of a passenger sitting on an automotive seat and more specifically to a seat weight measuring apparatus with advantages of being able to reduce costs or improve reliability of a circuit portion that determines the weight of the sitting passenger.
2. Description of a Related Art
Automobiles are equipped with seat belts and airbags to secure safety for passengers. In recent years, there is a trend for controlling the operation of such safety devices according to the weight of a passenger for improved performance of seat belts and airbags. For example, the amount of gas introduced into the airbag or an airbag inflating speed and a pre-tension of the seat belt are adjusted according to the weight of a passenger. For that purpose, means are needed for measuring the weight of a passenger sitting on a seat. An example of such means, which has been proposed by the applicant of this invention, involves arranging load sensors (strain gauges) at four corners of the bottom of a seat, measuring vertical loads acting on the strain gauges as voltages by electric circuits, and summing these voltages to determine the seat weight including the weight of a passenger.
First, the basic configuration of the electric circuits used in the above seat weight measuring apparatus will be described.
FIG. 9
shows a circuit configuration for one load sensor.
This sensor circuit
20
includes a power supply
21
for applying a predetermined voltage, a load sensor
22
of a full bridge configuration having four resistors R
1
-R
4
, an amplifier
23
for Amplifying the voltage from the load sensor
22
, and a positive polarity wire
24
and a negative polarity wire
25
for connecting the load sensor
22
to the amplifier
23
. This load sensor
22
has four strain gauges (not shown) attached to a sensor plate (not shown) that deflects when applied with a load, with a resistance of each resistor R
1
-R
4
changing according to the amount of strain of each strain gauge. The load sensor
22
is formed as a full bridge circuit including four resistors R
1
-R
4
so that it can cancel the strain change due to temperature change and the voltage change of the power supply
21
.
FIG. 10
shows a circuit configuration for all load sensors incorporated in the seat weight measuring apparatus.
The sensor circuit
26
includes load sensors
22
a
-
22
d
located at four corners of the bottom of a seat, amplifiers
23
a
-
23
d
connected to the respective load sensors
22
a
-
22
d
, positive polarity wires
24
a
-
24
d
and negative polarity wires
25
a
-
25
d
for connecting the load sensors
22
a
-
22
d
to the amplifiers
23
a
-
23
d
, an adder
27
for adding up voltages output from the amplifiers
23
a
-
23
d
, and a seat weight calculator
28
for determining the weight of the seat based on the voltage from the adder
27
. Each of the load sensors
22
a
-
22
d
is supplied with a predetermined voltage.
In
FIGS. 9 and 10
, the strain gauges forming the load sensor
22
are deformed by a vertical load from the seat (not shown). The amounts of strain of the strain gauges determine the resistances of the resistors R
1
-R
4
of the load sensor
22
. When a predetermined voltage is applied from the power supply
21
to the load sensor
22
as a resistor circuit, a voltage as determined by the supply voltage and the resistances (R
1
-R
4
) is applied to the amplifier
23
, which amplifies the voltage before outputting it to the adder
27
. The adder
27
adds up voltages from the four amplifiers
23
a
-
23
d
and outputs the sum voltage to the seat weight calculator
28
. The seat weight calculator
28
calculates the weight of the seat according to the voltage from the adder
27
.
In this way, the load from the seat can be measured by the load sensors located at four corners of the bottom of the seat.
In the seat weight measuring apparatus such as shown in
FIGS. 9 and 10
, however, each of the load sensors requires one amplifier and two wires (for a positive polarity and a negative polarity). Thus, a total of four amplifiers and eight wires are needed, giving rise to a problem of increased circuit and wiring costs. As the number of constitutional components increases, the probability of parts failure also increases, deteriorating the overall reliability of the sensor.
Japanese Patent Publication No. JP-A-10-297334 discloses a passenger weight detection apparatus that calculates a gravity center of a loaded seat based on a seat weight detected from a load acting on a front part of the seat and a seat weight detected from a load acting on a rear part of the seat and which corrects the seat weight according to the calculated gravity center and then, based on the corrected seat weight, estimates the weight of a passenger.
This official gazette, however, does not disclose a circuit configuration of the passenger weight detection apparatus. If a circuit configuration such as shown in
FIGS. 9 and 10
is used, this apparatus still has drawbacks of increased circuit and wiring costs and, because of a large number of constitutional parts, increased probability of parts failure which in turn degrades the overall reliability of the sensor.
SUMMARY OF THE INVENTION
The present invention has been accomplished with a view to overcoming these problems and its objective is to provide a seat weight measuring apparatus that can simplify the wiring between the sensors and the amplifiers and the sensor circuit configuration to reduce the circuit costs and improve the reliability. It is also an object of this invention to provide a seat weight measuring apparatus which, in the event of a failure of the load sensors, can immediately detect the sensor failure thereby improving the reliability.
To achieve the above objectives, the seat weight measuring apparatus according to the present invention, which measures a weight of an automotive seat including a weight of a passenger sitting on the automotive seat by detecting loads at a plurality of portions of the automotive seat, includes: a plurality of load sensors arranged at the plurality of portions of the automotive seat, each load sensor having at least one of a first output terminal and a second output terminal, the first and second output terminals having opposite polarities to each other; a detection means for detecting a difference between a signal output from the first output terminal of one load sensor and a signal output from the second output terminal of another load sensor; and a calculation means for calculating the weight of the automotive seat based on an output from the detection means.
According to the present invention, an output of one load sensor is connected in opposite polarity with respect to an output of another load sensor to form a bridge circuit as a whole. This can simplify the circuit configuration of the seat weight measuring apparatus. Further, because the circuit can be formed integral with the load sensors, the number of wires and components can be reduced, which in turn eliminates the problems of circuit costs and reliability.
REFERENCES:
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patent: 5570903 (1996-11-01), Meister et al.
patent: 5612876 (1997-03-01), Zeidler et al.
patent: 5624132 (1997-04-01), Blackburn et al.
patent: 5739757 (1998-04-01), Gloutsos
patent: 5821432 (1998-10-01), Sidler et al.
patent: 5988000 (1999-11-01), Adams
Kanesaka & Takeuchi
Takata Corporation
Tweel , Jr. John
Wu Daniel J.
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