U.S. patent number RE41,790 [Application Number 11/417,251] was granted by the patent office on 2010-10-05 for seat belt tension prediction.
This patent grant is currently assigned to TK Holdings Inc.. Invention is credited to James G. Stanley.
United States Patent |
RE41,790 |
Stanley |
October 5, 2010 |
Seat belt tension prediction
Abstract
A vehicle seat belt tension prediction system and method
comprises an accelerometer having an output signal responsive to
vertical acceleration of the vehicle, a seat weight sensor having
an output signal responsive to the force exerted by a mass resting
on the seat, and a processor means for calculating seat belt
tension. The processor is provided with a plurality of inputs
operatively coupled to the accelerometer output and seat weight
sensor output. Suitable programming is provided to instruct the
processor to calculate the average mass resting on the vehicle seat
and predict the force that should be exerted on the seat for a
measured level of vertical acceleration assuming zero belt tension.
The processor then compares the actual force measured by the seat
weight sensor with the predicted force to determine seat belt
tension thereby obviating the necessity of complex hardware in
physical contact with the seat belt system.
Inventors: |
Stanley; James G. (Novi,
MI) |
Assignee: |
TK Holdings Inc. (Auburn Hills,
MI)
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Family
ID: |
26723686 |
Appl.
No.: |
11/417,251 |
Filed: |
May 4, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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10326170 |
Dec 19, 2002 |
Re. 40096 |
|
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60046233 |
May 12, 1997 |
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Reissue of: |
09075584 |
May 11, 1998 |
06161439 |
Dec 19, 2000 |
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Current U.S.
Class: |
73/862.391;
280/735 |
Current CPC
Class: |
B60N
2/002 (20130101); B60R 21/01556 (20141001); G01G
19/4142 (20130101); B60R 21/01516 (20141001); B60R
2021/01317 (20130101); B60R 2021/01325 (20130101) |
Current International
Class: |
G01L
1/26 (20060101) |
Field of
Search: |
;73/862.391 ;280/735
;307/10.1 ;180/273 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
UniForce Technical Notes and Sensor Design Guide, Force Imaging,
3424 Touhy Avenue, Chicago, IL 60645-2717, pp. 1 through 8. cited
by other .
IMRC Prescon Sensors with Low Threshold Actuation, International
Microelectronics Research Corporation, 11132 E. Edition St.,
Tucson, AZ 85749-9773, pp. 1 thru 3 also 3 usage and applications
pages. cited by other .
FSR Integration Guide & Evaluation Parts Catalog with Suggested
Electrical Interfaces, Interlink Electronics, 546 Flynn Road,
Camarillo, CA 93012, pp. 1 through 27. cited by other .
UniForce Technical Notes #101 (Rev. Jul. 1995), Force Imaging
Technologies, 3424 Touhy Avenue, Chicago, IL 60645-2717, pp. 1
through 4. cited by other .
Tactile Sensing, 1990's Style by Wesley R. Iverson, Assembly
Magazine, Feb.-Mar. 1993 Issue, pp. 23 through 26. cited by
other.
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Primary Examiner: Thompson; Jewel
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
.Iadd.More than one reissue application has been filed for reissue
of U.S. Pat. No. 6,161,439. In particular, two applications for
reissue of U.S. Pat. No. 6,161,439 have been filed: Reissue
application Ser. No. 10/326,170, filed Dec. 19, 2002, and the
present reissue application, which is a divisional reissue
application thereof..Iaddend.
The instant application claims the benefit of U.S. Provisional
Application Ser. No. 60/046,233, filed May 12, 1997.
Co-pending U.S. application Ser. No. 08/993,701 entitled "Seat
Weight Sensor Having Fluid Filled Bladder", filed on Dec. 18, 1997,
claiming benefit of U.S. Provisional Application Ser. No.
60/032,380 filed on Dec. 19, 1996, and assigned to the assignee of
the instant invention discloses a hydrostatic weight sensor
comprising a fluid filled bladder and a pressure sensor for sensing
the weight of an occupant in a vehicle seat for controlling a
safety restraint system. U.S. application Ser. No. 08/993,701 also
discloses a load distributor for distributing loads across the load
bearing surface of the hydrostatic weight sensor. U.S. application
Ser. No. 08/993,701 and U.S. Provisional Application Ser. No.
60/032,380 are incorporated herein by reference.
Co-pending U.S. application Ser. No. 09/003,672 entitled
"Automotive Seat Weight Sensing System", filed on Jan. 7, 1997,
claiming benefit of U.S. Provisional application Ser. No.
60/034,018 filed on Jan. 8, 1997, and assigned to the assignee of
the instant invention discloses a seat weight sensing system
comprising a plurality of hydrostatic weight sensors each of which
is in accordance with U.S. application Ser. No. 08/993,701. U.S.
application Ser. No. 09/003,672 and U.S. provisional application
Ser. No. 60/034,018 are incorporated herein by reference.
Co-pending U.S. application Ser. No. 09/003,870 entitled "Vehicle
Seat Sensor Having Self-Maintaining Air Bladder", filed on Jan. 7,
1997, claiming benefit of U.S. provisional application Ser. No.
60/035,343 filed on Jan. 16, 1997, and assigned to the assignee of
the instant invention discloses an apparatus for automatically
maintaining the supply of sensing fluid in a hydrostatic weight
sensor. U.S. application Ser. No. 09/003,870 and U.S. Provisional
Application Ser. No. 60/035,343 are incorporated herein by
reference.
Co-pending U.S. application Ser. No. 09/003,868 entitled "Seat
Weight Sensor with Means for Distributing Loads", filed on Jan. 7,
1997, claiming benefit of U.S. Provisional Application Ser. No.
60/058,084 filed on Sep. 4, 1997, and assigned to the assignee of
the instant invention discloses a load distributor for distributing
sensed load across the load bearing surface of a hydrostatic weight
sensor. U.S. application Ser. No. 09/003,868 and U.S. Provisional
Application Ser. No. 60/058,084 are incorporated herein by
reference.
Co-pending U.S. application Ser. No. 09/003,673 entitled "Seat
Weight Sensor Having Self-Regulating Fluid Filled Bladder", filed
on Jan. 7, 1997, claiming benefit of U.S. Provisional Application
Ser. No. 60/058,119 filed on Sep. 4, 1997, and assigned to the
assignee of the instant invention discloses a hydrostatic weight
sensor having a means for automatically regulating the amount of
sensing fluid therein. U.S. application Ser. No. 09/003,673 and
U.S. Provisional Application Ser. No. 60/058,119 are incorporated
herein by reference.
Co-pending U.S. application Ser. No. 09/003,746 entitled "Seat
Weight Sensor Using Fluid Filled Tubing", filed on Jan. 7, 1997,
claiming benefit of U.S. Provisional Application Ser. No.
60/065,986 filed on Nov. 14, 1997, and assigned to the assignee of
the instant invention discloses a hydrostatic weight sensor
incorporating a fluid filled tube. U.S. application Ser. No.
09/003,746 and U.S. Provisional Application Ser. No. 60/065,986 are
incorporated herein by reference.
Co-pending U.S. application Ser. No. 09/003,744 entitled "Low
Profile Hydraulic Seat Weight Sensor", filed on Jan. 7, 1997,
claiming benefit of U.S. Provisional Application Ser. No.
60/065,832 filed on Nov. 14, 1997, and assigned to the assignee of
the instant invention discloses a hydrostatic weight sensor
constructed from plates or sheets of semi-rigid material and filled
with a liquid, grease, Bingham fluid or thixotropic material. U.S.
application Ser. No. 09/003,744 and U.S. Provisional Application
Ser. No. 60/065,832 are incorporated herein by reference.
Claims
I claim:
.[.1. A system for measuring seat belt tension in a vehicle having
an airbag control system and a seat, comprising: a.) an
accelerometer rigidly secured to said vehicle in proximity to the
seat thereof, said accelerometer having an output signal responsive
to the vertical acceleration of said vehicle; b.) a seat weight
sensor having an output signal responsive to the force exerted by a
mass on said seat; and c.) a computer processor having first and
second inputs, the first input being operatively coupled to the
output signal of said accelerometer and the second input being
operatively coupled to the output signal of said seat weight
sensor, wherein said processor calculates tension in said seat belt
by comparing the output signal of said seat weight sensor at
discrete time intervals with predicted fluctuations in the force
exerted on the seat caused by vertical acceleration acting upon the
mass, assuming no seatbelt tension..].
.[.2. The system of claim 1 wherein said seat weight sensor
comprises a hydrostatic seat weight sensor disposed within the
seat..].
.[.3. The system of claim 1 wherein said seat weight sensor
comprises a plurality of load cells adapted to be responsive to the
force exerted on the seat by said seat belt..].
.[.4. The system of claim 1 wherein said seat weight sensor
comprises a plurality of force sensitive resistive elements
disposed within the seat..].
.[.5. The system of claim 1 wherein said computer processor further
comprises an output operatively coupled to said air bag control
system for inhibiting said control system upon the calculation of
high seat belt tension..].
.[.6. The system of claim 2 wherein said computer processor further
comprises an output operatively coupled to said air bag control
system for inhibiting an operation thereof upon the calculation of
high seat belt tension..].
.[.7. The system of claim 3 wherein said computer processor further
comprises an output operatively coupled to said air bag control
system for inhibiting an operation thereof upon the calculation of
high seat belt tension..].
.[.8. The system of claim 4 wherein said computer processor further
comprises an output operatively coupled to said air bag control
system for inhibiting an operation thereof upon the calculation of
high seat belt tension..].
.[.9. A method for predicting seatbelt tension in a vehicle having
a seat, an accelerometer rigidly secured to said vehicle in
proximity to the seat, said accelerometer having an output signal
responsive to a vertical acceleration of said vehicle, a seat
weight sensor having an output signal responsive to a force exerted
by a mass acting on the seat, and a processor having a first input
operatively coupled to the output signal of said accelerometer and
a second input operatively coupled to the output signal of said
weight sensor comprising: a.) measuring an actual variation in
force due to vertical acceleration exerted on the seat over a
predetermined time period; b.) calculating an average mass on the
seat; c.) calculating a predicted variation in force due to
vertical acceleration exerted on the seat by multiplying the
average mass on the seat by the variation in vertical acceleration
over a predetermined time period; and d.) dividing the actual
variation in force by the predicted variation in force whereby a
quotient represents normalized seatbelt tension..].
.[.10. A method for predicting seatbelt tension in a vehicle having
a seat, an accelerometer rigidly secured to said vehicle in
proximity to the seat, said accelerometer having an output signal
responsive to a vertical acceleration of said vehicle, a seat
weight sensor having an output signal responsive to a force exerted
by a mass on the seat, and a processor having a first input
operatively coupled to the output signal of said accelerometer and
a second input operatively coupled to the output signal of said
weight sensor comprising: a.) measuring the force due to vertical
acceleration exerted on the seat at discrete time intervals; b.)
calculating an average mass on the seat; c.) calculating at
discrete time intervals a predicted force acting on the seat due to
vertical acceleration, assuming the tension in said seat belt is
zero; and d.) calculating at discrete time intervals a difference
between the measured force exerted on the seat and the predicted
force whereby the difference is indicative of seat belt
tension..].
.[.11. A method for predicting seatbelt tension in a vehicle having
a seat, an accelerometer rigidly secured to said vehicle in
proximity to the seat, said accelerometer having an output signal
responsive to a vertical acceleration of said vehicle, a seat
weight sensor having an output signal responsive to a force exerted
by a mass on the seat, and a processor having a first input
operatively coupled to the output signal of said accelerometer and
a second input operatively coupled to the output signal of said
weight sensor comprising: a.) measuring the force due to vertical
acceleration exerted on the seat at discrete time intervals; b.)
calculating an average mass on the seat; c.) measuring the vertical
acceleration acting on said vehicle at discrete time intervals; d.)
calculating at discrete time intervals a predicted force exerted on
the seat by multiplying the vertical acceleration at each time
interval by the average mass, assuming the tension in said seat
belt is zero; and e.) calculating at discrete time intervals a
ratio between the measured force exerted on the seat and the
predicted force exerted on the seat whereby the ratio is indicative
of seat belt tension..].
.Iadd.12. A system for controlling the actuation of a restraint
actuator in a vehicle, comprising: a.) an accelerometer operatively
coupled to the vehicle, wherein said accelerometer generates a
first signal responsive to a vertical acceleration of the vehicle
proximate to a seat thereof, wherein said seat is associated with
the restraint actuator; b.) a force responsive sensor operatively
coupled to said seat, wherein said force responsive sensor
generates a second signal responsive to a weight on said seat; and
c.) a processor operatively coupled to said accelerometer and to
said force responsive sensor, wherein said processor is adapted to
generate a third signal for controlling the actuation of the
restraint actuator, and said third signal is responsive to both
said first signal and said second signal..Iaddend.
.Iadd.13. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said
accelerometer is rigidly secured to the vehicle in proximity to
said seat..Iaddend.
.Iadd.14. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said force
responsive sensor comprises a hydrostatic seat weight sensor
disposed within said seat..Iaddend.
.Iadd.15. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said force
responsive sensor comprises a plurality of load cells adapted to be
responsive to the force exerted on said seat responsive to a seat
belt associated therewith..Iaddend.
.Iadd.16. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said seat
weight sensor comprises a plurality of force sensitive resistive
elements disposed within said seat..Iaddend.
.Iadd.17. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said third
signal is responsive to whether the mass on the force sensor is
free to travel vertically..Iaddend.
.Iadd.18. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said third
signal provides for discriminating a tightly belted mass on said
seat..Iaddend.
.Iadd.19. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said third
signal provides for predicting whether an occupant on said seat is
an adult or a child..Iaddend.
.Iadd.20. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 12, wherein said
restraint actuator comprises an air bag..Iaddend.
.Iadd.21. A method of controlling the actuation of a restraint
actuator in a vehicle, comprising: a.) generating a first signal
responsive to a vertical acceleration of the vehicle proximate to a
location of a seat, wherein said seat is associated with the
restraint actuator; b.) generating a second signal responsive to a
weight upon said seat of the vehicle; and c.) controlling the
actuation of the restraint actuator responsive to said first and
second signals..Iaddend.
.Iadd.22. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 21, wherein the operation
of controlling the actuation of the restraint actuator comprises:
a.) determining an average mass on said seat from said second
signal; b.) determining a first variation responsive to a plurality
of said second signals within a time period; c.) determining a
second variation responsive to a plurality of said first signals
within said time period; and d.) determining a quotient responsive
to a division of said first variation by said second variation and
by said average mass, wherein the operation of controlling the
actuation of the restraint actuator is responsive to said
quotient..Iaddend.
.Iadd.23. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 21, wherein the operation
of controlling the actuation of the restraint actuator comprises:
a.) determining an average mass on said seat from said second
signal; and b.) determining a quotient responsive to a division of
a measure responsive to said second signal by a measure responsive
to said first signal and by said average mass, wherein the
operation of controlling the actuation of the restraint actuator is
responsive to said quotient..Iaddend.
.Iadd.24. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 22, wherein the actuation
of the restraint actuator is inhibited if said quotient is less
than a threshold..Iaddend.
.Iadd.25. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 23, wherein the actuation
of the restraint actuator is inhibited if said quotient is less
than a threshold..Iaddend.
.Iadd.26. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 21, wherein the operation
of controlling the actuation of the restraint actuator comprises:
a.) determining an average mass on said seat from said second
signal; and b.) determining a difference between a measure
responsive to said second signal and a product of said average mass
and a measure responsive to said first signal, wherein the
operation of controlling the actuation of the restraint actuator is
responsive to said difference..Iaddend.
.Iadd.27. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 26, wherein the actuation
of the restraint actuator is inhibited if the magnitude of said
difference is greater than a threshold..Iaddend.
.Iadd.28. A method of controlling the actuation of a restraint
actuator in a vehicle as recited in claim 21, wherein said first
and second signals are generated as discrete time
intervals..Iaddend.
.Iadd.29. A system for controlling the actuation of a restraint
actuator in a vehicle as recited in claim 21, wherein said
restraint actuator comprises an air bag..Iaddend.
Description
TECHNICAL ART
The instant invention relates generally to automotive passenger
restraint systems and more specifically to a system and method for
predicting seatbelt tension in a vehicle utilizing a seat weight
sensor and an accelerometer.
BACKGROUND OF THE INVENTION
Automotive manufacturers and the National Highway Transportation
Safety Association are investigating methods to disable vehicle air
bags in situations where they may cause more harm than good.
Typically, airbags have been developed to deploy with enough force
to restrain a 175 lb. adult in a high velocity crash. Deployment of
the same air bags when children are seat occupants may cause
serious injury due to the force generated upon inflation of the
bag.
As a result, seat weight sensors and systems are being developed in
an attempt to determine when the passenger seat occupant is a
child. Such systems should identify when the occupant is small, or
even when a child is in a rear facing infant seat, a forward facing
child seat or a booster seat. Occupant weight measurement when a
child seat is present is further complicated by the downward force
applied to the child seat by the tension of a seat belt. When a
child seat is strapped tightly, the seat belt forces the child seat
into the vehicle seat and can bag deployment when children or
infants are present in the seat.
A variety of methods have been used for seat belt tension
measurement. Copending U.S. Provisional Application Ser. No.
60/067,071 entitled "Villari Effect Seat Belt Tension Sensor", and
copending U.S. Provisional Application Ser. No. 60/070,319 entitled
"Compressive Villari Effect Seatbelt Tension Sensor", both assigned
to the assignee of the instant invention, disclose two seat belt
tension measurement systems utilizing sensors that operate on the
principle known as the Villari effect. The Villari effect refers to
the tendency of certain materials with magnetostrictive properties
to inhibit or enhance the strength of an electromagnetic field
within the material when the material is being subjected to
compression or tensile stress. By measuring the field strength in
magnetostrictive material placed in line with a seat belt
mechanism, for example in a seat belt latch or a seat belt
retractor, the relative tension in the belt may be calculated.
Furthermore, belt deflection techniques which guide a seat belt
through a mechanical system that forces the belt out of a straight
line when there is low tension have been used. Under high tension
the seat belt forces the displacement of a mechanical deflector.
This force may then be sensed utilizing an electromechanical
switch. Tension measurement mechanisms have also been incorporated
in the buckle of the seat belt. In one embodiment, a sliding buckle
is biased back with a spring. When the belt is under heavy tension,
the buckle pulls forward to control a switch that provides feedback
to a vehicle processor.
The aforementioned seat belt tension measurement methods suffer
from a number of disadvantages. Initially, a great number of
additional parts are required for seat belt retractors or buckle
configurations. This adds complexity (and therefore cost) to
vehicle assembly and provides for considerable difficulty in
retrofitting existing vehicles. Additionally, several of the
aforementioned tension systems provide only a threshold level of
tension detection.
The present invention may be used to detect whether the seat belt
is under high tension thereby denoting that an infant seat is
present. Furthermore, significant tension in the belt can be
predicted without resorting to the complex instrumentation required
to measure actual belt tension. Known belt tension measurement
systems that directly contact the seat belt require additional
hardware and sensors that increase component count and vehicle
assembly complexity.
SUMMARY OF THE INVENTION
The instant invention overcomes the aforementioned problems by
providing a seat belt tension prediction system employing an
accelerometer and a seat weight sensor to accurately determine the
tension in a vehicle seat belt and thereby discriminate between the
presence of a tightly belted child seat or other object and an
adult occupant.
The instant invention measures the "bounce", or vertical
acceleration, experienced by a weight on a seat weight measurement
means by monitoring an accelerometer that is rigidly mounted to the
vehicle seat. The bounce can be thought of as the temporary
acceleration of the weight on the seat caused by the vehicle
traversing bumps or holes in the road. This road-induced bounce
causes oscillations in the force acting upon the seat that may be
measured by a seat weight sensor.
A "free" or unbelted mass positioned on a vehicle seat will bounce
up and down on the seat and may, for example, completely lose
contact with the seat in extreme cases. The weight sensor would
correspondingly interpret this extreme case as a "spike" of zero
force acting on the seat. Usually, however, the output signal
produced by the weight sensor will oscillate with a small amplitude
that is dependent upon the total mass acting upon the seat and the
amplitude of the road-induced vehicle bounce. When the force acting
downwardly on the seat is increased due to the tension in a tight
seat belt, the amplitude of oscillation of an output signal
produced by the weight sensor will be reduced because a component
of the force caused by the tension in the seatbelt is constant.
Accordingly, a seatbelt tension may be calculated by determining
the vertical acceleration of the vehicle and the variation in force
exerted on the seat as measured by the seat weight sensor.
A conventional accelerometer provides an electrical signal
proportional to the vertical acceleration that the seat, and
therefore the mass in the seat, experiences. When actual vertical
acceleration is compared to the oscillating output signal produced
by the weight sensor, a measure of the force on the seat
attributable to the tension in the seat belt may be calculated. The
road-induced vertical acceleration acting on the vehicle is used to
predict the amount of force exerted downwardly on the seat given
that no seat belt tension is present.
A conventional microprocessor is adapted to accept output signals
from the accelerometer and the seat weight sensor. The
accelerometer output is responsive to the amount of vertical
acceleration caused by road bounce acting on the vehicle seat and
the weight sensor output is responsive to the amount of force
exerted downwardly on the vehicle seat.
A normalized measurement of seatbelt tension may be calculated by
the processor by first calculating an average mass on the seat
using the weight sensor output. The expected variation in force is
then calculated by multiplying the aforementioned average mass on
the seat by the actual acceleration as measured by the
accelerometer over a pre-determined time period. A normalized
seatbelt tension may then be calculated by dividing the variation
in force as measured by the seat weight sensor over a predetermined
time period by the expected or calculated variation in force over
the aforementioned period.
The resultant scalar tension measure will approximate unity for
unbelted or loosely belted occupant situations where the mass
acting on the seat is free to travel vertically. Accordingly, the
normalized tension scalar will decrease when extremely high belt
tension is present thereby forcing the mass onto the seat.
Alternatively, the processor may calculate an expected force
exerted on the seat due to road-induced vehicle bounce at discrete
time intervals, assuming that no belt tension exists, and compare
the results with the measured force exerted on the seat at the each
discrete point in time. The ratio between the measured force and
the calculated or expected force exerted on the seat provides an
indication of belt tension.
Known seat weight sensors may comprise one or more pads employing
force sensitive resistive (FSR) elements disposed within the seat
to provide a weight measurement. These arrangements are typically
used as weight threshold systems that are used in conjunction with
a processor to disable a passenger air bag when the seat is
empty.
Conventional load cells attached to the seat mounting posts have
also been used in research applications. The use of load cells as
weight measurement means in the instant invention requires that the
seatbelts or passenger restraints are not mounted directly to the
vehicle seat because a load cell system that weighs the entire seat
and its contents including the seatbelts and their mounting points
will not be responsive to the force applied to the seat by the
tension in the seatbelt.
Mechanisms employing string actuated potentiometers to measure
downward seat displacement have also been utilized as weight
measurement means. In these mechanisms, a weight resting upon a
seat pad causes the pad to sag or curve downwardly, thereby
displacing a string that is positioned across the bottom of the
seat pad. One end of the string is connected to a potentiometer
shaft that is rotated when the string is displaced. The rotation of
the potentiometer shaft causes the resistance at the potentiometer
output to change. A processor is adapted to measure the changing
resistance at the potentiometer output, thereby providing a signal
proportional to string displacement, and therefore, the force
caused by a mass present on the seat.
Copending U.S. Application Ser. No. 08/993,701 further discloses a
weight sensor employing a gas filled bladder disposed within the
seat pad to calculate seat weight. When a load is applied to the
seat a differential pressure sensor operatively coupled to the
bladder generates a signal that is responsive to the pressure on
the fluid within the bladder and therefore indicative of the force
acting upon the seat. A signal processor having an input
operatively coupled to the pressure sensor then calculates the
force exerted on the seat as well as the mass present.
By determining the amount of mass present in a vehicle seat and the
amount of tension present in a passenger restraint belt, corrective
action may be taken to further protect a vehicle occupant by
adapting other restraint system components, such as the air bag
control system.
The ability to sense the tension present in a seat belt may be used
in conjunction with a seat weight sensor to determine the presence
of an occupant in a vehicle seat and the relative size of the
occupant. This information may be used either to deactivate
seatbelt pretensioners, and/or modify the inflation profile of an
air bag.
Furthermore, by sensing the amount of tension present in the seat
belt, the deployment of an airbag may be inhibited in the presence
of infant seats or in situations where occupants are small so as to
reduce their risk of injury from the inflating air bag. Therefore,
a system that can reliably predict the amount of tension present in
a seat belt may be used to great advantage in vehicle safety
systems.
One significant advantage of the instant invention is that it does
not require numerous ancillary components that are in direct
contact with the seat belt system. The present invention can
predict whether there is significant tension in the seat belt
without directly measuring seat belt tension.
Therefore, one object of the instant invention is to provide a seat
belt tension measurement system that does not require a mechanism
in direct contact with the seat belt or its associated
assembly.
Another object of the instant invention is to use road-induced
vertical acceleration exerted on every vehicle as a forcing
function for a seat weight sensor signal. The oscillation of an
accelerometer signal compared with the oscillation of a weight
sensor signal at discrete time intervals provides the data required
to calculate seat belt tension.
A yet further object of the present invention is to provide a seat
belt tension prediction system that requires minimal additional
components beyond a seat weight measurement means and the attendant
processor adapted to receive and process various vehicle
instrumentation signals. The instant invention requires only an
accelerometer or equivalent acceleration sensing device and a
conventional microprocessor or equivalent processing means in
conjunction with a seat weight sensor to accurately calculate seat
belt tension.
A yet further object of the instant invention is to provide a seat
belt tension prediction system that is useful in determining the
presence of an infant seat in a vehicle. The present invention
measures the component of force acting on a vehicle seat that is
attributable to tension in the seat belt as well as the component
of force attributable to the presence of a mass on the seat,
thereby providing a means to predict whether the occupant is an
adult or a child.
The instant invention will be more fully understood after reading
the following detailed description of the preferred embodiment with
reference to the accompanying drawings. While this description will
illustrate the application of the instant invention in an
automotive safety restraint system, it will be readily understood
by one of ordinary skill in the art that the instant invention may
also be utilized in other tension measurement systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatical view of a preferred embodiment of the
instant invention.
FIG. 2 is a diagrammatical view of an alternative seat weight
sensor arrangement taken along the line 2--2 of FIG. 1.
FIG. 3 is a diagrammatical view of an alternative embodiment of the
instant invention.
FIG. 4 is a diagrammatical view of an alternative embodiment of the
instant invention.
FIG. 5 is a view of the instant invention taken along the line 5--5
of FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring to FIG. 1, a seat belt tension prediction system and
method 10 for a vehicle 12 having a seat 14 is comprised of an
accelerometer 20 and a seat weight sensor 30. The accelerometer 20
is provided with an output signal 22 that is responsive to the
amount of vertical acceleration acting upon the vehicle 12 and,
therefore, on the vehicle seat 14. The accelerometer 20 must be
rigidly secured to a vehicle structural member 16 that experiences
the same vertical acceleration that the vehicle seat 14 is
subjected to when traversing variations in terrain. In a preferred
embodiment of the instant invention the resolution of the
accelerometer 20 is greater than 0.005 g to provide sufficient
sensitivity to small variations in vertical acceleration.
The seat weight sensor 30 is provided with an output signal 32 that
is responsive to the amount of force exerted downwardly on the
vehicle seat 14. Accordingly, the seat weight sensor output signal
32 will also be responsive to additional force upon the vehicle
seat 14 exerted by tension in a seat belt 34. The output signal 32
from the weight sensor 30 must have an update period small enough
to allow the weight sensor 30 to sense oscillations in force on the
seat 14 caused by the vehicle's vertical acceleration. In a
preferred embodiment of the instant invention the update period of
the weight sensor output signal 32 is less than 25 milliseconds.
Additionally, the weight sensor output signal 32 may be AC coupled
to filter low frequency signal oscillations that normally occur as
a result of occupant movement, thus ignoring those oscillations
that are not produced by road-induced vertical acceleration.
Furthermore, a processor 50 is provided, having a first input 52
operatively coupled to the accelerometer output signal 22 and a
second input 54 operatively coupled to the seat weight sensor
output signal 32. The processor 50 is further operatively coupled
to a vehicle airbag control system 60 whereby the processor 50 may
provide an output signal 56, or a plurality thereof, to the airbag
control system 60 to inhibit deployment of an airbag and/or to
modify its inflation profile.
The processor 50 may comprise an analog or digital microprocessor
or any equivalent thereof. Although the preferred embodiment of the
instant invention utilizes a conventional digital microprocessor,
it is readily understood by one having ordinary skill in the art
that alternative means such as relay logic circuitry, analog
processors, analog to digital converters and TTL logic circuitry
may be employed as processor means to practice the instant
invention.
In an alternative embodiment of the instant invention shown in FIG.
2, seat weight sensor 40 comprises a plurality of force sensitive
resistive elements 42 disposed within the vehicle seat 14 for
measuring force. The force sensitive resistive elements 42 provide
as an output signal 44 a variable electrical resistance responsive
to the amount of force acting on the elements 42, that may be
operatively coupled to the input 54 of processor 50. The variable
resistance output signal 44 is generally inversely proportional to
the amount of force acting on the seat 14.
Referring to FIG. 3 and as disclosed in U.S. application Ser. No.
08/993,701, a hydrostatic seat weight sensor 70 as incorporated in
an alternative embodiment of the instant invention, comprises a gas
filled bladder 72 mounted within the vehicle seat 14 and a
differential pressure sensor 74 operatively coupled to the bladder
72 for measuring the difference in pressure between the bladder 72
and the atmosphere. The differential pressure sensor 74 provides a
pressure sensor output 76 that is responsive to the force exerted
downwardly on the seat 14. The differential pressure sensor output
76 is operatively coupled to input 54 of processor 50 thereby
providing an indication of the force acting downwardly on the seat
14.
As shown in FIG. 4, an alternative seat weight sensor comprises a
plurality of load cells 80 disposed between the vehicle seat 14 and
the vehicle structure 16 such that the entire weight of the seat 14
rests upon the load cells 80. The load cells 80 are provided with
an output 82 that is responsive to the amount of force acting upon
the seat 14. When utilizing load cells 80 as a weight sensors, it
is critical that the seat belt 34 is mounted to the vehicle 12 such
that load cell 80 is responsive to the force upon the seat 14
generated by tension present in the seat belt 34. For example,
FIGS. 4 and 5 provide illustrations of a seat belt 34 configuration
wherein the load cells 80 are responsive to both the tension
applied by the seat belt 34 and the force resulting from a mass
resting on the seat 14.
In operation, and in accordance with the preferred embodiment of
the instant invention, the accelerometer 20 measures the vertical
acceleration of the seat 14 and provides an output signal 22 to the
processor 50. A normalized seatbelt tension measure is then
calculated by the processor 50 to detect high belt tension and
thereby determine the presence of a child seat.
The processor 50 is programmed to calculate an average mass of an
object resting on the seat by dividing the output 32 of the weight
sensor 30 by the earth's gravitational constant, g. This
calculation may be performed at a predetermined time during the
operation of the vehicle 12, or preferentially, performed
continuously by assuming that the vertical acceleration of the
vehicle 12 and the belt tension are negligible, and averaging the
resultant successive mass calculations.
A predicted variation in force exerted on the seat 14 is calculated
in the processor 50 by multiplying the aforementioned average mass
by the measured variation in vertical acceleration as provided by
the accelerometer 20 over a predetermined time period. The
variation in vertical acceleration over time may be determined by
integrating the absolute value of the difference between the
accelerometer output 22 and the earth's gravitational constant g
over the aforementioned time period.
The variation, or fluctuation of the actual force exerted on the
seat 14 is then determined by integrating the absolute value of the
difference between the seat weight sensor output 32 and the average
force exerted on the seat 14. The normalized tension measurement is
then calculated by dividing the variation in actual force exerted
on the seat over the same time period as measured by the weight
sensor 30, by the predicted variation in force exerted on the seat
14. The time period over which the predicted force variation is
calculated must be sufficient to allow road induced bounce to
impart vertical acceleration to the vehicle 12. In a preferred
embodiment of the instant invention the time period used to
calculate the normalized belt tension is .5 seconds.
In an alternative embodiment of the instant invention the processor
50 calculates the force exerted downwardly on the seat 14 at
discrete time intervals utilizing the vertical acceleration
measurement provided by the accelerometer 20, and assuming that no
seat belt 34 tension is present in the system, and then compares
the resultant predicted force with the actual measured force at
each discrete point in time to calculate belt tension. As an
example, the predicted force acting on the seat 14 may be
calculated by programming the processor 50 to perform the following
algorithm: F=M(g-A)+BT, where F is the force acting downwardly onto
the seat 14, M is the mass of the object on the seat 14, g is the
gravitational acceleration exerted on the mass M by the earth, A is
the vertical acceleration of the vehicle 12, excluding the earth's
gravity, and BT is the vertical component of the tension present in
the belt 34.
The vertical acceleration A of the vehicle 12 fluctuates around
zero and thus causes variations in the force F acting on the seat
14. The belt tension BT approximates a constant value that is near
zero for most occupant seating situations except for the presence
of tightly belted child seats. The belt tension BT is generally a
small value because belt tension greater than a few pounds of force
has been found to be uncomfortable for most vehicle occupants
thereby making it unlikely that an occupant is present when there
is significant tension in the seat belt 34.
As previously disclosed, the output signal 32 of the weight sensor
30 is divided by the earth's gravitational constant g by processor
50 to calculate the average mass M present in the vehicle seat 14.
The processor 50 then calculates a predicted force acting
downwardly on the seat 14 at discrete time intervals using the
aforementioned average mass, with the assumption that the belt
tension BT is zero. Still assuming zero belt tension BT, the
processor 50 then compares the actual value of the force F as
measured at each discrete point in time by the weight sensor 30
with the calculated or predicted force. The difference between the
predicted and actual values of force F provides an indication of
the tension present in the belt BT.
In an alternative method for predicting belt tension BT, the
processor 50 monitors the weight sensor output signal 32 at
discrete time intervals and measures the amplitude of the
oscillations of the output signal 32 at each discrete point in
time. The processor 50 further monitors the accelerometer output
signal 22 at the corresponding discrete time intervals and
calculates the amplitudes of the oscillations of the accelerometer
output signal 22. The resultant accelerometer amplitude
measurements are then sequentially multiplied by the average mass M
present in the vehicle seat 14 to calculate the predicted force
acting on the seat 14 at each discrete point in time. The ratio of
the actual force acting on the seat 14 to the calculated force at
each time interval thereby provides a measure of seat belt
tension.
A tightly belted mass present in the vehicle seat 14 will produce a
reduced ratio of actual force to predicted force as compared to the
ratio calculated when a "free" mass is positioned in the vehicle
seat 14. Therefore, the smaller the ratio between actual force as
indicated by the weight sensor 30 to predicted force as calculated
using the average mass M and the accelerometer output signal 22,
the greater the belt tension BT, and the higher the probability
that an infant seat is tightly belted down onto the vehicle seat
14. The processor 50 may be provided with a look-up table whereby
seat belt 34 tension may be determined given a specific calculated
tension ratio.
Accordingly, and as shown in FIG. 1, where the processor 50
calculates a level of tension in the seat belt 34 in excess of a
predetermined maximum, the processor 50 will generate an output 56
operatively coupled to an air bag control system 60 to inhibit
deployment of the air bag. Alternatively, where the processor 50
calculates a level of tension in the seat belt 34 below the
predetermined maximum and the seat weight sensor 30 indicates that
the occupant's weight is below a predetermined minimum, the
processor 50 will provide an output 56 to the air bag control
system 60 to reduce the inflation profile thereof according to the
measured weight of the occupant.
While specific embodiments of the instant invention have been
described in detail, those with ordinary skill in the art will
appreciate that various modifications and alternatives to those
details could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are
meant to be illustrative only and not limiting as to the scope of
the invention, which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
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