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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

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.

Claims

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.