Load cell and seat occupant weight sensing system

Abstract

A load cell particularly useful for a seat occupant weight sensing system includes a liquid filled chamber and a pressure sensor providing an electric signal indicating the pressure in the liquid. Four load cells supporting a seat provide four signals that are added to determine the weight of the seat occupant. The load cell comprises two flanged conical springs stressed to provide preload. One of the springs also forms part of the surface of the liquid filled chamber. The two springs operate in concert to resist side forces and moments. The load cell is responsive to both compressive and tensile forces while being substantially unaffected by lateral forces and moments. A seat belt tension sensor may be included to measure seat belt tension. Preferred manufacturing methods provide low cost,

Description

FIELD OF THE INVENTION [0001] This invention relates to systems that ascertain what is occupying a vehicle seat to assist in determining optimum airbag deployment. BACKGROUND OF THE INVENTION [0002] Airbags of occupant protection systems are expensive and in certain circumstances are dangerous. It is, therefore, worthwhile to prevent deploying an airbag into an empty seat to save repair cost. It is important to avoid deployment when circumstances do not warrant deployment or when deployment might do more harm than good. It is particularly important to deploy the airbag judiciously when the seat is occupied by a child or by a very small adult. Current law requires an occupant sensing system to reliably distinguish a 107-pound adult from a child. [0003] Occupant protection systems typically include a “sensor and diagnostic module” or “SDM” that performs functions related to sensing the severity of a vehicle crash, monitoring various components of the occupant protection system for pro...

AI Technical Summary

Benefits of technology

[0021] Further, in accordance with the certain embodiments of the invention, the two springs resist axial misalignment between the force input members. This is advantageous when the load cell is located between the seat and the vehicle floor because the load cell compels the part of the vehicle floor where the seat is attached and the part of the seat that is attached to the vehicle floor to be parallel to each other, which makes the stresses on the seat and the floor similar to stresses that occur when the seat is bolted directly to the vehicle floor as it would be if there were no load cells.

[0040] Further, in accordance with the preferred embodiments of the invention comprising a common calculating component that calculates temperature compensation for a multiplicity of load cells, each load cell includes the aforementioned part made of a metal having a larger thermal expansion coefficient than the other metal parts for compensating for temperature. In this design the larger part or preponderance of the temperature compensation results from thermal expansion of the metal part made of a metal having a larger thermal expansion coefficient than the other metal parts. The common calculating component operates to make small corrections that might be required if the temperature compensation caused by the metal with a larger thermal expansion coefficient than the other metal parts is not as precise as required. This design is advantageous in applications wherein more accurate thermal compensation is required because it saves the cost of a temperature sensor in the load cell because the temperature at the common calculating component is sufficiently accurate for making the small corrections.

Problems solved by technology

Airbags of occupant protection systems are expensive and in certain circumstances are dangerous.

If the weight is very small it may be assumed that the seat is unoccupied or occupied by a small child; in either case airbag deployment would not be desired.

Side forces have many causes: Mounting the load cell between the seat and the floor can cause side forces from differential thermal expansion between the car floor and the seat, stresses from attaching the seat to the vehicle, damage to the seat or the car floor and forces resulting from acceleration of the vehicle or actions of the seat occupant.

Thermal expansion of the floor can cause substantial horizontal stresses on load cells placed between the floor of a vehicle and the seat.

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