Land vehicles – Wheeled – Attachment
Reexamination Certificate
1999-04-09
2002-04-02
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Attachment
C073S862080, C073S862322, C073S862370, C073S862581, C073S862584
Reexamination Certificate
active
06364352
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems that ascertain what is occupying a vehicle seat for the purpose of deciding if and how air bags should be deployed.
BACKGROUND OF THE INVENTION
Air bags of occupant protection systems are expensive and in certain circumstances are dangerous. It is therefore desirable to prevent deployment when the seat is empty to save the cost of replacement. It is important to prevent deployment when circumstances do not warrant deployment or when deployment might do more harm than good. When the seat is occupied by a child or by a very small adult it is particularly important to deploy the airbag judiciously. A system is desired that can reliably distinguish a 100 pound adult from a 60 pound child in a child seat even when the belts retaining the child seat are under substantial tension.
Occupant protection systems typically include a “sensor and diagnostic module” or “SDM” which performs various functions related to sensing the occurrence of a vehicle crash, monitoring various elements of the occupant protection system for proper operation and initiating deployment of occupant protection devices. SDM's typically include a microprocessor, an accelerometer, an arming sensor, circuitry interconnecting the aforementioned components and switches for initiating deployment of the occupant protection devices. SDMs are often connected to receive input from such as side mounted and forward mounted crash sensors.
Many systems are known that sense properties of the occupant of a seat. Certain of these systems contain elements for weighing the occupant. If the weight is very small it may be assumed that the seat is unoccupied or occupied by a small child, and in either case deployment would not be desired. If the weight is intermediate, say between 25 and 40 kilograms, then the occupant is likely to be a child and whether or not an airbag should be deployed depends on factors such as how energetically the airbag deploys. If the weight is greater than 45 kilograms the seat occupant is likely to be an adult who would be protected by an airbag.
Three types of weight sensing systems for installation in vehicle seats are known: A first type of weight sensing system comprises an array of force sensors located immediately beneath the upholstery material of the seat cushion which operates to measure the pressure of the occupant against the seat at the points where sensors are located. These sensors are typically responsive to small forces applied over a small area and an array of force sensors tells a microprocessor the magnitude and distribution of the force the occupant applies to the cushion. The microprocessor ascertains the weight and other characteristics of the seat occupant from the information provided by the array of force sensors.
A second type of weight sensing system is useful in the type of seat having a fabric covered seat cushion of a foam of a rubbery material supported by a platform. The second type of weight sensing system includes, typically, four force sensors located at the four comers of the platform between the platform and the frame of the seat. The outputs of the four sensors are added to ascertain the total weight being supported by the platform and, therefore, by the seat cushion.
A third type of weight sensing system comprises sensors for sensing stress in structural members of the seat. For example, a chair with a force sensor sensing the weight carried by each leg. The outputs of the four (in the case of the example) sensors are added to ascertain the total weight of the occupant.
The known embodiments of the aforementioned weight sensing systems do not always measure the occupant's weight accurately and no design is widely accepted. Where the seat belts are attached to the structure of the vehicle, all of the aforementioned weight sensing systems may provide weight readings for a tightly belted child seat that are indistinguishable from weight readings from an adult.
Additionally, all known embodiments of the aforementioned weight sensing systems attempt to measure the total occupant weight but do so with a large margin of error because the feet of most normally seated adults (but not of children and very small adults) rest on the floor so that some of the weight is not sensed.
Force sensors placed immediately beneath the seat upholstery complicate manufacture and may affect the feel of the seat as sensed by the occupant.
Load cells comprising a piston sealingly movable in a cylinder to generate hydraulic pressure are well known. In certain applications there is a need for a load cell that responds to both tension and compression. A sensor based on a piston sealingly movable in a tube must be preloaded with such as spring under tension or compression to maintain a pressure in the liquid that diminishes when tension is applied to the load cell. Known means for providing spring force disadvantageously respond to changes in temperature because liquids typically have larger thermal expansion coefficients than metals which causes the deflection of the spring and therefore the spring force to vary with temperature.
Another disadvantage of load cells comprising a piston sealingly movable in a cylinder is friction between the piston and the cylinder which results from side forces that can result from many causes. Commonly encountered causes are forces caused by differential thermal expansion between the car floor and the seat, relative movement as the seat is being attached 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. It is particularly important to isolate the piston from angular misalignment between seat parts and car floor parts that occur because of production variations in the parts. A load cell is needed that is inherently insensitive to side forces and angular misalignments.
Seat occupant weight sensing systems responsive to stress in the seat structure must respond only to forces related to the weight of the seat occupant and not to stresses resulting from thermal expansion or attachment to the vehicle. This is not always easily achieved. However, force sensors mounted on the seat structure solve the aforementioned problem of belt forces causing a child to appear to be an adult: By anchoring the seat belts to the seat and placing the force sensors below the belt anchors the belt forces are not included in the weight.
Load cells responsive to applied force by pressurizing a liquid to which a pressure sensor responds may include an absolute pressure sensor. Absolute pressure sensors advantageously are less expensive to manufacture and allow the load cell to be closed to prevent penetration of fluids during events such as flooding or fluid spillage. The output of a load cell comprising an absolute pressure sensor responds to changes in atmospheric pressure. A change in output as a car is driven from sea level to Denver, Colo. will occur and might be on the order of three to ten pounds change in the force sensed by each load cell.
The type of sensor wherein the weight of an occupant sitting on a cushion is transmitted though the cushion and sensed at the platform supporting the cushion may fail to register an accurate weight because a fraction of the occupant's weight may be supported by the back of the seat rather than on the seat cushion and, therefore, not be sensed. Also, the fraction of the occupant's weight supported by the seat back varies with the angle to which the back is reclined.
Seat backs that can recline typically expose a larger area of cushion at greater seat back recline angles. This causes the weight of the head and body of an occupant to be applied farther toward the rear of the seat cushion when the seat. back is reclined.
Semiconductor pressure sensors are manufactured in large quantities by micromachining silicon wafers. Designs are based on various technologies and physical principles. Many of these sensors require additional circuitry to achieve a useful function. Typically, an integrated
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