Land vehicles – Wheeled – Attachment
Reexamination Certificate
2002-03-22
2004-11-23
Culbreth, Eric (Department: 3616)
Land vehicles
Wheeled
Attachment
C073S862581, C073S862584, C177S141000
Reexamination Certificate
active
06820896
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems that ascertain what is occupying a vehicle seat for the purpose of deciding how to best protect an occupant.
BACKGROUND OF THE INVENTION
Air bags of occupant protection systems are expensive and in certain circumstances are dangerous. It is therefore important to avoid deployment when the seat is empty to save the cost of replacement. 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. A system is desired to reliably distinguish a 105 pound adult from a child even when the child is in a child seat and 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 severity of a vehicle crash, monitoring various elements of the occupant protection system for proper operation, and initiating deployment of occupant protection means. SDMs 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 may be connected to receive input from such as side mounted and forward mounted crash sensors.
Knowledge of the weight of a seat occupant is useful. 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. If the weight is intermediate, say between 30 and 45 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 attributes of the seat occupant from the information provided by the array of force sensors.
The second type of weight sensing system is useful in the type of seat having a seat cushion supported by a platform. The second type of weight sensing system includes, typically, four force sensors located at the four corners of the platform where they can transfer force to 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.
The third type of weight sensing system comprises sensors for sensing stress in structural members of the seat. A chair having a load cell at each leg for sensing the weight carried by the leg with an adder for adding the inputs from each load cell would be an example of the third type of weight sensing system. The outputs of the sensors (four load cells in the case of the aforementioned chair) are added and the weight of the empty seat is subtracted to obtain the 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. Certain of the aforementioned weight sensing systems may provide weight readings for a tightly belted child seat that resemble weight readings for an adult.
Load cells comprising a piston sealingly movable in a cylinder to generate hydraulic pressure are well known. At the front of a reclined seat the seat may apply upward force to a load cell which requires a load cell that responds to both tension and compression. To measure tension, a sensor based on a piston sealingly movable in a tube must be preloaded by such as a spring to maintain a pressure in the liquid that diminishes when tension is applied. The output of load cells preloaded by springs may vary with temperature because liquids typically have larger thermal expansion coefficients than metals, which leads to varying spring deflection with temperature and, therefore, varying preload with temperature. A gel is often used as the liquid because it is easier to seal against leakage.
Load cells comprising a piston sealingly movable in a cylinder have friction between the piston and the cylinder when there are side forces. There are many causes for side forces. In a vehicle side forces can be caused by differential thermal expansion between the car floor and the seat, forces caused by 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. It is 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 resulting from the weight of the seat occupant and not to stresses resulting from thermal expansion or attachment to the vehicle. An advantage of seat occupant weight sensing systems responsive to stress in the seat structure is that they present a solution to the aforementioned problem of belt forces causing a child to appear to be an adult. Anchoring the seat belts to the seat frame and placing the force sensors between the belt anchors and the vehicle attachment points makes the measured weights independent of belt forces.
It is often desired to place four load cells between the vehicle floor and the seat. There are times when substantial forces can occur between a seat and the vehicle floor. For example, if a structural member of a seat is attached to the floor of a vehicle it can happen that the structural member remains at a temperature comfortable to the vehicle occupants while the vehicle floor goes from a very cold temperature caused by winter conditions to a very high temperature caused by heat rising from a catalytic converter. The result is relative thermal expansion of the floor that can cause substantial horizontal stresses that will be experienced by load cells placed between the floor of a vehicle and the seat.
Semiconductor pressure sensors are manufactured in large quantities by micromachining silicon wafers. Designs are based on various technologies and physical principles. These sensors may require additional components to meet needs for such as temperature compensation. Typically, but not necessarily, a second circuit assists the micromachined pressure sensing element. Certain micromachined sensors operate immersed in the liquid as they sense the pressure of the liquid.
The aforementioned need for temperature compensation and other needs such as compensation for nonlinear pressure response and variable overall span are typically met by including an inexpensive microprocessor or an “application specific integrated circuit” (ASIC), which is a purpose built microprocessor, in close proximity to the pressure sensor.
Load cells of the type that convert force to hydraulic pressure comprising absolute pressure sensors are less expensive than load cells comprising gauge pressure sensors because the micromachined sensors themselves are less expensive and because absolute pressure sensors simplify the design of load cell because it is not necessary to provide a duct from the pressure sensor to the outside atmosphere. The output of a force sensor comprising an absolute pressure sensor responds
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