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Load cell and seat occupant weight sensing systemLoad cell and seat occupant weight sensing system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060103192, Load cell and seat occupant weight sensing system. Brief Patent Description - Full Patent Description - Patent Application Claims
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 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. [0004] 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 the airbag should be deployed gently if at all. If the weight is greater than 45 kilograms the seat occupant is likely to be an adult who would be protected by an airbag. [0005] 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 pressure diminishing 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. Relative expansion of the liquid with temperature changes the preload with temperature. A gel may be used in place of the liquid because it is easier to seal against leakage. [0006] The aforementioned need for temperature compensation and other needs such as compensation for nonlinear pressure response and variable overall span are often met by including an inexpensive microprocessor or an "application specific integrated circuit" (ASIC), which is a purpose built microprocessor, typically located in close proximity to the pressure sensor where it can sense the temperature of the pressure sensor. [0007] In load cells comprising a piston movable in a liquid filled cylinder there is friction between the piston and the cylinder under non-axial or side forces. 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. This requires protecting the piston from angular misalignment between seat parts and car floor parts caused by production variations in the parts. A load cell is needed that is inherently insensitive to side forces and angular misalignments. [0008] 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 the seat belt can be attached to the seat above the weight sensor where seat belt tension for retaining a child seat does not affect the weight measurement. 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 seat belt forces and makes a seat belt tension sensor unnecessary. [0009] One location for four load cells is between the vehicle floor and the seat. 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. Thermal expansion of the floor can cause substantial horizontal stresses on load cells placed between the floor of a vehicle and the seat. [0010] Semiconductor pressure sensors are manufactured in large quantities by micro machining 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. An ASIC offers one way to meet those needs. Certain micro machined sensors operate immersed in the liquid the pressure of which they are sensing. [0011] Many force sensors based on strain gauge technology are commercially available. Ceramic disks to which strain gauge elements are attached provide an electric signal responsive to force applied between the center of the disk and the perimeter of the disk. It is also well known to apply strain gauge elements to stressed components of a structure to measure the stress and, thereby, to measure the force being received by the structure. [0012] Load cells of the type that convert force to hydraulic pressure are less expensive to make if they include absolute pressure sensors rather than gauge pressure sensors because the micro machined sensors themselves are less expensive and because absolute pressure sensors simplify the design of the 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 to changes in atmospheric pressure. Going from sea level to an altitude of 5,300 feet at Denver, Colo. with the same occupant weight can cause an apparent three to ten pound decrease in the force sensed by each load cell, which must be corrected if the measurement is to be accurate. [0013] It is well known to connect a sensor by only two electrical conductors. In typical designs the sensor simultaneously draws power needed to operate and also draws constant or pulsed current over and above the current it requires to operate. The additional current indicates the physical measurement. [0014] U.S. Pat. No. 6,259,167 issued to the present inventor describes a seat occupant weight sensing system based on torque sensed at the cushion of a seat and two seat occupant weight sensing systems responsive to torque at the seat frame. [0015] U.S. Pat. No. 6,259,167 also discloses a force sensor comprising a liquid filled injection stretch blow molded bottle having bellows shaped sides and a pressure sensor thereby being a force sensor responsive to axial force. The force sensor operates by converting axial force to pressure in the liquid for sensing by the pressure sensor. This patent is included herein by reference. [0016] U.S. Pat. No. 6,224,094 issued to the present inventor describes a load cell for generating an electric signal indicating applied force. The load cell has a pressure sensor and a means for converting applied force to pressure whereby its output becomes a force signal. The load cell is preloaded by a constant force spring whereby relative thermal expansion between the liquid and the structural parts of the load cell does not cause the pressure in the liquid to vary. The spring also provides a low friction bearing for axial movement and resists radial movement between two parts of the load cell. This patent is included herein by reference. [0017] Weight sensing systems comprising a platform supported by load cells are well known. For example, U.S. Pat. No. 4,056,156 issued to Arnold J. Dayton on Nov. 1, 1977 teaches a bathroom scale having four load cells each having a resilient metal bellows for pressurizing liquid and connected to a common plenum connected to a pressure sensor. These weight sensing systems can be quite sensitive to temperature if the bellows have a large spring constant unless provision is made to accommodate the change of volume of the liquid with temperature. One exception is if the liquid is water at room temperature because water has a very low thermal expansion coefficient between 5.degree. C. and 25.degree. C. For vehicle occupant weight sensing, accurate response is required between -40.degree. C. and +100.degree. C. and for this operating temperature range all known suitable liquids exhibit large thermal expansions relative to metals and most plastics. [0018] A general object of this invention is to provide a seat occupant weight sensing system offering low cost and superior performance and a load cell for use in the system, which also overcomes certain disadvantages of the prior art. SUMMARY OF THE INVENTION [0019] In accordance with preferred embodiments of the invention, a seat occupant weight sensing system comprises load cells adapted to receive and be responsive to the force the seat occupant applies to the seat. Each load cell comprises two force input members and a pair of springs that operate in concert to enable the load cell to accurately measure axial force while enabling the load cell to be unresponsive to moments and forces applied perpendicular to the axis. [0020] Further, in accordance with preferred embodiments of the invention, the two springs when unstressed are slightly conical springs unitary with cylindrical flanges at their inside and the outside diameters. The cone angle is preferably such that preloading the springs during load cell manufacture flattens the springs to make them substantially flat rather than cone shaped. The spring flanges are affixed or linked to the force input members. The springs allow frictionless axial movement of the force input members relative to each other while resisting radial movement between the force input members relative to each other. [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. Continue reading about Load cell and seat occupant weight sensing system... Full patent description for Load cell and seat occupant weight sensing system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Load cell and seat occupant weight sensing system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Load cell and seat occupant weight sensing system or other areas of interest. ### Previous Patent Application: Energy absorbing device and shoulder belt-type vehicle seats comprising such energy absorbing device Next Patent Application: Chair with retractable cable unit Industry Class: Chairs and seats ### FreshPatents.com Support Thank you for viewing the Load cell and seat occupant weight sensing system patent info. IP-related news and info Results in 0.14358 seconds Other interesting Feshpatents.com categories: Novartis , Pfizer , Philips , Polaroid , Procter & Gamble , 174 |
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