Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
2000-07-26
2001-11-06
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
Reexamination Certificate
active
06311571
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems that ascertain what is occupying a vehicle seat for 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 avoid deployment when the seat is empty to save the cost of replacement. It is desired 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 an 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 senses the severity of a vehicle crash, monitors elements of the occupant protection system for proper operation, and deploys occupant protection devices. 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 for receiving input from other sensors responsive to aspects of the occupancy of the seat.
To optimally deploy an airbag the SDM must take into account the weight of a seat occupant. Seat occupant weight sensors sense the weight of the occupant and communicate that weight to the SDM. With certain known seat occupant weight sensing systems seat belt tension affects the weight measurement therefore, for those systems, seat belt tension must be measured and communicated to a microprocessor of the SDM.
Capacitance sensing semiconductors are made by Quantum Research Group of Pittsburgh, Pa. and others. These devices sense small capacitances and certain of the designs provide output that varies linearly or monotonically with the capacitance being sensed.
A seat belt tension sensor must meet certain requirements: For accuracy and long life, friction in the mechanism must be minimized. The sensor must be accurate over a wide range of temperatures. The sensor must not rattle when the roads are rough. The seat belt tension sensor mechanism must withstand about one thousand pounds of seat belt force repeatedly without damage and not fracture or otherwise fail to restrain the occupant under about four thousand pounds of seat belt force, which could occur when the vehicle collides with an obstacle. No known design meets these requirements at a low cost.
Known force sensors must be protected from forces greatly in excess of the forces they are designed to measure. A seat belt tension sensor incorporating a known force sensor must protect the force sensor from the large forces that sometimes occur. Providing protection adds to the cost and complexity of the seat belt tension sensor. Accordingly, a force sensor that can measure forces on the order of thirty pounds while not being damaged by forces on the order of one thousand pounds is desired.
Of the known distance sensing means, capacitance sensing is advantageous for being inherently insensitive to temperature, not requiring permanent magnets, and being insensitive to the material used for sensing elements.
A general object of this invention is to provide a seat belt tension sensor offering low cost and superior performance which also overcomes certain disadvantages of the prior art.
SUMMARY OF THE INVENTION
In accordance with the invention, a new mechanism enables a low cost seat belt tension sensor. The mechanism comprises an anchor, a seat belt tension receiver, a moving arm force responder, and a preloading spring. The moving arm force responder comprises a base unitary with one or two arms. The tension receiver operates to apply force derived from seat belt tension to the base thereby causing the base to flex and the arm or arms to move. A sensor responsive to arm position provides an electric signal indicating seat belt tension.
Further, in accordance with the invention, the anchor comprises a flat plate having an opening for receiving a seat belt, the seat belt tension receiver and the moving arm force responder. A cross member of the anchor spans one side of the opening. The cross member is designed to withstand the largest seat belt forces encountered during a collision.
Further, in accordance with the invention an edge of the cross member has a groove with salient edges engaging the base of the moving arm force responder. Friction between the cross member and the moving arm force responder is minimized by designing the salient edges and the base of the moving arm force responder to minimize or eliminate relative movement therebetween while the base flexes, whereby long life and low hysteresis are achieved.
Further, in accordance with the invention, it has been discovered that a moving arm force responder comprising one or two arms unitary with a flexible base combined with a position sensor enables a superior and lower cost seat belt tension sensor that leads to a particularly advantageous design wherein the position sensor is responsive to capacitance.
Further, in accordance with the invention, the distance sensor comprises a semiconductor capacitance sensor responsive to capacitance between a capacitor plate and an arm of the moving arm force responder. When the base of the moving arm force responder flexes under the applied force and the arm moves, the capacitance between the capacitor plate and the arm of the moving arm force responder is changed. The change in distance is determined from the output of the capacitance sensor and the seat belt tension is computed therefrom.
Further, in accordance with the invention, an arm of the moving arm force responder moves sufficiently in response to forces less than thirty pounds to enable a capacitive distance sensor to respond to the movement. Under larger forces the base of the moving arm force responder “bottoms out” against the groove of the cross member, thereby being protected from being stressed to its yield stress.
Further, in accordance with the invention, the moving arm force responder is able to repeatedly withstand seat belt forces upwards of one thousand pounds applied to its flexible base without damage thereby remaining responsive to seat belt tension between zero and thirty pounds.
Therefore, the invention satisfies the unmet need for a low cost seat belt tension sensor responsive to small seat belt tensions while being able to withstand large seat belt tensions.
Further, in accordance with a preferred embodiment of the invention, the moving arm force responder comprises a pair of arms, and the distance sensor comprises two capacitor plates fixed with respect to the anchor. One capacitor plate is parallel to and in close proximity to one arm of the moving arm force responder. Whereupon, by the laws of Physics, there is a first capacitance therebetween. The other capacitor plate is parallel to and in close proximity to the other arm of the moving arm force responder, whereupon there is a second capacitance therebetween. The capacitance sensor senses the capacitance between the two capacitor plates, which is substantially the series capacitance of the aforementioned first and second capacitances. When seat belt tension is applied, the base of the tension receiver flexes to increase the distance between the arms which decreases the series capacitance.
Further, in accordance with the aforementioned preferred embodiment of the invention, the series capacitance is substantially determined by the distance between the arms of the moving arm force responder and not by the position of the capacitor plates, which are fixed with respect to the anchor. In other words, the series capacitance is not affected should the two capacitor plates become located to one side or the other of the central position between the arms. Accordingly, the measured capacitance is substantially dependent on the distance between the arms and
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