Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
1998-12-09
2001-03-27
Snow, Walter E. (Department: 2862)
Measuring and testing
Dynamometers
Responsive to force
C324S207200, C324S207260
Reexamination Certificate
active
06205868
ABSTRACT:
TECHNICAL ART
The instant invention relates generally to automotive passenger restraint systems and more specifically to a sensor for measuring seatbelt tension in a vehicle utilizing a Hall effect sensor.
BACKGROUND OF THE INVENTION
Automotive manufacturers and the National Highway Transportation Safety Association are investigating methods to disable vehicle air bags in situations where they may cause more harm than good. Typically, airbags have been developed to deploy with enough force to restrain a 175 lb. adult in a high velocity crash. Deployment of the same air bags when children are seat occupants may cause serious injury due to the force generated upon inflation of the bag.
As a result, seat weight sensors and seatbelt tension systems are being developed in an attempt to determine whether a seat occupant is a child. Such systems should identify when the occupant is small, or even when a child is in a rear facing infant seat, a forward facing child seat or a booster seat. Occupant weight measurement when a child seat is present is further complicated by the downward force applied to the child seat by the tension of a seat belt. When a child seat is strapped tightly, the seat belt forces the child seat into the vehicle seat and can often artificially increase the measured weight, which may lead to air bag deployment when children or infants are present in the seat.
Tension measurement mechanisms have been incorporated in the buckle of a seatbelt. In one embodiment, a sliding buckle is biased with a spring. When the belt is under heavy tension, the buckle pulls forward to control a switch that provides feedback to a vehicle processor.
Additionally, it is known to detect seat belt tension by attaching a spring steel bend sensor to one side of the belt. When belt tension increases, a resistance change occurs in the sensor and the analog signal is converted to an approximate belt tension. However, field test indicates that such sensors tend to drift with temperature and, therefore require temperature compensation.
The aforementioned seat belt tension measurement methods suffer from a number of disadvantages. Initially, a great number of additional parts are required for seat belt retractors or buckle configurations thereby adding complexity and cost to vehicle assembly and providing considerable difficulty in retrofitting existing vehicles. Additionally, mechanical switches and bend sensor systems have a limited service life, thereby requiring periodic replacement or adjustment.
The present invention may be used to detect whether the seat belt is under high tension thereby indicating that an infant seat or another inanimate object is belted into the seat. The instant invention can be used in conjunction with a seat weight sensor to determine whether an airbag should be deployed for a given occupant. Additionally, the instant invention provides a continuous measurement of seat belt tension and may be used to provide a threshold level of detection where desired.
SUMMARY OF THE INVENTION
The instant invention overcomes the aforementioned problems by providing a vehicle seat belt tension measurement system incorporating a Hall effect sensor capable of detecting the level of tension in a seatbelt.
The present invention measures tension by routing a seat belt through a sensor wherein the seat belt travels over a plunger biased upwardly by spring force. The plunger has a permanent magnet secured thereto that is brought in close proximity to a Hall effect sensor as increased seatbelt tension forces the plunger downwardly against the spring force.
The sensor comprises a plurality of belt guides for routing the seat belt over and across the shaped plunger. As tension in the seat belt increases, the plunger is displaced downwardly.
A “Hall effect” sensor secured to the sensor housing is responsive to the amount of magnetic flux therethrough. As the permanent magnet secured to the plunger comes in close proximity to the Hall effect sensor, the sensor is subjected to varying amounts of magnet flux produced by the magnet and generates an output responsive thereto. The output signal from the Hall effect sensor is operatively coupled to the input of a microprocessor for controlling a passenger restraint system. The microprocessor is correspondingly provided with an output, or a plurality thereof, to the passenger restraint system whereby an output signal is generated to inhibit deployment of an airbag or modify its inflation characteristics upon detection of high belt tension.
Hall effect sensors are known-in-the-art semiconductor devices that operate on the principle that a magnetic field applied perpendicular to the direction of a current flow through the semiconductor causes an electric field to be generated therein. This resultant electric field in the semiconductor material is generally perpendicular to both the direction of current flow and the magnetic field applied thereto. The electric field generates a voltage that may be measured across the semiconductor, thereby providing an indication of the magnetic field strength applied to the semiconductor. A variety of Hall effect sensors are readily available, from sensors that provide continuous analog output voltages to sensors that provide a digital output responsive to a predetermined level of magnetic flux. The latter can be used where threshold belt tension detection is desired. Hall effect sensors are robust and are insensitive to temperature fluctuations, thereby obviating the need for periodic recalibration and adjustment.
The microprocessor calculates seat belt tension from the voltage signal provided by the Hall effect sensor. The belt tension calculated by the microprocessor is used to determine the presence of an inanimate object or an infant seat. If a belt tension greater than ten pounds is detected, for example, it is unlikely that a person is present in the vehicle seat because belt tensions greater than ten pounds are generally uncomfortable for passengers. Accordingly, when high belt tension is detected, the microprocessor generates an output to the air bag control system that inhibits air bag deployment.
Furthermore, because commercially available Hall effect sensors have proven reliable in sensor technology applications, the instant invention provides a robust seat belt tension measurement system readily retrofitted to existing automobiles without the need for alteration or re-qualification of existing seat belt systems. This provides a significant advantage to automotive manufacturers by eliminating the cost and time involved in qualifying a safety restraint system to meet federal standards.
Therefore, one object of the instant invention is to provide a seat belt tension measurement sensor that incorporates reliable sensor technology to measure seatbelt tension and provide a signal to an airbag control system to inhibit deployment of an airbag when an infant seat is present.
Yet another object of the instant invention is to provide a seat belt tension measurement system having a simple mechanical design that does not require re-qualification of the seat belt system prior to use by automotive manufacturers.
A yet further object of the instant invention is to provide a seat belt tension measurement system that is insensitive to changes in temperature.
A yet further object of the instant invention is to provide a seat belt tension measurement system that generates either a continuous or threshold measurement of seat belt tension rather than threshold-type tension measurement.
The instant invention will be more fully understood after reading the following detailed description of the preferred embodiment with reference to the accompanying drawing figures. While this description will illustrate the application of the instant invention in the context of an automotive safety restraint system, it will be readily understood by one of ordinary skill in the art that the instant invention may also be utilized in other tension measurement applications unrelated to vehicle passenger restraints.
REFERENCES:
patent: 2452302 (194
Lyon P.C.
Snow Walter E.
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