Electricity: circuit makers and breakers – Special application – Change of inclination or of rate of motion responsive
Reexamination Certificate
2000-06-26
2002-08-06
Scott, J. R. (Department: 2832)
Electricity: circuit makers and breakers
Special application
Change of inclination or of rate of motion responsive
Reexamination Certificate
active
06429392
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to shock sensors in general and to shock sensors employing reed switches in particular.
BACKGROUND OF THE INVENTION
Reed switches have found wide use in shock sensors, particularly as safing sensors in automobiles. Typically, automobile crash sensing is performed by integrated micro device sensors which are incorporated onto chips which assess the magnitude and direction of the crash and employ preprogrammed logic to decide whether and how to deploy or activate various safety systems. These systems include airbags and seat belt retractors. Such micro sensors can be very cost-effectively incorporated into a safety system's control logic. However, such small-scale devices are subject to electromagnetic interference and related phenomena giving rise to possible false sensor outputs.
Thus macro scale sensors are needed to provide a safing sensor which provides the programmed logic with an indication that a crash of sufficient magnitude to warrant activation of safety systems is in fact occurring. Shock sensors employing reed switches meet the need for a large-scale device while at the same time allowing a relatively small sized package that can be directly mounted onto a circuit board. A reed switch is resistant to electromagnetic interference and the hermetic seal formed by the glass capsule about the reeds results in a highly reliable switch which is sealed from the atmosphere. Thus, reed switch based shock sensors are usually the design choice for safing sensors forming part of a vehicle safety system.
Reed switch based shock sensors have been designed with multiple axes of sensitivity, yet such devices are typically considerably more expensive than unidirectional shock sensors or are more sensitive to large-scale vibration. A typical reed switch based shock sensor has an acceleration-sensing magnetic that is held against a stop by a spring. The spring is typically pre-loaded so that no motion of the sensing mass takes place unless the acceleration loads exceed a selected value. What is needed is a bi-directional shock sensor with variable pre-load in each of two opposed directions.
SUMMARY OF THE INVENTION
The shock sensor of this invention employs an acceleration-sensing mass/magnet that is positioned about the center activation region of a reed switch. Motion of the sensing mass in either direction along the reed switch causes the reed switch to close. The shock sensor attains bi-directional sensing by employing two nested mechanisms about a single acceleration-sensing magnet. The first mechanism for sensing shock in a first direction is contained within a plastic sleeve. The sleeve has an inwardly extending flange on one side, and a lid on the other side, with a connecting cylindrical wall. The sleeve flange and lid ride on a plastic tube that contains the reed switch. The flange of the plastic sleeve forms an abutment and a shock-sensing magnet is biased against the flange by a spring that extends between the magnet and the lid. A second mechanism for sensing shock in a second opposed direction is formed by nesting the second mechanism about the first mechanism so that the sensing mass/magnet is used to sense shocks in both directions. Thus bi-directional sensing is achieved by nesting a second unidirectional mechanism about a first unidirectional mechanism. The second mechanism for sensing shock employs a second spring that biases the lid of the plastic sleeve against an abutment formed by a portion of a plastic capsule that encloses the entire shock sensor. The plastic tube, reed switch, plastic sleeve and first and second springs are contained within the plastic capsule which isolates them from the environment. Pairs of leads are welded to both the reed switch leads and extend down from the plastic capsule to mount the shock sensor to a circuit board. A pair of leads for making continuity checks is mounted to the plastic capsule so that placement of the shock sensor on the circuit board can be verified.
It is a feature of the present invention to provide a bi-directional shock sensor wherein the sensitivity in each of two opposite directions can be a selectable design variable.
It is another feature of the present invention to provide a hermetically sealed bi-directional shock sensor.
It is a further feature of the present invention to provide a bi-directional shock sensor that can be closed or open in the non-accelerated mode.
Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
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patent: 4877927 (1989-10-01), Reneau
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patent: 5212357 (1993-05-01), Reneau
patent: 5581060 (1996-12-01), Kobayashi et al.
patent: 0391582 (1990-10-01), None
patent: 1421487 (1976-01-01), None
patent: WO 01/01433 (2001-01-01), None
Bensley Martyn
Briers Marcel
Breed Automotive Technology Inc.
Drayer Lonnie
Scott J. R.
Stiennon Patrick
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