Pendulum mass acceleration sensor

Details Pendulum mass acceleration sensor Pendulum mass acceleration sensor

1999-09-22

2001-02-06

Donovan, Lincoln (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Permanent magnet-actuated switches

C200S06145M

Reexamination Certificate

active

06184764

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to shock sensors used to detect vehicle crashes in general, and to shock sensors employing a pendulum mass in particular.
BACKGROUND OF THE INVENTION
A typical motor vehicle manufactured today has a number of safety systems which function to deploy airbags, and possibly to retract seatbelts. The number of airbags provided in a vehicle continues to increase. Systems now in development deploy multiple airbags to protect vehicle occupants from front, rear, and side impacts, and to position the vehicle occupant's body to withstand acceleration. Deployment of safety systems requires sensors that can detect and characterize a crash as it occurs. Wide use of advanced active safety systems is dependent on producing systems that are sufficiently cost effective that they may be economically employed on a large number of vehicles.
Typically the lowest cost sensors are those formed on an integrated circuit chip using the technology used to form electronic circuitry. This technology is used to fabricate micro devices or accelerometers that can detect accelerations indicative of a vehicle crash. These sensors are particularly cost effective when the sensor can be fabricated together with the deployment logic circuitry using the same technology that is cost effective for large scale integration. However the very small size of these devices makes them sensitive to electromagnetic interference and the like, which can result in false indications of a crash.
Thus an important role remains for macro scale mechanical devices which are less prone to false readings. Such devices are used to verify the occurrence of an actual crash. These macro scale devices employ a sensing mass mounted on a spring or pendulum. Motion of the mass is detected by actuation of a reed switch or a magnetic field sensor of the Hall type.
DISCUSSION OF THE PRIOR ART
A typical reed switch shock sensor is a unidirectional sensor, principally because of the advances made in low cost and small packaging for this type of sensor, see for example U.S. Pat. No. 5,194,706.
Bidirectional sensors exist, for example U.S. Pat. No. 4,103,842, teaches a pendulum-mounted magnet which is positioned over a Hall effect sensor; or U.S. Pat. No. 5,450,049 which teaches a pendulum-mounted sensing mass and magnet positioned over a reed switch for detecting bidirectional acceleration. However, bidirectional or multidirectional shock sensors typically have proven too expensive or too bulky to satisfy the demand for a bidirectional shock sensor with the size and cost achieved by the unidirectional reed switch type sensors.
What is needed is a bidirectional shock sensor having a small package size and the simplicity of design to achieve cost effectiveness.
SUMMARY OF THE INVENTION
The shock sensor of this invention has a housing, which mounts directly to a printed circuit board. The housing contains a switch or sensor embedded in the housing and connected by leads to the circuit board. A pendulum sensing mass is suspended by two flexible pendulum arms, which are constructed of thin strips of spring material. The strips are planar and are arranged in spaced parallel relation where they engage the sensing mass and come together before being rigidly attached to the housing. The strips substantially constrain the mass to swing along an arc, which lies in a single plane. The plane containing the arc along which the mass swings is perpendicular to the planes defined by each pendulum arm. In the preferred embodiment a magnet either forms the sensing mass or is mounted to or within the sensing mass. The switch or sensor is encapsulated within the base of the housing. When a shock or acceleration which has a direction which is at least partially aligned with the arc along which the sensing mass swings is imposed on the housing, the resulting motion of the sensing mass and the magnet forming a part thereof is detected by the sensor or switch.
In the case of a reed switch acting as the sensor, and in which the reeds making up the switch are aligned in the plane in which the sensing mass pivots, the motion of the sensing mass and the magnet mounted thereto will cause the reed switch to change state from open to closed or from closed to open.
One embodiment of the shock sensor may employ a Giant Magneto-restrictive Sensor (GMR) which may be of the digital type, thus providing a switch-like response or the analog type which produces a value corresponding to the displacement of the magnet mounted to the sensing mass.
A further embodiment places a pair of mechanical contacts on either side of the sensing mass so that motion of the sensing mass along the arc through which it swings, causes the mass to engage one pair of mechanical contacts positioned on either side of the mass.
A feature of the present invention is a sensor that provides an indication of acceleration from opposed directions.
It is another feature of the present invention to provide a shock sensor that can provide a signal proportional to the magnitude of acceleration experienced by the shock sensor.
It is a further feature of the present invention to provide a shock sensor that incorporates both a binary switch and a sensor capable of providing a signal proportional to the displacement of a pendulum mass.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.


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