Abstract:
An omni-directional mechanical acceleration sensor is disclosed for use in applications including, but not limited to, vehicular seat belt systems, aircraft safety harness systems and initiation of airbag safety systems. The mechanical acceleration sensor incorporates at least two masses which, upon an acceleration event occurring, will cause a lever, to pivot thereby releasing the lever from engagement with an actuating means which would then initiate the applicable safety system.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit to U.S. Provisional Application No. 61/301,089, filed Feb. 3, 2010, and which is incorporated by reference herein in its entirety for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to omni-directional sensors and more specifically to mechanical omni-directional sensors which are suitable for applications such as seat belt restraints. 
     Acceleration sensors are used for many purposes. One widespread use is in automobiles for locking seat belts automatically upon detection of a predetermined positive or negative acceleration (deceleration). Such sensors are also used to inflate vehicular air bags when a specific, higher predetermined vehicle deceleration occurs. 
     One previous prior art design is disclosed in U.S. Pat. No. 5,636,807 issued to Warrick. This disclosure identifies a mechanical acceleration sensor that incorporates a heavy inertia mass suspended by two balls which are supported by two pivoting arms and supporting linkage. 
     Many automotive acceleration sensors have an inertia mass which senses acceleration in the generally horizontal directions of travel of the automobile. This mass can take the form of a tilting mass, a swinging pendulum, or a ball rolling up a ramp. In all, a mechanism responds to a predetermined movement of the mass to lock the reel which stores the belt webbing to prevent webbing payout. 
     Another application for deceleration sensors is to lock aircrew safety harness seat belt reels in response to aircraft acceleration. Since aircraft travel in multiple directions (combinations of vertical and horizontal), the automotive inertia mass movement types of sensors, described above, would be only partially effective, since they are limited in operability to sensing acceleration in generally horizontal directions, or in the plane of vehicle movement. 
     Most aircraft (and some automotive acceleration) sensors operate by sensing a predetermined acceleration of the storage reel as the harness webbing attempts to unreel from it. This results from aircraft movement which imposes unseating “G” forces on an aircrew member. These sensors sometimes use weights or masses which move sufficiently radially at a predetermined reel speed to actuate a locking mechanism. 
     Other aircraft sensors use an inertia mass connected to the reel by a screw mechanism. Acceleration of the reel by unwinding webbing accelerates the mass which, due to inertia, lags rotary movement of the reel. This relative motion turns the screw which moves a locking dog axially to engage the reel ratchet teeth and lock the reel. Such an aircraft acceleration sensor is illustrated in U.S. Pat. No. 4,801,105 issued to Frisk. 
     Such aircraft acceleration sensors do not react directly to vehicle acceleration, but only indirectly by reacting to resultant web and reel acceleration. Since they only indirectly respond to vehicle acceleration, they require some web payout to operate. Also, these types of sensors are use-specific, i.e. useful only with webbing reels or other reactive secondary movements, and cannot be utilized to perform other functions. 
     SUMMARY OF THE INVENTION 
     The disclosed device is an omni-directional mechanical acceleration sensor (hereafter referred to as “the acceleration sensor”), that can be used in applications where a mechanical output is desired resulting from a predetermined acceleration event acting on the sensor which may occur about any axis (X forward/aft, Y right to left and Z up and down) or combination thereof. 
     Preferably, the acceleration sensor can be operatively connected to either a means to inflate an airbag or to a locking means associated with a webbing reel or similar device, such as a spring-loaded plunger. The device operably connected to the acceleration sensor will be referred to hereafter as an “actuating means” and refers to embodiments known to those having ordinary skill in the art which can be operably connected to the acceleration sensor. 
     The acceleration sensor, upon a pre-determined acceleration rate or event being reached, will release itself from operative connection to the actuating means thereby causing the actuating means to perform its function; be it to engage the webbing reel or similar device and prevent further strap or seat belt unwinding, or inflate an airbag, etc. As defined herein, the term “predetermined acceleration event” means the threshold acceleration required to pivot the release lever to its activated position. Typically, the acceleration threshold is determined by the customer prior to assembling the sensor. 
     The disclosed acceleration sensor is designed to have a smaller footprint and be more reliable than prior art omni-directional mechanical sensors. 
     The acceleration sensor is capable of being positioned in any orientation. It comprises a pivotal release lever having a catch located at or near its distal end. Before an acceleration event occurs, the pivotal release lever remains in a first, non-activated position operably connected to the actuating means. Upon a predetermined acceleration event occurring, the release lever pivots to a second activated position which releases the actuating means from operable connection to the release lever. 
     In a preferred embodiment, the distal end of the release lever defines a catch which is the portion of the acceleration sensor operatively connected to the actuating means earlier described and the connection is released as the release lever pivots a predetermined distance to the activated position. 
     For situations where the actuating means refers to a seat belt harness system or the like and not to an airbag system, reconnection of the actuating means back to the acceleration sensor is possible. For example, once an acceleration event occurs and the release lever pivots releasing the actuating means from connection to the acceleration sensor, reconnection can occur preferably by manual movement of the actuating means back into operative connection with the sensor. 
     The catch is preferably designed with a tapered tip which allows the release lever to slightly pivot and allow the actuating means to slide back into operative connection with the release lever if displaced a sufficient distance. Also, the catch, rather than having its inner face being perpendicular to the release lever, has a slight negative angle that prevents creeping during random vibration events which might cause the release lever to pivot even through a predetermined acceleration event does not occur. The slight negative angle causes the release lever to be pulled back to the non-activated position. The catch is the part of the acceleration sensor which operatively connects to the actuating means. 
     The acceleration sensor has a release lever connected to a housing for pivoting from a non-activated position to an activated position and, at least one inertia mass which is operably connected to the release lever, where in response to a pre-determined acceleration event, the inertia mass will cause the release lever to pivot from the non-activated position to the activated position. 
     The acceleration sensor includes at least one inertial mass and at least one rocker mass positioned on opposing sides of the release lever. A stem is connected to the inertial mass and passes through a hole present in the rocker mass. A second pivot lever in combination with the inertia mass and stem is used to cause the release lever to pivot upon a predetermined acceleration event occurring in the +Z axis. The rocker mass is used to cause the release lever to pivot upon an acceleration event occurring in the X-Y plane or in the −Z axis. Accordingly, the rocker mass must have an appropriately sized surface or diameter which is sufficient to pivot the release lever in response to a predetermined acceleration event occurring. As defined herein, the Z axis refers to the axis along which the release lever pivots.  FIG. 1  provides an x-y-z coordinate system relative to the acceleration sensor. It should be understood that although the figures are presented in a slight perspective view, this should not detract from interpreting how the coordinate system is described in this specification. 
     The hole present in the rocker mass is sufficient to allow the stem to slidably pass through for operable contact with the second pivot lever. However, the rocker mass must be responsive to the tilting of the inertial mass. In other words, too large a hole through the rocker mass may make the rocker mass unresponsive. In a situation where the inertial mass is tilted, the stem would act upon the top surface of the rocker mass to cause the rocker mass to correspondingly tilt. The stem is also designed to have an end which will engage the bottom of the rocker mass in −Z acceleration events as will be discussed later. 
     Thus, the release lever, which pivots along one axis, is made responsive to omni-directional acceleration events by being operably connected to a second lever and the rocker mass. 
     The center of gravity of the inertia mass is located further away from the release lever than is the center of gravity of the rocker mass. For a predetermined acceleration event to occur, the inertia mass will tip in one direction while the rocker mass, which sits on a portion of the sensor housing, will correspondingly tip, raising a top surface edge to contact the release lever and cause the release lever to pivot to a sufficient degree to release the catch. For other acceleration events, either: 1) the inertia mass, stem and rocker mass will act directly to raise the release lever (−Z axis); or, 2) the inertia mass and stem will cause the secondary pivotal lever to pivot and raise the release lever (+Z axis). 
     In a preferred embodiment, the disclosed acceleration sensor comprises: a housing; a release lever pivotally connected to the housing at its proximal end and having a catch at its distal end; an aperture present through the release lever; an inertia mass; a rocker mass; a stem connected on one side of the release lever to the inertia mass and where the stem passes through the release lever and through a central hole in a rocker mass positioned directly below the release lever and seated upon a portion of the housing; a second lever pivotally connected to the housing and having a proximal end in contact with the end of the stem and a distal end which is contactable with the release lever between aperture and distal end of the release lever; and, a device such as a calibration spring or the like operatively connected to the release lever for exerting a force upon the same side of the release lever as is the inertia mass (in the +Z axis). The force applied by the calibration spring is to ensure that the release lever will not pivot to the activated position unless an acceleration event occurs. 
     When an acceleration event occurs in any direction, the inertia mass will cause the release lever to displace from a first non-activated position, where the catch is in operative contact with the actuating means, and pivot upward to a second activated position, which is defined here as the position of the release lever when the catch releases from operative contact with the actuating means. 
     At the conclusion of the acceleration event, the inertia mass will return substantially to its original position and thereby cause the release lever to return to its first non-activated position. Where the sensor is used with a seat belt or harness system, upon activation, the harness or seat belt will typically remain in the locked position until the user manually displaces the actuating means away from engagement with the webbing reel, typically by use of a slidable handle, to slide the actuating means back into engagement or operative contact with the catch of the acceleration sensor. 
     Thus, the release lever, pivotally connected to a housing, is designed to pivot in response to an acceleration event in any direction from a first non-activated position to a second activated position. The release lever can be displaced into the second activated position by one of the following: 
     a) an acceleration event occurs when the inertia mass tips with sufficient force to correspondingly tip the rocker mass so that a portion of the top edge of the rocker mass contacts the release lever and overcomes the force applied to the release lever by the calibration spring and pivot the release lever; 
     b) an acceleration event occurs when the inertia mass and stem apply enough force upon the proximal end of the second lever to overcome the force applied to the release lever by the calibration spring and pivot the distal end of the second lever into contact with, and pivot the release lever; 
     c) an acceleration event occurs when the inertia mass and the rocker mass apply enough force to overcome the force applied to the release lever by the calibration spring and pivot the release lever; 
     d) a combination of a) and b); or, 
     e) a combination of a) and c). 
     In preferred embodiments, the inertia mass and rocker mass of the disclosed acceleration sensor are constructed from a dense metal such as tungsten or brass. As a result, the mechanism can be designed with a higher gauge spring resulting in greater sensitivity for responding to an acceleration event. 
     The inertia mass can be designed in various configurations such as cylindrical although a conical shape is preferable. 
     Preferred embodiments include some type of alignment guide for ensuring that the release lever travels only in the pivot direction. Suitable alignment guides include, but are not limited to: a) elevated walls on either side of the release lever; or b) a hole appropriately sized and located on the release lever so that a dowel pin anchored to the housing, can extend through. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the acceleration sensor in the non-activated position; 
         FIG. 2  illustrates the acceleration sensor in an activated position resulting from an acceleration event occurring in the +Y axis; 
         FIG. 3  illustrates the acceleration sensor in an activated position resulting from an acceleration event occurring in the +Z axis; 
         FIG. 4  illustrates the acceleration sensor in an activated position resulting from an alternative acceleration event occurring in the −Y axis; 
         FIG. 5  illustrates the acceleration sensor in an activated position resulting from a second alternative acceleration event occurring in the +X axis; 
         FIG. 6  illustrates the acceleration sensor in an activated position resulting from an acceleration event occurring in the −Z axis. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The acceleration sensor  10  is illustrated in  FIG. 1  in the non-activated position. 
     Acceleration sensor  10  comprises a housing  12 , an elongated release lever  14  having a proximal end  16  and a distal end  18  having a release catch or tooth  20 . A pivot pin  22  pivotally mounts release lever  14  to housing  12 . Release lever  14  further has an inward facing surface  24 , an outward facing surface  26  and aperture  28 . 
     Acceleration sensor  10  further comprises a stem  30  extending through aperture  28  and having an inertia mass  32  mounted adjacent to outward facing surface  26 . Inertia mass  32  comprises top mass  32   a  and bottom mass  32   b  which create a jam nut to one another preventing further displacement along stem  30  once properly positioned on stem  30 . A rocker mass  34  is positioned on the side of release lever  14  opposite inertia mass  32 . Rocker mass  34  has a top surface  35  and a bottom surface  37 . Stem  30  has a headed end  31 . Rocker mass  34  has a hole of sufficient diameter which permits stem  30  to slide through while allowing rocker mass  34  to respond accordingly to the degree of tilt experienced by inertia mass  32 . 
     To provide a counter force upon release lever  14 , a rod  36  is threadably engaged to housing  12  on one end and extends through an aperture  38  in release lever  14 . A calibration spring  40  is positioned about threaded rod  36 , between an appropriately sized lock nut  42  threadably engaged to rod  36  and a counter bore in aperture  38 . Lock nut  42  can be adjusted to alter the compressive force spring  40  exerts upon release lever  14  for urging release lever  14  to remain in the first non-activated position. Use of lock nut  42  prevents vehicular vibrations from reducing the compressive force set upon spring  40 . 
     Acceleration sensor  10  also comprises a second lever  44  having a proximal end  46  and a distal end  48  and pivotally mounted by pivot pin  50  to housing  12 . Rocker mass  34  is seated on housing portion  41  that has opening  43  for allowing the end of stem  30  to contact proximal end  46  of second lever  44 . 
     Thusly, proximal end  46  is positioned for operable contact with stem  30  and inertia mass  32 ; and distal end  48  is positioned for operable contact with release lever  14 . 
     Rocker mass  34  comprises an appropriately sized top surface area  35  adjacent to inward facing surface  24  of release lever  14 . The appropriately sized top surface area  35  of rocker mass  34  means that in response to an acceleration event, a portion of top surface area  35  of rocker mass  34  will contact inward facing surface  24  with sufficient force to pivotally displace release lever  14 . 
     Acceleration sensor  10  may also include an alignment guide to ensure reliable pivotable movement of release lever  14 . In the preferred embodiment, the alignment guide comprises an appropriately sized dowel pin  52  secured to housing  12  and extending upward through aperture  54  on release lever  14 . In another embodiment of an alignment guide, housing  12  can have elevated sides to maintain a proper pivot tract for release lever  14 . 
       FIG. 1  illustrates acceleration sensor  10  in the non-activated position meaning that engagement tooth  20  is connected to an actuating means such as a spring-loaded plunger or the like which in turn is operatively connected to an inertia reel or other applicable system (not shown). In the non-activated position, the inertia reel operably connected to an actuating means is free to wind and unwind. However, in response to an acceleration event of a pre-determined magnitude, release lever  14 , will pivot sufficiently to release tooth  20  from engagement with the actuating means which then locks an inertia reel (not shown). 
     In the preferred embodiment, a portion of the inside facing surface  24  of release lever  14  rests on housing  12  to prevent unnecessary movement. 
     Release lever  14  pivots about the pivot pin  22  and is held in a non-activated position by the force being applied by calibration spring  40  preventing a premature release of operative connection between tooth  20  and the actuating means (not shown). Tooth  20 , rather than having its inner face being perpendicular to release lever  14 , has a slight negative angle of approximately 2 degrees that prevents creeping during random vibration events which might cause release lever  14  to pivot even though a predetermined acceleration event does not occur. The slight negative angle urges release lever  14  to the non-activated position. 
     The sensitivity of the acceleration sensor  10  can be calibrated by increasing or decreasing the force exerted by spring  40  with nut  42 . Depending on the specific acceleration event requested by the customer, the pivot point of second lever  44  to housing  12  will vary and the precise fulcrum point will be established at the design stage. 
     Sensitivity of acceleration sensor  10  can be calibrated by displacing inertia mass  32  higher or lower on stem  30 . A slip fit hole exists between rocker mass  34  and stem  30  which allows stem  30  and inertia mass  32  to slide downward. The bottom end  31  of stem  30  is in contact with the proximal end  46  of second lever  44 ; this contact occurs because of a clearance hole  43  in housing  12  to allow the end of stem  30  to protrude for contact. 
     The force resulting from a predetermined acceleration event are designated as “F” in  FIGS. 2-6  and illustrate how force F affects the operation of acceleration sensor  10  when applied in different directions. 
     Accelerations in X and Y plane 
     For acceleration in the X and Y plane, inertia mass  32  tends to ‘tip’ as illustrated in  FIG. 2 ,  FIG. 4  or  FIG. 5 . This is due to inertia mass  32  being larger with respect to rocker mass  34 . The tendency of inertia mass  32  to tip is enhanced by rocker mass  34  being positioned in a cup or spot face area of housing  12 . As inertia mass  32  tips over, it causes release lever  14  to pivot to the activated position thus signaling that a predetermined acceleration event has occurred. 
     There is a leverage difference depending on whether: a) the top surface edge or lifting edge of rocker mass  34  which is closest to pivot pin  22 ; or, b) the top surface edge or lifting edge of rocker mass  34  which is furthest from pivot pin  22  contacts release lever  14 . 
     Referring to  FIG. 2  and  FIG. 4 , because a lever is used, more force is required to be applied at the contact of rocker mass  34  to release lever  14  in  FIG. 2  than the force required to lift release lever  14  in  FIG. 4 . 
     In order to ensure that the same acceleration will trigger an event, the side walls of housing  12  adjacent to rocker mass  34  are designed so that in the direction where less force is required, i.e. in  FIG. 4 , the top portion of the sidewall of rocker mass  34  contacts the housing sidewall, the location of contact illustrated as tipping edge  60 . 
     In the direction where more force is required, i.e. in  FIG. 2 , the middle portion of the sidewall of rocker mass  34  contacts the housing sidewall at a lower level than for the direction illustrated in  FIG. 4 . The location of contact illustrated as tipping edge  62 . 
     An alternative embodiment to ensure pivoting of release lever  14  in an up and down direction is possible where, instead of the use of a dowel pin, raised sides are used to ensure a proper up and down track. 
     Accelerations in −Z Axis 
       FIG. 6  illustrates acceleration in the −Z axis. For acceleration in the −Z axis (minus Z), the inertia of stem  30 , inertia mass  32  and rocker mass  34  and release lever  14  will react or pull upward on release lever  14  causing release lever  14  to move or rotate upward about pivot pin  22  thus signaling that the acceleration has met or exceeded the pre-determined set point. 
     Accelerations in +Z Axis 
       FIG. 3  illustrates acceleration in the +Z axis. For acceleration in the +Z (positive Z) the inertia of stem  30  and inertia mass  32  displace into operative contact with proximal end  46  of second lever  44 . In response to this operative contact, second lever  44  rotates about second pivot pin  50  and distal end  48  of second lever  44  contacts inward facing surface  24  of release lever  14 . If sufficient acceleration occurs which connotes a predetermined acceleration event, then sufficient force is applied in the +Z for distal end  48  to displace release lever  14  a sufficient distance to release the actuating means from contact with release catch  20 . 
     In other words, in response to an acceleration event in the +Z direction, stem  30  can displace through a hole in rocker mass  34  until stem head  31  is in contact with proximal end  46  with sufficient force to pivot second lever  44  and distal end  48  into contact with release lever  14  and pivot release lever  14  from its non-activated position to a second activated position. 
     It is to be noted that in order for release lever  14  to pivot from the non-activated position illustrated in  FIG. 1 , to the activated position illustrated in  FIG. 3 , there must be a sufficient length of stem  30  between release lever  14  and the base of inertia mass  32  so that inertia mass  32  does not contact release lever  14  during a predetermined acceleration event in the +Z axis. In other words, stem  30  must have sufficient length from inertia mass  32  to pivot second lever  44  without inertia mass interfering with release lever  14  being able to pivot to the second activated position.