Abstract:
A deceleration impact detector for detecting a vehicle collision or the like is composed of a rotor having an eccentric gravity center, a spring biasing the rotor to its initial position, a cam connected to rotor, and a pair of contacts consisting of a movable contact and a stationary contact. The rotor rotates together with the cam when a deceleration exceeding a predetermined level is imposed on the rotor. The pair of contacts are closed by the cam thereby to generate an electrical signal to inflate an air-bag. The movable contact is made of a resilient leaf spring, while the stationary contact is made of a plate having a high rigidity, so that resonant vibrations of the stationary contact otherwise caused by a high deceleration impact are avoided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-199397 filed on Jun. 29, 2001, the content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a detector for detecting a deceleration impact exceeding a predetermined level caused by an accidental collision or the like. The detector is used, for example, to generate a signal for inflating an air-bag mounted on an automotive vehicle.  
           [0004]    2. Description of Related Art  
           [0005]    A conventional collision detector is disclosed, for example, in JP-A-2000-182488. The collision detector disclosed in this publication, as shown in FIG. 10, is composed of a rotor  110  rotatably supported by a rotor shaft  100 , a cam  120  fixed to the rotor  110 , a pair of contact springs  130 ,  140  which are closed by the cam  120  when the rotor  110  rotates by a predetermined rotational angle, and a printed circuit board  150  having an electrical circuit for generating a signal upon closing of the pair of contact springs  130 ,  140 .  
           [0006]    Referring to FIGS. 11 and 12, operation of this collision detector will be explained. When a deceleration is caused by a vehicle collision, the rotor  110  rotates in a direction shown by “b” against a biasing force Tset (in a direction shown by “a”) of a contact spring  130 . The contact spring  130  is pushed by the cam  120  rotating together with the rotor  110  and is resiliently deformed thereby to contact the other contact spring  140 . Upon closing of the contact springs  130 ,  140 , an electrical signal (an ON signal) for inflating an air-bag is generated.  
           [0007]    However, there are following problems in this collision detector. (1) After the contact spring  130  contacts the other contact spring  140 , the other contact spring  140  resonantly vibrates due to a collision impact, and thereby a contact between two contact springs  130 ,  140  cannot be maintained. Accordingly, a stable and reliable signal is not obtained form the collision detector. (2) Since the contact spring  130  biases the rotor  110  toward its initial position, an abrasion torque is always applied to the rotor  110 . A dispersion of the abrasion torque causes a functional dispersion of the collision detector. (3) The contact spring  130  contacts the other contact spring  140  at a rotational angle, i.e., at an ON position shown in FIG. 12. Since after the ON position, the resilient force of the contact spring  140  is additionally applied to the rotor  110 , a value Tset/MR (Tset is a biasing force in the direction “a” and MR is a rotational moment of the rotor in a direction “b”) rapidly increases. Therefore, it is difficult to maintain the ON signal for a long time. (4) Since a housing base  170  is connected to a housing  160  supporting the rotor shaft  100 , as shown in FIG. 11, a dimensional dispersion in connecting the housing base  170  to the housing  160  causes a dispersion in function of the collision detector. (5) A rotor assembly mounted on the housing  160  is inserted into an inside space of a casing  180 , and a gap between the housing  160  and the casing  180  has to be sealed. If a sealing material is supplied into the gap, it leaks into the casing  180 . Therefore, instead of using the sealing material, a packing  190  covering the bottom end of the casing  180  is disposed to provide a hermetical sealing, as shown in FIG. 10. Further, a lid  200  covering the packing  190  is connected to the bottom end of the casing  180  by heat-staking the bottom end. Use of the packing  190  and performing the heat-staking require an additional manufacturing cost.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an improved deceleration impact detector which functions with a high stability and reliability and can be manufactured at a low cost.  
           [0009]    The deceleration impact detector is used for detecting a high deceleration generated by an accidental collision of a vehicle or the like. An air-bag for protecting a passenger is inflated upon receipt of an electrical signal from the deceleration impact detector. The deceleration impact detector includes a rotor having its gravity center eccentric relative to a rotational center of the rotor, a coil spring biasing the rotor to its initial position, a cam connected to the rotor, and a contact member consisting of a resiliently movable contact and a stationary contact. When a deceleration exceeding a predetermined level is imposed on the rotor, the rotor rotates so that the cam connected to the rotor pushes the movable contact thereby to close the contact member. Upon closing the contact member, the detector generates an ON signal for operating the air-bag.  
           [0010]    The movable contact is made of a resilient leaf spring and the stationary contact is made of a plate having a high rigidity, thereby to avoid resonant vibrations of the stationary contact upon receipt of a high deceleration impact. The movable contact is positioned apart from the cam, forming a certain space therebetween, when the rotor is at its initial position. In this manner, rotation of the rotor is not restricted by the resilient force of the movable contact.  
           [0011]    The cam includes a first surface for pushing the movable contact and a second surface continuing from the first surface. The second cam surface is formed in a circular curvature around the rotational center of the rotor, so that the movable contact is not further pushed according to the rotation of the rotor after the contact member is closed. The electrical ON signal is maintained by the second cam surface while avoiding the resilient force of the movable contact from being applied to the rotor.  
           [0012]    Components of the detector including the rotor, the coil spring and the contact member are mounted on a housing having a rectangular housing base. The rectangular housing base is press-fitted into a rectangular opening of a casing thereby to contain the housing in the casing. Flanges extending from the four corners of the housing base are formed, so that the flanges are tightly received on receiving surfaces formed at corners of the casing. The housing base and the casing are hermetically sealed with a filler material filling small spaces between the housing base and the casing. The housing base may be separated into two parts, a base frame and a base plate press-fitted into the base frame, both parts being connected by crank-shaped connecting pins formed by molding.  
           [0013]    According to the present invention, the deceleration impact detector stably functioning with a high reliability and having a simple structure is manufactured at a low cost.  
           [0014]    Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a cross-sectional view showing a deceleration impact detector according to the present invention, taken along line I-I shown in FIG. 2;  
         [0016]    [0016]FIG. 2 is a cross-sectional view showing the deceleration impact detector, taken along line II-II shown in FIG. 1;  
         [0017]    [0017]FIG. 3 is a cross-sectional view showing the deceleration impact detector, taken along line III-III showing in FIG. 2;  
         [0018]    [0018]FIG. 4A is a plan view showing a housing base having flanges used in the deceleration impact detector;  
         [0019]    [0019]FIG. 4B is a partial plan view showing the flange of the housing base in an enlarged scale;  
         [0020]    [0020]FIG. 4C is a partial cross-sectional view showing a structure connecting the housing base to a casing, taken along line IVC-IVC shown in FIG. 4B;  
         [0021]    [0021]FIG. 5 is a drawing showing a rotor assembly to be housed in a casing of the deceleration impact detector;  
         [0022]    [0022]FIG. 6 is a graph showing a relation between a value of Tset/MR and an rotational angle of a rotor;  
         [0023]    [0023]FIG. 7 is a front view showing a modified form of a housing of the deceleration impact detector;  
         [0024]    [0024]FIG. 8 is a cross-sectional view showing the modified form of the housing, taken along line VIII-VIII shown in FIG. 7;  
         [0025]    [0025]FIG. 9 is a cross-sectional view showing a housing base of the modified form of the housing, taken along line IX-IX shown in FIG. 7;  
         [0026]    [0026]FIG. 10 is a cross-sectional view showing a conventional collision detector;  
         [0027]    [0027]FIG. 11 is a drawing showing a rotor assembly used in the conventional collision detector; and  
         [0028]    [0028]FIG. 12 is a graph showing a relation between a value of Tset/MR and a rotational angle in the conventional collision detector. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    A preferred embodiment of the present invention will be described with reference to FIGS.  1 - 6 . A deceleration impact detector  1  detects an accidental collision of an automotive vehicle, for example. As shown in FIGS. 1 and 2, the deceleration impact detector  1  is substantially composed of: a rotor  3  having a cam  2 ; a coil spring  4  for biasing the rotor  3  to its initial position; a contact member consisting of a movable contact  5  and a stationary contact  6 , that is closed when the rotor  3  rotates by a predetermined rotational angle from its initial position; a printed circuit board  7  having an electrical circuit for generating an ON signal when the contact member is closed; and a casing  8  for containing a rotor assembly “A” shown in FIG. 5 therein.  
         [0030]    A rotor shaft  10  connected to the rotor  3  is rotatably supported by a pair of upright walls  9   a  of a housing  9  as shown in FIG. 2. A weight  11  is connected to the rotor  3  so that a gravity center of the rotor  3  is eccentrically positioned with respect to the rotor shaft  10 . The cam  2 , as shown in FIG. 1, includes a first cam surface  2   a  and a second cam surface  2   b , both surfaces being formed continuously to each other. The first cam surface  2   a  is formed at a tip end of the cam  2  with a slant angle so that it pushes the movable contact  5  toward the stationary contact  6  to close both contacts when the rotor  3  rotates by a predetermined rotational angle. The second cam surface  2   b  has a circular curvature with respect to the rotational center of the rotor shaft  10 , so that the movable contact  5  is not further pushed toward the stationary contact  6  by the second cam surface  2   b  after both contacts  5 ,  6  are once closed. In other words, the movable contact  5  maintains its position after it once contacts the stationary contact  6  even if the rotor  3  further rotates.  
         [0031]    The coil spring  4  is fixed to the housing  9  at its one end and is connected to the rotor  3  at the other end. The rotor  3  is biased to its original position, being pushed against a stopper  12  formed in the housing  9  by a resilient force of the coil spring  4 . The contact member is composed of the movable contact  5  made of a resilient leaf spring and the stationary contact  6 , both contacts being fixed to a housing base  13  at their ends. More particularly, as shown in FIG. 1, the resilient movable contact  5  is anchored to the housing base  13  at its one end and abuts against an angled stopper  14  at the other end. The movable contact  5  includes a projected portion which is pushed toward the stationary contact  6  by the cam  2  when the rotor  3  rotates by a predetermined rotational angle. When the rotor  3  stays at its initial position, a certain space is formed between the first cam surface  2   a  and the projected portion of the movable contact  5 .  
         [0032]    The stationary contact  6  is made of a metallic plate having a thickness several times thicker than that of the movable contact  5  to secure a sufficient rigidity not to cause resonant vibrations when a high collision impact is imposed on the stationary contact  6 . An end portion of the stationary contact  6  is bent toward an opposite side of the cam  2 , as shown in FIG. 1, not to interfere with rotation of the rotor  3 . The printed circuit board  7  having an electric circuit thereon is mounted on the housing base  13  after the rotor assembly “A” shown in FIG. 5 is disposed in the casing  8 . Terminal portions of the movable contact  5  and the stationary contact  6 , lead out through the housing base  13 , are electrically connected to the printed circuit board  7 . One end of an output terminal  15  and a resistor  16  are also electrically connected to the circuit board  7 .  
         [0033]    The rotor  3  having the cam  2 , the coil spring  4 , the movable contact  5  and the stationary contact  6  are all mounted on the housing  9  having the housing base  13  and the upright walls  12   a , forming the rotor assembly “A” shown in FIG. 5. The rotor assembly “A” is contained in the casing  8  so that the housing base  13  closes an rectangular bottom opening  8   a  of the casing  8 , as shown in FIGS.  4 A- 4 C. The housing base  13  is press-fitted to the rectangular bottom opening  8   a . The housing base  13 , as shown in FIG. 4A, has flanges  13   a  formed at four corners thereof, while the casing  8 , as shown in FIG. 4C, includes surfaces  8   b  for receiving the flanges  13   a  thereon. After the rotor assembly “A” is contained in the casing  8  and the printed circuit board  7  is electrically connected to the rotor assembly “A”, a bottom surface of the printed circuit board  7  is covered with a lid  18 , as shown in FIGS. 1 and 2. A space between the lid  18  and an outer periphery of the housing base  13  and a space between the lid  18  and an inner periphery of the casing  8  are hermetically sealed with a filler material  17 , as shown in FIGS.  1 - 3 . Then, the casing  8  containing all the components therein is inserted in a outer casing  19  having a mounting bracket  20 . The deceleration impact detector  1  thus made is mounted on a vehicle via the mounting bracket  20 .  
         [0034]    Operation of the deceleration detector  1  will be described with reference to FIGS. 5 and 6. When a deceleration caused by a collision is imposed on the deceleration impact detector  1 , a rotational moment MR is generated in the rotor  3  due to its inertia in a direction “b” shown in FIG. 5. If the rotational moment MR exceeds a biasing force Tset of the coil spring  4  exerted in a direction “a”, the rotor  3  rotates in the direction “b”. When the rotor  3  rotates to a predetermined angular position (an ON position shown in FIG. 6), the first cam surface  2   a  pushes the movable contact  5  toward the stationary contact  6 . The movable contact  5  resiliently deforms and contacts the stationary contact  6 .  
         [0035]    As the rotor  3  further rotates, a contact point between the cam  2  and the movable contact  5  moves from the first cam surface  2   a  to the second cam surface  2   b . Since the second cam surface  2   b  is formed in a circular arc around the rotational center of the rotor shaft  10 , the position of the movable contact  5  does not change during a period in which it contacts the second cam surface  2   b . Therefore, a contacting force between the movable contact  5  and the stationary contact  6  is maintained unchanged when the rotor  3  further rotates from the ON position. Accordingly, the rotation of the rotor  3  is not unduly restricted by the resilient force of the movable contact  5 . Only an abrasion force between the second cam surface  2   b  and the movable contact  5  is applied to the rotor  3 . As shown in FIG. 6, the value Tset/MR gradually increases according to the rotational angle of the rotor  3 .  
         [0036]    Advantages of the present invention will be summarized below. Since the stationary contact  6  has a high rigidity and a movable contact  5  is resilient, the stationary contact  6  does not resonantly vibrates due to a high collision impact after both contacts are closed. Therefore, a stable ON signal can be obtained from the detector  1 . Since a certain space between the movable contact  5  and the cam  2  is provided until the first cam surface  2   a  contacts the movable contact  5 , no abrasion force is applied from the resilient movable contact  5  to the cam  2 . Therefore, the rotational torque of the rotor  3  is not affected by a dispersion of the abrasion force. Accordingly, a dispersion of the rotational angle at which the ON signal is generated can be made small. Since the movable contact  5  abuts against the stopper  14  with its resilient force, the movable contact  5  does not erroneously contact the stationary contact  5  if a small shock is applied thereto by driving on a rough road.  
         [0037]    Since the second cam surface  2   b  is formed in a circular shape around the rotational center of the rotor shaft  10 , the position of the movable contact  5  does not change during a period in which the movable contact  5  is contacting the second cam surface  2   b . Further, since the resilient force of the movable contact  5  is applied to the rotor  3  in a direction toward the rotational center of the rotor shaft  10 , the resilient force of the movable contact  5  does not suppress the rotation of the rotor  3 . The force suppressing the rotation is only a small abrasion force between the movable contact  5  and the second cam surface  2   b . Therefore, the rotor  3  smoothly rotates after the ON point, and the ON signal is stably generated.  
         [0038]    Since the flanges  13   a  formed at four corners of the housing base  13  are closely mounted on the receiving surfaces  8   b  of the casing  8 , as shown in FIG. 4C, the filling material  17  filling a space between the housing base  13  and the casing  8  is prevented from flowing out into the inside space of the casing  8 . Therefore, the inside space of the casing  8  is hermetically sealed by the filling material  17 , and it is not necessary to fix the lid  18  to the bottom of the casing  8  by heat-staking as done in a conventional detector. Further, it is not necessary to use a packing for providing the hermetical sealing. Accordingly, the manufacturing cost of the detector  1  can be reduced.  
         [0039]    The housing base  13  may be modified to a form shown in FIGS.  7 - 9 . In this modified form, the housing base  13  is composed of a base frame  13 A having a pair of upright walls  9   a , and a base plate  13 B. The base plate  13 B supports the movable contact  5  and the stationary contact  6  thereon. The base plate  13 B is press-fitted into the base frame  13 A and connected thereto by connecting pins  21 . The connecting pins  21  are formed by a secondary molding after the base plate  13 B is inserted into the base frame  13 A. The connecting pins  21  are formed in a crank-shape as shown in FIG. 9. The base plate  13 B and the base frame  13 A can be firmly connected by the crank-shaped connecting pins  21 .  
         [0040]    While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.