Abstract:
A sensor for triggering a vehicle occupant restraint system, in particular a locking mechanism of a belt retractor, comprises an inertia body, a lower shell in which the inertia body is received, and an upper shell which rests on the inertia body and into which it projects. The upper shell is part of a pivotally mounted sensor lever which swings on displacement of the inertia body and activates the locking mechanism. At least one of the shells has at least one projecting support section for abutment of the inertia body.

Description:
TECHNICAL FIELD 
   The invention relates to a sensor for triggering a vehicle occupant restraint system, in particular the locking mechanism of a belt retractor. 
   BACKGROUND OF THE INVENTION 
   Conventional sensors usually have an inertia body, a lower shell in which the inertia body is received, and an upper shell which lies on the inertia body and into which it projects, the upper shell being part of a pivotally mounted sensor lever which swings on displacement of the inertia body and activates the locking mechanism. 
   Such a vehicle-sensitive sensor is known for example from the DE 298 22 610 and is installed into vehicle safety belt retractors. In the case of an impact of the vehicle, the inertia body, preferably a steel ball, moves and leads to the swinging of the sensor lever. A coupling catch on the sensor lever is thereby guided into the coupling teeth of a blocking mechanism, which finally blocks the belt spool and prevents a withdrawal of belt band. The triggering of the sensor also takes place, however, at a particular inclined position of the vehicle. 
   BRIEF SUMMARY OF THE INVENTION 
   According to the invention, a sensor is provided in which the predetermined angle of tilt for triggering the sensor can be maintained within narrow limits. Furthermore, a smaller noise development is to occur, which is caused in that in operation, on contact of the control lever and the control disc on the belt retractor, rattling noises could occur. This reduction of the rattling noises must not lead to the smooth running and the problem-free locking engagement of the control lever being impaired. 
   These advantages are achieved in a sensor which comprises an inertia body, a lower shell in which the inertia body is received, and an upper shell which rests on the inertia body and into which it projects. The upper shell is part of a pivotally mounted sensor lever which swings on displacement of the inertia body and activates the locking mechanism. At least one of the shells has at least one projecting support section for abutment of the inertia body. 
   In prior art, the shells were either constructed as cups or as mountings in the shape of a truncated cone, i.e. as a support surface of revolution which is as smooth as possible. The invention differs from this by not in fact aiming for a continuously smooth, uniform surface, but rather providing projecting support sections. These may be formed, e.g. with respect to a cone-shaped side wall which defines the inner side of the shell, in that either the at least one support section projects (or, preferably, several support sections project) from this cone-shaped side wall, or that the support sections complement each other externally to the cone-shaped side wall and are only interrupted by grooves in the cone-shaped side wall. Between the grooves, a support section is then produced, projecting with respect to the base of the groove. 
   As has been found out in tests, through an interruption of the hitherto continuous support surface, a damping is achieved to reduce the noise formation and also a very precise triggering is achieved at the predetermined angle of tilt. Particularly when grooves are provided, a further effect also occurs. The dirt which is deposited in the course of time on the inertia body can be deposited in the pockets formed by the grooves. Also, the projecting support sections can lead to the dirt, which is deposited on the ball, being constantly stripped off. 
   Several punctual projections, e.g. in the form of spherical segments, can form the support sections, preferably at least three punctual projections being provided in the form of spherical segments, so that the inertia body in normal driving operation only rests on these projections. 
   In the preferred embodiment, the punctual projections in the form of spherical segments are arranged lying on a circle and spaced apart from each other circumferentially. This circle preferably has a center point which runs through the axis of symmetry of the inner side of the shell realized so as to be of revolution. 
   Another possibility for forming one or more support sections consists in forming one or more linear projections, for example by a ring-shaped projection, preferably in the form of a circular ring, being provided. Also, several concentric projecting rings can form the support sections. 
   Vice versa, of course also, as already mentioned, ring-shaped grooves can be formed in the shell, so that support sections projecting between the grooves are available for the abutment of the inertia body. 
   Another embodiment again makes provision to construct radial, substantially linear projections or grooves running along the shell. Therefore, a type of star-shaped pattern is produced on the shell, the rays of the star either being formed by grooves or by the projecting support sections. 
   The inertia sensor according to the invention is constructed such that in the basic position of the sensor lever, i.e. when the locking catch is not yet guided in, the inertia body rests exclusively on the projecting support sections. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a sectional view through a belt retractor with a sensor according to the invention, 
       FIGS. 2  to  5  show perspective views of variously constructed sensor levers as part of the sensor according to the invention and 
       FIGS. 6   a  to  8   b  show top views onto the sensor housing with the lower shell according to various embodiments and also detail views of the shell surface. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1  a sensor  10  is shown for the vehicle-sensitive triggering of the locking mechanism of a safety belt retractor. Reference  12  designates the housing of the safety belt retractor, in which the sensor  10  is housed.  14  in turn designates the diagrammatically illustrated control disc with its teeth. The sensor consists substantially of three parts, namely an inertia body in the form of a ball  18 , a sensor lower part, also known as sensor housing  20 , which has a lower shell  22  to hold the ball  18 , and of a sensor lever  24 . The sensor lever  24  is constructed as a one-armed lever, which is pivotally connected with the sensor housing  20  by means of a swivel bearing  26 . At the opposite end, a control catch  28  is formed onto the sensor lever  20 , which control catch  28  can engage into the teeth  16  when the sensor lever  24  swings upwards. In addition, an upper shell  30  is formed onto the sensor lever  20 , which upper shell  30  rests on the ball  18  and into which the ball  18  projects. The ball  18  is therefore secured between the lower and the upper shell  22  and  30 , respectively. 
   With the alteration of the angle of the vehicle or decelerations of the vehicle, the ball  18  can move in the shells  22 ,  30  and in a known manner can lead to the deflection of the sensor lever  24  and for the engaging of the control catch  28  into the control disc  14  and hence to the triggering of the locking mechanism of the belt retractor. 
   When the word “shell” is used below, this therefore always means in the following the inner face of the shell-shaped mounting. 
   Various sensor levers are illustrated in  FIGS. 2  to  5 , which lead to the angle of tilt, at which the sensor responds, being exactly maintained and which avoid a development of noise, as previously mentioned. 
   Each of the shells  22 , but also the shells  30 , has a cone-shaped or cup-shaped side wall  40 , the surface of which is uniformly smooth. 
   According to  FIG. 2 , a so-called support section  42  in the form of a ring, more precisely a circular ring, projects from the cone-shaped side wall  40 . With this support section  42 , projecting with respect to the side wall  40 , the shell  22  and hence the sensor lever  24  rests on the ball  18 . 
   The circular ring has a center Z which lies on the imaginary central axis of the side wall  40  of revolution. 
   In the embodiment according to  FIG. 3 , instead of the ring-shaped projecting support section, numerous punctual projecting support sections  142  are provided in the form of spheres or hemispheres which, however, are arranged on an imaginary circular ring, the center Z of which, as in  FIG. 2 , coincides with the imaginary central axis of the side wall  40 . 
   Whereas in the embodiment according to  FIG. 3 , eight spherical or, more generally, punctual, projecting support sections  142  are provided, in the embodiment according to  FIG. 4  only four punctual or spherical projecting support sections  142  are provided on the side wall  40 . However, these again also lie on an imaginary circle around the center Z. 
   In the embodiment according to  FIG. 5 , the support surface for the ball  18  is composed of numerous star-shaped linear support sections  242 , running radially outwards with respect to the center Z and along the side wall  40 . These individual support sections  242  are formed in that between adjacent support sections  242  grooves or, more generally, depressions  244 , are worked into the originally continuous cup- or cone-shaped side wall  40 . The support sections  242  therefore project with respect to these grooves. 
   Owing to the support sections  42 ,  142  and  242 , the ball can not deposit any dirt in the shell in the region of the contact lines or contact points. 
   In the embodiment according to  FIG. 5 , however, the ball can deposit the dirt in the depressions  244 , which act as pockets. 
   The sensor according to the invention preferably also has on its lower shell  22  a surface shape which deviates from the hitherto usual cup shape or cone shape. This can be seen well in  FIGS. 6   a  to  8   b.    
   In the embodiment according to  FIGS. 6   a  and  6   b , as in the embodiment according to  FIG. 5 , linear support sections  342  are formed, which run outwards in a star shape and are formed in that groove-shaped depressions  344  are provided between adjacent support sections  342 . The ball can deposit dirt in these depressions  344 . 
   In the enlarged illustration of  FIG. 6   b  it can be seen that the projection running out in the support section  342  is cone-shaped in cross-section and tapers upwards at an acute angle. 
   In the embodiment according to  FIGS. 7   a  and  7   b , the similarly constructed support sections  442  are formed by projections which are trapezoidal in cross-section, i.e. do not taper at an acute angle. Groove-shaped depressions  444  are provided between adjacent support sections  442 . 
   In the embodiment according to  FIGS. 8   a  and  8   b , in a similar manner to that according to  FIG. 2 , support sections  542  are formed by numerous concentrically projecting rings, between which groove-shaped depressions  544  are provided for the depositing of dirt. Just like in the embodiments according to  FIGS. 5  to  7   b , also in this embodiment each support section  542  lies on a cup-shaped or, preferably, cone-shaped side wall  40 , which is only interrupted by the depressions  544 . 
   The ball  18  lies in its basic position, i.e. when the sensor lever  24  is not deflected for engagement into the teeth  16 , in all embodiments exclusively on projecting support sections. 
   It is to be stressed that the various types of projection are only by way of example. Of course, other forms of projection are also possible, and also a combination of the possibilities of embodiment of the projection presented in the drawings. 
   Although it is in fact advantageous for the improvement of the angle of tilt and the noise reduction and also the deposit of dirt, if both the lower and also the upper shell  22 ,  30  are provided with the projecting support sections, it would of course also be possible to either only construct the lower or only the upper shell  22 ,  30  with such projecting support sections. The support sections only project a few tenths of a millimeter up to a few millimeters with respect to the side wall  40  or with respect to the base of the depressions. 
   It is to be noted that the depressions can be provided with through-holes or slits allowing the dirt to leave the corresponding shell.