Abstract:
The underframe of a motor vehicle seat is equipped with weight sensors for sensing a weight load on the motor vehicle seat. The weight sensors are interposed between a first structure part, such as a seat profile of a longitudinal guide, and a second structure part, such as a console or a seat shell, and sense the weight exerted through the second structure part on the first structure part. The weight sensors are fastened to the first structure part and comprise sensor bolts projecting upward. Holes for the sensor bolts are provided in the second structure part. The sensor bolts extend through the holes and one nut, which forms a surrounding grip around the holes, is associated with each of the sensor bolts. The holes of the second structure part each comprise one hole region that surrounds the holes and is configured as a cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to German Application No. DE102005033730.9, filed Jul. 15, 2005, the contents of which are expressly incorporated by reference in their entirety as part of the present disclosure.  
       BACKGROUND  
       [0002]     The application relates to an underframe of a motor vehicle seat, the underframe is equipped with weight sensors for sensing a weight load on the motor vehicle seat.  
         [0003]     A motor vehicle seat is known from DE 199 05 363 C1 in the seat part of which there is disposed a seat occupant weight sensing system with a planar pressure sensor such as a foil pressure sensor. From DE 196 02 088 C2 there is known a seat occupancy recognition device in spring-mounted vehicle seat mounts, the recognition device sensing the lengthening of at least one of the springs in the seat part. A force transducer for determining the seat load is known from DE 101 22 316 A1. DE 199 20 378 A1 describes a vehicle seat that is connected to an underbody via weight sensors.  
         [0004]     Weight sensors as they may be utilized for sensing the weight in automotive vehicle seats are sold by the industry, the AWS-type sensors of Siemens VDO Automotive AG, Regensburg and the sensors sold in the trade name of MSG by Texas Instruments are referred to; they are silicon strain gages.  
         [0005]     When, in practice, such type weight sensors are utilized in the structure of a motor vehicle seat, purely practical problems arise from the fact that assembly tolerances are unavoidable. As contrasted with normal screws, weight sensors cannot tolerate transverse forces. Therefore, assembly must be free of transverse forces.  
       SUMMARY  
       [0006]     It is therefore the object of the invention to develop the prior art proposals for underframes with weight sensing systems using sensors in such a manner that, as far as practicable and taking into account the assembly tolerances, no transverse forces are generated and only forces in the direction that the sensor senses forces are generated. The solution to this object is an underframe of a motor vehicle seat comprising weight sensors for sensing a weight load on the motor vehicle seat, the weight sensors being interposed between a first structure part, such as a seat profile of a longitudinal guide, and a second structure part, such as a console or a seat shell, and sensing the weight exerted through the second structure part on the first structure part.  
         [0007]     The weight sensors are fastened to the first structure part and include sensor bolts projecting upward with holes for the sensor bolts provided in the second structure part such that the sensor bolts extend through the holes. Further included is at least one nut, which forms a surrounding grip around the holes, each nut associated with one of the sensor bolts. The holes of the second structure part each define at least one hole region that surrounds the holes and is configured as a cap.  
         [0008]     In this underframe, the weight sensors are interposed between two parts of the underframe, namely between the first structure part and the second structure part. The first structure part is for example a seat profile of a longitudinal guide for adjusting the position of the seat forward and backward. The second structure part is for example a console or a seat shell disposed thereon. All the loads generated in the vertical direction are transmitted through the weight sensors. Put another way, an imaginary separating plane in which only the weight sensors are located may be drawn through the underframe. The weight forces acting onto the second structure part are induced into the first structure part through the weight sensors only; there is no other way of transmitting the forces. Usually, there are provided at least four weight sensors, which are more or less associated with the four corners of the underframe.  
         [0009]     The weight sensors are appropriately fastened to the first structure part where they may be screwed, soldered or disposed by any other means for example. The weight sensors have a substantially vertically upright sensor bolt that is extending upward and is provided with a threading. The hole regions about the holes in the second structure part through which the sensor bolt extends are configured in the form of a cap. This cap shape allows positioning the sensor bolt in a certain angular range relative to the hole. This permits to correct for mounting inaccuracies. During mounting it is now possible to mount the weight sensor in such a manner that no forces oriented in the x-y plane act thereon due to mounting. As a result, during mounting the sensor bolt is loaded in its longitudinal direction only and the sensor bolt is not loaded in the transverse direction relative to the sensor housing. Accordingly, the weight sensor is not loaded with transverse forces as a result of mounting. Transverse forces may occur later, for example in the event of an accident. But under normal load conditions, the forces occurring are only oriented in the longitudinal direction of the sensor bolt and, as a result thereof, substantially in the z-direction.  
         [0010]     In a particularly preferred development, a cap-shaped perforated disk is provided underneath each hole region forming a surrounding grip around the sensor bolt. This lower cap-shaped perforated disk may already be part of the weight sensor itself, that is to say it may be solidly connected thereto, but it may also be a separate part and abut a portion of the sensor bolt. An upper cap-shaped perforated disk is further proposed, the perforated disk forming a surrounding grip around the sensor bolt and resting from the top on the hole region. Above this upper cap-shaped perforated disk there is the nut used for fastening the second structure part. The upper cap-shaped perforated disk may be a separate part, but it may also be configured on and, more specifically, integral with the nut that is screwed onto the sensor bolt. Preferably, there is respectively provided both a lower cap-shaped perforated disk and an upper cap-shaped perforated disk.  
         [0011]     The at least one cap-shaped perforated disk allows for improved abutment of the sensor bolt on the second structure part. If both a lower and an upper cap-shaped perforated disk are provided, the hole region of the second structure part is clamped in a planar manner in the mounting state, this allowing for precise fastening. Preferably, the spherical radii of the curvatures of the cap in the hole region and of the cap-shaped perforated disks are intermating. The planar abutment is improved as a result thereof.  
         [0012]     It is preferred that the hole be oversized with respect to the outer diameter of the sensor bolt, thus making it possible to orient the sensor bolt within the admissible region of the hole and allowing the sensor bolt to adopt various tilt positions within a conical angular range. The oversize is selected to still achieve sufficiently large abutment surface between the hole region and the at least one cap-shaped perforated disk.  
         [0013]     With a separately configured upper cap-shaped perforated disk, it is advantageous to have each of its two end or annular faces equipped with a concave cap surface. For practical use, one cap surface is needed only, the other one is not. A cap-shaped perforated disk with concave surfaces provided on either side thereof has the advantage that it is not necessary to mind the placing direction during assembly. No matter how the cap disk is placed onto the sensor bolt, one of the cap surfaces will always be turned toward the hole region.  
         [0014]     The hole region is preferably curved so as to show an arch pointing upward in the positive z-direction, so as to appear convex when viewed from the top (looking in the negative z-direction). The radius of curvature of the cap surface preferably ranges from 10 to 40 mm. Further, the cap surfaces are preferably spherical surfaces.  
         [0015]     Preferably, at least two of the various cap surfaces have a common center. It is particularly preferred that all of the cap surfaces have a common center.  
         [0016]     Other features and advantages of the invention will become more apparent upon reviewing the appended claims and the following non restrictive description of embodiments of the invention, given by way of example only with reference to the drawing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the drawing:  
         [0018]      FIG. 1  is a perspective illustration showing an assembly drawing of portions of a side part of an underframe of a motor vehicle seat;  
         [0019]      FIG. 2  is an end view of an arrangement similar to  FIG. 1 ;  
         [0020]      FIG. 3  is an end view like  FIG. 2 , but in another mounting position of the second structure part;  
         [0021]      FIG. 4  is an end view like  FIG. 2 , but again in another mounting position of the second structure part;  
         [0022]      FIG. 5  is a sectional view through a weight sensor with integrated perforated disk;  
         [0023]      FIG. 6  is a sectional view through a combined part uniting a nut and a perforated disk; and  
         [0024]      FIG. 7 a  perspective illustration showing an assembly drawing of a second configuration of an underframe of a motor vehicle seat. 
     
    
     DETAILED DESCRIPTION  
       [0025]     Of an underframe of a motor vehicle seat,  FIG. 1  shows a longitudinal adjustment device  20  of which a pair of rails is shown, the pair of rails comprising one floor profile  22  and one seat profile  24 .  FIG. 7  shows two pairs of rails. In a known manner, these profiles  22 ,  24  are slidable with respect to each other in their longitudinal direction, with rolling or sliding means (not shown) being provided for this purpose. Further, there is provided a catch device interposed between the two profiles or an electric drive (both not shown).  
         [0026]     In the first exemplary embodiment of the invention, which includes  FIGS. 1 through 4 , the seat profile  24  forms a first structure part  26 . Two weight sensors  28  are fastened thereon, each by means of two screws  27  or other suited fastening means. The sensors used are, for example, but not limited to, the AWS sensors sold by Siemens VDO. They have an electric connection region  30  and a sensor bolt  32  that extends substantially in the z direction and is preferably threaded. Connection with all the other parts of the motor vehicle seat located above the sensors (in  FIG. 1 ) occurs via the sensor bolts  32 . If the sensor bolts  32  are untightened from the parts located above them, the seat profile  24  and the floor profile  22  associated therewith can be separated from the motor vehicle seat. Accordingly, the sensors are part of the motor vehicle seat and need not be mounted separately.  
         [0027]     Above the weight sensors  28 , there is a second structure part  34  that is formed in the present case by a console  36  that extends in the longitudinal direction of the profiles  22 ,  24  and has substantially the same length as these. The console  36  is connected to a seat side part  42  through a front parallelogram arm  38  and through a rear parallelogram arm  40  that are each linked to the console  36 . A seat back  44  is hinged to the seat side part. A seat cushion  46  is carried by the two seat side parts  42  provided in all for each motor vehicle seat. Lastly, a bracket  48  is provided on the console  36  shown and is secured accordingly together therewith. The receiving part (not shown) of a safety belt can be fastened to this bracket.  
         [0028]     In the console  36  there are provided holes  48  that are located directly above the sensor bolts  32 . They have a diameter that is oversized with respect to the outer diameter of the sensor bolts  32 . A hole region  50  surrounds each of the holes  48  and forms a border around each of the holes  48 . The hole regions  50  are configured to be caps which, when viewed from the top and contemplated in the negative z direction, are convex and located on a spherical surface. Other forms such as paraboloides are possible. The hole regions  50  are formed from the same sheet material from which the console  36  is made and integrally merge into the remaining region of the console. The hole regions  50  have an upper cap surface  52  that has the convex curvature described and a lower cap surface  54  that shows a mating convex curvature (when looking into the viewing direction z). Beneath this lower cap surface  54 , there is provided a lower cap-shaped perforated disk  56 . It has an inner hole that is dimensioned sufficiently large for the perforated disk  56  to be freely placed onto the sensor bolt  32 . When viewed from the top, the perforated disk has a convex curvature, the curvature conforming to the lower cap surface  54 . In the assembled condition, the lower cap-shaped perforated disk  56  fits against the lower cap surface  54 . The lower cap-shaped perforated disk  56  in turn abuts the sensor bolt, for example the projection or rim provided thereon. In a preferred embodiment shown in  FIG. 5 , the lower cap-shaped perforated disk  56  is a component part of the sensor bolt  32 .  
         [0029]     Likewise, an upper cap-shaped perforated disk  58  is located above the hole region  50 , namely above the upper cap surface  52 . On its two annular surfaces it has the shape of a convex cap. No matter how it is placed onto the sensor bolt  32 , one convex cap surface is pointing downward and can come into contact with the upper cap surface  52 . The other convex cap surface of this perforated disk  58  is not needed; it is only provided to prevent mounting errors. The lower cap-shaped perforated disk  56  may also be configured this way.  
         [0030]     Above the perforated disk  58 , there is located a normal disk and a nut  60 . Fastening occurs through this nut  60 , which is screwed onto the sensor bolt  32  and tightened for this purpose.  
         [0031]     With reference to the  FIGS. 2 through 4 , the various positions the two structure parts  26 ,  34  are capable of adopting with respect to each other will be discussed. At first,  FIG. 2  shows the normal, upright position of the second structure part  34 ; this position corresponding to the ideal mounting position, meaning without any differences due to tolerances and so on. If mounting could be performed in the manner shown in  FIG. 2  and performed on all of the four connecting points of the lower part of the underframe with the upper parts located above, no transverse forces due to mounting would occur.  
         [0032]     In the configuration according to  FIG. 2 , the sensor bolt  32  extends centrally through the hole  48  and the free space about the hole  48  can be seen. The lower cap-shaped perforated disk  56  fits against the lower cap surface  54 . Likewise the upper cap-shaped perforated disk  58  has one of its two cap surfaces fitting against the upper cap surface  52  with a planar fit. The parts mentioned are held together by the disk and the nut  60 . As can be seen from  FIG. 3 , one leg  62  of the console is vertical, meaning parallel to the x-z plane.  
         [0033]     In the configuration according to  FIG. 3 , the console  36  is displaced toward the right and additionally as far as practicable inclined toward the right within the free space of the hole  48 . As a result, the leg  62  is no longer parallel to the x-z plane but is rather tilted an angle of several degrees, for example of up to 3°, and possibly even of up to 7°. It can be seen that the configuration of the perforated disks  56 ,  58  is also different from the one in  FIG. 2 , with the position of the disk remaining the same. The perforated disks  56 ,  58  are displaced toward the left in the direction counter to the direction of the console  36  so that they overlap the air gap between the hole region  50  and the sensor bolt  32  on the right.  
         [0034]      FIG. 4  shows a configuration that is the mirror image of the configuration shown in  FIG. 3 . The hole  48  in the console  36  is now displaced toward the left to such an extent that, on the right side, the threaded bolt contacts the rim of hole  48  and, as a result thereof, the hole region  50 . Again, the perforated disks  56 ,  58  are displaced in the opposite direction, meaning toward the right in the present case. The leg  62  is now tilted toward the left, out of the x-z plane in the direction counter to the tilting direction of  FIG. 3 .  
         [0035]     It can be seen that various positions are possible for the console  36 , with all intermediate positions between  FIGS. 3 and 4  being admissible. This allows for accommodating tolerances that may have different causes. It is achieved that, in the assembled and unloaded underframe, no transverse forces, meaning no forces in the plane in which the four weight sensors  28  of a motor vehicle seat are located, act onto the weight sensor  28 .  
         [0036]     In  FIG. 3 , a center of the spherical surfaces of the cap surfaces  52 ,  54  and of the cap-shaped perforated disks  56  and  58  is labelled at  64 . It can be seen that the cap surfaces lie on concentric spherical surfaces, with the radius of these spherical surfaces lying on the spherical caps being approximately 22 mm and ranging between 15 and 40 mm. The cap surfaces  52 ,  54  and the cap surfaces on the two perforated disks  56 ,  58  have a diameter of about double the diameter of the sensor bolt  32 . The outer diameter of these cap surfaces may range between 150% and 300% of the diameter of the sensor bolt  32 .  
         [0037]      FIG. 5  is a sectional view of a sensor  28  with a sensor bolt  32  that is disposed on the upper side of an approximately loop-shaped sensor body  66 . The sensor body  66  itself is resilient and more specifically has two lateral spring regions. Opposite the sensor bolt  32  there is a screw socket  68  for screw connection with a first structure part  26 . Through strain gages or the like, which are disposed in the spring region, the axial displacement in the direction of the longitudinal axis of the sensor bolt  32  and of the coaxial screw socket  68  is sensed. In this sensor  28  configuration, the lower cap-shaped perforated disk  56  is provided directly at the foot region of the sensor bolt  32 , with the perforated disk being integrated in the sensor body  66 . The cap surface about the foot point of the weight sensor  28  can be seen. It has its center at  64 . Accordingly, this implementation has two features. First, the sensor bolt  32  is solidly connected to the part that forms the lower cap-shaped perforated disk  56 ; put another way, the sensor bolt has a collar which forms the perforated disk  56 . Other alternatives are possible; for example, the sensor bolt may comprise a collar or a projection that forms an abutment for the perforated disk  56 , but is not associated with the sensor body  66 . Second, the lower cap-shaped perforated disk  56  is integrated in the actual sensor and, therefore, does not need to be configured as a separate component part.  
         [0038]      FIG. 6  shows a corresponding solution for the upper cap-shaped perforated disk  58 . The combined part shown is composed of a nut  60  and an upper cap-shaped perforated disk  58 . Again, the center  64  of the cap surface is shown.  
         [0039]      FIG. 7  shows a complete second exemplary embodiment. As contrasted with the implementation according to the  FIGS. 1 through 4 , the first structure part  26  is now formed by a front transverse bar and by a rear transverse bar for connecting the two seat profiles  26  together. The weight sensors  28  are disposed at a distance of approximately 3 to 5 cm from the seat profile  24 ; concretely, they are located in a tub-shaped depression of the profile of the transverse bars  26 .  
         [0040]     Above the transverse bars  26 , there is shown a seat shell  70  defining holes  48  corresponding to the sensor bolts  32 . The hole region  50  is formed in the shape of a cap. Above each hole  48  there is provided an upper cap-shaped perforated disk  58  and a nut  60 . The perforated disk  58  has a convex cap region on its underside only.  
         [0041]     As may be recognized by those skilled in the pertinent art based on the teachings herein, numerous changes and modifications may be made to the above-described underframe of a motor vehicle seat and sensor configuration without departing from the spirit and scope of the invention as defined in the appended claims. Accordingly, this detailed description is to be taken in an illustrative, as opposed to a limiting sense.