Abstract:
A steering device for motor vehicles has a steering shaft that is guided by a guide box ( 3 ) which is connected to a retaining console and, for example, clamped. The console has at least one sliding surface ( 8 ) along the axis of the shaft ( 1 ) which allows for a displacement path ( 20 ) with respect to the chassis ( 18 ) in case of a collision. A clamp ( 17 ) is provided for axial retention of the console ( 6 ) in an initial position of the displacement path ( 20 ). In this way at least one part of the clamped surface is slanted in relation to the vertical clamping device so that the clamping surfaces can move away from each other when the steering shaft is displaced and clamping is reduced.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a steering device for motor vehicles with a steering shaft. 
     Steering devices for motor vehicles are frequently implemented in two parts, one slidable into the other such that in the event of a frontal collision the steering device does not endanger the driver whereby the steering device upon an impact of the body onto the steering wheel yields and the impact energy is absorbed. In the known devices conventionally the slidable steering shaft tube, which receives the control wheel-side steering shaft, is disposed in a casing which is clamped with respect to the motor vehicle chassis by machine screw fastening in predetermined position. The machine screw fastening is herein implemented such that upon impact the steering wheel-side shaft end with the machine screwed casing bracket in the axial direction, in the clamped state is displaceable by a specific path. The impact energy is correspondingly absorbed by the clamping. In order to make the energy absorption more uniform in the event of impact, additional energy absorption elements had been disposed between the longitudinally slidable shaft part and the chassis of the motor vehicle. An energy absorption element, which is implemented as a sheet metal tongue which can be torn away, is for example known from GB 1,390,889. 
     One disadvantage of the known crash system for steering columns comprises that, on the one hand, the break-free force could not be defined over wide ranges substantially independently of the energy absorption force. The absorption behavior could also not be reproducibly preset. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to propose a crash system for a steering column configuration, which eliminates the disadvantages of the prior art. The object comprises in particular realizing a crash system for steering columns which permits a defined break-free force and a defined energy absorption under reproducible behavior. In addition, the configuration is to be simple to mount and economical in production. 
     According to the invention the configuration is implemented such that in the event of an impact the break-free force is decoupled from the energy absorption force upon sliding of the steering shaft. 
     Thus, in the event of a crash the clamping is to be released immediately, for the purpose of which serves a so-called break-free element in order to dissipate the impact energy after the breaking free of the clamping substantially onto an energy absorption element. Therewith is attained that the energy absorption over the defined displacement path is substantially no longer affected by undefined clamping forces and the absorption effect is specifically presettable through the implementation of the absorption element. 
     For an embodiment of the break-free element, for this purpose in the region of the clamping securement where the high clamping forces between casing bracket and the stationary chassis part occur, the facing portions pressed onto one another through the clamping are slightly inclined with respect to the sliding direction, i.e. disposed at a specific wedge angle such that already with a short displacement path the original clamping is immediately reduced thereby that the two wedge face parts move apart depending on the angular slope. In this way, in the case of an impact the clamping is already broken after a displacement of a few tenths mm and the further displacement is no longer determined by undefined clamping forces. The casing bracket, which fixes the steering shaft tube, is connected with the chassis via a tear-away strip. The implementation of this tear-away strip now determines essentially the degree and the [time] course of the energy absorption behavior. Through appropriate dimensioning of this tear-away flap the energy absorption behavior can be laid out correspondingly optimally gently for the driver. 
     A further preferred embodiment comprises that in the region of the compressed slide facing elevations are disposed on both sides of the facing, which are staying each other over a short path distance wherewith the slide facing is developed substantially in the short contact zones of the elevations and in the case of displacement, i.e. in the event of a breaking-free, the one elevation slides already after a short path distance, for example of a few millimeters, from the other elevation and thus generates the desired breaking free in the event of a crash. A further especially simple, preferred embodiment of a break-free element comprises that at least on a subregion of the clamped facing parts these opposing clamping faces are [stair]-stepped such that the clamping force is reduced after a short displacement path. 
     An especially cost-effective and space-saving steering column configuration with crash system for the energy absorption is obtained thereby that the steering shaft is supported in a guide box which, in turn, is fixedly connected with a retaining bracket, comprises laterally flange-like slide faces which, for example, are clamped tightly on the motor vehicle chassis by being machine screwed. The clamping is implemented such that in the event of a crash the steering shaft can be yieldingly displaced for example by several centimeters with the bracket. The energy absorption element is connected, on the one hand, stationarily with the chassis and, on the other hand, connected where the energy absorption takes place via the bracket with the steering shaft. The absorption element is implemented preferably as a sheet metal part with tear-away flap, which, developed, for example, in the form of a yoke as a tear frame, is mounted between the bracket flange and the chassis. This embodiment has the great advantage that the attachment of the configuration on the chassis is possible using only two attachment means, preferably two machine screws. This simplifies the implementation considerably and also permits a rapid mounting which has a positive effect on the total cost. The tightening torque of the machine screws are herein advantageously in the range from 15 to 35 Nm. This highly simple implementation of the configuration and, in particular the feasibility of securing the entire configuration with only two attachment machine screws without separate bracket guidance, permits also in simple application cases the use without the previously described special break-free elements. But in this case the defined separation between break-free force and energy absorption is less unique, but in exchange, the configuration is in this case realizable especially cost-effectively. 
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     In the following the invention will be explained in further detail in conjunction with embodiment examples with schematic figures. Therein depict: 
     FIG. 1 a side view of the retaining configuration for steering columns according to the invention, 
     FIG. 2 a  a cross section through the retaining configuration according to FIG. 1, 
     FIG. 2 b  a detailed representation of the clamping securement in cross section, 
     FIG. 3 a  a detailed representation of a clamping facing configuration in longitudinal section with inclined clamping faces, 
     FIG. 3 b  a top view of the clamping configuration in detail according to FIG. 3 a,    
     FIG. 4 a crash force measurement diagram which shows the behavior according to prior art, 
     FIG. 5 a crash force measurement diagram which shows the behavior according to the invention, 
     FIG. 6 a detailed representation of a further clamping facing configuration in longitudinal section with elevations as spacer elements between the slide faces, 
     FIG. 7 a detailed representation of a further clamping facing configuration in longitudinal section with stair-stepping in the clamping region. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A steering shaft with the steering shaft axis  1  is connected with a steering wheel  2  and supported in a guide box  3 , which, as is shown in FIG. 1, is fixedly connected, for example clamped, with a retaining bracket  6 . The guide box  3  can additionally be disposed so as to be height- and/or longitudinally adjustable. The bracket  6 , in turn, is secured on the chassis  18  of the motor vehicle. Shaft  1  is implemented telescopingly slidable in the event of a crash, wherewith the bracket  6  for the crash event must also be supported longitudinally displaceable in a range of up to 50 mm with respect to the chassis  18 . The bracket  6  is preferably developed U-shaped and at least partially encompasses the guide box  3  to be received. The bearing guide part  4  is for example fixed by retainers  5  between the bracket part  6 . On the sides of the bracket  6  are disposed on both sides, for example, slide faces  8 , which receive a longitudinal slot  20 . This is developed as a running slot and serves for receiving the securement elements  13 ,  16 ,  17  as well as bolts or preferably clamping machine screws  17 . 
     Bracket  6  is preferably implemented as a sheet metal part which can be manufactured particularly cost-effectively if it is punched out and implemented as a bent part. Apart from the cost advantage, this has also the advantage that a greater bending strength is possible than is the case, for example, with welded constructions. 
     Through the clamping machine screws  17  the bracket  6  is screwed tightly on the chassis  18  such that in the event of impact the steering shaft with the guide box  3  is displaceable within the length of the running slot. In order to break free the clamping even with short displacement paths, in the terminal region of the running slot  20  in the initial clamping position the one bracket-side clamping face  22  is implemented as a wedge shoe  1  inclined at a wedge angle  15 . The wedge shoe  13  is preferably developed such that in the event of displacement it slides in the running track  20 . Since the clamping faces with respect to the clamping direction are now no longer disposed at an angle of 90°, the immediate breaking free of the clamping force is also possible with short displacement paths. Suitable wedge angles are from 2° to 15°, preferably from 3° to 8°. 
     The bracket  6  is for example screwed tightly on the chassis  18  for example directly with machine screws  17 , wherein the slide shoe  13  is preferably disposed at the screw head side with a washer disk  21 . In FIG. 2A the disposition is shown in cross section, from which the preferred manner of securement is depicted on both sides of the shaft axis  1  on chassis  18 . The wedge shoe  14  can for example with its wedge face be worked directly into the bracket  6 . But it the wedge shoe can be manufactured simpler and more precisely if it is manufactured as a separate disk-form part and is secured on the bracket  6 . 
     The bracket  6  is for example screwed tightly on the chassis  18  for example directly with [machine] screws  17 , wherein the slide shoe  13  is preferably disposed at the screw head side with a washer disk  21 . In FIG. 2 the disposition is shown in cross section, from which the preferred manner of securement is depicted on both sides of the shaft axis  1  on chassis  18 . The wedge shoe  14  can for example with its wedge face be worked directly into the bracket  6 . But it [the wedge shoe] can be manufactured simpler and more precisely if it is manufactured as a separate disk-form part and is secured on the bracket  6 . 
     For the defined determination of the energy absorption behavior additionally an energy absorption element  9  is provided which is preferably developed as a sheet metal part with tear-away strip and retaining flap  9 . The sheet metal part  7  is advantageously developed as retaining frame  7  which encompasses the U-form bracket  6  in its upper region and is fixed stationarily remaining in the initial position, with the clamping of the bracket  6  on chassis  18 . The tear-away flap  9  is provided with advantage in the upper flat metal part, developed in the shape of a U, of the tear frame  7 . The tear-away flap  9  is bent as a portion of the tear frame  7  toward the bracket  6  such that the flap  9  can be fixed with respect to the bracket, for example can be clamped or fixed with a welding connection  11 . The tear-away strip with retaining flap  9  is disposed between notched tracks  10  and is set through the material thickness of the tear frame metal, through the material strength, as well as through a rolling rotational width with corresponding rolling radius. It is possibly desired, for example by varying the rolling width, to be able to vary the absorption force profile over the path. 
     The above described constructional implementation of the entire retaining configuration, in which the tear frame  7  is clamped with the slide faces  12  between the bracket flange  6 ,  8  and the chassis  18 , has also particular advantages without the use together with the special break-free elements  13 ,  14 ,  22 ,  26 ,  27 ,  29 . It permits the simple mounting with cost-effective implementation, good operational behavior and high stability of the configuration, in particular if the configuration, as preferred, is secured with only two machine screws  17  on the chassis  18 . 
     As shown in FIG. 3 a , the slide shoe  13  is implemented such that a portion of it can slide torsion-tightly in the running slot  20  during the displacement of the bracket  6  relative to the slide shoe  13 . The wedge faces  22  between the wedge shoe  14  and the slide shoe  13  herein move apart and the clamping is broken free, wherein then the retaining force or the energy absorption is determined by the tear-away strip. 
     The tear frame  7  is implemented in the securement region with advantage on both sides as a sheet metal tongue, which is disposed between the chassis  18  and the slide flange face of the bracket  6  and is also clamped by machine screw fastening  17  stationarily relative to the chassis  18 . In the event of impact thus the bracket  6  is displaced maximally corresponding to the running slot length  20  together with the wedge shoe  14 , which consequently moves away from the stationary slide shoe  13  wherein the tear frame  7  also remains stationary and the tear flap  9 , which is fixed on a bracket part  6 , is torn away. In order to establish a connection which is free of play between slide shoe  13  and the tear frame  7 , the bore in the tear frame  7  is advantageously provided with a crimping  16  such that the slide shoe  13  is guided together with the crimping  16  as is also evident in FIG. 2 b . This configuration is shown in top view in FIG. 3b, where the running slot  20  is evident. 
     A further improvement of the reproducibility of the break-free behavior can be attained thereby that the clamping faces  22 , which means the inclined slide shoe face  13  and the wedge shoe face  14  is surface-treated definitively. This can take place, for example thereby that the surfaces are specifically roughened and/or coated and/or also lubricated. 
     The tightening torque of the clamping screws is advantageously set with torsional moment monitoring in the range from 15 to 35 Nm. In FIG. 4 in a break-free diagram the measured behavior of the break-free force is shown over a path of 45 mm, wherein the machine screw fastening takes place with a torsional moment of 25 Nm. This demonstrates that the break-free force was above 9000 N and only decreases after a relatively long path of approximately 5 mm, but wherein a relatively high residual clamping force effect of approximately 6000 N remains indeterminately until the path of 45 mm has been finished. Under the same measuring conditions in FIG. 5 the behavior according to the invention is shown with a configuration according to FIG.  1 . The machine screw fastening was also set with 25 Nm torsional moment. The break-free force reaches 6000 N and immediately decreases steeply and definitively after a path of 1 mm, in order to remain subsequently on a low level with break-free elements with inclined faces below 2000 N uniformly over the entire path of 45 mm. In the configuration according to the invention thus after the short break-free process the absorption energy is determined defined, reproducible and presettable through the absorption element, such as preferably a tear-away flap is preset for example with energy absorption forces of 1200 to 5500 N. 
     A further highly suitable feasibility for realizing a break-free element, such as is shown in FIG. 6, comprises, for example, disposing between the slide faces  8 ,  12  elevations  26 ,  27 , in order to retain the slide faces in the initial position at a slight distance of a few tenths of a millimeter up to approximately 3 mm. The elevations  26 ,  27  are to be disposed on both sides of the slide faces substantially symmetrically such that there where the elevations are clamped onto one another, short slide faces  12  are generated which in the event of displacement, i.e. in the event of a crash, slide off one another and thus reduce in a short distance in the mm range the clamping force effect, wherewith subsequently the energy absorption is assumed definitively by the absorption element  7 ,  9 ,  11 . Such elevations can be developed, for example, in the manner of knubs and be disposed on both sides in the longitudinal direction of the shaft axis of the screw securement  17 . But it is also possible to dispose several knub-like elevations adjacently or successively to one another or further stair-stepped or also on an inclined plane, depending on the requirement of the clamping forces, the friction forces and the display paths, or the dimensioning of the entire configuration. In the present case the slide shoe  13  is realized, for example, as a simple shim. But it is also possible to provide these knub-like formations in the region of the slide shoe  13 . 
     In FIG. 7 a further embodiment extremely advantageous and simple to realize, of a break-free element is shown. In this embodiment the contacting clamped faces of the slide shoe  13  and of the original wedge shoe  14  are not implemented in the form of a wedge but rather are developed in the form of stairs. The step width of the staircase-like development herein defines the break-free path. This embodiment is especially simple and cost-effectively realizable. The above listed various types of the break-free elements can also be used in combination with one another. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims and next to and forming a part of this disclosure and are entirely Based on the priority application no. CH 1127/98.