Abstract:
A vehicle for separating a pedal lever ( 14 ) pivotable about a spindle ( 5 ) from the structure of a motor vehicle, in which the support ( 21 ) acting especially as a pressure pipe between the pedal lever ( 14 ) and a braking force amplifier ( 3 ) has a deformable rod section.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a device for detaching a pedal mounting which can be pivoted around a spindle (pedal spindle) from the structure of a motor vehicle, with the pedal lever being mounted on the vehicle structure via the pedal spindle and a supporting element being connected to a vehicle component in such a manner that the pedal lever can be pivoted around the pedal spindle with a specified actuating force. 
     In order to prevent injury to the passengers as a result of sliding of the pedal unit into the interior of the vehicle in the case of an accident, particularly a rear-end collision, a known method is to detach the mounting of one or more of the pedals so that the risk of injuries is reduced. 
     The object of the invention is to provide a device of the type mentioned above in which it is possible to detach at least one of the pedals from the vehicle structure without requiring a complex design. 
     SUMMARY OF THE INVENTION 
     The invention achieves this object in that the supporting element can be moved from its supporting position by excessive forces acting on the vehicle from outside. 
     Specifically, this makes it possible to move the pedal lever with a small degree of force around its bearing in the area of the pedal spindle. The force required for moving the supporting element from its supporting position may be produced from various sources. For example, for this purpose, the movement and/or deformation of a component of the vehicle (a vehicle component such as the front wall) which separates the interior of the vehicle from the engine compartment caused by the excessive external force acting on the vehicle can be utilized and transferred to the supporting element. Moreover, a mechanically or pyrotechnically-acting energy-storing device which is triggered by the excessive external force acting on the vehicle can provide the required kinetic energy to move the supporting element from its supporting position. 
     Preferably, the movement of the supporting element from its supporting position takes place against a force which holds the supporting element in its supporting position. 
     In a practical example of the invention, the pedal spindle may be supported by a pedal spindle bearing, which in turn is supported by a supporting element on a vehicle component which can be moved with respect to the vehicle structure when acted upon by an excessive external force, with the supporting element being moveable when the component moves from its supporting position as a pedal spindle bearing in order to release the mounting of the pedal spindle. 
     In this case, the moveable arrangement of a vehicle component, i.e., a component supported by springs, is utilized so that the movement of this component with respect to the vehicle structure on excessive acceleration or braking is utilized in order to release the pedal, specifically the pedal spindle bearing, from its mounting on the vehicle structure. Preferably, the invention is used to release the mounting of the brake pedal. In this case, one can utilize the fact that the power brake cylinder is attached via springs, specifically cup springs, to the vehicle structure, e.g., the front wall, in the engine compartment. The vehicle component, e.g., the power brake unit, can execute a wobbling/tilting motion when acted upon by external forces. This movement takes place against the force of the springs, specifically the cup springs, by means of which the unit is supported on the vehicle structure. 
     This movement of the vehicle component is transferred to the supporting element, which is preferably rigidly attached to the vehicle component. The supporting element, specifically in the form of a rod, then moves from its supporting position, thus releasing the mounting of the pedal. 
     Preferably, the release of the mounting of the pedal takes place along a specified guide segment. Along this guide segment, a frictional force can act on the pedal, specifically the pedal spindle bearing, which can be guided along the guide segment. This reduces the danger of injury if the driver pushes the released pedal in a panic. For this purpose, a stroke groove may be provided for the pedal spindle bearing along which the pedal spindle bearing is guided in a damped manner or while acted upon by a frictional force. At the end of the guide segment or the guide groove, the pedal spindle bearing is completely released. 
     It is also possible for the pedal spindle bearing to be immediately or suddenly released from its supporting position after the movement of the supporting element. 
     Release of the pedal, specifically the pedal spindle bearing, may take place by means of a force which supports said release. This force may be produced by an energy-storing device such as a spring. Specifically, a spring which pretensions the pedal spindle bearing against the supporting element is particularly well-suited for this purpose. 
     Preferably, the guided movement of the pedal spindle bearing or the pedal spindle into the release position should be a pivoting movement around a pivoting axis. In this case, the pedal spindle and the pedal spindle bearing are pivoted around this pivoting axis. At the end of the pivoting movement, complete release of the pedal spindle and the pedal spindle bearing takes place in that the pivoting axis moves out of its bearing on the vehicle structure. 
     In order to prevent unintentional or improper release of the supporting element from its supporting position, a sensor-activated locking device may be provided which is triggered by the acceleration sensor only if excessive vehicle acceleration or braking occurs. 
     In another practical example of the invention, the supporting element is a functional component which is already located on the vehicle. For example, this may be an actuating rod with which the operation of the pedal is transferred between the pedal lever and the vehicle component. For example, this may be a connecting rod by means of which the pedal motion is transferred from the brake pedal to the power brake unit. 
     In order to release the mounting, the supporting element may be completely moved away from its supporting position. However, it is also possible, by deforming the supporting element, to move it away from its supporting position or its supporting function. If the supporting element is in the form of an actuating rod, a deformation component which can be moved perpendicular to the axial direction acts upon it to deform it. The deforming force acting in this case can be produced by means of an energy-storing device triggered by a vehicle-sensitive sensor, specifically, a pyrotechnic energy-storing device, or by deformation or movement of a vehicle component on application of excessive external force to the vehicle, e.g., in the case of an accident. 
     Moreover, a rod-shaped supporting element, which specifically serves as a connecting rod to transfer the pedal pressure to the power brake unit, may be designed in such a manner that in normal operation, the forces exerted by operating the pedal can be transferred without difficulty, and in the event of excessive external forces acting on the vehicle, specifically in the case of an accident, it is ensured that the mounting of the pedal on the vehicle will be released. For this purpose, the supporting element may have a tube-shaped cross section, at least in its deformable rod area. For this purpose, the supporting element may essentially be formed over its entire length in a tube shape. The tube shape may be easily manufactured in that shaping forces, specifically forces acting from outside in a radial direction toward the inside, act on a tube-shaped blank to form the special shape of the supporting element, which specifically acts as a connecting rod between a brake pedal and a power brake unit. Specifically, these shaping forces may be produced by rotary kneading of the tube-shaped blank, which is the starting material for the hollow connecting rod. 
     In shaping the supporting element, articulated bearings may be formed on both ends of the supporting element for articulated support of the supporting element on the vehicle component, which is specifically a power brake unit, and on the pedal lever (brake pedal). A possible embodiment is one in which the articulated bearing supported on the pedal lever is in the form of a solid sphere and, for example, is connected to the hollow cross-section of the supporting element by welding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained in greater detail with reference to the practical examples shown in the figures. The figures show the following: 
     FIG.  1 : A side view illustrating a practical example of the invention; 
     FIG.  2 : A top view of the practical example of FIG. 1; 
     FIG.  3 : A side view similar to FIG. 1 showing the example in the operating position after release of the supporting element; 
     FIG.  4 : A side view showing the example in the operating position in which the pedal is moved into its release position; 
     FIG.  5 : A side view showing the final release of the mounting of the pedal; 
     FIG.  6 : A side view showing a frame pedal used in the practical example; 
     FIG.  7 : A schematic side view of a further practical example in the normal position; 
     FIG.  8 : A side view showing the operating position of the practical example of FIG. 7 after disengagement of the pedal; 
     FIG.  9 : A side view showing a third practical example in normal operation; 
     FIG.  10 : A side view showing the third practical example with the pedal disengaged; 
     FIGS.  11 ( a )- 11 ( d ): Cross-sectional views showing various shapes of the supporting elements for use in the practical examples in FIGS. 7 through 10; 
     FIG. 12 shows a further practical example in its normal operating position; 
     FIG. 13 shows the example of FIG. 12 with the parts in positions to which they are moved during the course of an accident; 
     FIG. 14 shows the example of FIG. 12 with the parts in positions to which they are located after an accident; 
     FIG.  15 : A practical example of a connecting rod which transfers pedal movements to a power brake unit of the vehicle; 
     FIG.  16 : A sectional view of a practical example of the connecting rod shown in FIG. 15; and 
     FIG.  17 : A sectional diagram of a further practical example of a connecting rod. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The practical example shown in FIGS. 1 through 6 has the basic position shown in FIG. 1 in the case of normal operation of the vehicle. The practical example shows a pedal lever  14  which is supported in a pivoting manner on a pedal spindle  5  via a pedal spindle bearing  1  on the vehicle structure. The pedal spindle  5 , which is formed by a bearing pin  17 , is placed near the two ends of the bearing pin in first recesses  16  of the vehicle structure  8  (FIG.  6 ). The recesses  15  are provided in two frame panels  16  (FIG. 2) belonging to the vehicle structure  8 , and constitute mounting points for the bearing of the pedal spindle  5 . Moreover, the bearing pin  17  forming the pedal spindle  5  is supported in a pivoting manner by two bearing plates  18 . The two bearing plates  18  are firmly connected to a stop  4  which is provided on a projecting lever arm  19 . The bearing pin  17  is supported in a pivotable manner by the bearing plates  18  which are provided near the two ends of the bearing pin  17 . The bearing plates  18  are components of the pedal spindle bearing  1  and are rigidly connected to each other via a connecting stirrup piece  20 . 
     In the two frame panels  16 , a second recess  12  curved around the pedal spindle  5  is also provided, which forms a guide groove or guide segment. This recess  12  is closed at one of its ends, and opens at its other end into a third recess  23 , into which the first recess  15 , which serves as an axial support in the basic position (FIGS.  1  and  2 ), opens. 
     In the basic position (FIGS.  1  and  2 ), a guide element  24  is provided on each bearing plate  18 , for example, in the form of a roll body. This guide element rests against the closed end of the second recess  21  in the basic position. 
     Pretensioning springs  25  engage with the two bearing plates  18 . The springs  25  exert a pretensioning force on the two bearing plates  18  or the pedal spindle bearing  1 , to which the lever  19  with the accompanying stop  4  belongs. Due to the action of the pretensioning force of the springs  25 , the stop  4  rests against a supporting element  2 . This supporting element  2 , which is in the form of an extension arm, is rigidly connected to a vehicle component  3 , which in the practical example shown is a power brake unit. The vehicle component  3  is supported in a tiltable manner via springs  9 , specifically cup springs, on the vehicle structure  8  against the force of the springs  9 . This tilting motion may take place around attachment sites  26  located at the top. 
     The pedal movements around the pedal spindle  5  into the vehicle component  3  in the form of a power brake unit are initiated via an actuating rod  21 . 
     In the basic position shown in FIG. 1, the pretensioning force of the springs  25  rigidly supports the pedal spindle bearing  1  against the supporting element  2 , which is preferably rigidly connected to the vehicle component  3 , in the area of the stop  4 . The pretensioning force of the springs  25  acts on the pedal spindle bearing  1  in such a way that torque acts on the pedal spindle bearing  1  with respect to the pedal spindle  5 . For this purpose, a connecting piece  27  is provided which extends from the respective pretensioning spring  25  along a curved rope guide up to a respective point of action  28  on the bearing plate  18 . Due to the interaction of the function of supporting the pedal spindle bearing  1  exerted by the supporting element  2  and the pretensioning force of the springs  25  acting on the pedal spindle bearing  1 , proper mounting of the pedal spindle  5  on the vehicle structure  8  in the first recesses  15  and second recesses  21  of the frame panels  16  is achieved. 
     Moreover, a locking device  11  supported on the vehicle structure  8  is provided which locks the supporting element  2  against unintentional motion or motion due to improper use. The locking device  11  is triggered only when an acceleration sensor  10  detects excessive vehicle acceleration or braking. 
     For example, in the case of an accident, when a case of this type occurs, the locking device  11  is released. Moreover, forces act on the vehicle component  3  from outside in such a manner that the spring or springs  9  is/are pressed together and the vehicle component is tilted or pivoted around the upper attachment sites  26 . This movement is transferred to the supporting element  2  which, as shown in FIG. 3, is moved away from the stop  4  on the pedal spindle bearing  1 . Under the effect of the pretensioning springs  25 , the two bearing plates  18  are then pivoted around a pivoting axis  6  of the pedal spindle bearing  1 , which, in the practical example shown, coincides with the pedal spindle  5 . This pivoting axis  6  may also be provided at another location parallel to the pedal spindle  5  supported on the vehicle component  8 . 
     During this pivoting motion, the guide elements  24  are guided along their accompanying second recesses  21 . The guide elements  24  may have a frictional and damping action in conjunction with the boundary surfaces of the second recesses  21 . In the practical example shown, frictional force pairs are formed in this manner which act between the two pivoted bearing plates  18  and the vehicle structure  8 . The bearing plates  18  and the lever arm  19  connected thereto are pivoted, as shown in FIG. 4, in the direction of an arrow  13  around the pivoting axis  6 , which, as explained above, is the pedal spindle  5  in the practical example, in a direction toward the open end of the recess  21 . In this case, the guide elements move into the third recess  23 , into which the open end of the second recess  21  opens. 
     During the movement of the bearing plates  18  along the guide segment formed by the second recess  21 , if the brake pedal is operated in a panicky manner, the danger of injury to the passenger operating the brake pedal is reduced by the damping and/or frictional action of the guide elements  24 . The guide elements  24  and the bearing plates  18  move into the enlarged third recess  23 , into which the bearing pin  17 , which forms the pedal spindle  5 , is also moved. This is made possible by the fact that the first recess  15  is opened in the direction of the third recess  23  and the bearing pin  17  is completely detached from its mounting with the frame panels  16  of the vehicle structure  8 . 
     In the practical example shown in FIGS. 7 through 14, the supporting element is the actuating rod  21 , which operates between the pedal lever  14  and the vehicle component (power brake system)  3  and serves to transfer the pedal motion to the vehicle component  3 . In FIGS. 7,  9  and  12  the normal operating position with the supporting element  21  in its supporting position is shown. In this position, the movements of the pedal lever  14  in an axial direction are transferred via the actuating rod  21 , which acts as a connecting rod, to the power brake unit which forms the vehicle component  3 . In this normal position, the pedal lever  14  is supported on the vehicle structure via the pedal spindle bearing  1  and a supporting site  38  on the vehicle structure. The supporting site  38  forms the articulated connecting site between the pedal lever  14  and the actuating rod  21 . The pedal lever  14  is therefore mounted on the vehicle structure in the normal operating position in such a manner that it can be pivoted around the pedal spindle. 
     In order to detach this mounting, in the two practical examples of FIGS. 7 through 14, means are provided which deform the actuating rod  21 , specifically bending it, as shown in FIGS. 8,  10 ,  13 , and  14 . For this purpose, there is a respective point of action  31  which, in the event of excessive force applied to the vehicle during an accident, is moved perpendicular to the axial direction of the actuating rod  21  so that the actuating rod is deformed or bent away from its supporting position. In this case, as is specifically shown in FIGS. 8,  10 , and  14 , the pedal lever  14  is moved from the normal operating position away from the feet of the driver. Moreover, mechanical disengagement from the mounting of the pedal lever  14  shown in FIGS. 7,  9 , and  12  may also occur. 
     The risk of injury on sudden operation of the pedal (panic operation), is also reduced by the fact that after disengagement on operation of the pedal, a certain degree of deformation resistance is still present in the deformed actuating rod  21  (FIGS. 8,  10 , and  13 ), thus preventing the pedal from being pushed completely to the floor without any resistance. Moreover, disengagement of the pedal provides additional free space as the pedal is moved out of the foot area. 
     In the practical examples shown, the deformation or movement of a vehicle component, specifically the front wall  22 , is utilized in order to produce the forces necessary to deform the actuating rod  21 . For this purpose, in the practical examples shown in FIGS. 7,  8 , and  12  through  14 , the point of action  31  is supported via rigid struts  39  and  40  on supporting points  32  and  33  of the vehicle structure. On deformation of the front wall toward the interior of the vehicle, the rigid struts, which are supported on the front wall  22  at supporting point  32  and at the supporting point  33  diagonally above the point of action  31  on the vehicle structure, cause forces to occur whose resultant force acts on the point of action  31  at right angles to the axial direction of the actuating rod  21  in such a manner that the actuating rod  21  is deformed or bent, as shown in FIGS. 8 and 13. In this case, the supporting point  33  remains essentially stationary, while the supporting point  32  provided on the front wall  22  moves inward in the direction of the vehicle interior. 
     In the practical example shown in FIGS. 9 and 10, a crank  34  is provided which can be rotated around a crank axis  37 . This rotation is caused by a deformation of the front wall or movement of another component of the vehicle. The movement or deformation is transferred via a force- or motion-transfer site  36  to the crank  34 . A catch  35  is rigidly connected to the crank  34 , said catch having a point of action  31  in the form of a rod which runs transversely. On rotation of the crank  34 , the point of action  31  is moved upward so that the actuating rod  21 , as shown in FIG. 10, is deformed or bent. In this case as well, the metal lever  14  is disengaged from the mounting, which is present in the normal position shown in FIG.  9 . 
     In order to produce the deforming force which acts at the point of action  31 , an energy-storing device, specifically a pyrotechnic energy-storing device, may be provided, which is triggered by a vehicle-sensitive sensor device. Known examples of such energy-storing devices include arrangements for driving a tightener for tightening a safety belt (DE 4,200,360 A1 and 4,305,049 A1). These driving arrangements may act directly at the point of action  31 , or indirectly, e.g., via the crank shown in the practical examples of FIGS. 9 and 10. 
     FIGS.  11 ( a )- 11 ( d ) show various shapes for the actuating rod. In FIG.  11 ( a ), a round shape is shown, and in FIG.  11 ( b ), an elliptical shape is shown. Preferably, in the case of this shape, as seen in FIG.  11 ( b ), the point of action  31  acts from above or from below as shown in FIGS. 7 through 10 on the actuating rod  21 . In FIG.  11 ( c ), a tube-shaped design is shown, and in FIG.  11 ( d ), a rectangular shape is shown. In this case as well, the point of action  31  is provided on the actuating rod  21  from above or from below. 
     FIGS. 12 through 14 show an embodiment of the practical example shown in FIGS. 7 and 8. In this embodiment, in the area of a transverse steering tube, a rigid articulated support ( 30 ) is attached in a pivoting manner at the supporting point  33  on the vehicle structure. At the lower end of the articulated support  30 , there is a point of action  31  which is guided in a restricted manner by the strut  39 . The strut is attached in a pivoting manner in the area of the power brake unit  3  on the front wall  22  at the supporting point  32 . On movement of the power brake unit or the front wall opposite to the direction of travel, i.e., in a direction toward the interior of the vehicle, restricted guiding of the articulated support  30  and the point of action  31  through the rigid strut  39  takes place. In this case, the point of action  31  moves upward, essentially at right angles to the axial direction of the actuating rod  21 , causing it to be deformed, as can be seen in FIGS. 13 and 14. 
     In the practical examples of FIGS. 7 through 14, specifically those of FIGS. 7,  8 , and  12  through  14 , by appropriate arrangement of the strut  39  and the articulated support  30 , and thus the point of action  31  with respect to the actuating rod  21 , one can obtain a specified pedal counterforce on deformation of the actuating rod  21 . By means of this pedal counterforce, the kinetic energy of the braking foot on deflection of the brake pedal, specifically during panic braking, can be reduced by the deformation of the actuating rod  21 . In this way, one can avoid high contact speeds between the sloping part of the foot and heel of the foot operating the pedal. In this manner, one achieves a definite reduction in pedal force. In normal operation, the point of action  31  is disengaged from the foot pedal, as shown in FIG.  12 . 
     In the embodiments shown in FIGS. 7,  8 , and  12  through  14 , the relative movement of the pedal with respect to a component of the vehicle which remains stationary, specifically the transverse steering tube  41 , is utilized in order to deform the actuating rod  21  and disengage it from the pedal. 
     In the practical example of FIGS. 12 through 14, the area near the pedal  50  of a vehicle is shown. The pedal lever  14 , specifically the brake pedal, is supported on the vehicle structure in such a manner that it can pivot around the pedal spindle  5 . A connecting rod, additional practical examples of which are shown in FIGS. 15 through 17, is connected in an articulating manner as a further supporting element  21  to the pedal lever  14 . The connecting rod  21  extends in a roughly horizontal direction up to the entrance side of the power brake unit  3 , which constitutes a vehicle component. In order to connect the connecting rod  21  to the pedal lever  14  in an articulated manner, the connecting rod  21  has an articulated bearing  43  at one of its ends. In order to connect an actuating component to the power brake unit  3  in an articulated manner, the connecting rod  21  has an additional articulated bearing  42  at its other end. During normal automotive operation, when the brake pedal is pushed, the movement of the pedal is transferred via the pedal lever  14  and the connecting rod  21  to the power brake unit  3  in order to operate the brakes. 
     In order to prevent injuries to the passengers resulting from the pedal unit  50  being pushed into the interior of the vehicle during an accident, particularly a rear-end collision, the mounting of the pedal lever  14  is detached in such a way that the connecting rod  21  is deformed perpendicular to its longitudinal axis  49 . In this case, the support provided for the pedal lever by the connecting rod  21  during normal operation of the vehicle is released, and specifically, the pedal lever  14  is pivoted away from the vehicle passengers. As described above, a point of action  31 , which constitutes the connection point between the ends of the articulated support  30  and the strut  39  is used to deform the connecting rod  21 . The articulated support  30  has a supporting site  33  on the vehicle structure near a transverse steering tube  41 . At its other end, the strut  39  has the supporting site  32  on the pedal frame of the vehicle structure. The ends of the articulated support  30  and the strut  39  facing the connecting rod  21  are connected to each other in an obtuse angle at the point of action  31 . 
     In the event of movement of the front portion of the pedal frame, specifically in the area of the supporting site  32  toward the interior of the vehicle, e.g., during an accident, the point of action  31  is guided in a restricted manner by the strut  39  and the articulated support  30  so that it moves approximately perpendicular to the longitudinal axis  49  of the connecting rod  21 , and the connecting rod  21  is deformed, as shown, for example, in FIG.  13 . 
     FIGS. 15 through 17 show practical examples of the connecting rod  21 . 
     The connecting rod according to the practical examples has a deformable rod area  44  which is in the form of a hollow cylinder. There are articulated bearings  42  and  43  at the ends of the connecting rod  21 . In the practical example shown in FIG. 15, the articulated bearings  2  and  3  are also hollow. In the practical example shown in FIG. 17, the articulated bearing  42 , which is connected to the actuating component of the power brake unit  3 , is hollow. At the other end, the articulated bearing consists of a solid sphere. This articulated bearing  43  is connected to the pedal lever  14 . The articulated bearing  43  shown in FIG. 17, which is in the form of a solid sphere, is connected via a weld  51  to the other portion of the connecting rod, which has a hollow shape. In the practical example of FIG. 16, the connecting rod has a hollow shape over its entire length. 
     Between the articulated bearing  42 , which is connected to the power brake unit  3 , and the end of the deformable rod area  44 , there is a rod component  45  in the shape of a hollow truncated cone. The rod component in the shape of a hollow truncated cone  45  is connected via a hollow cylindrical rod component  48  to the hollow cylindrical deformable rod area  44 . At the other end, the rod component  45  in the form of a hollow truncated cone is connected via the hollow cylindrical rod component  47  to the articulated bearing  42 . 
     At the other end, the deformable rod area  44  is connected to the articulated bearing  43  via a rod component  46  in the form of a hollow truncated cone. 
     The hollow cylindrical rod component  48  has a smaller external and internal diameter than the deformable rod area  44 . The hollow cylindrical rod component  47  has a smaller external and internal diameter than the hollow cylindrical rod component  48 . 
     The point of action  31 , which is moved in FIG. 12 from the top to the bottom approximately perpendicular to the longitudinal axis  49  of the connecting rod  21 , acts on the hollow cylindrical deformable rod area  44 . Because of the hollow shape, specifically in the case of an accident, if the components of the vehicle located in front of the pedal unit  50  move toward the interior of the vehicle in the event of an accident, one thus achieves a specified deformation of the connecting rod  21 , thus moving the pedal lever  14  out of the danger area in which injuries may be caused, particularly to the legs of the passengers. 
     Because the connecting rod  21  has a hollow shape, one can also achieve a specified reduction in the force applied to the pedal in the event of panic braking. This specified reduction in force is achieved by correspondingly adjusting the wall thickness of the tube shape, particularly in the deformable rod area  44 . 
     Preferably, the tube shape of the connecting rod of the practical examples shown is formed from a tube-shaped blank by shaping forces acting from the outside. A preferable method for this purpose is plastic deformation using a rotary kneading process. The special tube components  44  through  48  and the hollow articulated bearings  42  and  43  may be produced by means of this rotary kneading process. 
     The external diameter of the connecting rod  21  is approx. 7 mm to 15 mm, and preferably 10 mm. The wall thickness of the connecting rod is approx. 1 to 2 mm, and preferably 1.5 mm. The ratio of wall thickness to external diameter in the deformable rod area  44  of the connecting rod  21  is between 0.06 and 0.3, and preferably 0.15.