Abstract:
A drive shaft, in particular a longitudinal shaft for a motor vehicle, includes at least one hollow shaft cross-section and at least one homocinetic joint whose external hub is connected to the hollow shaft cross-section. The homocinetic joint is sealed off from the hollow shaft section by a lid, the lid and the hollow shaft section being configured and disposed so that the inner hub of the homocinetic joint does not penetrate significantly into the hollow shaft section as a result of an axial force that act on it, such as an axial force resulting from an accident.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicant claims priority under 35 U.S.C. §119 of German Application No. 20 2005 002 641.7 filed Feb. 17, 2005. Applicant also claims priority under 35 U.S.C. §365 of PCT/EP2006/000992 filed Feb. 4, 2006. The international application under PCT article 21(2) was not published in English. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a drive shaft, particularly a longitudinal shaft for motor vehicles, which shaft has at least one hollow shaft section and at least one constant velocity joint, the outer hub of which joint is connected with the hollow shaft section, and which joint is sealed off, with regard to the hollow shaft section, by way of a lid. Furthermore, the invention relates to a constant velocity joint that can be used in such a drive shaft. 
     2. Description of the Related Art 
     A constant velocity joint for a drive shaft, of the type stated above, is known from DE 102 09 933 A1. In the case of this joint, which is configured as a counter-track joint, the outer hub is surrounded by an accommodation part, whereby a sealing disk, i.e. a lid, is provided between the accommodation part and the outer hub, which lid is supposed to prevent the penetration of dirt into the joint. In the case of a frontal collision, for example, high axial forces act on the drive shaft, by means of which forces the constant velocity joint can be destroyed, so that the inner hub can penetrate into the hollow shaft connected with the outer hub. In this connection, the lid, which merely serves to seal the joint, does not form any noteworthy resistance, but rather already allows itself to be pushed into the hollow shaft, together with the inner hub, at relatively low forces. 
     In motor vehicles, the drive shaft is nowadays designed in view of possible crash stresses, among other things, so that the drive shaft absorbs energy and deforms in the case of a high axial force that occurs as the result of an accident, for example. In this connection, the deformation is supposed to take place in such a way, if at all possible, that the drive shaft cannot penetrate into the interior of the vehicle, in order to thereby keep the risk of injury to the occupants low. For this purpose, a drive shaft is proposed in DE 42 27 967 A1, which has a zone demonstrating plastic deformation behavior that can be reproduced in defined manner. This zone is designed in such a manner that the sections of the drive shaft, which is configured as a hollow shaft, fold onto one another and push into one another by regions. In the case of this configuration of a drive shaft, also referred to as a collapsible tube, the drive shaft is deformed, with a high absorption of energy, if a defined axial force is exceeded. 
     If a drive shaft configured in this manner has a constant velocity joint described above, a rapid increase in the force can occur in the case of a high axial force that occurs as the result of an accident, with a slight deformation path, until the constant velocity joint is destroyed. Afterwards, the inner hub of the constant velocity joint, together with the lid, can be pushed into the hollow shaft, by a certain path distance, with comparatively little force, before the hollow shaft makes contact with the transmission or the differential, for example. Only then will the shaft deform, absorbing a greater amount of force. Because of this increase, drop, and renewed increase in the deformation force, alternating accelerations act on the vehicle occupants, and these can bring about injuries, for example whiplash syndrome, or even more serious injuries. 
     SUMMARY OF THE INVENTION 
     It is therefore the task of the present invention to create a drive shaft of the type stated initially, as well as a constant velocity joint, which are further optimized with regard to their crash behavior. 
     This task is accomplished, according to the invention, essentially in that in the case of a drive shaft, the lid and the hollow shaft section are configured and disposed in such a manner that the inner hub of the constant velocity joint cannot penetrate, at least not significantly, into the hollow shaft section, as the result of an axial force that acts on it, particularly an axial force resulting from an accident. The force required for deformation of the drive shaft and of the constant velocity joint consequently increases rapidly, without decreasing for an essentially force-free displacement of the inner hub in the hollow shaft. In the case of the drive shaft according to the invention, defined deformation of the drive shaft can consequently take place essentially immediately after destruction of the constant velocity joint, so that the delays that act on the vehicle occupants are as uniform as possible. 
     In this connection, the hollow shaft section of the drive shaft preferably has a zone demonstrating defined plastic deformation behavior. In particular, the drive shaft can be configured in the manner of a collapsible tube, in which a high absorption of energy takes place during deformation. 
     The task underlying the invention is furthermore accomplished by means of a constant velocity joint in which the lid defines a contact surface that limits an axial displacement of the inner hub relative to the outer hub, particularly a displacement related to an accident. So that the lid does not impair the maximal deflection of the inner hub relative to the outer hub that is required in operation, at least a slight distance is preferably provided between the inner hub and the lid. In this way, the axial displacement of the inner hub relative to the outer hub is limited to less than 25 mm, for example. In order to expose the vehicle occupants to as uniform a delay as possible, it is preferred, however, if the maximal displacement between the inner hub and the outer hub by means of the lid is limited to less than 15 mm, for example to approximately 10 mm. 
     In order to initiate targeted deformation of the drive shaft after destruction of the constant velocity joint as the result of a high axial force, the lid must withstand an axial force transferred by the inner hub of at least 50 kN, by means of a suitable selection of its geometry and/or its material. The amount of this axial force to be absorbed by the lid is dependent on the amount of the force at which the targeted deformation of the drive shaft starts. It is therefore frequently necessary for the lid to withstand an axial force of more than 100 kN, preferably more than 150 kN or approximately 250 kN. 
     In order to limit the path by which the inner hub can be displaced relative to the outer hub, the lid preferably has a projection that faces the inner hub, which forms the contact surface for the inner hub. In addition or alternatively to this, the lid can be provided with beads, ribs, edgings, or the like, in order to reinforce it. If the lid is not already designed, by means of its shape and/or contour, in such a manner that it can withstand a high axial force, the lid can also consist of a high-strength metal or of a fiber-reinforced plastic, for example. 
     In order to fix the lid in place on the outer hub and/or on the drive shaft in suitable manner, the outer hub can be surrounded, at least in certain regions, by an accommodation part, particularly one that forms a hollow shaft section, so as to rotate with this part, whereby the lid is held in this accommodation part. Of course, the lid can also be welded to the outer hub and/or the drive shaft, or connected in some other suitable manner. For this purpose, the accommodation part, the outer hub and/or the drive shaft can have a step, a notch, or the like, against which the lid can rest. 
     According to a preferred embodiment of the invention, the inner hub is connected with a sleeve, particularly in one piece, which sleeve has an inner tooth system for a fixed connection, so as to rotate with it, to a transmission journal or differential journal. In the case of this configuration, the inner hub can be set directly onto a journal of the transmission output shaft or the differential input shaft, thereby not only making the drive shaft easy to install, but also optimally centering it. 
     Furthermore, it is preferred if the constant velocity joint is configured similar to the structure described in DE 102 09 933 A1, as a counter-track joint, in which the cage is guided in the outer hub by means of cage centering surfaces. 
     The drive shaft and/or constant velocity joint configured according to the invention can be used not only in longitudinal shafts of motor vehicles, but also are suitable for installation in a side shaft. Since the maximal deflection of a joint required in operation in a side shaft usually lies clearly above the deflection required for a longitudinal drive shaft, the distance of the lid from the joint parts, such as, in particular, the inner hub, must be selected in such a manner that sufficiently great deflection of the joint, of about 10°, is made possible in the case of a longitudinal shaft, or about 20° in the case of a side shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further developments, advantages, and application possibilities of the invention are evident from the following description of an exemplary embodiment and of the drawing. In this connection, all of the characteristics described and/or shown in the figures form the object of the invention, in themselves or in any desired combination, independent of how they are summarized in the claims or their antecedents. 
       The sole FIGURE shows a section through an embodiment of a constant velocity joint in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The single FIGURE schematically shows a section through a constant velocity joint  1  according to the invention, which has an inner hub  2 , an outer hub  3 , and balls  5  accommodated in a cage  4 , to transfer torque between the inner hub  2  and the outer hub  3 . 
     The constant velocity joint  1  is configured as a counter-track joint, so that both the inner hub  2  and the outer hub  3  have first inner running grooves and first outer running grooves as well as second inner running grooves and second outer running grooves disposed so that they are distributed alternately about the circumference. The first inner running grooves  2   a  shown in the FIGURE, together with the first outer running grooves  3   a , represent a running groove pair in which a ball  5  is accommodated, in each instance. 
     In the inner surface of the outer hub  3 , first and second cage centering surfaces, which are adjacent to one another, in pairs, are formed between the outer running grooves; of these, only the first cage centering surfaces  3   b  can be seen in the FIGURE. The first cage centering surfaces  3   b  border on the first outer running grooves  3   a , in each instance, while the second cage centering surfaces border on the second outer running grooves. The first and second cage centering surfaces run from opposite ends of the outer hub  3 , in each instance, in opposite directions, without undercut, and in this connection approach the outer hub axis. The cage  4  can be guided in the outer hub  3  by means of the cage centering surfaces configured in this manner. 
     The inner hub  2  is configured as a sleeve-like component on the outer surface of which the inner running grooves are provided, and the inner surface of which is provided, in certain regions, with an inside tooth system  6 , so that the inner hub  2  can be set onto a transmission output shaft or a differential input shaft, for example. 
     In the embodiment shown, the outer hub  3  is surrounded by an accommodation part  7  that is connected with the outer hub  3  so as to rotate with it. On the side facing the inner hub  2 , the accommodation part  7  forms a hollow shaft section  8  that can make a transition, in one piece, into a drive shaft, or can be connected with the latter in suitable manner, for example by means of welding. A stair-like step  9  is formed in the transition between the accommodation part  7  and the hollow shaft section  8 , into which step a lid  10  is set. In this connection, the lid  10  seals the constant velocity joint  1  off with regard to the hollow shaft section  8 . Lid  10  can be formed from a high-strength metal or a fiber reinforced plastic, for example. 
     As is evident from the FIGURE, the lid  10  is provided with a central projection  11 , which extends in the direction towards the inner hub  2 . A gap  12  remains between this projection  11  of the lid  10  and the inner hub  2 , so that the inner hub  2  can be pivoted with regard to the outer hub  3 , without the inner hub  2  making contact with the lid  10 . However, the gap  12  is selected to be as small as possible, and amounts to about 10 mm, for example. Several beads  13  that run radially are placed in the lid  10  to reinforce it. 
     If an axial force indicated in the FIGURE by the arrows acts on the constant velocity joint  1 , for example as the result of an accident, the joint is destroyed, so that the inner hub  2 , which is held firmly in the outer hub  3  in the operating state becomes freely displaceable in the outer hub  3 , in the axial direction. The inner hub  2  is displaced by a distance defined by the gap  12 , as the result of the axial force, until the inner hub  2  lies against the projection  11  of the lid  10 , which thereby forms a contact surface for the inner hub  2 . See reference number  15  in the FIGURE, which indicates the axial displacement of the inner hub  2  relative to the outer hub  3 . Because of the great rigidity of the lid  10 , and because the latter is held in place, in the axial direction, in the step  9 , the inner hub  2  cannot penetrate further into the hollow shaft section  8 . If the axial force acting on the constant velocity joint  1  increases further, the drive shaft, not shown, therefore deforms in defined manner, for example in the form of a collapsible tube. See reference number  14  in the FIGURE, which indicates the zone for a defined plastic deformation in the manner of a collapsible tube. When this happens, a great amount of energy is absorbed. 
     Consequently, both the maximal displacement path that can be traveled by the inner hub  2  and the force absorption of the lid  10  can be established, in defined manner, by way of the contour, the material and/or the shape of the lid  10 . Thus, the lid  10  can support an accident-related axial force of about 150 kN to 200 kN, without the inner hub  2  being able to penetrate into the hollow shaft section  8 . 
     The configuration of the lid  10  shown in the FIGURE, with the projection  11 , is selected in such a manner that the inner hub  2  can perform the deflection relative to the outer hub  3  that is necessary for operation of the constant velocity joint, without the inner hub  2  entering into contact with the projection  11 . A deflection of the inner hub  2  relative to the outer hub  3  that goes beyond this, however, can be limited by contact of the inner hub  2  with the projection  11  of the lid  10 , so that the balls  5  cannot fall out of the running grooves during assembly, for example, because of overly great deflection of the joint. 
     As an alternative to the contour of the lid  10  and of the projection  11  shown, any other desired configurations can be selected, for example with a projection that is rectangular in cross-section, as long as the maximal displacement path of the inner hub  2  that occurs in case of a high axial force caused by an accident, for example, is kept as short as possible.