Title of Invention	A DISPLACEMENT UNIT FOR A JOINT SHAFT
Abstract	The invention relates to a displacement unit and to a joint shaft comprising said type of displacement unit. Said displacement unit is formed by an external part and an internal part which can be displaced in an axial direction therein, which comprise running paths provided with balls which are arranged therein for the transmission of torque.

Full Text

FORM 2 THE PATENT ACT 1970 (39 of 1970) The Patents Rules, 2 003 COMPLETE SPECIFICATION (See Section 10, and rule 13) 1. TITLE OF INVENTION DISPLACEMENT UNIT AND JOINT SHAFT COMPRISING A DISPLACEMENT UNIT 2. APPLICANT(S) a) Name b) Nationality c) Address SHAFT-FORM-ENGINEERING GMBH GERMAN Company DIESELSTRASSE 59, 63165 MUEHLHEIM, GERMANY 3. PREAMBLE TO THE DESCRIPTION The following specification particularly describes the invention and the manner in which it is to be performed : - ENGLISH TRANSLATION VARIFICATION CERTIFICATE u/r. 20(3)(b) I, Mr. HIRAL CHANDRAKANT JOSHI, an authorized agent for the applicant, SHAFT-FORM-ENGINEERING GMBH do hereby verify that the content of JEnglish translated complete specification filed in pursuance of PCT International application No. PCT/EP2006/009343 thereof is correct and complete. The invention relates to a displacement unit with a tubular outer part, the inner face of which has outer running tracks at least in part, with an inner part which is axially displaceable in the outer part and the outer face of which has inner running tracks at least in part, and with balls arranged for torque transmission, respectively, in outer running tracks and inner running tracks assigned to each other in pairs. The invention further relates to a jointed shaft with a displacement unit. Displacement units of this type are known, for example, from German publications DE 198 31 010 C2, DE 198 31 016 C2 or DE 199 11 111 CI and are used to compensate a telescopic displacement, which is necessary for assembly and/ or occurs in operation of a shaft that is used, for example, in the drivetrain of a motor vehicle. Beyond the normal displacement path that is provided in these displacement units in operation or is possible during assembly, a further axial telescoping of the displacement unit or the shaft connected therewith is not provided or possible. In a head-on collision of a motor vehicle, the entire vehicle is compressed, partly substantially depending on the severity of the collision. As a result, a partly substantial axial load acts also on the longitudinal vehicle shaft. To safely prevent the shaft from buckling and penetrating the passenger compartment, the shaft must therefore be capable of axially contracting. In the known displacement units, this is possible only to a very limited degree, so that the longitudinal shaft can buckle and can potentially endanger the vehicle occupants. Further, in German publication 199 43 880 CI, a drive arrangement is proposed in which two shaft sections of a longitudinal drive shaft are interconnected by a center joint. The diameters of the two shaft sections are such that the shaft sections can telescope into each other in case of a collision. To this end the cage of the center joint is designed as a predetermined breaking point which fails in a collision and thereby enables the two shaft sections to telescope. In addition, the transmission-side joint and the differential-side joint are designed as plug-in connections. Particularly in applications requiring relatively large, non-destructive changes in the axial length of the drive shaft for assembly and/or in operation, the comparatively small nondestructive displacement path of the plug-in connections has proven to be a disadvantage in this known drive arrangement. It is therefore an object of the present invention to provide a displacement unit and a jointed shaft, which enable a largely force-free axial reduction in length if a predefined axial force is exceeded and which are meant to prevent an uncontrolled buckling of a shaft or a shaft section. A further object of the invention is to make the fixed constant velocity joints especially compact, to save weight and to reduce the residual imbalances in a jointed shaft. Also, the axial forces acting on the center bearing are to be substantially reduced and the vibration behavior of the intermediate bearing is to be improved, so that noise development is also reduced. It is a further object of the present invention to make the jointed shaft particularly cost-effective to manufacture and to use as many identical components as possible. In addition, assembly and disassembly are to be made easier and different assembly sequences are also to be made possible. In a displacement unit of the above-described type, these objects of the invention are essentially achieved by connecting the outer part via a predetermined breaking point to a connecting segment whose inside diameter is greater than, or substantially equal to, the outside diameter of the outer part. As a result, the predetermined breaking point ruptures in a head-on collision because of the axial force acting on the displacement unit, such that the outer part can be displaced into the connecting segment and the hollow shaft tube that is optionally connected therewith. To enable a largely force-free displacement of the outer part within the connecting segment, the inside diameter of the connecting segment is preferably greater than, or at most equal to, the outside diameter of the outer part. Alternatively, it may make sense to absorb deformation energy during the change in length of the displacement unit in a crash. This can be achieved by making the connecting segment or the adjoining tubular shaft slightly smaller than the outside diameter of the outer part, optionally downstream of an insertion section. The outer part can then still be reliably inserted into the connecting segment, without the risk that it will buckle, but impact energy is dissipated in addition. This can also be achieved, for example, by providing the inner face of the connecting segment and/or the outer face of the outer part with relatively easily deformed ribs or similar protrusions. In any case, however, the displacement unit according to the invention makes possible a deformation of the displacement unit in a defined direction when a defined force is exceeded. The force at which the predetermined breaking point of the displacement unit fails can be set in a defined manner. Because in the displacement unit according to the invention the entire outer part, together with the inner part received by it, can be displaced into the connecting segment and the optionally connected tubular shaft, the realizable crash path is very large. Unlike in a shaft section that is configured as a collapsible tube, however, this does not mean that different and, in particular, larger tube diameters of the individual shaft sections must be provided. Therefore, the overall space required for the displacement unit according to the invention can be kept small. According to a preferred embodiment of the invention, the predetermined breaking point is formed as a connecting region radially between the inner face of the outer part and the outer face of the connecting segment. To facilitate rupture of the predetermined breaking point, the transitions between the outer part and the connecting segment can be realized with small curvature radii. It is also possible to make the predetermined breaking point S-shaped or Z-shaped in cross section. As an alternative or in addition, the predetermined breaking point can be a constriction, notching, perforation and/or a similar weakening of the material. With these measures the force at which the predetermined breaking point fails can be adjusted depending on the requirements. The outer part, the connecting segment and the predetermined breaking point are configured in such a way that when a defined force acting axially on the outer part is exceeded, the predetermined breaking point fails and the outer part is displaceable into the connecting segment to realize a large crash path. If a cover is provided on the outer part, on the connecting segment and/or on the predetermined breaking point, the outer part can be closed in the direction toward the connecting segment. The cover can then serve as a limit stop for the inner part to prevent the inner part from being displaced out of the outer part in operation or in a crash. However, the cover can also be mounted to the outer part, the connecting segment and/ or the first breaking point via an additional predetermined breaking point, so that in a crash, the cover is also separated and the inner part can be displaced out of the outer part. Depending on the design of the displacement unit and the components connected thereto, this can provide an additional displacement path. The object underlying the invention is further achieved by a jointed shaft which can be used, in particular, as a longitudinal vehicle shaft and which has at least one displacement unit and at least one shaft tube that is connected to a connecting segment of a displacement unit and has an inside diameter greater than, or substantially equal to, the outside diameter of the outer part of the at least one displacement unit. In principle, this is to enable a nearly force-free displacement of the" outer part of the displacement unit into the jointed shaft. However, if a defined reduction of the crash force is to occur when the displacement unit is displaced into the tubular shaft, this can be achieved by the measures described above. A preferred embodiment of the jointed shaft according to the invention provides for at least two shaft sections, each having a shaft tube, interconnected by a center joint. At their ends opposite the center joint, the shaft sections have a transmission-side and a differential-side joint. Preferably, the transmission-side joint, the differential-side joint and the center joint are configured as fixed joints, particularly as opposed path joints, whose cage is guided in the outer hub of the respective opposed path joint. This embodiment of the jointed shaft therefore makes it possible to use three at least substantially similarly constructed joints so as to minimize the production costs of the jointed shaft. In addition, compared to plug-in connections, each of these fixed joints is adapted to allow particularly large angles in operation between the individual shaft sections or the components connected thereto. The configuration of the fixed joints as opposed path joints with cages guided in the outer hub makes possible a particularly cost-effective production and at the same time provides good reliability in operation. Independent of the features described above, a jointed shaft according to the invention has two roller displacement units, at least one of which is assigned to and disposed near the center joint, such that the two shaft sections are axially movable relative to each other. Arranging the roller displacement units at a point remote from the transmission output or the differential input makes it possible to make both the roller displacement units and the fixed constant velocity joints particularly compact. This results in considerable weight savings and smaller residual imbalances because of the smaller masses. Noise development during operation of the jointed shaft according to the invention can be reduced as a result. The axial forces acting on the center bearing are also substantially reduced because at least one roller displacement unit is arranged near the center joint and therefore near the intermediate bearing. This axial force decoupling also has the effect of reducing noise in operation. Furthermore, in the embodiment of the jointed shaft according to the invention an intermediate bearing does not have to be axially flexible, so that possible noise development because of the vibration behavior of the intermediate bearing is also reduced. A further development of the inventive concept provides for two roller displacement units to be assigned and arranged close to the center joint of the jointed shaft. If both roller displacement units are positioned substantially in the center of the jointed shaft, it is possible to use three identically constructed fixed constant velocity joints for the jointed shaft. The jointed shaft according to the invention is therefore made of only a very small number of different components, which results in substantial cost savings based on the principle of using identical parts. To minimize the masses present in the area where the jointed shaft is connected to a transmission or differential, the roller displacement units are arranged as far from the connecting points as possible, for example, in the center of the jointed shaft. Thus, in the jointed shaft, at most the very small masses of the outer fixed constant velocity joints contribute to potential imbalances of the entire system through possible minimal journal eccentricities. In this embodiment of the jointed shaft, assembly is also facilitated compared to conventional jointed shafts. For example, the two shaft sections can be axially moved in relation to each other, thereby enabling a very large displacement path. This results in a very small installation and deinstallation length, making assembly and disassembly significantly easier. In addition, different assembly sequences can be used as a function of the other requirements and boundary conditions. Assembly can also be carried out on the vehicle floor, for example, starting with the center bearing. According to another embodiment of the invention, one of the two roller displacement units can be assigned to and arranged near the center joint and the other of the two roller displacement units can be assigned to and arranged near the transmission-side or differential-side fixed constant velocity joint. The two roller displacement units can be provided on the same shaft section or each on a different shaft section. These two embodiments each ensure that the two shaft sections are axially displaceable in relation to each other and at least one roller displacement unit is positioned near the center joint. A particularly compact jointed shaft can be realized by connecting the inner part of the second displacement unit to the inner hub of the center joint and the inner part of the first displacement unit to the outer hub of the center joint. The inner part of the second displacement unit can even be integrally formed with the inner hub of the center joint, or it can be directly inserted therein. Likewise, the outer hub of the center joint can be integrally formed with the inner hub of the first displacement unit. In a preferred embodiment, however, the inner part of the first displacement unit is connected to a cap of the outer hub of the center joint. A further development of this inventive concept provides that the inner part of a displacement unit, preferably the first displacement unit, is supported in an intermediate bearing. The center joint is therefore held in the intermediate bearing, which is fixed, for example, to the chassis of a vehicle, so that axial vibrations from the two displacement units assigned to the center joint can be compensated in operation and during assembly. To save weight and ensure telescopability of the shaft in a head-on crash, the two shaft sections of the jointed shaft are at least partly tubular. Preferably the fixed constant velocity joints provided at the ends of each shaft section opposite the center joint, i.e., the transmission-side and the differential-side fixed joints, are each connected to the shaft sections with their outer hubs. The inner hub of the transmission-side or the differential-side fixed joint can be provided with a profiled receiving opening, so that a transmission output journal or a differential input journal can be inserted into the inner hub in a rotationally fixed manner. This simplifies assembly compared to the known flanged connection. To prevent imbalances, jointed shafts are typically balanced at the end of production. A problem in the known jointed shafts, which are connected by flanged connections, that is to say over a large diameter, is that possible eccentricities, which result at the connecting points only when the shaft is installed in the vehicle, negatively affect the balance quality of the entire system despite the high balance quality of the jointed shaft as an individual component. In the jointed shaft according to the invention, centering at the connecting points is realized directly via journals that are inserted into the inner hubs of the fixed constant velocity joint. This has the effect of substantially reducing imbalances because of the improved centering via the journal connection. Noise occurring in operation can also be reduced as a result. The elimination of the flange in this insertion solution further saves weight in the fixed constant velocity joints. In addition, the highly compact design of the fixed constant velocity joint with a plug-in connection increases the design freedom regarding the remaining vehicle components and reduces the overall space required. The center joint can likewise be provided with an inner hub, which makes possible a plug-in coupling with one of the roller displacement units, for example. Further developments, advantages and possible applications of the invention will become evident from the following description of an embodiment and the drawing. All the features described and/or illustrated, either by themselves or together in any combination, constitute the subject matter of the invention, regardless of their summarization in the claims or the relationship of the claims. The following show schematically: FIG 1 a longitudinal section of a jointed shaft according to the invention, FIG 2 a longitudinal section of the outer part of a displacement unit according to the invention, and FIG 3 a longitudinal section of the outer part according to FIG 2 after a crash. The jointed shaft shown in FIG 1 consists of a first shaft section 1 and a second shaft section 2, each of which is formed as a hollow shaft tube. The two shaft sections 1 and 2 are interconnected by a center joint 3, which in the embodiment shown is designed as a fixed opposed path joint. The transmission-side end opposite the center joint of the first shaft section 1 is connected to a transmission-side joint 4. Likewise, the differential-side end opposite the center joint 3 of the shaft section 2 is connected to a differential-side joint 5. The transmission-side joint 4 and the differential-side joint 5 are also designed as fixed opposed path joints. The center joint 3 is assigned a first displacement unit 6 through which the center joint 3 is connected to the first shaft section 1, and a second displacement unit 7 through which the center joint 3 is connected to the second shaft section 2. The center joint 3 is further assigned an intermediate bearing 8, which in the embodiment shown is mountable to a vehicle chassis via an elastic member. The intermediate bearing 8 is positioned on the first displacement unit 6. The fixed opposed path joints 3, 4 and 5 each have an inner hub 9 configured as a sleeve, into which an axle stub or a shaft end can be inserted in the transmission-side joint 4 and the differential-side joint 5. On the outer face of the inner hub 9 inner tracks are formed. The fixed opposed path joints further have an outer hub 10 each, on the inner face of which outer tracks are formed. Balls for torque transmission are arranged in the tracks, which are configured, for example, as described in German publication DE 102 09 933 B4. The balls are received in the openings of a cage, which is centered and guided in the outer hub 10, particularly in cage centering surfaces of the outer hub 10, of the fixed opposed path joints. The two displacement units 6 and 7 each have an inner part 11 and an outer part 12 in which the inner part 11 is displaceable. On the outer face of the inner part 11 and on the inner face of the outer part 12, inner tracks 13 and outer tracks 14 are formed, respectively, which extend at least substantially in axial direction. In this embodiment, in the inner tracks 13 and the outer tracks 14, which are assigned to each other in pairs, a plurality of balls 15 is provided for torque transmission and guided in a cage. As shown in FIG 1, the inner part 11 of the second displacement unit 7 is connected to the inner hub 9 of the center joint 3. The inner part 11 of the first displacement unit 6 is connected to a cap 16, which encloses the outer hub 10 of the center joint 3 and is rotationally fixed thereto. In this manner, the two displacement units 6 and 7 are assigned to the center joint 3 and are arranged close thereto, so that axial movements of the two shaft sections 1 and 2 are compensated by the displacement units 6 and 7 and are not transmitted via the center joint 3. As may be seen from the schematic of FIG 2, a connecting segment 17 is formed on the outer part 12 to connect the outer part 12 of the displacement unit 7 to the first shaft section 2. The connecting segment 17 is connected to the outer part 12 by a predetermined breaking point 18, which in the embodiment shown extends radially. The predetermined breaking point 18 can have a weakening of the material, such as a constriction, notching, perforation, or the like. In the embodiment shown, the inside diameter of the shaft tube of the second shaft section 2 and the inside diameter of the connecting segment 17 are larger than the outside diameter of the outer part 12 of the second displacement unit 7. The first displacement unit 6 is likewise connected to the shaft tube of the first shaft section 1 by a connecting segment 17 and a predetermined breaking point 18. In the first displacement unit 6, the outside diameter of the outer part 12 is again smaller than the inside diameter of the first shaft section 1 or the connecting segment 17. The outer part 12 of the two displacement units 6 and 7 is closed by a cover 19, which is connected to the outer part 12 by electron welding, for example. Unlike in the embodiment depicted in FIG 2, the cover 19 can also be connected to the predetermined breaking point 18 or the connecting segment 17. The cover 19 limits the displacement path of the inner part 11 in the outer part 12. The connection between the cover 19 and the outer part 12 can also be formed as a predetermined breaking point. If, in a crash, for example, a large axial force acts on the shaft sections 1 and 2 and thereby also on the outer parts 12 of the displacement units 6 and 7, the respective predetermined breaking points 18 of the two displacement units fail at the end of the displacement path of the displacement units 6 and 7, as illustrated in FIG 3. As a result, the outer part 12 of each displacement unit can be displaced into the corresponding shaft section 1 or 2 in a substantially force-free manner. This prevents the jointed shaft from buckling because the displacement units 6 and 7 are guided in the shaft sections 1 and 2. The large axial length of the two displacement units 6 and 7 combined makes it possible in such a crash-related failure of the two predetermined breaking points 18 to realize a very large additional displacement path (crash path), without the vehicle occupants being placed at risk. WE CLAIM: 1. A displacement unit, particularly for a jointed shaft, with a tubular outer part, the inner face of which has outer tracks at least in part, with an inner part which is axially displaceable in the outer part and the outer face of which has inner tracks at least in part, and with balls which for torque transmission are arranged in outer tracks and inner tracks that are assigned to each other in pairs, characterized in that, the outer part is connected by a predetermined breaking point to a connecting segment, the inside diameter of which is greater than, or substantially equal to, the outside diameter of the outer part. 2. A displacement unit as claimed in claim 1, characterized in that the predetermined breaking point is configured as a connecting region disposed radially between the inner face of the outer part and the outer face of the connecting segment. 3. A displacement unit as claimed in claim 1 or 2, characterized in that the predetermined breaking point is formed by a restriction, notching, perforation or a similar weakening of the material. 4. A displacement unit as claimed in any one of claims 1 to 3, characterized in that the outer part, the connecting segment and the predetermined breaking point are configured in such a way that when a defined force acting axially on the outer part is exceeded, the predetermined breaking point fails and the outer part is displaceable into the connecting segment. 5. A displacement unit as claimed in any one of claims 1 to 4, characterized in that a cover is provided on the outer part, the connecting segment and/or the predetermined breaking point to close the outer part in the direction toward the connecting segment. 6. A displacement unit as claimed in claim 5, characterized in that the cover is fixed to the outer part, the connecting segment and/or the first predetermined breaking point via an additional predetermined breaking point. 7. A jointed shaft, particularly a longitudinal vehicle shaft, with at least one displacement unit as claimed in any one of the preceding claims and with at least one shaft tube, which is connected to a connecting segment of the at least one displacement unit and the inside diameter of which is greater than, or substantially equal to, the outside diameter of the outer part of the at least one displacement unit. 8. A jointed shaft as claimed in claim 7, characterized in that at least two shaft sections, each with a shaft tube, are provided, which are interconnected by a center joint and which have, respectively, a transmission-side and a differential-side joint at their ends opposite the center joint. 9. A jointed shaft as claimed in claim 8, characterized in that the transmission-side joint, the differential-side joint and the center joint are configured as fixed joints, particularly as opposed path joints, the cages of which are guided in the outer hub of the respective opposed path joint. 10. A jointed shaft as claimed particularly in claims 7 to 9 with two shaft sections, which are connected to each other in a rotationally fixed manner by a center joint which is configured as a fixed opposed path joint, wherein a fixed constant velocity joint is arranged at the ends opposite the center joint of each shaft section, wherein two roller displacement units are provided and at least one of the roller displacement units is arranged near the center joint. 11. A jointed shaft as claimed in claim 10, characterized in that the two shaft sections are axially movable relative to each other. 12. A jointed shaft as claimed in claim 10 or 11, characterized in that two roller displacement units are assigned to the center joint and are arranged close thereto. 13. A jointed shaft as claimed in claim 10, characterized in that one of the two roller displacement units is assigned to the center joint and is arranged close thereto and the other of the two roller displacement units is assigned to a fixed constant velocity joint at the end of the shaft section and is arranged close thereto. 14. A jointed shaft as claimed in claim 13, characterized in that the two roller displacement units are assigned to the same shaft section. 15. A jointed shaft as claimed in claim 13, characterized in that the two roller displacement units are assigned to different shaft sections. 16. A jointed shaft as claimed in any one of claims 10 to 15, characterized in that the inner part of the second displacement unit is connected to the inner hub of the center joint, and the inner part of the first displacement unit is connected to the outer hub of the center joint. 17. A jointed shaft as claimed in any one of claims 7 to 16, characterized in that the inner part of a displacement unit, particularly the first displacement unit, is supported in an intermediate bearing. 18. A jointed shaft as claimed in any one of claims 7 to 17, characterized in that the two shaft sections are at least partly tubular, wherein the fixed constant velocity joints provided at the ends opposite the center joint of each shaft are each connected to the shaft sections by their outer hubs. ABSTRACT The invention relates to a displacement unit and to a joint shaft comprising said type of ■ displacement unit. Said displacement unit is formed by an external part and an internal part which can be displaced in an axial direction therein, which comprise running paths provided with balls which are arranged therein for the transmission of torque. To, The Controller of Patents, The Patent Office, Mumbai

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