Abstract:
A sliding universal joint comprises a male element (1) intended to be fixed to a first shaft and including arms (6). Each arm bears a ball-type journal (7) which is integral therewith. A female element (20 intended to be fixed to a second shaft defines two guide paths which are situated on either side of each journal. Intermediate member (3, 4) are interposed between each journal and the associated guide paths. These intermediate members comprise a first member (3) which interacts with a first path (8) of the guide paths and has properties, with respect to the transmission and/or generation of vibration, which are different from those exhibited by the interaction between the second member (4) and the second guide path.

Description:
The present invention relates to a s1iding universal joint of the type comprising: a male element intended to be fixed to a first shaft and including arms, each of which bears a ball-type journal which is integral therewith. A female element is intended to be fixed to a second shaft and defines two guide paths which are respectively situated on either side of each journal; and Intermediate members are interposed between each ball-type journal and the associated guide paths. 
     In known universal joints of this type, many attempts have been made to reduce the resistance to the free axial sliding under torque and at an angle, so as to prevent the transmission of vibration to the structure of the vehicle, and to reduce the creation of cyclic axial excitations under torque and at an angle. Effective solutions have been proposed, but at an expense involving an increase in the complexity and in the cost of the joints (see, for example, FR-A 2,506,872 and 2,628,803 in the name of the Applicant Company). 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a sliding universal joint whose design, better suited to actual operating conditions, makes it possible, at a reduced cost, to obtain a similar result throughout virtually the entire lifetime of the joint. 
     To this end, the subject of the invention is a universal joint of the aforementioned type, characterized in that the intermediate members comprise a first member which interacts with a first of the guide paths and has properties, with respect to the transmission and/or generation of vibration, which are different from those exhibited by the interaction between the second member and the second guide path. 
     The universal joint according to the invention may include one or more of the following characteristics: 
     - the first guide path is plane, and the first intermediate member is a pad which is spherical on the inside, and of which the opposite face from the journal is plane and moves along the first guide path via a row of needles; 
     - the first guide path is cylindrical with circular cross-section, and the first intermediate member comprises on the one hand a strip, especially a self-recentering strip, which on the journal side has a spherical recess and on the opposite side has at least one track with circular cross-section and, on the other hand, at least two balls which run along this or these tracks and along the first guide path; 
     - the first guide path is cylindrical, and the first guide member is a torus sector on the outside which is spherical on the inside and which runs along this guide path; 
     - the second guide path is cylindrical, and the second intermediate member is a portion which is spherical on the inside and cylindrical on the outside to slide in this guide path; 
     - the second guide path is plane, and the second intermediate member is a pad which is spherical on the inside, and of which the opposite face from the journal is plane and slides directly along this guide path; 
     - the second guide path is cylindrical, and the second intermediate member is a torus sector on the outside which is spherical on the inside and which runs along this guide path; 
     - the second guide path is cylindrical with circular cross-section, and the second intermediate member comprises on the one hand a strip, especially a self-centering strip, which exhibits on the journal side a spherical recess and on the opposite side at least one track with circular cross-section and, on the other hand, at least two balls which run along this or these tracks and along the second guide path; 
     - the guide paths have a straight overall axis parallel to the axis of the female element; 
     - the male element is a tripot. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described with respect to the appended drawings, in which: 
     - FIG. 1 represents diagrammatically, in transverse section taken on the line I--I of FIG. 2, one third of a universal joint according to the invention; 
     - FIG. 2 is a view taken in section on line II--II of FIG. 1; and 
     - FIGS. 3 to 16 are similar views of other embodiments, FIGS. 3, 5, 7, 9, 11, 13 and 15 corresponding to FIG. 1 and being taken in section, respectively, on lines III--III, V--V, VII--VII, IX--IX, XI--XI, XIII--XIII and XV--XV of FIGS. 4, 6, 8, 10, 12, 14 and 16, whereas FIGS. 4,6,8,10,12,14 and 16 are taken in section, respectively, on lines IV--IV, VI--VI, VIII--VIII, X--X, XII--XII, XIV--XIV and XVI--XVI of FIGS. 3, 5, 7, 9, 11, 13 and 15. 
     Figure 17 is a cross-sectional view taken along lines XVII of FIG. 18 and FIG. 18 is a cross-sectional view taken along lines XVIII of FIG. 17, these Figures being similar to FIGS. 1 and 2 and of a further embodiment according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The universal joint represented in FIGS. 1 and 2 is intended to connect two shafts (not represented) which can slide with respect to each other, either in mutual alignment or at an angle of discontinuity which may typically reach approximately 25°. It essentially comprises a male element or tripod 1, a female element or jaw 2, three assemblies 3 with pad and needles, and three torus sectors 4. 
     The tripod is made as a single piece and comprises a central hub 5 designed to be secured to one of the two shafts, and from which three arms 6, spaced at angles of 120°, project radially. The radially outer part of each arm is shaped into a spherical journal 7. 
     The jaw 2 defines, for each arm 6, a pair of facing runway paths: a first runway path 8 consisting of a straight slot with a flat bottom, parallel to the axis X--X of the jaw, and a second runway path 9 consisting of a cylindrical slot with circular cross-section and an, of axis parallel to the axis X--X. 
     The assembly 3 comprises a pad 10 with a spherical internal face substantially matching the journal 7 and interacting with it, and with a plane external face moving along the bottom of the slot 8 with interposition of a row of needles 11 which are perpendicular to the axis X--X, and retained by a cage 12. The assembly 3, which is described, for example, in the aforementioned FR-A-2,506,872, has very low resistance to running, especially under torque and at an angle. 
     The torus sector 4 includes a spherical internal face substantially matching the journal 7 and interacting with it, and a toric external face substantially matching the runway path 9 and interacting with it. In this way, the sector 4 runs along this path 9, but with a resistance to running which is obviously greater than that of the assembly 3. In contrast, the sector 4 is markedly simpler and less expensive than the assembly 3 and, in addition, it is easier and more economical to machine the cylindrical runway path 9 than the plane runway path 8. 
     In service, the joint is mounted in a motor-vehicle transmission in such a manner that, in a forwards gear, the engine torque is transmitted from the tripod to the jaw via the three assemblies 3. Under torque, a slight clearance arises on the sectors 4 side, so that the resistance to sliding is practically that defined by the assemblies 3 and is therefore very low, even at an angle. In other words, in a forwards gear, that is to say almost all of the operating life of the joint, the level of axial excitations transmitted by the joint to the structure of the vehicle is particularly low. 
     In reverse gear, it is the resistance to running of the sector 4 which defines the resistance to sliding of the joint. This resistance is greater than that corresponding to a forwards gear, but is acceptable given the very short time for which the vehicle operates in reverse gear. 
     In the joint of FIGS. 3 and 4, the assembly 3 is the same as in FIGS. 1 and 2, but the torus sector 4 is replaced by a portion 13 which is cylindrical on the outside, substantially matching the cylindrical runway path 9 and interacting with it, and spherical on the inside, substantially matching the journal 7 and interacting with it. In this way, during axial sliding of the joint, the portion 13 slides in the path 9, consequently offering a resistance to sliding which is greater than that displayed by the torus sector 4 of FIGS. 1 and 2. 
     The joint of FIGS. 5 and 6 again includes the aforementioned assembly 3, whereas the guide path 9 is plane and the associated intermediate member is a pad 10A similar to the pad 10 but sliding directly along this guide path. 
     The universal joints of FIGS. 7-8, 9-10 and 11-12 are identical, respectively, to those of FIGS. 1-2, 3-4 and 5-6, with just two differences. 
     On the one hand, the slot 8 is cylindrical, with circular cross-section, the axis of which is parallel to the axis X--X, and the external shape of the jaw 2 is modified correspondingly. On the other hand, the assembly 3 is replaced by an assembly 3A consisting of a self-recentering strip 14 and two balls 15. The strip 14 internally includes a spherical recess substantially matching the journal and interacting with it, and externally includes two runway tracks 16 with circular cross-section which are separated by a middle projection 17. The tracks 16, viewed in plan, are the extension of one another; in lateral view (FIG. 8), they diverge progressively from the path 8 starting from the projection 17. Each ball 15 is interposed between one of these tracks and the runway path 8, and the shape of the two tracks ensures self-recentering of the two balls, as described in the aforementioned FR-A-2,628,803. The assembly 3A is supplemented by a cage 18 for retaining the balls. 
     The assembly 3A exhibits a resistance to running which is approximately as low as the assembly 3 of FIGS. 1 to 5, so that the comments made above on the subject of these figures again apply. 
     FIGS. 13 to 16 represent universal joints in which the forwards gear side part, with low resistance to running, is identical to the reverse gear side part of FIGS. 1-2 and 7-8, that is to say comprises a torus sector 4 which runs in a cylindrical runway path 8. 
     In the case of FIGS. 13-14, the reverse gear side part of the joint is identical to that of FIGS. 3-4 and 9-16 (externally cylindrical portion 13). 
     In the case of FIGS. 15-16, it is identical to that of FIGS. 5-6 and 11-12 (externally plane pad 10A sliding directly along a plane guide path 9). 
     Another alternative shown in FIGS. 17 and 18 consists in combining a pad 10A/needles 11/cage 12 assembly on one side of the journal 7, and a strip 14/balls 15/cage 18 assembly on the other side of this journal. 
     From the above description it can be seen that in each embodiment the first and second intermediate members have different configurations. That is, they are structured differently. As a result, intermediate members 3 and 4 exhibit different properties in interaction with their respective guide paths 8 and 9 with respect to at least one of vibration transmission and vibration generation. Indeed, it can be seen that a number of embodiments involving a roller element for one intermediate member results in one of the intermediate members having a smaller amount of resistance to free axially sliding than the other of the intermediate members when the respective intermediate members are in contact with their respective guide paths.