Abstract:
The invention relates to a differential assembly in the form of a crown gear differential, more particularly for being used in the driveline of a motor vehicle. The differential assembly comprises a differential carrier ( 3 ) which is produced in one piece, which is rotatingly drivable around an axis of rotation A and which, in a casing portion ( 26 ), comprises two radial openings for mounting sideshaft gears ( 15, 16 ) and differential gears ( 14 ). Per opening ( 20 ), there is provided a bearing disc ( 19 ) which is inserted into said opening ( 20 ) and which comprises a central bore ( 30 ) in which there is held a journal end ( 28 ) of a bearing journal ( 27 ) for a differential gear ( 14 ).

Description:
TECHNICAL FIELD 
     The invention relates to a differential assembly which forms part of a differential drive and, more particularly, serves to be used in the driveline of a motor vehicle. 
     BACKGROUND 
     Differential assemblies commonly comprise a differential carrier which is rotatingly drivable around an axis of rotation, two sideshaft gears which are rotatably held in the differential carrier and serve to transmit torque to two sideshafts, as well as a plurality of differential gears which rotate together with the differential carrier and whose teeth engage those of the sideshaft gears. 
     From DE 198 54 215 A1 there is known a differential assembly with integrated constant velocity joints and a multi-part differential carrier. The differential carrier comprises a cylindrical carrier part which is closed after the set of gears has been mounted. 
     From DE 101 44 200 A1 there is known a differential assembly in the form of a crown gear differential. The differential carrier is provided in one part and is substantially cylindrical in shape. In its axial centre, the differential carrier comprises four uniformly circumferentially distributed openings for mounting the differential gears. Radially inwardly directed ribs are formed on to the webs between said openings and are connected to a journal element. The journals project into the four openings and, at their ends, comprise annular grooves which are engaged by axial securing rings for fixing the differential gears. The crown gears are inserted at the ends of the differential carrier and supported in the differential carrier by large axial securing rings. 
     U.S. Pat. No. 5,951,431 proposes a differential assembly in the form of a bevel gear differential with a one-part differential carrier. For mounting the set of gears, the differential carrier comprises two opposed assembly openings whose shape deviates from the circular shape and which are asymmetric with reference to a longitudinal central plane and a cross-sectional plane. Between the openings, in the circumferential direction, there are provided bores into which a journal part for supporting the two conical differential gears is inserted after the set of gears has been mounted. 
     In principle, one-part differential carriers require relatively large openings in the casing portion for mounting the sideshaft gears and the differential gears. Such openings reduce the stiffness of the differential carrier. Furthermore, the differential carrier is also weakened by the bores positioned between the assembly openings and provided for receiving the journals. 
     SUMMARY OF THE INVENTION 
     The present invention proposes a differential assembly having a high degree of strength and a rotational stiffness and has a compact design. 
     In accordance with the invention, a differential assembly is provided in the form of a crown gear assembly, more particularly for being used in the driveline of a motor vehicle. The differential assembly comprises a differential carrier which is produced in one piece, which is rotatingly drivable around an axis of rotation (A) and which, in a cylindrical portion, comprises two radial openings for mounting sideshaft gears and differential gears in the mounted condition, the sideshaft gears. In the differential carrier are rotatably held on the axis of rotation (A). The differential gears rotate jointly with the differential carrier around the axis of rotation and meshingly engage the sideshaft gears. Per opening, a bearing disc is inserted into the opening and includes a central bore in each of which there is held a journal end of a bearing journal for a differential gear. 
     In accordance with the invention, the objective is achieved by a differential assembly in the form of a crown gear assembly, more particularly for being used in the driveline of a motor vehicle, comprising a differential carrier which is produced in one piece, which is rotatingly drivable around an axis of rotation A and which, in a cylindrical portion, comprises two radial openings for mounting sideshaft gears and differential gears, wherein, in the mounted condition, the sideshaft gears in the differential carrier are rotatably held on the axis of rotation A and wherein the differential gears rotate jointly with the differential carrier around the axis of rotation and meshingly engage the sideshaft gears, and per opening, comprising a bearing disc inserted into said opening and having a central bore in each of which there is held a journal end of a bearing journal for a differential gear. 
     By arranging the bearing discs in the assembly openings, there is obtained a high degree of rotational stiffness and strength of the differential carrier because the bearing discs have a stiffening effect in the circumferential direction. There is a need for only two openings through which it is possible to insert both the differential gears and the sideshaft gears into the differential carrier. By providing the differential in the form of a crown gear differential, there is obtained a short axial length of the differential assembly with a relatively low weight. The two openings are preferably circumferentially offset relative to one another by 180°, wherein the differential carrier being designed in a through-aperture-free way in webs formed in the circumferential direction between the two openings. This applies to the use of preferably two differential gears and there is achieved a differential carrier with a particularly high degree of torsional stiffness. 
     According to one preferred embodiment, the bearing discs are held in a play-free way relative to the differential carrier, at least in the circumferential direction of the latter. There is thus ensured a play-free transmission of the torque introduced from the differential carrier to the bearing discs and the journal assembly connected thereto. Preferably, at each of the openings, the differential carrier comprises two supporting faces which are arranged opposite one another in the circumferential direction and with which the associated bearing disc is a contact in a play-free way in the mounted condition. In order to achieve a circumferentially directed introduction of force from the differential carrier into the bearing discs, the supporting faces are positioned on a cross-sectional plane through the journal axis or adjoin same. It is advantageous for the bearing disc to be in contact with the differential carrier in further points. For example, the shape of the opening relative to the bearing disc can be such that, in a radial view there is achieved a three-point contact or four-point contact around the circumference of the bearing disc. In a preferred embodiment, in the circumferential portions between the bearing disc and the opening, which circumferential portions are arranged between the contact points, there are formed gaps, so that the production tolerances can remain rough in these regions. This has an advantageous effect on the production costs. According to a preferred embodiment, the bearing discs are circular-disk-shaped, with other shapes not being excluded. 
     In order to avoid any undesirable out-of-balance, the two openings are preferably identical. Furthermore, the openings are preferably symmetrical with reference to the longitudinal central plane. The openings are asymmetric with reference to a cross-sectional plane arranged perpendicularly relative to the axis of rotation in order to minimize their surface area. The openings are preferably formed by two overlapping areas, of which a first area circumscribes a circle and of which a second area is greater than a radial projection of the sideshaft gears. In a radial view, the circle circumscribed by the first area corresponds approximately to the outer circumference of the bearing discs. The second area is preferably provided in the form of a slot extending in the circumferential direction. In respect of its shape, the slot approximately corresponds to the radial projection of the two sideshaft gears and is just large enough for the two sideshaft gears, while aligned in their respective operating positions, to be able to be threaded into the differential carrier. In a further embodiment, the differential carrier comprises an integrally formed-on flange for torque transmitting purposes, with the slot, with reference to the cross-sectional plane, being arranged so as to be remote from the flange. It is thereby ensured that the region of torque transmission of the differential carrier between the flange and the circumferentially positioned contact faces of the bearing disc is subject to a minimum amount of weakening only. In this way, there is achieved a particularly high degree of stiffness. 
     The journals of the journal assembly are inserted into the bores of the opposed bearing discs and axially fixed relative thereto, preferably by securing rings which engage annular grooves of the journals. According to a preferred embodiment with exactly two differential gears, the journal, in a central region, comprises flattened portions which can be engaged by sideshafts, which, for rotational safety purposes, can be drivingly connected to the sideshaft gears. In this way, the journal is prevented from rotating relative to the bearing discs. 
     Preferred embodiments of the inventive differential assembly will be described below with reference to the drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section of an inventive differential assembly in a first embodiment. 
         FIG. 2  shows the differential assembly of  FIG. 1  in a cross-sectional view through the assembly opening with a modified journal. 
         FIG. 3  shows the differential assembly of  FIG. 1  in a radial view of the assembly opening. 
         FIG. 4  shows an inventive differential assembly in a second embodiment in a radial view of the assembly. 
         FIG. 5  shows an inventive differential assembly in a third embodiment in a radial view of the assembly opening. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 to 3  will be described jointly below. They show a differential assembly  2  with a one-part differential carrier  3  which has to be supported in a stationary housing (not illustrated). For this purpose, there are provided two rolling contact bearings  4 ,  5  which receive two sleeve-shaped bearing projections  6 ,  7  of the differential carrier  3  which point in opposite directions. The differential carrier  3  is produced in one piece as a casting, so that it comprises a high degree of stiffness. The differential assembly  2  forms part of a differential drive in the driveline of a motor vehicle and serves to transmit torque from a propeller shaft (not shown) to two sideshafts  8 ,  9 . The differential carrier is provided with a formed-on flange  10  to which there is secured a ring gear  12  for introducing the torque into the differential assembly  2 . Via a plurality of differential gears  14  which are rotatably supported on a journal  27  and jointly rotate with the differential carrier  3 , the introduced torque is transmitted to sideshaft gears  15 ,  16  engaging said differential gears  14 . The sideshaft gears  15 ,  16  are axially supported relative to the differential carrier  3  commonly by friction reducing abutment discs  17 ,  18 . 
     The differential assembly  2  is provided in the form of a crown gear differential, with the sideshaft gears  15 ,  16  being provided in the form of crown gears and the differential gears  14  in the form of spur gears. There is thus achieved a compact design and low weight. In the case of crown gear differentials, the crown gear teeth of the sideshaft gears  15 ,  16  are aligned radially towards the axis of rotation A, and the spur gear teeth of the differential gears  14  are aligned parallel to the journal axis B. As a result, the differential gears  14 , in principle, can radially move on the journal axes B. When the differential assembly  2  rotates, the differential gears  14  are accelerated by centrifugal forces radially outwardly and abut the bearing discs  19  which are inserted into assembly openings  20  in a casing portion  25  of the differential carrier  3 . In order to prevent the differential gears from moving radially inwardly towards the axis of rotation A at low speeds, the sideshaft gears  15 ,  16  have axial projections  22 ,  23  which are directed towards the journal axis B and which can be abutted by the differential gears  14  by corresponding abutment faces  24 . 
     The two openings  20  are positioned diametrically opposite one another, comprise the same contour and are symmetrical with reference to the longitudinal central plane in order to avoid any undesirable out-of-balance. Each opening  20  is just large enough for inserting the sideshaft gears  15 ,  16  and the differential gears  14  into the differential carrier  3 . The webs  26  formed in the circumferential direction between the openings  20  do not comprise a through-aperture. The circular-disc-shaped bearing discs  19  are arranged in the assembly openings  20  without any play, so that the torque introduced into the differential carrier  3  can be transmitted in a play-free way on to the bearing discs  19  and from there to the journal  27 . The journal  27 , by means of its journal ends  28 , is inserted into respective bores  30  of the bearing discs  19  arranged opposite one another. In the journal ends  28 , there are provided annular grooves which are engaged by a securing ring  29  each for securing the journal  27  relative to the bearing discs  19 . In the case of the embodiment shown in  FIG. 1 , the journal  27 , in a central portion, comprises lateral flattened portions  31  which can be engaged by the sideshafts  8 ,  9  connected in a rotationally fast way to the sideshaft gears  15 ,  16 . In this way, the journal  27  is rotationally secured relative to the bearing discs  19 . According to an alternative embodiment as shown in  FIG. 2 , the journal  27 ′ is rotationally symmetric and comprises a central portion  31 ′ with a circular cross-section whose diameter is reduced relative to the bearing portions. In this embodiment it would be necessary to provide different anti-rotation means. 
     It is particularly obvious from  FIG. 3  that the openings  20  are formed by two overlapping areas of which a first area  32  circumscribes a circle and of which the second area  33  is greater than a radial projection of the sideshaft gears  15 ,  16 . The circle circumscribed by the first area  32 , in a radial view, approximately corresponds to the outer circumference of the bearing discs  19 . The second area  33  is provided substantially in the form of a circumferentially extending slot which comprises a base  13  which extends parallel to the flange  10  and which is positioned in a cross-sectional plane formed by the journal axis B. The slot  33 , in respect of shape, approximately corresponds to the radial projection of the two sideshaft gears  15 ,  16  and is just large enough to allow the two sideshaft gears  15 ,  16 , aligned in their respective operating positions, to be threaded into the differential carrier  3 . The transition regions between the base face  13  and a radial head face  11  of the slot  33  are formed by radii in order to avoid a notch effect and to achieve a high degree of stiffness. 
     The two areas  32 ,  33  are arranged in such a way that the opening  20  is formed entirely by the circular first face  32  in a region between a cross-sectional plane formed by the journal  27  and a flange  30  integrally formed on to the differential carrier  3 . This means that the slot  33 , with reference to the cross-sectional plane, is arranged away from the flange  30 . The force transmission range between the flange and the contact points relative to the bearing disc  19  is thus subjected to minimum weakening only. The contact points are formed by two circumferentially opposed supporting faces  34 ,  35  against which the bearing disc  19  is supported. The torque is transmitted from the differential carrier to the bearing disc  19  via the supporting faces  34 ,  35  in the cross-sectional plane formed by the journal  19 . It is thus advantageously ensured that the forces generated by the torque act in the circumferential direction only and do not comprise an axial force component. In the embodiment shown in  FIG. 3 , the bearing disc  19 , in a radial view, is supported in a total of four points  34 ,  35 ,  36 ,  37  two of which are positioned opposite one another in the circumferential direction and two in the axial direction. The tolerances are selected to be such that in the contact points  34 ,  35 ,  36 ,  37  there exists a slight pressure fit between the bearing discs  19  and the differential carrier  3 . In the partial circumferential portions between the contact points  34 ,  35 ,  36 ,  37 , between the bearing disc  19  and the opening  20 , there are formed gaps  38 , so that the production tolerances can be kept rough in these regions. 
     Below, there will follow a description of the assembly sequence of the sideshaft gears  15 ,  16  and the differential gears  14  in the differential carrier  3 . First, the sideshaft gear  15  adjoining the flange  10  is introduced into the opening  20  and axially displaced, until its radial contact face contacts the abutment disc  17 . Thereafter, the sideshaft gear  16  being arranged at a distance from the flange  10  is introduced into the aperture  20  and, by means of its contact face, is made to contact the abutment disc  18 . The sideshaft gears  15 ,  16  are introduced into the differential carrier  3  with their axes being aligned so as to extend approximately parallel to the axis of rotation A and without tilting laterally. Subsequently, the two differential gears  14 , are introduced through the openings  20  into the differential carrier  3 , with their respective axes being aligned so as to extend approximately perpendicularly relative to the axis of rotation and with their teeth being made to engage the teeth of the two sideshaft gears  15 ,  16 . The next stage consists in inserting the bearing discs  19  into the openings  20 . Then the journal  27  is inserted through the bores  30  of the bearing discs  19  and the differential gears  14  and is axially secured by the securing rings  29  relative to the bearing discs  19 . 
       FIG. 4  shows an alternative embodiment of an inventive differential assembly  2 ′. As far as design is concerned, it largely corresponds to that of  FIGS. 1 to 3 , which is the reason why reference is made to the above description. The opening  20 ′ of the present differential assembly  2 ′ has been modified relative to that shown in the above embodiment in that the first area  32 ′ is formed by a semi-circle. The radius of said semi-circle corresponds to the radius of the bearing disc  19 ′. There is thus formed a surface contact  34 ′,  35 ′,  36 ′ between the bearing disc  19  and the differential carrier  3 ′ in the region between the cross-sectional plane and the flange  10 ′, which leads to a higher degree of stiffness. The slot-like second area  33 ′ of the opening  20 ′, on its side removed from the flange  10 ′, is formed by three radii and comprises a central supporting portion  37 ′, with the radius of the central supporting portion  37 ′ corresponding to the radius of the bearing disc  19 ′, so that the latter rests in a planar way against the supporting portion  37 ′. In this embodiment, too, the tolerances have been selected to be such that the bearing disc  19  can be inserted with a slight interference fit into the respective opening  20 ′. 
       FIG. 5  shows a further embodiment of an inventive differential assembly  2 ″ which, in respect of design, largely corresponds to that shown in  FIGS. 1 to 3 . To that extent, reference is made to the above description. In contrast to the above embodiments, the bearing disc  19 ″ of the present differential assembly  2 ″ is not supported relative to the differential carrier  3 ″ in the region between the two supporting faces  34 ″,  35 ″. There is provided a sickle-like gap  38 ″ between the bearing disc  19 ″ and the differential carrier  3 ″, so that, in this region, the production tolerances can be kept rough. The supporting faces  34 ″,  35 ″ which contact the bearing disc  19  in a plane through the journal axis B, which plane extends perpendicularly relative to the axis of rotation A, can be axis-parallel in a first region before they change into the adjoining concave region. The slot-like second area  33 ″ of the opening  20 ″, in a radial view, corresponds to a radial projection of the sideshaft gears  15  to the inserted at the flange end, with the transition regions being rounded off by radii. A supporting portion  37 ″ axially removed from the flange  10  is formed by a radius which corresponds to the radius of the bearing disc  19 . The bearing disc, in this region, thus rests against the supporting portion  37 ″ in a planar way. In the axially opposite direction, i.e. towards the flange  10 , the bearing disc  19 ″ is directly supported against the differential carrier  3 ″ via the journal  27 ″, the differential gear  14  and the sideshaft gear  15  engaging the latter. The bearing disc  19 ″ is thus axially held even without an additional axial contact point relative to the differential carrier  3 ″. The tolerances in the contact regions  34 ″,  35 ″,  37 ″ have been selected to be such that the bearing discs  19 ″ are inserted into the respective opening  20 ″ with a slight interference fit.