Abstract:
In a gearwheel pairing, in which one of a pair of gearwheels has, at least at one side thereof a lid-shaped stop structure for engaging the other gearwheel for retaining it in engagement with the other gear wheel. The arrangement is expediently used in a differential transmission in particular a crown-wheel differential transmission.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a gearwheel pairing and, to its use for a differential transmission.  
           [0002]    WO 92/01877 already discloses a gearwheel pairing which is used in a crown-wheel differential. The gearwheel pairing comprises a crown wheel and a spur wheel meshing with the latter. The spur wheel is supported by the casing in the direction outwards from the crown-wheel differential and on a sleeve of the differential bolt in the inward direction so that meshing engagement between the crown wheel and the spur wheel is always ensured.  
           [0003]    Furthermore, DE 195 36 800 A1 shows a rear-axle transmission, in which the drive includes a pinion shaft with a spur wheel gear driving the differential casing.  
           [0004]    The object of the invention is to provide a gearwheel pairing comprising at least two gearwheels, in particular for a differential, wherein the gearwheel pairing requires a relatively small number of components for ensuring engagement of the teeth of the gears.  
         SUMMARY OF THE INVENTION  
         [0005]    In a gearwheel pairing, one of the gearwheels has, at least at one side thereof, a lid-shaped stop structure for engaging the other gearwheel for retaining the gear wheels in engagement with one another. The arrangement is expediently used in a differential transmission in particular a crown-wheel differential transmission.  
           [0006]    One advantage of the invention is that a displacement of the second gearwheel at least in one direction is prevented as a result of a stop structure provided on the second gearwheel. Since the stop structure extends at least between a plurality of teeth, it can be brought into bearing contact with the teeth of the first gearwheel. There is no longer any need for further components in order to support the second gearwheel in this direction.  
           [0007]    In a particularly advantageous embodiment of the gearwheel pairing a crown-wheel/spur wheel pairing is provided, with the result that two gearwheels can be arranged at angle of 90° to one another. With the spur wheel being provided with radial teeth, no forces from the first gearwheel are introduced into the stop structure or the second gearwheel. This is advantageous in terms of efficiency and of wear.  
           [0008]    If the radial extent of the stop structure corresponds to the tip circle diameter of the teeth, a compact design can be achieved along with the maximum possible support of the second gearwheel with respect to the first gearwheel.  
           [0009]    Preferably, there is a second stop structure which extends opposite the axial end of the second gear wheel. In this way, a displacement of the second gearwheel in its two axial directions is prevented by means of the two stop structures in that the respective stop structures bear against the teeth of the first gearwheel in both directions.  
           [0010]    With the stop structure firmly connected to, or being part of, the second gear wheel particularly high forces can be transmitted. By virtue of the rotationally fixed connection between the second gearwheel and the stop structure or even by their being integrally formed with one another, a particularly high tooth-root strength is achieved.  
           [0011]    Preferably, the first gear wheel is connected to an axle shaft and the second gear wheel is a differential wheel to provide the gearwheel pairing according to the invention for a differential, in particular a crown-wheel differential. In this case, a differential bolt/differential cross may be dispensed with which is a particularly advantageous.  
           [0012]    If the differential casing is provided with, or carries, the stop structure, high drive torques can be transmitted through the differential. This is achieved in that the drive torque is not introduced from the casing of the differential into a differential bolt, but into the stop structure, the latter having a disc-shaped design. This disc-shaped design makes it possible to provide a radial mounting in the casing with respect to the geometric axis of the differential wheel. The bearing surface on the casing is large in comparison with a differential bolt, resulting in a correspondingly low surface pressure in spite of high drive torques.  
           [0013]    Use in a drive toothing of a differential makes it possible to transmit particularly high drive torques, since the tooth-root strength of the toothing of the gearwheel of the pinion shaft is particularly high.  
           [0014]    In an advantageous embodiment, the gearwheel pairing is formed by a crown wheel and a spur wheel. As compared with the conventional hypoid toothings, there are advantages in terms of efficiency and of the bearing load of the pinion shaft.  
           [0015]    Further advantages of the invention are obtained if the crown wheel has teeth with inwardly projecting ribs shaped corresponding to the stop structure of the spur wheel.  
           [0016]    The invention will be described in greater detail on the basis of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 shows a crown-wheel differential in a sectional perspective illustration,  
         [0018]    [0018]FIG. 2 shows the crown-wheel differential of FIG. 1 in a sectional two-dimensional illustration,  
         [0019]    [0019]FIG. 3 shows the crown-wheel differential in a section taken along line III-III of FIG. 2,  
         [0020]    [0020]FIG. 4 shows the crown-wheel differential of FIG. 1 to FIG. 3 in a perspective illustration, only one of two spur wheels being illustrated,  
         [0021]    [0021]FIG. 5 shows a gearwheel pairing which is used in a crown-wheel differential according to FIG. 1 to FIG. 4,  
         [0022]    [0022]FIG. 6 shows a gearwheel pairing according to FIG. 5 in a sectional illustration, the section being taken through a plane which is spanned between the axis of rotation of a crown wheel and the geometric axis of a spur wheel meshing with the latter, and  
         [0023]    [0023]FIG. 7 shows a detail of a crown-wheel differential, in which a pinion shaft has a gearwheel with two disc-shaped stop structures. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    [0024]FIG. 1 shows a crown-wheel differential  1  of a rear-axle transmission in a sectional perspective illustration, the section being taken through a plane which is spanned between an axis of rotation  2  of the crown-wheel differential  1  or of crown wheels  5   a ,  5   b  and a geometric axis  7  of differential wheels  4   a ,  4   b.    
         [0025]    This crown-wheel differential  1  comprises a cylindrical casing  3 , the axis of rotation  2  of which is congruent in the usual way with a geometric axis of axle shafts of the vehicle wheels, which are not shown. The designations “axial” and “radial” used below relate to this geometric axis of rotation  2  if the designations do not refer explicitly to a particular rotationally symmetrical body.  
         [0026]    At one axial end, the casing  3  is provided with a ring gear (not shown) for driving the casing in the usual manner.  
         [0027]    The casing  3  has, axially in the center, two diametrically opposite casing recesses  13   a ,  13   b , in which the spur-toothed differential wheels  4   a ,  4   b  are radially supported with respect to their geometric axis  7 . The casing recess  13   b  can also be seen in FIG. 4. The differential wheels  4   a ,  4   b  have a spur toothing  17   a  and  17   b . The geometric axis  7  is perpendicular to the axis of rotation  2 . Arranged centrally in these differential gears  4   a ,  4   b  are openings  8   a ,  8   b , of which one opening  8   b  is indicated in FIG. 3. Each of the two differential wheels  4   a  and  4   b  has, with respect to its axis  7 , axially on the top side and underside, a disc-shaped stop structured body  9   a ,  10   a , and  9   b ,  10   b , through which the openings  8   a ,  8   b  extend. These disc-shaped stop structures  9   a ,  10   a  and  9   b ,  10   b  are in the form of annular bodies mounted radially in the casing  3  in partcircular the end areas  11   a ,  12   a ,  20   a ,  14   a , and  11   b ,  12   b ,  20   b ,  14   b  of the two casing openings  13   a ,  13   b , of which end areas only one circular end area  11   a  can be partly seen in FIG. 1. These circular end areas  11   a ,  12   a ,  20   a ,  14   a ,  11   b ,  12   b ,  20   b ,  14   b  are disposed circumferentially with respect to the axis of rotation  2 , in order to transmit a drive torque from the casing  3  to the differential wheels  4   a ,  4   b  over as large an area as possible. The casing openings  13   a ,  13   b  have, in the axial direction, edge areas  15   a ,  15   b ,  16   a ,  16   b , which are spaced apart from the differential wheels and which ensure the passage of a lubricant and consequently provide for a reliable supply of lubricant for the radial support of the differential wheels  4   a ,  4   b  and for tooth engagement. In this tooth engagement, the differential wheels  4   a ,  4   b  mesh with the crown wheels  5   a ,  5   b , which are oriented concentrically to the axis of rotation  2  and which receive the axle shafts, not illustrated in any more detail, fixedly in terms of rotation by means of a spline engagement. The crown wheels  5   a ,  5   b  are supported, in the direction in which they point away from one another axially, against displacement in relation to the casing  3  by means of an axial ring (DIN 472). Between the respective crown wheel  5   a  and  5   b  and its securing ring is arranged in each case a spacer disc for setting the axial distance between the two crown wheels  5   a ,  5   b.    
         [0028]    [0028]FIG. 2 shows the crown-wheel differential  1  of FIG. 1 in a sectional two-dimensional illustration. The one differential wheel  4   a , which lies above the sectional plane, is additionally illustrated.  
         [0029]    [0029]FIG. 3 shows the crown-wheel differential  1  in a plane section taken along the line III-III of FIG. 2. This plane section III-III is taken perpendicularly to the axis of rotation  2  and contains the axis  7  of the differential wheels  4   a ,  4   b.    
         [0030]    The disc-shaped stop structures or bodies  9   a  or  10   a  or  9   b  or  10   b  in each case bear radially, with respect to the axis  7  of the differential wheels  4   a ,  4   b , on two circular end areas  11   a ,  12   a , or  20   a ,  14   a  or  11   b ,  12   b  or  20   b ,  14   b  of the respective differential casing  3 . Between the two circular end areas  11   a ,  12   a  or  20   a ,  14   a , or  11   b ,  12   b , or  20   b ,  14   b  is an interrupted annular groove  30   a ,  30   b  which allows a flow of lubricant through the mutually corresponding spur toothings of the differential wheels  4   a ,  4   b  and prevents friction between the spur toothing  17   a  and  17   b  and the casing  3 . This also reliably ensures lubrication at the toothing between the differential wheels  4   a ,  4   b  and the crown wheels  5   a ,  5   b.    
         [0031]    Furthermore, in FIG. 3 the openings  8   a ,  8   b  of the differential wheels  4   a ,  4   b  can be seen, the openings having a varying diameter. The diameter of the two openings  8   a ,  8   b  in this case increases radially inwards.  
         [0032]    To mount the crown-wheel differential  1 , the two differential wheels  4   a ,  4   b  are inserted from outside into the casing openings  13   a ,  13   b . Subsequently, the two crown wheels  5   a ,  5   b  are inserted into the casing  3  and, followed by the installation of the spacer discs. They are secured by means of DIN 472 spring securing rings.  
         [0033]    [0033]FIG. 5 shows a gearwheel pairing which is used in a crown-wheel differential  1  according to FIG. 1 to FIG. 4. This gearwheel pairing shows one of the differential wheels  4   a  and one of the crown wheels  5   a  meshing with the differential wheel  4   a.    
         [0034]    [0034]FIG. 6 shows the gearwheel pairing according to FIG. 5 in a sectional illustration, the section being taken along a plane which is spanned between the axis of rotation  2  and the axis  7 .  
         [0035]    The top disc-shaped stop structure  9   a  of the differential gear  4   a  can be brought with its underside to bear on the outer cylindrical surface of the crown wheel  5   a . By contrast, the lower disc-shaped stop structure  10   a  of the differential gear  4   a  can be brought with its topside to bear on the inner surface of the crown-wheel toothing. In this arrangement, each tooth of the crown-wheel toothing has a rib  21  extending radially inwards. These ribs  21  have spherical concave surface areas, which roll on correspondingly spherical convex surfaces areas of the lower disc-shaped stop structure  10   a . These spherical convex surfaces are disposed in tooth interspaces of the disc-shaped stop structures  10   a . The spherical convex or spherical concave surface has a radius r to the point of intersection of the axis of rotation  2  with the axis  7 .  
         [0036]    In the normal driving mode of a vehicle, in which the crown-wheel differential  1  is installed, a centrifugal force acts on the differential wheel  4   a  as a result of rotation about the axis of rotation  2 . By virtue of this centrifugal force, the lower disc-shaped stop structure  10   a  bears on the crown wheel  5   a , whereas the top disc-shaped stop structure  9   a  has play in relation to the crown wheel  5   a.    
         [0037]    [0037]FIG. 7 shows, as a detail, a crown-wheel differential, in which a pinion shaft  260  has a gearwheel  262  with two disc-shaped stop structures  209 ,  120 . The gearwheel  262 , together with a crown wheel  205  connected fixedly to a casing  203  of the crown-wheel differential, forms a drive toothing  261 .  
         [0038]    The two disc-shaped stop structures  209 ,  210  are formed as integral parts of the gearwheel  262 .  
         [0039]    The use of the gearwheel pairing for a differential is not restricted to crown-wheel differentials for rear-axle transmissions. Thus, differentials for front-axle transmissions and longitudinal differentials may also be envisaged.  
         [0040]    To act as a stop, the stop structure does not necessarily have to be rotationally fixed with respect to the toothing of the differential wheel. Thus, to make it easier to machine the spur toothing of the differential wheel, for example, a disc may be provided, which is arranged fixedly in terms of rotation or rotatably on a basic gear body. In this case, discs may be disposed at opposite sides of the basic gear body and attached by means of a central screw connection or by riveting. Furthermore, it is possible for the discs to be adhesively bonded to the basic gear body in a rotationally-fixed manner.  
         [0041]    On the assumption of appropriate lubrication, a helical toothing may be used instead of a spur toothing. The forces as a result of the helical toothing, which endeavor to push the differential wheel inwards, or outwards, are in this case supported by the stop structures.  
         [0042]    To make mounting easier, the casing of the crown-wheel differential may have attached to it a stop or step which prevents the differential wheels from falling into the casing after being installed in the casing, but before the installation of the crown wheels.  
         [0043]    The embodiments described are merely illustrative designs. A combination of the described features for different embodiments is possible.