Abstract:
A differential transmission for a motor vehicle comprising a driving gear wherein the driver gear introduces torque to the transmission; a first output element and a second output element wherein the first and second output elements output torque from the transmission; a differential cage designed for transmitting torque from the driving gear to the first output element, wherein the differential cage is non-rotatably connected to the driving gear, and the first output element is rotationally arranged to the differential cage; a sliding sleeve wherein the sliding sleeve is arranged between the differential cage and the first output element, wherein the sliding sleeve has a lubricating recess which extends in a spiral shape in the circumferential direction and is operatively arranged to provide a lubricating film.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is the U.S. national stage application pursuant to 35 U.S.C. §371 of International Application No. PCT/DE2014/200552, filed Oct. 14, 2014, which application claims priority from German Patent Application No. DE 10 2013 222 731.0, filed Nov. 8, 2013, which applications are incorporated herein by reference in their entireties. 
     
    
     FIELD 
       [0002]    The disclosure relates to a differential transmission for a motor vehicle, the differential transmission comprising a driving gear, by means of which the torque can be introduced into the transmission, and comprising a first output element and a second output element, by means of which the torque can be outputted from the transmission, comprising a differential cage, which is designed for transmitting the torque from the driving gear to the first output element, wherein the differential cage is non-rotatably connected to the driving gear; and the first output element is arranged in such a way that the first output element can be rotated in relation to the differential cage; wherein a sliding sleeve is arranged between the differential cage and the first output element. 
       BACKGROUND 
       [0003]    German patent DE102011085119B3, discloses differential transmissions. Thus, this document discloses a spur gear differential, comprising a planetary gear carrier and two sun gears, which can be rotated in relation to the planetary gear carrier, at least one friction disk and at least one spring means, which biases the sun gears relative to the planetary gear carrier. In this case the spring means is spring-mounted, on the one hand, against a sun gear or the planetary gear carrier and, on the other hand, against an axial bearing. The geometrical and functional features, Which are disclosed in the German patent, shall be considered to be incorporated herein. 
         [0004]    An earlier application, which was filed by the applicant and which is not a prior publication, discloses a differential transmission in the form of a planetary gear transmission with at least one sun gear (wheel) and at least one planet carrier, which is arranged coaxially and rotatably to the sun gear (wheel). In this case a bearing sleeve is inserted between the at least one sun gear (wheel) and the planet carrier in such a way that the bearing sleeve has a supporting effect on the sun gear (wheel) axially and/or radially relative to the planet carrier. 
         [0005]    The object of the disclosure is to provide a differential transmission that exhibits optimized lubrication and guide, low bearing play, optimized running characteristics, optimized utilization of the installation space and/or easy assembly. Furthermore, the wear resistance and the service life shall be improved, and the production costs and running noises, occurring in service, shall be reduced. 
       SUMMARY 
       [0006]    The object, on which the disclosure is based, is achieved by means of a device, conforming to its genre, in that the sliding sleeve or sliding bearing sleeve has a lubricating recess, groove or lubricating pocket, which extends in a spiral shape in the circumferential direction and is operatively arranged to provide a lubricating film. In this case the lubricating film is provided between two components, which can be rotated relative to each other and are supported on each other, for example, in the radial direction. 
         [0007]    Advantageous embodiments of the disclosure are claimed in the dependent claims and will be explained in greater detail below. 
         [0008]    The term “in a spiral shape” is defined, according to the disclosure, to include, in particular, spiral shapes with constant pitch as well as such geometrical configurations of varying slope. A single spiral or a plurality of spirals may be provided. The lubricating recess may extend in a meander shape, in particular, in the circumferential direction. In other words, the lubricating recess may be designed in the form of a spiral with alternating direction of curvature. 
         [0009]    The driving gear may be designed as a driving gearwheel. The first output element and/or the second output element can be designed as the output gearwheels. 
         [0010]    The sliding sleeve is manufactured preferably without machining. It may be, in particular, a sheet metal component, which is produced by means of cold forming, for example, deep drawing and/or stamping. Then the sliding sleeve is very inexpensive and lightweight. As an alternative, the sliding sleeve can be produced by molding methods and optionally can be mechanically finish machined. 
         [0011]    According to one embodiment of the disclosure, the sliding sleeve is inserted, preferably pressed, into the differential cage in a force fining manner. As an alternative, the sliding sleeve may be put, in particular, pressed onto the output element in a force fitting manner. The sliding sleeve is mounted in the differential cage or more specifically on the output element in such a way that its position is stable, an arrangement that has the effect of reducing play and backlash. Furthermore, in the case of a continuous lubricating recess in the radial direction, it is possible to seal the lubricating recess in the radial direction in a very simple and effective way. 
         [0012]    In one embodiment the sliding sleeve forms a bearing element, preferably a single bearing element, with which the differential cage and an output element are mounted and positioned relative to each other in the axial and/or radial direction. The sliding sleeve can be made in such a way that it is hardened, in particular, in sections, in particular, in the area of the running or supporting surfaces. 
         [0013]    The lubricating recess can extend from a starting area to an end area, which is offset in the axial direction without interruption or may be interrupted by at least one reinforcing web. In this way it is possible to achieve, on the one hand, a particularly uninterrupted lubricating film design, even with a heavy radial load, and, on the other hand, a particularly stable embodiment, i.e. an exemplary embodiment that absorbs high radial forces. 
         [0014]    According to one embodiment of the disclosure, the lubricating recess is formed as a continuous groove. As an alternative, there may be a plurality or number of reinforcing webs that divide the lubricating recess into individual lubricating pockets, preferably into discrete, separate lubricating pockets. The provision of such lubricating pockets makes it possible to optimize the lubrication of the sliding bearing and also its operating characteristics, in particular, the load carrying capacity of the sliding sleeve. The lubricating pockets may be distributed, in particular, may be evenly distributed over the running surface of the sliding sleeve in the axial direction and/or in the circumferential direction, so that even in the vicinity of a lubricating pocket there is always a sufficient support surface area for a bearing arrangement in both the circumferential direction and the axial direction. 
         [0015]    Even though the objective of achieving a component that has a particularly high load bearing capacity has been met, the manufacturing costs can be kept very low, if the sliding sleeve is manufactured without machining, in particular, if the sliding sleeve is a sheet metal component. In this case deep drawing processes or even molding processes are useful. 
         [0016]    It is preferred that the lubricating recess be formed as a through-hole from a radially inner surface as far as up to a radially outer surface. Such a design is particularly easy to manufacture by punching the lubricating recess and offers a lubricating recess with an especially large volume, based on the strength (thickness) of the sliding sleeve, so that sufficient lubricant can be accommodated in the recess. 
         [0017]    The lubricating recess may be introduced, preferably punched, as a through-hole from the inside to the outside. In particular, the lubricating recess may be introduced, for example, by punching, as a through-hole from a running surface of the sliding sleeve in the direction of a surface that is opposite the running surface. Such a design achieves the advantage that the lubricating recess can be easily formed on the side of the running surface and is easy to make without burr, so that there is no need for special additional manufacturing steps for deburring. The lubricating recess is introduced into the sliding sleeve preferably without machining. 
         [0018]    In another advantageous embodiment a lubricating pocket extends more or less in the circumferential direction of the sliding sleeve. In particular, the lubricating pocket can be elongated in the circumferential direction; in particular, it may be elongated in an oval fashion. The lubricating pocket has preferably a length that allows a load bearing lubricating film in the radial direction. 
         [0019]    In the case of a plurality or number of lubricating pockets, these lubricating pockets may he offset from one another in the axial direction of the sliding sleeve. The lubricating pockets may overlap or cover each other, in particular, in the circumferential direction of the sliding sleeve or in the axial direction of the sliding sleeve. 
         [0020]    Preferably the width of a lubricating pocket, measured in the axial direction, is equal to approximately ⅕ to approximately ⅓ of length of the lubricating pocket, measured in the circumferential direction. It is especially preferred that the width of a lubricating pocket be equal to approximately ¼ of the length thereof. This feature makes it possible to build up a load bearing lubricating film in an advantageous manner, while at the same time the supporting surface of the sliding sleeve is reduced as little as possible in the axial direction. 
         [0021]    The differential transmission may be designed, in particular, as a planetary gear differential transmission, a bevel gear differential transmission or a spur gear differential transmission. In the case of a planetary differential transmission, the differential cage forms a planet carrier. This planet carrier may be constructed in two parts. The first drive element forms a first sun gear, in particular, a first sun gearwheel; and the second drive element forms a second sun gear, in particular, a second sun gearwheel. Then the sliding sleeve is arranged between the planet carrier and a sun gear. The sliding sleeve can position and mount the planet carrier and the sun gear relative to each other in the radial and/or axial direction. 
         [0022]    It can also be said that the disclosure relates to the mounting of a sun gearwheel of a lightweight differential. Owing to the openings, which are located on the periphery of the sliding sleeve in the shape of a spiral and which form the lubricating pockets, the contact between the sun gearwheel and the sliding bearing sleeve can be optimized. The sliding or bearing sleeve can be used to support the sun gear or the sun gears in both the radial and also the axial direction. The bearing point is usually subject to forces acting on the bearing point by way of an axle, supporting a compensating joint. The bearing sleeve, which is provided with openings on the periphery in the shape of a spiral, makes sure that there is sufficient lubrication at the bearing point. In particular, the openings may be continuous from the inside to the outside. The oil pockets are formed by pressing the sliding bearing sleeve into the support flange; and a limited, but sufficient oil reservoir is stored in these oil pockets. The disclosure can be used, in particular, in lightweight differentials for final drives in passenger vehicles. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Various embodiments are disclosed, by way of example only, with reference to the accompanying drawing in which corresponding reference symbols indicate corresponding parts, in which: 
           [0024]      FIG. 1  shows a longitudinal view of a differential transmission according to the invention; 
           [0025]      FIG. 2  shows an enlarged view of the connecting region between the differential cage and an output element of the differential transmission according to  FIG. 1 ; 
           [0026]      FIG. 3  is a perspective view of a variant of an inventive differential transmission with the sliding sleeve installed; 
           [0027]      FIG. 4  is a perspective view of a sliding sleeve; and, 
           [0028]      FIG. 5  is a sectional view of the sliding sleeve from  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
         [0030]    Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the claims. 
         [0031]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing the example embodiments. 
         [0032]      FIG. 1  shows an inventive differential transmission  1  according to the disclosure. The differential transmission  1  is designed as a planetary gear transmission, in particular, as a spur gear differential. The differential transmission has a driving gear  2 , a first output element in the form of a first sun gear  3 , a second output element in the form of a second sun gear  4 , a differential cage in the form of a planet carrier  5  and a sliding sleeve  6  as a sliding bearing sleeve. 
         [0033]    The differential transmission  1  has several pairs  12  of planet gears  13  and  14 . In contrast to the second planet gear  14 , the first planet gear  13  has a longer axial length. The axial length is measured along the axis of rotation of the differential transmission  1 . The varying axial length of the two planet gears  13  and  14  can be seen in  FIGS. 1 and 3 . 
         [0034]      FIG. 1  shows only the first planet gear  13  of the planet gears  13  and  14  of the differential transmission  1  in its entirety; of the planet gear  14 , only a part of the teeth can be seen, because the teeth are covered for the most part by the planet gear  13 . The sun gear  3  meshes with the first planet gear  13 ; and the other sun gear  4  meshes with the second planet gear  14 . The two planet gears  13  and  14  of a pair  12  of planet gears also mesh with each other. 
         [0035]    The planet gear  13  is mounted on a bolt  15 . The bolt  15  is disposed in sleeves  16 , which are hardened, in particular, fully hardened, in the planet carrier  5 . The sleeves  16  have radially projecting flanges  27 , which rest against the planet gear  13  and determine the axial position thereof. The planet gear  14  may be mounted accordingly. 
         [0036]    The two sun gears  3  and  4  have internal teeth  29 , by means of which the torque can be transmitted on transmitting elements, which are not shown in the figures, to the wheels of a motor vehicle. A friction disk  28  is disposed between the two sun gears  3  and  4 . The friction disk may also be referred to as the friction ring. 
         [0037]    It should be noted that the tip circle diameters of the two sun gears  3  and  4  are different. In this case the tip circle diameter of the small sun gear  4  is smaller than the root circle diameter of the large sun gear  3 . The small sun gear  4  is approximately 20% smaller than the large sun gear  3 . In traction mode the smaller planet gear of the pair  12  of planet gears  13 ,  14  runs ahead of the large planet gear. The inventive solution reduces the noise emission. Any problems arising with respect to the support width are also minimized. Even limited slip values of up to 30% can be achieved without any major problems. In this way it is possible to generate a so-called Torsen differential. 
         [0038]    In the exemplary embodiment that is shown, the planet carrier  5  is a sheet metal component. The planet carrier has a first planet carrier subelement  24  and a second planet carrier subelement  25 . The bolt  15  for mounting the planet gears  13 ,  14  is received in the manner described above, on the one side, in the first planet carrier subelement  24  and on the opposite side in the second planet carrier subelement  25 . The first planet carrier subelement  24  is connected to the second planet carrier subelement  25  by means of screw connections  26 , which are distributed over the periphery and of which only one is shown in  FIG. 1 .  FIG. 3  shows two screw connections  26  in their entirety and a third screw connection  26  in part. The planet carrier  5 , which is designed as a sheet metal component in the exemplary embodiments that are shown herein, may also be made as a cast or forged part. 
         [0039]    As shown, in particular, in  FIGS. 1 and 2 , the sliding sleeve  6  is disposed as a bearing sleeve between the sun gear  3  and the planet carrier  5  (the differential cage).  FIG. 1  shows, in particular, that a sliding sleeve  6  may also be disposed between the sun gear  4  and the planet carrier  5 , so that this mounting arrangement is designed in conformity with the mounting arrangement between the sun gear  3  and the planet carrier  5 . The sliding sleeve  6  is described below with reference to the sliding sleeve  6 , which is shown on the left in  FIG. 1 , for the sun gear  3 , but also relates accordingly to the right sliding sleeve  6  for the sun gear  4 . 
         [0040]    The sliding sleeve  6  is designed in such a way that it has a supporting effect on the sun gear  13  in the axial and radial direction and keeps the sun gear spaced apart from the planet carrier  5  in the axial and radial direction. In addition, the sliding sleeve has a bulge  17  or a plurality of bulges  17 , which is or are located between a radially outwards projecting support area  18  and an axially aligned contact area  19 . 
         [0041]    The sliding sleeve  6  is press connected to the planet carrier  5  in the contact area  19 . In this case the surface of the contact area  19  that faces the sun gear  3  forms a running surface  20 , on which the sun gear  3  is slidably mounted and relative to which the sun gear rotates. As an alternative, the sliding sleeve  6  may be pressed onto the sun gear  3 , in which case its outer surface  21  forms the running surface, in such a way that the running surface can slide relative to the planet carrier  5 . 
         [0042]    The bulge  17  may exhibit a first hardening area  22 , which extends in the axial direction. In particular, the entire running surface  20  may be hardened. The bulge can have a second hardening area  23 , which is arranged at right angles thereto and which extends in the radial direction. Additional hardening areas may also be provided. In order to form a hardening area  22 ,  23 , an induction hardening process may be useful. Case hardening is also possible. 
         [0043]    It is apparent from the figures that the running surface  20  and/or a part of the bulge  17  form and/or forms a radial bearing section for the sun gear  3 , whereas the bulge  17  forms an axial bearing area for this purpose. The sliding sleeve  6  may have spring characteristics at least in sections, in order to compensate for tolerances and to dampen any shocks that might occur. 
         [0044]    In the installed state there is play between the first hardening area  22  of the bulge  17  and a flange region of the sun gear  3  that extends in the axial direction. Similarly play is present between the second hardening area  23  or more specifically the running surface  20  and a section of the sun gear  3  that extends in the radial direction. In this area a load bearing lubricating film builds up. The bulge  17  may also follow the outer contour of the sun gear  3  in an area that is bent by 90 deg. and may maintain a distance that is as small as possible. 
         [0045]    The smallest diameter of the sliding sleeve  6  ranges between 43 mm and 45 mm and is preferably 44 mm. The outside diameter in the region of the axially aligned contact area  19  is preferably approximately 10% more, in particular, preferably 47.9 mm. The entire outside diameter at the largest point has a value of preferably 68 mm. It is advantageous for the outside diameter at the largest point to be one-third larger than the inside diameter at the smallest point of the sliding sleeve  6 . Furthermore, it is advantageous for the axial length to be more than one quarter of the inside diameter, but less than half of the inside diameter, preferably 16 mm. 
         [0046]    The sliding sleeve  6  has a wall of constant thickness. It is very clear from  FIGS. 4 and 5  that the sliding sleeve is provided with the lubricating recess  7 . This lubricating recess is interrupted by several reinforcing webs  10 , so that a plurality of separate lubricating pockets  11  are formed, where in this case consecutive lubricating pockets  10  are separated from each other by a reinforcing web  10 . 
         [0047]    The lubricating recess  7  and the consecutive lubricating pockets  10  with the in-between reinforcing webs  11  are arranged in a spiral shape in the circumferential direction of the contact area  19  of the sliding sleeve  6 . It is especially clear from  FIG. 5  that the lubricating pockets  10  can overlap each other in the axial direction. At the same time not only the consecutive, but also the non-consecutive lubricating pockets  10  can overlap each other in the circumferential direction. In the latter case the lubricating recess  7  is shaped in a meandering manner; or there are several lubricating recesses  7 , for example, as a double or triple spiral, that is, with a plurality of turns. In particular,  FIG. 4  shows that somewhere in the circumferential direction at least one lubricating pocket  10  is disposed preferably in each axial region of the running surface  20 , so that this completely covering lubricating film can form on the running surface  20 . 
         [0048]    The lubricating pockets  10  are elongated in the circumferential direction and are more or less oval. The width of the lubricating pocket  10  is equal preferably to approximately ⅕ to ⅓ of the length of the lubricating pocket. It is especially preferred that its width be equal to approximately ¼ of its length. In the exemplary embodiment that is shown herein, the length of the lubricating pocket  10  in the circumferential direction ranges between approximately 5 mm and approximately 10 mm, preferably between approximately 7 mm and approximately 9 mm, in particular, is preferably approximately 8 mm. In the exemplary embodiment that is shown herein, the width of the lubricating pocket  10  in the axial direction ranges between approximately 3 mm and approximately 7 mm, preferably between approximately 4 mm and approximately 8 mm, in particular, is preferably approximately 5 mm. 
         [0049]      FIG. 3  shows the planetary differential  1  without the planet carrier subelement  25  in a perspective view. Shown is the sliding sleeve  6  for the first sun gear  3 . It can be seen that due to the press fit of the sliding sleeve  6  together with the lubricating recess  7  or more specifically the lubricating pockets  10  the surface of the sun gear  3  that is located below the sliding sleeve  6  forms a volume, which is only open in the direction of the running surface  20 , for purposes of receiving a lubricating medium.  FIG. 3  also shows the end regions of the bolts  15  with the sleeves  16  arranged thereon. In addition, it is shown that the driving gear  2  may have helical teeth. 
         [0050]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  differential transmission 
           2  driving gear 
           3  output element, sun gear 
           4  output element, sun gear 
           5  differential cage, planet carrier 
           6  sliding sleeve 
           7  lubricating recess 
           8  starting area 
           9  end area 
           10  reinforcing web 
           11  lubricating pocket 
           12  pair 
           13  first planet gear 
           14  second planet gear 
           15  bolt 
           16  sleeve 
           17  bulge 
           18  support area 
           19  contact area 
           20  running surface 
           21  outer surface 
           22  hardening area 
           23  hardening area 
           24  first planet carrier subelement 
           25  second planet carrier subelement 
           26  screw connection 
           27  flange 
           28  friction disk 
           29  internal teeth