Abstract:
An axial bearing for a turbocharger contains a through hole for a shaft and at least one at least partially or completely circulating segment section on a first and second side of the axial bearing. At least one bearing surface is disposed in the segment section. At least one oil pocket is on the first side of the axial bearing. The oil pocket is connected to at least one recess opening outwards, the recess being configured such that it connects the oil pocket for oil supply purposes to the respective segment section and the bearing surface(s) thereof on the first and second side of the axial bearing.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an axial bearing which can be used in particular with turbochargers in, for example, vehicles. 
     In general, turbochargers are used to improve the efficiency of an internal combustion engine, and hence to raise its power. For this purpose, a shaft is mounted in the housing of the turbocharger, for example by means of two radial bearings, so that it can rotate about its longitudinal axis. Appropriately arranged on the shaft are a turbine wheel and a compressor wheel. Due to fluid flows, which impact on the turbine wheel and the compressor wheel, strong axial forces can arise. Such axial forces cannot be suitably accommodated by the radial bearings, so that accordingly at least one axial bearing is provided. 
     The shaft bearings in a turbocharger are normally subject to very high demands. Thus, the turbocharger is exposed to very high temperatures because, for example, hot exhaust gas is used to drive the turbine wheel. Furthermore, the shaft of a turbocharger reaches very high rotational speeds, for example up to 300,000 r.p.m. For this reason, the rotating parts of the turbocharger must be very precisely balanced up, to keep the incidence of vibrations as low as possible. 
     Damage to the axial and radial bearings can easily arise from rapid engine starts, for example in cold ambient conditions, as a result of the delay in the feeding of oil to the turbocharger. 
     An axial bearing is known from the prior art, as disclosed in EP 1 619 356, in which wedge-shaped surfaces are arranged around a through hole. Here, the wedge-shaped surfaces are separated from each other by several grooves, through which the wedge-shaped surfaces are supplied with lubricating oil. Here, some of the grooves are extended towards the outside, and open out into oil pockets. In addition, the bearing surfaces are surrounded by a circumferential groove, through which the lubricating oil can flow away after it has flowed through the bearing, the cross-sectional area of this groove being smaller than the cross-sectional area of the extended grooves, to ensure an adequate oil flow for the shaft. In operation, the oil pocket receives lubricating oil under pressure. The oil flows through the grooves to the rotating shaft and is distributed by it in a circumferential direction, by which means even the grooves which are arranged on the other side of the axial bearing can be supplied with lubricating oil. 
     Also known, from EP 0 599 520, is a thrust bearing for a turbocharger in which an oil reservoir is connected via a borehole to a through hole. 
     However, thrust bearings in which oil pockets located at the outside are connected via a borehole with a segment area located further inside have the disadvantage that chips and burrs form in production. The chips, in particular, can easily block up the boreholes if they are not cleanly removed. Furthermore, burrs can also lead to a narrowing of the borehole, if they project into it. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide an axial bearing, which has a simple construction and which permits suitable lubrication, by which blockage of the oil feed can be prevented. 
     Correspondingly, in accordance with the invention an axial bearing is provided, in particular for a turbocharger, with:
         a through hole for a shaft,   with at least one segment section which runs at least partially or completely around the circumference on a first side and on a second side of the axial bearing, at least one contact surface being arranged on the segment section,   at least one oil pocket on the first side of the axial bearing,   wherein the oil pocket is connected with at least one recess which is open towards the outside, which is designed in such a way that it connects the oil pocket with the segment section concerned and its contact surface or surfaces, as applicable, on the first and second sides of the axial bearing, to provide an oil feed.       

     The axial bearing thereby has the advantage that it is possible to provide in a very simple manner a suitable oil feed for the segment sections on both sides of the axial bearing. Here the lubricating oil is not, as in the prior art, fed to the other side of the axial bearing via the through hole for the shaft, for example, of a turbocharger. Furthermore, the recess, which is open in the upward direction, can be very simply manufactured, without any resulting chips or burrs which block up or narrow the recess, as is the case with state of the art bore holes. 
     Advantageous embodiments and developments of the invention emerge from the subclaims and the description which makes reference to the drawings. 
     In accordance with one embodiment of the invention, the recess is designed in the form of a slot. This slot can then be provided to such a depth in the axial bearing that it affords an oil feed to the segment sections and their contact surfaces on both sides of the axial bearing. Here, the slot has the advantage that it can be very simply manufactured, for example by means of milling. Alternatively, the slot can also be shaped into the axial bearing. 
     In another embodiment of the invention, the recess is in the form of a groove and a through cut-out. Here, the groove is designed in such a way that it connects the oil pocket to the segment section on the first side of the axial bearing. In addition, the through cut-out is arranged in such a way, for example, that it connects the groove and/or the segment section on the first side of the axial bearing with the segment section on the second side and thus establishes an oil feed to the second segment section. 
     In a further embodiment of the invention, the groove is, for example, manufactured by milling or is shaped into the axial bearing. The through cut-out can also be formed into the axial bearing or manufactured by boring or milling. In this way, the cut-out in accordance with the invention can be very easily manufactured. Furthermore, the boring or milling step can here be simply incorporated into a production process. 
     According to a further embodiment of the invention, the slot or groove, as applicable, can be designed in addition with at least one transitional chamfer. 
     In a further embodiment of the invention the through hole, through which the shaft passes, is provided with an inner shoulder on the first and/or the second side. This inner shoulder is to prevent oil from simply flowing completely unhindered out of the segment section or segment space, as applicable, into the through hole. The quantity of oil in the through hole can be reduced by this inner shoulder without a detrimental effect on the oil supply to the load-bearing segments or contact surfaces, as applicable. 
     The inventive axial bearing is suitable, for example, as a bearing for a shaft in a turbocharger used in motor vehicles or other vehicles. Basically, however, the use of the inventive axial bearing is not restricted to the application situations cited above, but it can be used in numerous different areas in which axial bearings are required. 
     The invention is explained in more detail below, by reference to the exemplary embodiments shown in the schematic figures in the drawings. These show: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIGS. 1   a, b  a perspective sectional view of an axial bearing in a first embodiment of the invention; and 
         FIG. 2  a perspective sectional view of an axial bearing in accordance with a second embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     In all the figures, elements and devices which are the same or functionally the same, as applicable, are given the same reference marks, unless otherwise specified. 
       FIGS. 1   a  and  1   b  show a perspective sectional view of an axial bearing  10  in accordance with a first embodiment of the invention. Here, the axial bearing  10  has for example a form which is essentially disk-shaped. 
     Here, the axial bearing  10  is provided with a through hole  12  through which, for example, the shaft of a turbocharger (not shown) can be passed. In addition, at least on a first side  14  the axial bearing  10  has a segment section  18  or segment space, as applicable, in the form of a depression which preferably runs around its circumference. Arranged in the segment section  18  are contact surfaces  20  or segments, as applicable. The contact surfaces  20  or segments, as applicable, are here wedge-shaped in design for example and are arranged radially around the through hole  12 . The contact surfaces  20  can however also have any other shape which is suitable as a contact surface. 
     The axial bearing  10  has, in addition, at least one oil pocket  22  on the first side  14  of the bearing, the oil pocket  22  being arranged above the segment section  18 . The oil pocket  22  is here connected via a recess  24  to the through hole  12 . The recess  24  here is embodied, for example, as a slot  28  which is, for example, milled into the surface of the axial bearing  10  by means of a milling cutter. The recess  24  or slot  28 , as applicable, is here designed such that it connects at least the oil pocket  22  to the segment section  18  on the same side of the axial bearing  10 . 
     In the same way as on the first side  14 , a segment section  18  or segment space, as applicable, can also be arranged on the second side  16  of the axial bearing, together with contact surfaces  20  or segments, as applicable. Like the contact surfaces  20  on the first side  14 , the contact surfaces  20  can here be wedge-shaped in design, for example, or can have some other suitable shape. Here, the second side  16  can be designed without an oil pocket  22 . 
     The recess  24  or slot  28 , as applicable, provided in the axial bearing  10  can here be of such a depth that it connects the oil pocket  22  with the segment sections  18  on both sides  14 ,  16  of the axial bearing  20 , as shown in  FIGS. 1   a  and  1   b . It is very simply possible in this way to realize an oil feed for both segment sections of the axial bearing. 
     Lubricating oil is directed via the oil pocket  22  through the recess  24  or the slot  28 , as applicable, towards the through hole  12 , or to be more accurate, to the segment sections  18  and the contact surfaces  20  on the two sides  14 ,  16  of the axial bearing  10 . 
     In a further embodiment of the invention, there is the optional possibility of providing the through hole  12  in the axial bearing  10  with an inner shoulder  26  which stands proud of at least the segment section  18  on the first and/or the second side  14 ,  16  of the axial bearing  10  and delimits the relevant segment section  18  or segment space, as applicable. 
     Arranging the inner shoulder  26  directly on the through hole  12  in the axial bearing  10  essentially prevents lubricating oil from passing unhindered out of the segment space or segment section  18 , as applicable, into the space in the through hole  12  for the shaft. The inner shoulder  26  reduces the quantity of oil in the through hole  12 , without having any effect on the oil supply to the load-bearing segments or contact surfaces  20 , as applicable. This makes it possible to forgo expensive oil feed arrangements for keeping the oil quantity low, such as are known from the prior art, where such arrangements have in turn a direct effect on the load-bearing capacity of an axial bearing. 
     It is already known from the prior art that the oil which is churned around in the region of the axial bearing by the shaft of the turbocharger leads to an increased power loss in this region. A reduction in the quantity of oil leads to a reduction in the losses, and hence ultimately to an improvement in the overall efficiency of a turbocharger. 
     A recess  24  in the form of a slot  28  which is open in the upward direction has the advantage that the slot  28  can easily be integrated as a constructional element in an existing processing step. In addition, with such a slot  28  it is possible to avoid such problems as exist with holes known from the prior art which are fully enclosed. Thus, in the manufacture of an open slot  28  no chips or burrs are produced by which the oil feed can be narrowed or even blocked up, as is the case with enclosed holes. In particular if the holes are relatively long, they can only be poorly cleaned, and are easily blocked. 
     Furthermore, the slot  28  can very easily be manufactured by a milling process. Chips which arise when doing so can be removed without problem, because the slot  28  is open towards the outside and, unlike a bored hole, is not completely surrounded. Alternatively, it is also conceivable that instead of manufacturing the slot  28  by milling, the axial bearing  10  is made by shaping it with an appropriate slot  28 . 
     Optionally, the slot  28  can be manufactured with a transitional chamfer (not shown) on one or both sides  14 ,  16  of the axial bearing  10 . Here, the oil feed is realized by the slot  28 , which starts at the central through hole  12  and ends in the oil pocket  22 . 
     In a second, alternative embodiment of the invention, such as is shown in  FIG. 2 , the axial bearing  10  has a recess  24  which, instead of being a slot  28  is a groove  30  on the first side  14  of the axial bearing  10 , together with a through cut-out  32 . Here, the groove  30  extends from the oil pocket  22  to the segment section  18  on the first side  14 , in order to supply this and the contact surfaces  20  there with lubricating oil. 
     In the segment section  18 , at least one through cut-out  32  is provided in addition, in order to supply the segment sections  18  on the second side of the axial bearing  10  with lubricating oil. In doing this it is in principle possible again to provide the groove  30  of the recess  24  with a transitional chamfer (not shown) on one or both sides  14 ,  16  of the axial bearing  10 . 
     As in the first embodiment, an optional possibility is to provide in addition an inner shoulder  26  on at least one or both sides  14 ,  16  of the through hole  12 . It is thereby possible to ensure an oil supply for the oil feed to the oil pocket  22  on the second side  16 , via the through cut-out  32 . As in the embodiment shown in  FIGS. 1   a  and  1   b , the lubricating oil passes from the oil pocket  22  through the through cut-out  30  to the other side  16  of the axial bearing  10  and in this way is fed to the segment section  18  or segment space there, and to the contact surfaces  20  or segments, as applicable. 
     The groove  30 , which like the slot  28  is also open towards the outside, has the advantage that it too enables the formation of chips and burrs to be avoided, as is the case for holes conforming to the state of the art. Apart from this, the manufacture of the short groove  30  can also be very simply integrated into an existing processing step, such a groove  30  being overall very much easier to realize than a bored hole, so that manufacturing costs can be reduced. 
     The through cut-out  32  in the recess  24  has in addition the advantage that it is very simply possible to achieve an oil feed from the oil pocket  22  to the opposite-side segment section  18 , on the second side  16  of axial bearing. 
     The through cut-out  32  can here be manufactured by boring or milling. The chips which result from doing so can be very easily removed because the hole is relatively short, as shown in  FIG. 2 . Alternatively, the axial bearing  10  with its through cut-out  32  can also be produced by shaping, wherein the through cut-out  32  need not necessarily be round, but can have any arbitrary shape. 
     Furthermore, in accordance with the invention it is possible to provide one, two or more such through cut-outs  32  or slots  28  in the axial bearing  10 . 
     Although the present invention has been described above by reference to the preferred exemplary embodiments, it is not restricted to them, but can be modified in diverse ways. In doing so, the embodiments described above, in particular individual features of them, can be combined with each other. 
     So, for example, the slot  28  can also be combined with a through cut-out  32  in a recess  24 . Here, the slot  28  does not need to be formed too deeply, but it is sufficient in this case if the slot  28  connects together the oil pocket  22  and the segment section  18  or its contact surfaces  20  on the first side  14  of the axial bearing  10 , as appropriate. On the other hand, the through cut-out  32  establishes the connection to the segment section  18  on the second side  16  of the axial bearing  10 . In principle, the through cut-out  32  can in this case be provided in the segment section  18 , as shown in  FIGS. 1   a ,  1   b  and  2 . However, it can also be provided in the region of the slot  28  or the groove  30  or in a transition area between the slot  28  or the groove  30 , as applicable, and the relevant segment area  18 . In addition, the inner shoulder  26  on one or both sides of the axial bearing  10  is an optional feature.