Abstract:
A bearing unit for a turbocharger, including a bearing housing extending in an axial direction and also including a bearing cartridge arranged within the bearing housing, wherein between the outer circumference of the bearing cartridge and the bearing housing there is formed an intermediate space with an oil film, and wherein the bearing housing has a supply bore formed for the supply of oil to the oil film. The bearing cartridge includes a rolling bearing, the outer cartridge ring of which is mounted in a freely rotatable manner in the oil film. A bearing unit for a turbocharger, the bearing cartridge of which includes a rolling bearing, the bearing outer ring of which is mounted in a freely rotatable manner in the oil film. By means of bearing units of such design, it is possible to ensure the secure mounting of a shaft even without a separate twist prevention device.

Description:
[0001]    The invention relates to a bearing unit for a turbocharger, comprising a bearing housing, extending in an axial direction, and a bearing cartridge which is arranged inside the bearing housing, wherein an interspace with a vibration-damping oil film is formed between the outer circumference of the bearing cartridge and the bearing housing, and wherein the bearing housing has a supply hole which is designed for the oil supply of the oil film. 
         [0002]    Furthermore, the invention relates to a bearing unit for a turbocharger, comprising a bearing housing, extending in an axial direction, and a bearing cartridge, having an outer bearing ring and a carrier ring, which is arranged inside the bearing housing, wherein an interspace with a vibration-damping oil film is formed between the outer circumference of the outer bearing ring and the carrier ring, and wherein the bearing housing has a supply hole which is designed for the oil supply of the oil film. 
       BACKGROUND 
       [0003]    A turbocharger customarily serves for the power augmentation of internal combustion engines by utilizing exhaust gas energy. For this purpose, the turbocharger consists of a compressor and a turbine which are interconnected via a shaft which is supported inside a bearing housing. During operation, the turbine is set in rotation by means of an exhaust gas flow and, via the shaft, drives the compressor which inducts and compresses air. The compressed air is directed into the engine, wherein as a result of the increased pressure during the induction cycle a large amount of air makes its way into the cylinder. As a result of this, the oxygen content which is required for the combustion of fuel correspondingly increases so that with each intake cycle more oxygen makes its way into the combustion chamber of the engine. 
         [0004]    This leads to an increase of the maximum torque, as a result of which the power output, that is to say the maximum power at constant working volume, is increased. This increase especially allows the use of a more powerful engine with approximately the same dimensions or alternatively enables a reduction of the engine dimensions, that is to say enables a comparable power to be achieved with a smaller and lighter engine. 
         [0005]    During the operation of a turbocharger, the shaft rotates with increasing engine rotational speed at high rotational velocity. As a result of the high rotational velocity, vibrations which for example are caused by the rotation of the shaft are transmitted to the bearing and its individual components. In order to minimize as far as possible an unwanted contact of the bearing cartridge with the bearing housing during this and to ensure a trouble-free operation of a turbocharger, use is customarily made of bearing units which by means of a so-called trapped oil film can damp the occurring vibrations. 
         [0006]    A bearing device for a turbocharger is known from DE 35 31 313 A1. The bearing device comprises a bearing cartridge with a bearing which is designed as a ball bearing. The bearing is accommodated in a bush which in turn is positioned in a bearing housing. Recesses are introduced in the outer circumferential surface of the bush and also in the inner circumferential surface of the bearing housing and together form a hole. For the positioning of the bush inside the bearing housing, provision is made for a locking element, designed as a pin, which is inserted loosely into the recesses or into the hole. 
         [0007]    As a result of the aforesaid design, a rotation of the outer bearing ring of the inserted bearing can certainly be prevented even at high rotational speeds of the shaft, but the use of a multiplicity of necessary separate bearing components and the cost intensive assembly effort which is associated therewith do not constitute a permanent solution for a bearing arrangement or for a turbocharger. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the invention to provide a bearing unit for a turbocharger which is improved compared with the prior art and which with an inexpensive and simple production enables a secure positioning of the bearing and therefore a secure support of a shaft in a turbocharger. 
         [0009]    The present invention provides a bearing unit for a turbocharger, comprising a bearing housing, extending in an axial direction, and a bearing cartridge which is arranged inside the bearing housing, wherein an interspace with an oil film is formed between the outer circumference of the bearing cartridge and the bearing housing, and wherein the bearing housing has a supply hole which is designed for the oil supply of the oil film. In this case, it is provided that the bearing cartridge comprises an anti-friction bearing, the outer cartridge ring of which is supported in the oil film in a freely rotatable manner. 
         [0010]    The invention takes into consideration the fact that the use of anti-rotation devices, for example in the form of separate locking elements, do not permanently satisfy the economical demands for the further development of turbo-bearings or their bearing units on account of the additional costs and the increased assembly effort. In addition, the frictional moment, which is caused as a result of the friction during the rotation of a shaft during the operation of a turbocharger, is transmitted to the outer cartridge ring which is supported on the bearing housing via the locking elements or the anti-rotation device. The anti-rotation device therefore transmits the so-called structure-borne noise, which has a negative effect upon the components of the bearing arrangement. Overall, the self-centering of the bearing cartridge inside the bearing housing is impaired as a result of this, which in turn results in an unwanted contact between the individual components of the bearing unit. 
         [0011]    The invention correspondingly recognizes that dispensing with an anti-rotation device or locking elements can basically provide an opportunity for preventing the transmission of torque or structure-borne noise to the bearing housing. In this case, it is basically to be taken into consideration, however, that an unsecured bearing cartridge or an unsecured outer cartridge ring acts like a plain bearing in which high frictional moment occurs between the individual components. The frictional moment is correspondingly transmitted from the shaft onto the outer cartridge ring and from this onto the bearing housing so that in this case also the required self-centering of the bearing cartridge inside the bearing housing cannot be ensured. 
         [0012]    Taking into consideration the aforesaid, the invention finally recognizes that this problem can then be eliminated in a surprisingly simple manner if the bearing cartridge comprises an anti-friction bearing, the outer cartridge ring of which is supported in the oil film in a freely rotatable manner. 
         [0013]    In other words, the outer cartridge ring is supported on the housing via the oil film so that the use of an anti-rotation device can be dispensed with. 
         [0014]    As a result of the combination of an anti-friction bearing with an outer cartridge ring which is supported in the oil film, a lock-free support of the bearing cartridge or of the outer cartridge ring becomes possible. The oil film serves for the support of the outer bearing ring and absorbs the rotational moment which is transmitted from the shaft onto the outer cartridge ring. The vibrations of the outer cartridge ring are therefore damped by means of the oil film so that there is no fear of any contact with the bearing housing. A correspondingly contact-related wear of the individual bearing components can be excluded at this point. 
         [0015]    The lock-free or anti-rotation device-free support of the outer cartridge ring in the oil film is therefore enabled as a result of the combination of an anti-friction bearing with the vibration-damping oil film. The rotational moment which is transmitted in an anti-friction bearing is absorbed by the oil film and transmission of the rotational moment onto the bearing housing can be overcome. Thus, the self-centering can also be maintained and contact between the individual bearing components can be prevented. 
         [0016]    Overall, the outer cartridge ring, as a result of the freely rotatable support in the oil film, that is to say as a result of the support on the bearing housing via the vibration-damping oil film, also by dispensing with a separate anti-rotation device, is positioned in such a way that a reliable functioning of the turbocharger is ensured. 
         [0017]    The oil film, in which the outer bearing ring is rotatably supported, depending upon the design of the bearing arrangement, has a corresponding thickness, or the interspace with the oil film has the necessary width. The size of the respective components as well as the dimensions of the interspace for the oil film, for example, are to be taken into consideration in this case. Furthermore, the density and the viscosity of the oil are also to be taken into consideration. 
         [0018]    The anti-friction bearing serves in the present case especially for the secure support of the shaft, wherein it absorbs the radial and axial forces and at the same time enables the rotation of the shaft. An anti-friction bearing generally consists of two bearing rings with integrated running tracks. Rolling bodies, which roll on the running tracks, are arranged between the bearing rings. As rolling bodies, common bearing types, for example balls, cylindrical rollers, needle rollers or tapered rollers, can be used, depending upon requirement. In this case, either a design with a cage which guides the rolling bodies, or, for example, even a fully spherical variant without a cage, is possible. 
         [0019]    With regard to the loads of the bearing unit during operation of a turbocharger, the bearing rings are produced especially from temperature-resistant and corrosion-resistant materials. Both the inner bearing ring and the outer bearing ring can be produced in one part or in a multiple of parts. 
         [0020]    The anti-friction bearing in the present case is part of the bearing cartridge. The bearing cartridge, for example in addition to or alternatively to the anti-friction bearing, may comprise a carrier ring in which the anti-friction bearing is arranged with the outer cartridge ring. As a result of this, it becomes possible to design the bearing cartridge with flexibility according to the respective requirement and to preassemble it according to the client&#39;s wishes, for example. 
         [0021]    The outer cartridge ring can be designed in this case as an outer bearing ring or as a carrier ring, for example. 
         [0022]    Alternatively, the bearing cartridge can comprise both an outer bearing ring and an outer cartridge ring which is designed as a carrier ring. In this case, there is basically the possibility that in addition to the oil film which is formed between the outer circumference of the carrier ring and the inner circumference of the bearing housing, an oil film is additionally formed between the outer circumference of the outer bearing ring and the inner circumference of the carrier ring. In the case of such a design, both the outer bearing ring and the carrier ring can then be supported in the oil film in a freely rotatable manner. 
         [0023]    The bearing housing, in which the bearing cartridge is arranged, can be produced from different materials. On account of the high loads during operation of a turbocharger, temperature-resistant and corrosion-resistant metal materials are especially suitable in this case. The bearing housing is especially designed with a locating hole for the bearing, wherein the inside diameter of the locating hole is slightly larger than the outside diameter of the bearing cartridge. The interspace and the oil film, which is formed in this, between the bearing cartridge and the bearing housing are correspondingly determined by the dimensions of the locating hole and of the outer cartridge ring. 
         [0024]    The supply hole in the bearing housing serves for the oil supply of the interspace. Via the supply hole, oil is pushed from the engine oil circuit into the interspace between the inner circumference of the bearing housing and the outer circumference of the bearing cartridge so that the required oil film for a lock-free support of the outer cartridge ring in the bearing housing is enabled. The number of supply holes is basically not limited in this case. 
         [0025]    Correspondingly more supply holes, which are provided for the supply of the oil film, are preferably formed in the bearing housing. The supply holes in this case are expediently introduced into the bearing housing at a sufficient axial distance apart so that a uniform distribution of the oil over the entire circumference of the outer cartridge ring is ensured. 
         [0026]    The diameter of the supply hole is expediently adapted to the oil pressure and to the quantity of oil which is required for the forming of the oil film. The quantity of oil in this case is especially dependent upon the size of the interspace which in turn is predetermined by the ratio between the outside diameter of the bearing cartridge and the inside diameter of the bearing housing. The length of the supply hole is expediently adapted to the dimensions of the bearing housing. The supply hole in this case can be oriented inside the bearing housing either vertically to the bearing housing axis or can be inclined in relation to the bearing housing axis. 
         [0027]    Basically, it is also possible to connect the supply hole with a so-called pressure distribution chamber. The pressure distribution chamber serves as an accumulator and can be supplied with oil via the supply hole so that the oil is pushed from the pressure distribution chamber into the interspace on the outer circumference of the outer cartridge ring. 
         [0028]    In an advantageous embodiment of the invention, the supply hole is connected in a communicating manner to a groove which encompasses the bearing cartridge in the circumferential direction. The oil, which is pushed through the supply hole into the bearing housing, can be distributed from the groove both in the axial direction and over the circumference of the bearing cartridge in such a way that a uniform oil film is formed between the bearing cartridge and the inner wall of the bearing housing. As a result of this, the reliable and contact-free support of the outer cartridge ring is made possible. 
         [0029]    In particular, a multiplicity of grooves can also be formed on the bearing cartridge and connected in a communicating manner to a multiplicity of supply holes in the bearing housing so that the supply of the oil film can be carried out at a plurality of points at the same time. 
         [0030]    The outer cartridge ring preferably comprises a multiplicity of holes for drainage of oil. The holes expediently extend radially outward in the installed state of the outer cartridge ring and enable the drainage of oil from the anti-friction bearing even with a rotating outer cartridge ring. As a result of a multiplicity of holes, flooding of the bearing can be excluded regardless of the position of the outer cartridge ring. The number of holes, and that of the oil drainage holes, are variable in dependence upon the axial length of the outer cartridge ring. 
         [0031]    The outer cartridge ring is advantageously constructed in two parts, wherein the two ring parts of the outer cartridge ring are axially spaced apart. A two-part design enables a simple production of the ring parts and reduces the assembly cost of the bearing unit. Furthermore, both the costs and the transporting expenditure can be reduced. The axial spacing can be achieved by means of a spring element, for example, which is positioned between the two ring parts. The spring element forces the two ring parts apart and so keeps them in the intended position by spring action. The axial spacing of the ring parts in relation to each other is especially provided in this case by means of the pretension of the spring element. The spring element can be designed as a metal spiral spring, for example. 
         [0032]    The outer cartridge ring is preferably supported inside the bearing cartridge in a floating manner, that is to say in an axially movable manner. In other words, the outer cartridge ring inside the bearing cartridge has a certain axial clearance. In the case of a floating support of the outer cartridge ring, a shaft can be displaced in relation to the bearing housing by the axial clearance, for example. The axial clearance is fixed in this case in dependence upon the required guiding accuracy so that the anti-friction bearings are not axially distorted even in the case of unfavorable thermal conditions. For the floating arrangement, deep-groove ball bearings, self-aligning ball bearings, or self-aligning roller bearings, for example, are conceivable as suitable types of bearing construction. Even with a certain desired axial clearance, it also necessary in this case that a reliable support of the outer cartridge ring in the region of the clearance naturally also has to continue to be ensured. 
         [0033]    For the axial securing of the outer cartridge ring, at least one locking element is expediently included. The locking element serves as an axial end stop and so prevents an unwanted axial slipping of the outer cartridge ring inside the bearing housing. The locking element can basically have different shapes and sizes and either be connected to the bearing housing, in manner fixed to the housing, or be positioned in holes which are formed inside the bearing housing. The locking element can be designed as a locking plate, for example, which is attached on the end face of the bearing housing in a manner fixed to the housing. 
         [0034]    Furthermore, bolts, pins or spigots, which for example are formed with a section for engaging in a recess or a hole inside the bearing housing, can also be used as a locking element. 
         [0035]    In the case of a two-part construction of the outer cartridge ring, that is to say when this comprises two ring parts, so-called spring rings or piston rings can also be used as locking elements, for example. These spring rings or piston rings can be positioned in grooves inside the bearing housing, for example. The grooves, depending upon the design of the outer cartridge ring, can be introduced in this case either in the outer bearing ring, in the carrier ring, or even in both. 
         [0036]    The outer cartridge ring preferably comprises a splash-oil hole for applying lubricant to the bearing. The oil in this case is pushed from the grooves, which encompass the bearing cartridge in the circumferential direction, into the interior of the bearing and so can also be used for example for lubrication and cooling of the bearing components there. 
         [0037]    In an advantageous embodiment of the invention, the outer cartridge ring is designed as an outer bearing ring. For the guiding of rolling bodies, the outer bearing ring preferably has a rolling-body running track on the inner circumference. The oil film is then formed between the outer circumference of the outer bearing ring and the inner circumference of the bearing housing. 
         [0038]    The bearing cartridge preferably comprises a carrier ring with a hole which is connected in a communicating manner to the splash-oil hole via the groove which encompasses the outer cartridge ring on its outer circumference. The hole is expediently connected to the supply hole inside the bearing housing and so enables the dosing of oil from the engine&#39;s oil circuit right up to the splash-oil hole. As a result of the hole in the carrier ring, when it is used, for one thing the forming of the oil film in the interspace and also an adequate bearing lubrication and cooling of the bearing components is therefore also ensured. 
         [0039]    When using a carrier ring and an outer bearing ring as part of the bearing cartridge, as already mentioned in the introduction, in addition to the oil film between the outer circumference of the outer bearing ring and the inner circumference of the carrier ring, an oil film can also be formed between the outer circumference of the carrier ring and the inner circumference of the bearing housing so that the carrier ring is positioned in the bearing housing in a freely rotatable manner and the outer bearing ring is positioned inside the carrier ring in a freely rotatable manner. The interspaces and therefore the oil films are expediently matched to each other in this case with regard to their depth. 
         [0040]    In this case, in addition to the hole, provision can be made in the carrier ring for an additional groove, for example, which is connected to the hole in each case. Via this groove, an oil film can also be formed between the carrier ring and the bearing housing. The groove encompasses the carrier ring preferably in the circumferential direction so that the oil, which is pushed through the supply hole into the bearing housing, can be distributed from the groove both in the axial direction and over the circumference of the carrier ring. In this way, when using a carrier ring, a uniform oil film can also be ensured between this and the inner wall of the bearing housing. 
         [0041]    The bearing housing expediently comprises an oil drainage hole. This oil drainage hole can be connected in a communicating manner to an oil drainage groove which is introduced on the outer circumference of the outer cartridge ring so that the oil which is fed via the supply hole to the interspace can drain off continuously. 
         [0042]    Naturally, further embodiments of the bearing arrangement, which enable the use of an anti-friction bearing without an additional anti-rotation device, can be covered. 
         [0043]    For example, there is also the possibility that the shaft which is to be supported comprises a rolling-body running track for the guiding of the rolling bodies. In the case of such an embodiment, the shaft itself undertakes the function of the inner bearing ring of the anti-friction bearing so that the use of inner bearing rings which are to be installed separately can be dispensed with and the expenditure and assembly cost during the production of these can be reduced. 
         [0044]    A second object of the invention is achieved according to the invention by means of a bearing unit for a turbocharger, comprising a bearing housing, extending in an axial direction, and a bearing cartridge, having an outer bearing ring and a carrier ring, which is arranged inside the bearing housing, wherein an interspace with a vibration-damping oil film is formed between the outer circumference of the outer bearing ring and the carrier ring, and wherein the bearing housing has a supply hole which is designed for the oil supply of the oil film. In this case, it is also provided that the bearing cartridge comprises an anti-friction bearing, the outer bearing ring of which is supported in the oil film in a freely rotatable manner. In other words, the outer bearing ring is also supported on the bearing housing via the oil film in the case of such an embodiment. 
         [0045]    The carrier ring can basically be positioned in the bearing housing in a rotation-resistant manner or in a freely rotatable manner. 
         [0046]    In the case of a rotation-resistant arrangement, the carrier ring can be fixed in the bearing housing in a frictionally locking or form-fitting manner, for example. In the case of such an embodiment, the interspace for the lock-free support of the outer cartridge ring in a vibration-damping oil film is correspondingly formed between the inner circumference of the carrier ring and the outer circumference of the outer bearing ring of the anti-friction bearing. 
         [0047]    In the case of the freely rotatable design of the carrier ring, the bearing unit additionally has an interspace with a vibration-damping oil film between the carrier ring and the bearing housing, in which the carrier ring can be supported in a freely rotatable manner. The interspaces between the individual components of the bearing unit and therefore also the thickness of the oil film are preferably matched to each other. 
         [0048]    Further advantageous embodiments feature in the claims which are directed towards the first bearing unit and which can correspondingly be transferred to the second bearing unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]    In the following text, the invention is explained with reference to a drawing. In this case, in the drawing: 
           [0050]      FIG. 1  shows in a longitudinal section a bearing unit for a turbocharger with an outer bearing ring supported in a floating manner, 
           [0051]      FIG. 2  shows in a top view the bearing unit according to  FIG. 1 , 
           [0052]      FIG. 3  shows in a longitudinal section a further bearing unit for a turbocharger with an outer bearing ring supported in a floating manner and also a carrier ring, 
           [0053]      FIG. 4  shows in a top view the bearing unit according to  FIG. 3 , 
           [0054]      FIG. 5  shows in a longitudinal section a further bearing unit for a turbocharger with an outer bearing ring supported in a floating manner and also a carrier ring, 
           [0055]      FIG. 6  shows in top view the bearing unit according to  FIG. 5 , 
           [0056]      FIG. 7  shows in a longitudinal section a further bearing unit for a turbocharger with an outer bearing ring supported in a floating manner, 
           [0057]      FIG. 8  shows in a top view the bearing unit according to  FIG. 7 , 
           [0058]      FIG. 9  shows in a longitudinal section a further bearing unit for a turbocharger with an outer bearing ring supported in a floating manner and also a carrier ring, 
           [0059]      FIG. 10  shows in a top view the bearing unit according to  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0060]      FIG. 1  shows in a longitudinal section a bearing unit  1  for a turbocharger. The bearing unit  1  comprises a bearing cartridge  3  which is arranged in an axially extending metal bearing housing  5 . As part of the bearing cartridge  3 , an anti-friction bearing  7  is positioned in this. The bearing  7  is designed with an outer cartridge ring  9 , which is designed as an outer bearing ring, and also with an inner bearing ring  11 . The inner bearing ring  11  is constructed in two parts and in the installed state is arranged on a shaft, which is not shown in the present case. As rolling bodies  15 , balls are installed between the bearing rings  9 ,  11 , wherein in the present case a cage is not provided. 
         [0061]    An interspace  17  with an oil film  19  is formed between the outer circumference of the outer bearing ring  9  and the bearing housing  5 . The interspace  17  or the oil film  19  is supplied with oil via two supply holes  21 ,  23  in the installed state. To this end, both supply holes  21 ,  23  are connected in a communicating manner to grooves  25 ,  27  which encompass the outer bearing ring  9  on its outer circumference in each case. From the grooves  25 ,  27 , the oil can be distributed both in the axial direction and over the circumference of the bearing cartridge  3  in such a way that a uniform oil film  19  is formed in the interspace  17  between the bearing cartridge  3  and the inner wall of the bearing housing  5 . 
         [0062]    The interspace  17  is of such width in the present case that the oil film  19  enables an adequate thickness for vibration insulation between the outer cartridge ring  9  and the bearing housing  5 . Overall, by using the anti-friction bearing  7 , a lower friction moment is transmitted than in the case of a plain bearing so that a separate anti-rotation device can be dispensed with. 
         [0063]    Furthermore, the outer bearing ring  9  is provided with an oil drainage groove  29  on its outer circumference, via which the oil of the oil film  19  can drain off. In the installed state of the bearing  7 , the oil drainage groove  29  is connected in a communicating manner to an oil drainage hole  31 , the diameter of which is dimensioned so that a problem-free drainage of oil is ensured. In this way, a constant oil film  19  can be ensured. In addition, the oil also drains off in the axial direction outwardly between the outer bearing ring  9  and the bearing housing  5 . 
         [0064]    In addition, the oil is pushed from the grooves  25 ,  27  in the outer bearing ring  9  into the bearing interior  37  via two splash-oil holes  33 ,  35  and is made available for lubrication and cooling of the bearing components. 
         [0065]    The axial locking of the outer bearing ring  9  is realized in the present case by the contact of its end faces on mating faces which are fixed on the housing in each case. To this end, a locking plate  39 , fixed to the housing, is arranged on the end face of the bearing housing  5 . The outer bearing ring  9  has an axial clearance and can rotate inside the bearing housing  5  if the frictional moment of the anti-friction bearing drives this during operation. If, in this case, in the installed state an axial force occurs on the shaft, then the outer bearing ring  9 , depending on the axial force direction, is supported in the axial direction on the locking plate  39  or on the bearing housing  5 . 
         [0066]    The overall resistance of the outer bearing ring  9  increases in comparison to the resistance during axial force-free operation. In this case, the hydrodynamic load-bearing percentage of the oil film  19  is established in dependence upon the rotational speed. 
         [0067]    In order to ensure the central oil drainage from the anti-friction bearing  7  via the oil drainage hole  31  even with a rotating outer bearing ring  9  and therefore to exclude flooding of the bearing  7 , radially extending holes are introduced in the axially center region of the outer bearing ring but are not visible on account of the view. They can be gathered from  FIG. 2 , however. By means of the holes, the necessary drainage of oil can be ensured in any position of the outer bearing ring  9 . 
         [0068]      FIG. 2  shows in a top view the bearing unit  1  according to  FIG. 1 . With the aid of this view, the interspace  17  which encompasses the outer circumference of the outer bearing ring  9  is clearly visible. The supply holes  21 ,  23  for the supply of the interspace  17 , and also the grooves  25 ,  27  which encompass the outer bearing ring  9  on its outer circumference are not all visible in the present case on account of the view. 
         [0069]    However, five radially extending holes  41 ,  43 ,  45 ,  47 ,  49 , which are introduced into the outer bearing ring  9 , are clearly visible here. As a result of this, as already described above, the central oil drainage from the anti-friction bearing  7  via the oil drainage hole  31  is enabled regardless of the positioning of the outer bearing ring  9  in the interspace  17 . The number of oil drainage holes can correspondingly be adapted to requirements in this case so that even more oil drainage holes are possible. 
         [0070]    For the further description of the individual bearing components of the bearing unit  1 , reference is made at this point to the detailed description in  FIG. 1 . 
         [0071]      FIG. 3  shows in a longitudinal section a further bearing unit  61  for a turbocharger. The bearing unit  61  comprises a bearing cartridge  63  which is arranged in an axially extending metal bearing housing  65 . As part of the bearing cartridge  63 , an anti-friction bearing  67  is positioned in this. The bearing  67  is designed with an outer cartridge ring  69 , which is designed as an outer bearing ring, and also an inner bearing ring  71 , wherein as rolling bodies  72  balls are installed between the bearing rings  69 ,  71 . The balls are guided in a cage  73 . The inner bearing ring  71  is constructed in one part and in the installed state is arranged on a shaft. The shaft is not shown in the present case. 
         [0072]    In contrast to  FIGS. 1 and 2 , the bearing cartridge  63  comprises a carrier ring  75 . The carrier ring  75  is arranged inside the bearing housing  65  in a manner fixed to said housing. The bearing  67  is arranged inside the carrier ring  75  so that the interspace  77  with the oil film  79 , which is provided for the lock-free support of the outer bearing ring  69  is correspondingly formed in the present case between the inner circumference of the carrier ring  75  and the outer circumference of the outer bearing ring  69 . The outer bearing ring  69  is therefore supported in a floating manner inside the bearing cartridge  63  without the use of locking elements. 
         [0073]    The interspace  77  or the oil film  79 , according to  FIG. 3 , is also supplied with oil via two supply holes  81 ,  83  in the bearing housing  65 . The supply holes  81 ,  83  are connected in this case to grooves  85 ,  87  in each case which are introduced in the carrier ring  75 . The grooves  85 ,  87  open into holes  89 ,  91  in each case which are introduced in the carrier ring  75  on the inner circumference of this. The holes  89 ,  91  in turn open into the grooves  93 ,  95  which encompass the outer circumference of the outer bearing ring  69 . As a result of this, admission of oil into the interspace  77  and therefore the floating support of the outer bearing ring  69  are ensured. 
         [0074]    In addition, the grooves  93 ,  95  in the outer bearing ring are connected to two splash-oil holes  97 ,  99  so that the oil is pushed from the grooves  93 ,  95  into the bearing interior  101  and so can be used for lubrication and cooling of the bearing components. 
         [0075]    A further difference to  FIGS. 1 and 2  lies in the design of the outer bearing ring  69 . This is designed in two parts in the present case and correspondingly consists of two axially spaced apart ring parts  103 ,  105 . The axial spacing is achieved in this case by means of a spring element  107  which is designed as a metal spiral spring. The spring element  107  forces the two ring parts  103 ,  105  apart and so keeps them in the intended position by spring action. The axial distance of the ring parts  103 ,  105  from each other is provided in this case by the pretension of the spring element  107 . 
         [0076]    In addition, the axial locking of the ring parts  103 ,  105  is achieved two locking elements  109 ,  111 . The locking elements  109 ,  111  are designed as spring rings which are arranged on the circumference of the carrier ring  75 . The carrier ring  75  in this case has grooves  113 ,  115  in which the spring rings  109 ,  111  engage. The ring parts  103 ,  105  of the outer bearing ring  69 , in the event of an axial force acting upon the supported mounted shaft, are supported in the axial direction on the spring rings  109 ,  111  and so prevent an unwanted axial slipping of the ring parts  103 ,  105  inside the carrier ring  75 . Furthermore, the spring rings  109 ,  111  serve as a transporting lock for the carrier ring  75 . 
         [0077]    The floating support of the outer bearing ring  69  or of the ring parts  103 ,  105  is basically dependent upon a certain clearance. The clearance in this case is dependent upon the temperature. The bearing arrangement  61  is correspondingly designed so that adequate clearance is provided at each temperature. 
         [0078]    Via the oil drain  117  provided, oil can drain off from the interspace  77 . The oil drain  1179  is connected in a communicating manner to an oil drainage hole  119  of the bearing housing  65  in the installed state of the bearing  67 . 
         [0079]    In  FIG. 4 , the bearing unit  61  according to  FIG. 3  is to be seen in a top view. The positioning of the carrier ring  75 , in a manner fixed to the housing, is clearly seen in the present case. The bearing  67  is arranged inside the carrier ring  75  accordingly. The interspace  77  with the vibration-damping oil film  79 , which is designed for the lock-free support of the outer bearing ring  69 , is formed between the inner circumference of the carrier ring  75  and the outer circumference of the outer bearing ring  69 , wherein this is not visible on account of the view. Instead, the spring element  107 , which serves for the axial spacing of the ring parts  103 ,  105  of the outer bearing ring  69 , is visible. The ring parts  103 ,  105  are not shown either in the present case. 
         [0080]    For the further description of the individual bearing components of the bearing unit  61  reference is made at this point to the detailed description in  FIG. 3 . 
         [0081]    In  FIG. 5 , a further bearing unit  131  for a turbocharger is shown in a longitudinal section. As in  FIGS. 3 and 4  also, the bearing unit  131  comprises a bearing cartridge  133  which is arranged in an axially extending metal bearing housing  135 . The bearing cartridge  133  comprises an anti-friction bearing  137  with an outer bearing ring  139  and with an inner bearing ring  141 , wherein the inner bearing ring  141  is arranged on a shaft in the installed state. A shaft is not shown, however, in the present case. 
         [0082]    As rolling bodies  143 , balls, which are arranged in a cage  145 , are guided between the bearing rings  139 ,  141 . The inner bearing ring  141  is furthermore designed in two parts, wherein the two ring parts  146 ,  147  of the inner bearing ring  141  are fastened to each other by means of a locking element  148  which is designed as a locking clip. The locking element  148  serves equally as a transporting lock. 
         [0083]    Furthermore, the bearing cartridge  133  comprises a carrier ring  149  in which the bearing  137  is arranged. In contrast to  FIGS. 3 and 4 , the carrier ring  149  in the present case is arranged inside the bearing housing  135  in a manner not fixed to the housing, however, but arranged in a freely rotatable manner in relation to this. Therefore, a first interspace  151  with an oil film  153  is formed between the outer circumference of the carrier ring  149  and the inner circumference of the bearing housing  135 . 
         [0084]    The outer bearing ring  139  of the bearing  137  is again supported inside the carrier ring  149  in a floating manner and without locking elements for rotation prevention. An interspace  155  with an oil film  156  is therefore also provided between the outer bearing ring  139  and the carrier ring  149 . Accordingly, the outer bearing ring  139  is rotatably supported relative to the carrier ring  149  and the carrier ring  149  is rotatably supported relative to the bearing housing  135 . Also in the case of this embodiment, locking elements for rotation prevention can be completely dispensed. 
         [0085]    Both the interspace  151  with the oil film  153  and the interspace  155  with an oil film  156  are supplied with oil via two supply holes  157 ,  158  in the bearing housing  135  which are connected in a communicating manner in each case to holes  163 ,  165  via grooves  159 ,  161  which are introduced in the carrier ring  149 . From the holes  163 ,  165 , oil can spread out in the interspace  151  between the bearing housing  135  and the carrier ring  149  so that the vibration-damping oil film  153  is created there. 
         [0086]    Both vibration-damping oil films  153 ,  156  are matched to each other with regard to their thickness so that a support is possible without the use of locking elements, that is to say lock-free. 
         [0087]    Furthermore, the holes  163 ,  165  in the outer bearing ring  139  open into grooves  167 ,  169  which encompass the outer bearing ring  139  on its outer circumference. As a result of this, an admission of oil into the interspace  155  and therefore the floating support of the outer bearing ring  139  are ensured. 
         [0088]    In addition, the grooves  167 ,  169  in the outer bearing ring  139  are connected to two splash-oil holes  171 ,  173  so that the oil can be pushed into the bearing interior  175  and can be used for lubrication of the bearing components. 
         [0089]    The outer bearing ring  139  is designed in two parts and, as in  FIGS. 3 and 4  also, consists of two axially spaced apart ring parts  181 ,  183 . For the axial spacing, use is made of a spring element  185  which is designed as a metal spiral spring and which by means of its pretension forces the two ring parts  181 ,  183  apart. 
         [0090]    As an axial end stop for the two ring parts  181 ,  183 , two locking elements  187 ,  188 , which are designed as spring rings, are attached on the inner circumference of the carrier ring  149 . The ring parts  181 ,  183  in this case engage in grooves  189 ,  191  of the carrier ring  149 . In addition to their function as an axial locking device, the spring rings  187 ,  188  also serve as a transporting lock for the carrier ring  149 . 
         [0091]    In order to enable drainage of oil, the carrier ring  149  has an oil drainage groove  193  on its outer circumference which is connected in a communicating manner to the oil drainage hole  195 . In the present case, the carrier ring  149  has radially extending oil drainage holes in this case in order to also be able to exclude flooding of the bearing  137  during a rotation of the bearing components. Not all the holes are visible on account of the sectioned view. 
         [0092]    In  FIG. 6 , the bearing unit  131  according to  FIG. 5  is to be seen in a top view. The carrier ring  149 , which is supported inside the bearing housing  135 , is visible. The carrier ring  149 , in contrast to  FIG. 4 , is not supported in the interspace  151  in a manner fixed to the housing, but in a rotatable manner, which, however, is not visible on account of the view. However, also visible here, as in  FIG. 4 , is the spring element  185  which serves for the axial spacing of the ring parts  181 ,  183 , which are not shown, of the outer bearing ring  139 . 
         [0093]    For the further description of the individual bearing components of the bearing unit  131 , reference is correspondingly made at this point to the detailed description in  FIG. 5 . 
         [0094]      FIG. 7  shows in a longitudinal section a further bearing unit  201  for a turbocharger. The bearing unit  201  basically corresponds to the embodiment of the bearing unit  61  according to  FIGS. 3 and 4  so that reference can be made at this point to the detailed description there. The description and function of the individual components described there can correspondingly be transferred to the bearing unit  201 . 
         [0095]    The bearing unit  201  also comprises a bearing cartridge  203  which is arranged in an axially extending metal bearing housing  205 . As part of the bearing cartridge  203 , an anti-friction bearing  207  is positioned in this. The bearing  207  is designed with an outer bearing ring  209  and also with an inner bearing ring  211 , wherein as rolling bodies  213  balls are installed between the bearing rings  209 ,  211 . The balls  213  are guided in a cage  215 . The inner bearing ring  211  is constructed in one part as well as being installed on a shaft in the installed state as in the already stipulated figures. 
         [0096]    The difference to the bearing unit  61  according to  FIGS. 3 and 4  lies in the fact that the bearing cartridge  203  of the bearing unit  201  does not include a carrier ring. The interspace  218  with the oil film  219 , which is provided for the lock-free support of the outer bearing ring  209 , is correspondingly formed in the present case between the inner circumference of the bearing housing  205  and the outer circumference of the outer bearing ring  209 . The interspace  218  is also formed with an oil film  219  in the present case, which enables an adequate thickness for vibration insulation between the outer bearing ring  209  and the bearing housing  205 . In this way, the outer bearing ring  209  can be supported inside the bearing cartridge  203  in a lock-free and floating manner, that is to say with an axial clearance. 
         [0097]    Two supply holes  221 ,  223 , which are introduced in the bearing housing  205  and are connected in a communicating manner in each case to grooves  225 ,  227  which encompass the outer bearing ring  209  on its outer circumference, serve for the supply of the oil film  219 . From the grooves  225 ,  227 , the oil can be distributed both in the axial direction and over the circumference of the bearing cartridge  3  in such a way that the oil film  219  is formed uniformly in the interspace  218 . 
         [0098]    The oil is additionally pushed from the grooves  225 ,  227  in the outer bearing ring  209  via two splash-oil holes  229 ,  231  into the bearing interior  233  and is available for lubrication of the bearing components. 
         [0099]    The outer bearing ring  209  is also designed in two parts with two axially spaced apart ring parts  235 ,  237 . For the axial spacing, use is made of a metal spiral spring  239  which forces the two rings parts  235 ,  237  apart and so keeps them if the intended position by spring action. 
         [0100]    Furthermore, two locking elements  241 ,  243 , which are designed as spring rings, are used for the axial locking of the ring parts  235 ,  237  and are arranged on the circumference of the bearing housing  205 . For fastening of the locking elements  241 ,  243 , the bearing housing  205  has two encompassing grooves  245 ,  247  in which the locking elements  241 ,  243  engage. 
         [0101]    Furthermore, the outer bearing ring  209  is provided with an oil drain  249  on its outer circumference, via which the oil can drain from the interspace  227 . The oil drain  249  in the installed state of the bearing  207  is connected in a communicating manner to an oil drainage hole  251 . 
         [0102]    In  FIG. 8 , the bearing unit  201  is shown in a top view. The supported rolling bodies  213 , which are guided on the inner bearing ring  211 , are clearly visible. Furthermore, also visible, in addition to the spring element  239 , are the locking elements  241 ,  243  which are used for the axial locking of the ring parts  235 ,  237  of the outer bearing ring  209 . The locking elements  241 ,  243  are arranged on the inner circumference of the bearing housing  205 . The ring parts  235 ,  237  are not visible in the present case. 
         [0103]    The further detailed description of the bearing unit  201  can be gathered from the description in relation to  FIG. 7 . 
         [0104]      FIG. 9  shows in a longitudinal section a further bearing unit  261  for a turbocharger. The bearing unit  261  is designed in this case basically just like the bearing unit  61  according to  FIGS. 3 and 4 . Therefore, the description can be correspondingly transferred here also. 
         [0105]    The bearing unit  261  comprises a bearing cartridge  263 , with an anti-friction bearing  267 , which is arranged in an axially extending metal bearing housing  265 . The bearing  267  is designed with an outer bearing ring  269  and also an inner bearing ring  271 , wherein balls are used as rolling bodies  273 . The balls are guided in a cage  275 . The inner bearing ring  271  is constructed in one part. 
         [0106]    Furthermore, the bearing cartridge  263  comprises a carrier ring  279  which is arranged on the inner circumference of the bearing housing  265  in a manner fixed to the housing. The anti-friction bearing  267  is arranged in this case inside the carrier ring  279 . For the lock-free and floating support of the outer bearing ring  269 , the interspace  281  with the oil film  283  is correspondingly formed between the inner circumference of the carrier ring  279  and the outer circumference of the outer bearing ring  269 . 
         [0107]    The oil film  283  is supplied with oil via two supply holes  285 ,  287  in the bearing housing  265 , wherein here also the supply holes  285 ,  287  are connected in each case to grooves  289 ,  291  which are introduced in the carrier ring  279 . The grooves  289 ,  291  open in each case into holes  293 ,  295  on the inner circumference of the carrier ring  279 . From the holes  293 ,  295 , the oil is conveyed from the engine&#39;s oil circuit into two grooves  297 ,  299  which encompass the outer circumference of the outer bearing ring  269  so that an admission of oil into the interspace  281 , or the forming of the oil film  283  and therefore the desired anti-rotation device-free support, is ensured. 
         [0108]    In addition, here also the grooves  297 ,  299  of the outer bearing ring  269  are connected to two splash-oil holes  301 ,  303  so that the oil is pushed into the bearing interior  305  and can be used there for lubrication of the bearing components. 
         [0109]    In contrast to  FIGS. 3 and 4 , in the present case the axial stop of the outer bearing ring  269  is achieved via two pins  307 , fixed to the carrier ring, which are positioned equidistantly along the circumference of the bearing cartridge  263 . By means of a multiplicity of pins  307 , tilting can be prevented in the case of a floating outer ring  269 , that is to say in the case of a clear axial clearance  269 . In addition, the pins  307  serve as a transporting lock for the carrier ring  279 . 
         [0110]    The pins  307 , which are fixed to the carrier ring, are designed as hollow bushes in the present case which project into the oil drainage groove  309  which is formed on the circumference of the carrier ring  279 . The hollow design of the pins  307  enables an adequate drainage of oil. The oil drainage groove  309  is additionally connected in a communicating manner to an oil drainage hole  311  in the installed state of the bearing  267 . 
         [0111]    Furthermore, the outer bearing ring  269  is designed in two parts with two axially spaced apart ring parts  313 ,  315 , the axial spacing of which, as in the previously described figures also, is achieved by means of a spring element  317  which is designed as a metal spiral spring. 
         [0112]      FIG. 10  shows the bearing unit  261  in a top view. Two of the four pins  307 , which are designed as hollow bushes, are visible here. The pins  307  are arranged opposite each other on the circumference on the bearing arrangement  261  and are fixedly connected to the carrier ring  279 . The pins  307  prevent an unwanted axial displacement of the ring parts  313 ,  315  of the outer bearing ring  269  which are supported in a floating and lock-free manner. 
         [0113]    In this case, it is to be taken into consideration that on account of the floating support of the ring parts  313 ,  315  a certain axial clearance between the locking elements, that is to say the pins  307 , and the ring parts  313 ,  315  is naturally always established on account of the movement which is transmitted from a shaft. The axial clearance is fixed in this case in dependence upon the required guiding accuracy so that the anti-friction bearing  267  cannot be axially distorted even in the case of unfavorable thermal conditions. 
         [0114]    The further detailed description of the bearing unit  261  can be gathered in the present case from the description in relation to  FIG. 10 . 
       LIST OF DESIGNATIONS 
       [0000]    
       
           1  Bearing unit 
           3  Bearing cartridge 
           5  Bearing housing 
           7  Anti-friction bearing 
           9  Outer bearing ring 
           11  Inner bearing ring 
           15  Rolling bodies 
           17  Interspace 
           19  Oil film 
           21  Supply hole 
           23  Supply hole 
           25  Groove 
           27  Groove 
           29  Oil drainage groove 
           31  Oil drainage hole 
           33  Splash-oil hole 
           35  Splash-oil hole 
           37  Bearing interior 
           39  Locking plate 
           41  Hole 
           43  Hole 
           45  Hole 
           47  Hole 
           49  Hole 
           61  Bearing unit 
           63  Bearing cartridge 
           65  Bearing housing 
           67  Anti-friction bearing 
           69  Outer bearing ring 
           71  Inner bearing ring 
           72  Rolling bodies 
           73  Cage 
           75  Carrier ring 
           77  Interspace 
           79  Oil film 
           81  Supply hole 
           83  Supply hole 
           85  Groove 
           87  Groove 
           89  Hole 
           91  Hole 
           93  Groove 
           95  Groove 
           97  Splash-oil hole 
           99  Splash-oil hole 
           101  Bearing interior 
           103  Ring part 
           105  Ring part 
           107  Spring element 
           109  Locking element 
           111  Locking element 
           113  Groove 
           115  Groove 
           117  Oil drain 
           119  Oil drainage hole 
           131  Bearing unit 
           133  Bearing cartridge 
           135  Bearing housing 
           137  Anti-friction bearing 
           139  Outer bearing ring 
           141  Inner bearing ring 
           143  Rolling bodies 
           145  Cage 
           146  Ring part 
           147  Ring part 
           148  Locking element 
           149  Carrier ring 
           151  Interspace 
           153  Oil film 
           155  Interspace 
           156  Oil film 
           157  Supply hole 
           158  Supply hole 
           159  Groove 
           161  Groove 
           163  Hole 
           165  Hole 
           167  Groove 
           169  Groove 
           171  Splash-oil hole 
           173  Splash-oil hole 
           175  Bearing interior 
           181  Ring part 
           183  Ring part 
           185  Spring element 
           187  Locking element 
           188  Locking element 
           189  Groove 
           191  Groove 
           193  Oil drainage groove 
           195  Oil drainage hole 
           201  Bearing unit 
           203  Bearing cartridge 
           205  Bearing housing 
           207  Anti-friction bearing 
           209  Outer bearing ring 
           211  Inner bearing ring 
           213  Rolling bodies 
           215  Cage 
           218  Interspace 
           219  Oil film 
           221  Supply hole 
           223  Supply hole 
           225  Groove 
           227  Groove 
           229  Splash-oil hole 
           231  Splash-oil hole 
           233  Bearing interior 
           235  Ring part 
           237  Ring part 
           239  Spring element 
           241  Locking element 
           243  Locking element 
           245  Groove 
           247  Groove 
           249  Oil drain 
           251  Oil drainage hole 
           261  Bearing unit 
           263  Bearing cartridge 
           265  Bearing cartridge 
           267  Anti-friction bearing 
           269  Outer bearing ring 
           271  Inner bearing ring 
           273  Rolling bodies 
           275  Cage 
           279  Carrier ring 
           281  Interspace 
           283  Oil film 
           285  Supply hole 
           287  Supply hole 
           289  Groove 
           291  Groove 
           293  Hole 
           295  Hole 
           297  Groove 
           299  Groove 
           301  Splash-oil hole 
           303  Splash-oil hole 
           305  Bearing interior 
           307  Pins 
           309  Oil drainage groove 
           311  Oil drainage hole 
           313  Ring part 
           315  Ring part 
           317  Spring element