an exhaust - gas power - recovery turbine 1 and its rotor 1 . 1 can be seen in fig1 with a plurality of turbine blades 1 . 2 , which are arranged in the exhaust gas stream ( see direction arrows ) of an internal combustion engine ( non - represented ). as can be seen , the exhaust - gas power - recovery turbine 1 is designed as a radial - axial - turbine , which means that the turbine blades 1 . 2 are exposed to the flow of exhaust gas radially from the outside which then leaves it in axial direction ( flows out ). the rotor 1 . 1 is carried by a turbine shaft 2 — to be more accurate , is formed as a single - part therewith . in that case , the rotor 1 . 1 of the exhaust - gas power - recovery turbine is flush therewith on an axial end of the turbine shaft 2 . a pinion 3 is arranged on the turbine shaft 2 , i . e . on the opposite second axial end of the turbine shaft 2 ; to be more accurate said pinion 3 is carried by said shaft 2 . in this instance , the pinion 3 is suspended on the turbine shaft 2 and is held there by an appropriate mechanical locking system , to be more accurate by spacers . alternately , the pinion 3 could also be formed as a single piece with the turbine shaft 2 . the pinion 3 meshes with a gear 11 , which is connected in a torque - proof manner to the pump wheel 12 of a hydrodynamic coupling 13 . the gear 11 is here relatively supported on a coupling shaft 14 together with the pump wheel 12 , which means that it rotates with another rotation speed than the shaft . the coupling shaft 14 carries the turbine wheel 15 of the hydrodynamic coupling in a torque - proof manner , which turbine wheel 15 forms together with the pump wheel 12 a hydrodynamic work space 16 . the drive power can thus be transmitted hydrodynamically to the turbine wheel 15 via the pinion 3 , the gear 11 , the pump wheel 12 , and from there to the crankshaft ( or generally the output shaft ) of the internal combustion engine via the coupling shaft 14 , which is arranged in a torque - proof manner , by means of the coupling shaft pinion 17 . the represented mounting of the pump wheel 12 of the hydrodynamic coupling or of the coupling shaft 14 can be designed independent of the configuration of the arrangement or of the mounting of the turbine shaft 2 in the illustrated form , in particular with four roller bearings 18 connected behind one another in axial direction , among which both middle bearings can be combined to constitute a double bearing . it is particularly referred to the fact that said bearing arrangement or generally the mounting of the coupling shaft 14 and of the corresponding components in the region of the hydrodynamic coupling 13 in particular in turbo compound systems can be formed without the mounting of the turbine shaft of the exhaust - gas power - recovery turbine , illustrated according to the invention , with a radial plain bearing and a radial roller bearing . according to fig1 , the turbine shaft 2 is supported in the area of the rotor 1 . 1 by means of a radial plain bearing 4 and in the area of the pinion 3 by means of a radial rolling - element bearing 5 . both bearings 4 , 5 are hence arranged between the pinion 3 and the rotor 1 . 1 as seen in axial direction and the single radial bearings , by means of which the turbine shaft 2 is supported , so that the rotor 1 . 1 as well as the pinion 3 are arranged or supported cantilevered on the turbine shaft 2 . the radial rolling - element bearing 5 as well as the radial plain bearing 4 are enclosed by a common housing 7 in around the periphery . the bearings can hence , as already mentioned , be supplied with pressurised oil via a pressurised oil system 19 or lubricating oil ( without overpressure ). the radial plain bearing 4 particularly advantageously includes a so - called floating bushing , which means that as seen in radial direction , two lubricating oil - filled annular gaps are arranged behind one another . one or both annular gaps can be filled with pressurised oil , to exert a damping effect on the dynamic forces , to which the turbine shaft 2 is subject . the radial plain bearing 4 has for instance a bearing ring 4 . 1 , in particular a cylinder ring , which is arranged in radial direction of the turbine shaft 2 between the turbine shaft 2 and a housing 7 , and forms both aforementioned annular gaps 8 , 9 with the housing 7 or with the turbine shaft 2 . in the illustrated embodiment , the radial rolling - element bearing 5 has conversely no such floating bushing or squeeze oil damper . far more , the bearing outer ring ( non - represented ) of the radial rolling - element bearing 5 is inserted directly and in a torque - proof manner in the housing 7 and the bearing inner ring ( non - represented ) is mounted on the turbine shaft 2 directly and in a torque - proof manner . a plurality of rolling elements is arranged between the bearing outer ring and the bearing inner ring , so that the bearing outer ring and the bearing inner ring roll off each other over the rolling elements ( non - represented ). in the exemplary embodiment illustrated in fig1 , the turbine shaft 2 is held by an axial plain bearing 6 . this is positioned in the area of the pinion 3 and can , as represented , be mounted outside on the housing 7 and in particular be covered by a bearing shield 20 from the outside . in this instance , the axial plain bearing 6 comprises a fixed bearing ring 6 . 1 mounted in or on the housing 7 , which is supported via respectively a lubricating oil film on two spacers mounted fixedly in axial direction on the turbine shaft 2 . it is of course also possible to provide one or also three or more spacers instead of the two illustrated spacers . the embodiment according to fig2 differentiates from that of fig1 in that the turbine shaft 2 has no axial plain bearing and the radial plain bearing 5 fulfills the function of an axial bearing at the same time . for that purpose , the radial roller bearing 5 ( then axial - radial - roller bearing ) is supported either via rolling elements on the housing and / or an axial base of the turbine shaft 2 or via a lubricating oil , for instance again between a bearing ring of the bearing 5 and spacers on the turbine shaft 2 . other embodiments can be envisioned . the embodiment according to fig3 differentiates from that of fig1 in that the radial roller bearing 5 is also fitted with a so - called floating bushing . in the illustrated embodiment variation , a bearing ring 5 . 1 is provided to that end , which the outer ring of the radial rolling - element bearing 5 is pressed into . an annular gap is formed between the bearing ring 5 . 1 and the housing 7 , which is filled with lubricating oil , in particular pressurised oil . the dynamic forces acting on the turbine shaft 2 or the bearing 5 are hence attenuated , and the wear of the bearing can be reduced . the bearing ring 5 . 1 can for instance be fixed , as already mentioned , by circlips in axial direction , similar to the bearing ring 4 . 1 of the radial plain bearing 4 illustrated in the figures . the pressurised oil in the annular gap 10 between the bearing ring 5 . 1 and the housing 7 can be made available for instance again using the pressurised oil system 19 , which is in a correspondingly conductive connection with the annular gap 10 . alternately or additionally , a corresponding lubricating oil or pressurised oil - filled annular gap may also be provided between the bearing inner ring and the turbine shaft 2 . the features illustrated in fig1 , 2 and 3 can be provided independently from one another or in non - represented combinations . it is of course also possible to realise the radial plain bearing 4 without the floating bushing , that is to say with a single lubricating oil - filled annular gap between the housing 7 and the turbine shaft 2 . other modifications can be envisioned . the turbine shaft 2 of a turbo compound system according to the invention rotates for instance with rotation speeds of up to 70 , 000 rpm , in particular with maximum rotation speeds above 20 , 000 , 30 , 000 or 40 , 000 rpm . the lubricating oil or pressurised oil - filled bearing spaces or annular gaps 8 , 9 , 10 of the bearings 4 , 5 , in particular the annular gap 10 in the radial roller bearing 5 , can be sealed with respect to the housing 7 and the respective bearing ring 5 . 1 , 4 . 1 , for instance can be designed with a contactless or a contacting shaft seal , such as a tip - to - tip seal , a labyrinth seal or an o - ring . in the embodiment according to fig4 , in which matching components are again designated with matching reference signs , the turbine shaft 2 is supported in the area of the rotor 1 . 1 by means of a floating bushing 21 in a housing 22 . the component designated here as a floating bushing 21 corresponds in its function to the bearing ring 4 . 1 according to fig1 , whereas accordingly the radial plain bearing 4 according to fig1 could also be designated as a floating bushing bearing . as can be seen in fig4 , the floating bushing 21 forms an external oil - filled bearing gap 23 with respect to the housing 22 and an internal oil - filled bearing gap 24 with respect to the turbine shaft 2 . besides , the floating bushing 21 is relatively rotatable with respect to the housing 22 and with respect to the turbine shaft 2 . in the area of the pinion 3 conversely , the turbine shaft 2 is only supported by means of a simple plain bearing 25 in the housing 22 ( or another component ), and a single oil - filled bearing gap 26 has no rolling elements between the turbine shaft 2 and the housing 22 or the other component . it is hence sufficient according to the invention to provide a single simple plain bearing in the area of the pinion 3 for supporting the turbine shaft , whereas the bearing can be positioned either on the side pointing to the rotor 1 . 1 or also on the side of the pinion 3 facing away from the rotor 1 . 1 . in an embodiment of the rotor 1 . 1 being a compressor rotor , which is arranged in a fresh air flow of an internal combustion engine , as will be described more in detail below , several plain bearings can also be provided close to the pinion 3 according to a deviating form of embodiment , in particular exactly two plain bearings , advantageously one on each side of the pinion 3 , which then either all or both are designed as a simple plain bearing , or among which only one or several , however not all of them , can be designed as straightforward plain bearings and the remaining one ( s ) as floating bushing bearings . an axial plain bearing 6 is also provided in the form of embodiment illustrated in fig4 or also in this special case on the side of the simple plain bearing 25 facing away from the rotor 1 . 1 and close to the pinion 3 . fig5 illustrates the third arrangement according to the present invention . the pinion 3 is this time not supported cantilevered , but rather between the bearing close to the pinion 3 and the bearing close to the rotor 1 . 1 . it would of course be also possible to support the pinion 3 in a cantilevered manner , or vice versa , in the embodiments illustrated previously , the pinion 3 , as represented in fig5 , could also be supported in a non - cantilevered manner . according to fig5 , the turbine shaft 2 is supported in the area of the rotor 1 . 1 by means of a roller bearing 27 , which is enclosed by a plain bearing 28 with an oil - filled bearing gap 29 . the external bearing ring of the roller bearing 27 rotates by the plain bearing 28 with respect to the facing surface of the housing 22 . if conversely the external bearing ring of the roller bearing 27 is held stationary according to an embodiment of the invention and nevertheless is enclosed by an oil - filled bearing gap 29 , into which in particular pressurised oil is injected , the term oil damper or squeeze oil damper would be more suitable than the designation plain bearing . such an oil damper has already been described with reference to fig3 as regards the bearing close to the pinion 3 . the bearing close to the pinion 3 in the region of the other end of the turbine shaft 2 according to fig5 conversely is designed as a simple roller bearing without floating bushing , which means that no oil - filled bearing gap without rolling elements is provided in said bearing . this straightforward roller bearing is indicated by the reference sign 30 . both bearings 27 , 30 according to the embodiment variation in fig5 thus differentiate from each other in that the bearing close to the rotor is supported as a roller bearing 27 over a plain bearing 28 with a bearing gap 29 in the housing 22 ( or another appropriate component ) whereas conversely the roller bearing 30 close to the pinion 3 is directly supported in the housing 22 ( or another appropriate component ), that is to say without interposition of a plain bearing . in deviation from the illustration of fig5 , two oil - filled bearing gaps can also be provided outside the roller bearing 27 inasmuch as the roller bearing 27 for instance is supported in a floating bushing , which forms a first oil - filled bearing gap with respect to the roller bearing 27 and a second oil - filled bearing gap with respect to the housing 22 or another appropriate component . alternately or additionally , such a floating bushing bearing assembly having two oil - filled bearing gaps or only one oil - filled bearing gap could also be provided between the roller bearing 27 and the turbine shaft 2 . in a turbo charger system ( non - represented ), whose exhaust gas turbine which is in drive connection with a fresh air compressor of the internal combustion engine in particular directly via a rigid shaft , and which in particular is arranged in the flow direction of exhaust gas upstream of the exhaust - gas power - recovery turbine , the mounting concept illustrated in this instance for the exhaust - gas power - recovery turbine can also be designed accordingly and more precisely regardless whether a turbo compound system is provided . although the present invention has been illustrated previously using an exhaust - gas power - recovery turbine for a turbo compound system , it can similarly be used with a turbo compressor for a turbo compound system or for a turbo charger , in particular of a motor vehicle . in such a case , the turbine shaft is suitably designated as a drive shaft and the rotor is a compressor rotor , not a turbine rotor . moreover , the rotor is driven by the drive power applied by the pinion to the drive shaft and compresses a fresh air flow fed to the internal combustion engine , instead of converting exhaust gas energy into drive power . the drive power can be made available by a turbine , in particular exhaust gas turbine or by the crankshaft of the internal combustion engine . a gas turbine or a vapour can be envisioned as well instead of an exhaust gas turbine , for instance a steam turbine in a steam cycle , wherein steam in particular is generated by means of exhaust gas energy . incidentally , the features described previously are accordingly relevant for the configuration of a turbo compressor according to the invention . this applies in particular to the arrangement and embodiment of the bearing , in particular of the axial bearing respectively its integration into the radial rolling - element bearing , as well as the embodiment as a floating bushing . but the other features described with reference to the exhaust - gas power - recovery turbine can also be used with the embodiment as a turbo compressor . while this invention has been described with respect to at least one embodiment , the present invention can be further modified within the spirit and scope of this disclosure . this application is therefore intended to cover any variations , uses , or adaptations of the invention using its general principles . further , this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims .