according to the invention , in a radial roller bearing according to the preamble of claim 1 , this object is achieved in such a way that the cage is formed by individual hollow rollers consisting of a shape memory alloy , which are arranged between two roller rolling bodies each and which , when the radial roller bearing is assembled , are deformed in cross section to the dimension of the free space between a rim of the outer bearing ring and a rim of the inner bearing ring and can be inserted into the radial roller bearing through the free space between these rims of the bearing rings and , after insertion into the radial roller bearing , automatically assume their original shape when a predetermined temperature is reached . shape memory alloys or memory alloys , as they are known , have for a long time been the subject of application - oriented material research and are distinguished in that , after suitable treatment , they change their configuration as a function of the temperature or else of pressure by virtue of a transformation from austenite to martensite . workpieces consisting of such alloys can , in their low - temperature shape , be deformed permanently , that is to say ostensibly plastically , whereas , under heating to above the transformation temperature , they resume their original shape . when these workpieces are cooled once again , they can be deformed plastically once again , but , insofar as they are heated appropriately , resume their macroscopic original high - temperature shape by a return of their microstructure to austenite . a basic distinction can be made , in the shape memory behavior , between the one - way effect and the two - way effect . in the one - way effect , a material which has been deformed at a low temperature resumes its original shape when it has been heated to a higher temperature . the material , as it were , remembers its original shape when it is heated and also maintains this shape during subsequent cooling . by contrast , what is designated as a two - way effect is the phenomenon in which , both during a temperature rise and during cooling , the material remembers its inculcated shape , that is to say one shape at a high temperature and another shape at a low temperature . proceeding from this , in an expedient development of the radial roller bearing designed according to the invention , it is therefore proposed that the hollow rollers consisting of a shape memory alloy , which are designed as a cage for the roller rolling bodies , have in their original shape the same outside diameter and the same length as the roller rolling bodies of the radial roller bearing and be designed in cross section preferably with a thin - walled material thickness . the advantage of hollow rollers designed in this way and arranged between the roller rolling bodies is that both these and the roller rolling bodies roll on the raceways of the inner and of the outer bearing ring and are guided , in the same way as the roller rolling bodies , on these raceways by the rims . owing to this and owing to the exact distance - filling fit of the hollow rollers between the roller rolling bodies , the roller rolling bodies are driven in exact alignment by the hollow rollers , so that neither the roller rolling bodies nor the hollow rollers can tilt or tip on edge . since shape memory alloys are extremely stable in their high - temperature shape and , accordingly in their hard phase , this ensures at the same time , in spite of and because of the thin - walled design of the hollow rollers , that the hollow rollers , on the one hand , can withstand even high circumferential loads and , on the other hand , have the necessary elasticity in order to appropriately damp both the impacts occurring upon the entry of the roller rolling bodies into the load zone of the bearing and other vibrations of the roller rolling bodies . furthermore , as an advantageous embodiment of the radial roller bearing designed according to the invention , it is also proposed that the hollow rollers consisting of a shape memory alloy be designed preferably of a nickel / titanium alloy with a one - way or two - way characteristic which is easily deformable in its martensitic low - temperature phase and assumes its original manufacturing shape during the transition into its austenitic high - temperature phase . when a nickel / titanium alloy with a one - way characteristic is used , therefore , the hollow rollers remain in their original manufacturing shape after their transition into their austenitic high - temperature phase , so that the radial roller bearing can no longer be demounted . by contrast , the use of a nickel / titanium alloy with a two - way characteristic has the advantage that this “ remembers ” both its shape in the low - temperature phase and its shape in the high - temperature phase , so that , during a cooling of the radial roller bearing to the low temperature of the shape memory alloy for the purpose of demounting the radial roller bearing , the hollow rollers resume their deformed shape and can therefore easily be removed from the bearing . an especially advantageous embodiment of a roller bearing designed according to the invention is if both the martensitic low - temperature phase and the austenitic high - temperature phase of the shape memory alloy for the hollow rollers are fixed outside the typical operating temperatures of the roller bearing . in a cylindrical roller bearing designed according to the invention , which is used , for example , as a fixed bearing for a machine tool spindle or the like , the low - temperature phase of the shape memory alloy is fixed , for example , approximately at the nitrogen boiling temperature (− 77 ° c .) and the high - temperature phase is fixed approximately at the freezing point of water ( 0 ° c . ), so that , when the cylindrical roller bearing is in operation , the situation is ruled out where the hollow rollers are deformed in a nondesirable way due to external temperature influences and to an associated automatic transition from the austenitic high - temperature phase of the shape memory alloy into its martensitic low - temperature phase , or vice versa . however , the respective transition temperatures of the shape memory alloy can be set individually and can thus be adapted correspondingly to the operating conditions of the roller bearing which are to be expected in each case . thus , the radial roller bearing designed according to the invention , with raceway rims which are continuous both on the outer and on the inner bearing ring , has the advantage , as compared with the identical radial roller bearings known from the prior art , that , by the cage for the roller rolling bodies being formed from hollow rollers consisting of a shape memory alloy , it has a simply mountable cage which both withstands high circumferential loads and , by the hollow rollers also rolling on the raceways of the bearing rings , reduces the frictional wear between the roller rolling bodies and the cage to a minimum . simultaneously , the hollow rollers ensure at any time a reliable guidance of the roller rolling bodies in the bearing and have an impact - and vibration - damping action , by virtue of which impacts occurring upon the entry of the roller rolling bodies into the load zone of the bearing or other vibrations of the roller rolling bodies are minimized . a preferred embodiment of the radial roller bearing designed according to the invention is explained in more detail below with reference to the accompanying drawings , in which : fig1 shows a side view of a radial roller bearing designed according to the invention with a partial break ; fig2 shows an enlarged illustration of a partial cross section through a radial roller bearing designed according to the invention . a radial roller bearing 1 designed as a cylindrical roller bearing is clearly apparent from fig1 and 2 and consists essentially of an outer bearing ring 2 and of an inner bearing ring 3 and also a number of roller rolling bodies 4 which are arranged between the bearing rings 2 , 3 and which roll on raceways 9 , 10 , delimited laterally by two continuous rims 5 , 6 and 7 , 8 , of the outer bearing ring 2 and of the inner bearing ring 3 and are guided at uniform distances from one another by means of a cage . it is likewise apparent from fig1 and 2 that the cage of this radial roller bearing 1 is formed , according to the invention , by individual hollow rollers 11 consisting of a shape memory alloy which are arranged in each case between two roller rolling bodies 4 and which , as indicated in fig1 , when the radial roller bearing 1 is assembled , are deformed elliptically in cross section to the dimension of the free space 12 between a rim 6 of the outer bearing ring 2 and a rim 8 of the inner bearing ring 3 and can be inserted into the radial roller bearing 1 through the free space 12 between these rims 6 , 8 of the bearing rings 2 , 3 . the broken partial view in fig1 in this case makes it clear that these hollow rollers 11 , after insertion into the radial roller bearing 1 , automatically assume , when a predetermined temperature is reached , their original shape in which the hollow rollers 11 have the same outside diameter and the same length as the roller rolling bodies 4 of the radial roller bearing 1 . the hollow rollers 11 are designed in cross section with a thin - walled material thickness , so that the hollow rollers 11 , on the one hand , can withstand even high circumferential loads and , on the other hand , have the necessary elasticity in order to damp correspondingly both the impacts occurring upon the entry of the roller rolling bodies 4 into the load zone of the radial roller bearing 1 and other vibrations of the roller rolling bodies 4 . fig1 and 2 also reveal , merely in outlines , that the hollow rollers 11 consisting of a shape memory alloy and of a nickel / titanium alloy are designed with a two - way characteristic which is easily deformable in its martensitic low - temperature phase and assumes its original manufacturing shape during the transition to its austenitic high - temperature phase . both the martensitic low - temperature phase and the austenitic high - temperature phase of this shape memory alloy are in this case fixed outside the typical operating temperatures of the radial roller bearing 1 in such a way that the low - temperature phase of the shape memory alloy lies at a temperature of − 77 ° c . corresponding approximately to the nitrogen boiling temperature , while the high - temperature phase of the shape memory alloy is arranged at a temperature of 0 ° c . corresponding for example to the freezing point of water . when a cylindrical roller bearing designed in this way is used in the drive of a machine tool , this rules out the situation where the hollow rollers 11 are deformed in an undesirable way due to external temperature influences and to an associated automatic transition from the austenitic high - temperature phase of the shape memory alloy into its martensitic low - temperature phase , or vice versa . at the same time , such a cylindrical roller bearing is demountable again as a result of cooling to the nitrogen boiling temperature and the associated elliptic reshaping of the hollow rollers 11 .