in the two embodiments shown in fig1 to 8 of a belt retractor with a belt tensioner , a belt reel 12 is rotatably mounted between the sides of a load - bearing housing 10 . the belt webbing 14 is wound on the belt reel 12 . the two embodiments shown of the belt retractor correspond in part to each other , so that the following description of the design of the belt retractor refers to both embodiments , insofar as no differences are indicated . on the left side of the housing 10 as shown in fig1 are a conventional and therefore not illustrated automatic blocking device with a trigger mechanism for blocking the belt reel and a winding spring which engages in the end of the belt reel 12 and which acts on the belt reel 12 in the winding direction of the belt . a pawl 16 blocks the rotation of the belt reel 12 in the unwinding direction of the belt , in a vehicle - sensitive and / or belt webbing - sensitive manner . on the opposite side of the housing 10 are the functional parts required for the belt tensioning function and a subsequent energy transformation function . these include a draw cable 18 , on which tensile force acts when the belt tensioning drive unit is triggered , for example through a pyrotechnical linear drive unit , an inertial mass , a pretensioned spring or the like . the draw cable 18 engages on the circumference of a cable reel 20 , around which it is placed with at least one winding . in accordance with the embodiment and fig1 and 2 , the cable reel 20 is located on a first cylindrical shoulder of a ratchet wheel 22 as part of a first coupling mechanism and positively coupled to the ratchet wheel 22 . in the embodiment shown in fig3 to 8 the cable reel 20 is connected to the ratchet wheel 22 as one piece . on the surface of its circumference the ratchet wheel 22 has four swivel - mounted pawls 24 spaced in the direction of the circumference . the pawls 24 are offset in pairs by half a tooth pitch in relation to a 90 ° pitch in order to guarantee secure coupling engagement . leaf springs 28 are attached to a disk 26 to stress the pawls 24 radially inwards with respect to the ratchet wheel 22 , so that these can only swing out by overcoming the spring resistance . the disk 26 is concentrically located on the ratchet wheel 22 . the ratchet wheel 22 is rotatably mounted on one end turned towards the belt tensioner of a torsion bar 30 which is located coaxially in the interior of the belt reel 12 . an inner wheel 32 is formed as one piece with a cylindrical wheel 32a which encompasses the ratchet wheel 22 with an internal coupling toothing allocated to the ratchet wheel 22 and which is coaxially arranged with this around the torsion bar 30 and is positively connected to the torsion bar 30 . the pawls 24 are swivel - mounted on the surface of the circumference of the ratchet wheel 22 in such a way that at a certain rotational acceleration of the first ratchet wheel 22 and the connected cable reel 20 they swing out , engage in the internal coupling toothing of the inner wheel 32 and thus couple the cable reel 20 to the belt reel 12 via the inner wheel 32 and the torsion bar 30 . on its external surface shell the inner wheel 32 has external coupling toothing in the form of saw - toothed gearing , whereby fig1 only shows some of the teeth . around the inner wheel 32 is an outer ring 40 with internal coupling toothing in the form of saw - toothed gearing , said ring being located in a bearing device connected with the housing 10 . the internal coupling toothing is coarser than that of the external gearing ( cf . fig4 to 8 ). the teeth of both coupling units are arranged at such an angle that in spite of the contact between the units these slide against each other without torque transmission when the belt is tensioned , engage when the belt webbing is unwound and securely couple the inner wheel 32 and the outer ring 40 with each other . on the side facing the housing 10 , the outer ring 40 has a radial cam 42 , which engages the pawl 16 when the outer ring 40 rotates in the belt unwinding direction and moves said pawl downwards into an inactive position . the blocking mechanism is thus disabled . in addition , the outer ring 40 has a limit stop part 44 on the surface of its circumference . the housing 10 has a limit stop 46 corresponding to this limit stop part 44 on its side facing the belt tensioner ( cf . fig5 ). between the limit stop part 44 and the limit stop 46 is a pressure spring 48 by means of which the outer ring 40 is prestressed in a direction leading away from the limit stop 46 . when the inner wheel 32 engages in the outer ring 40 , the latter is rotated against the resistance of the pressure spring until the limit stop part 44 strikes the limit stop 46 and any further rotation of the outer ring 40 is blocked . at its axial end facing away from the belt tensioner , the torsion bar 30 has a knurled head piece 50 which is inserted in a suitably shaped recess 52 of the belt reel 12 to form a positive connection . the belt reel 12 consists essentially of two lateral flanges 12a , 12b and an essentially hollow cylindrical shell 12c , which has a slot for the passage of the belt webbing 14 to be wound on the belt reel 12 , said slot not being illustrated here . the torsion bar 30 extends through the hollow cylindrical interior of the shell 12c of the belt reel 12 . the end of the belt webbing 14 forms a loop which is pushed on to the torsion bar 30 and which is connected to the belt reel 12 by the knurled head piece 50 in such a way that it cannot rotate . in idle state ( cf . fig2 and 5 ) the coupling toothings of the outer ring 40 and of the inner wheel 32 as well as the pawls 24 of the ratchet wheel 22 with their assigned inner coupling toothing are disengaged , so that the belt reel 12 with the torsion bar 30 can rotate unimpeded . as shall be explained later with reference to operation of the belt retractor , the inner wheel 32 is radially movably mounted in such a way that the belt tensioning process leads to a radially outward movement of the inner wheel 32 until the external coupling toothing engage in the internal coupling teeth of the outer ring 40 . to permit this radial movement , at least one radially yielding bearing which is assigned to the second coupling mechanism is necessary . the design of the bearings differs in the two embodiments shown . in the embodiment shown in fig2 several radially yielding bearings are provided for , but they do not all necessarily have to be present together in a belt retractor to allow the movement of the inner wheel 32 . in the embodiment shown in fig3 on the other hand , only one radially yielding bearing is provided for . in accordance with fig2 a radially flexible bearing is formed by the inner wheel 32 itself , which is manufactured from flexible plastic containing glass fibre reinforcement . the front side of inner wheel 32a as part of the inner wheel 32 has several recesses 110 , which can be designed as through or non - through recesses . furthermore , the belt reel 12 , in which the inner wheel 32 , as shown in fig2 can be partly accommodated , is radially yieldingly mounted . to this end , an integrally connected bearing extension 104 has several recesses 111 , which extend axially through the bearing extension 104 , so that the belt reel and thus all parts mounted in it can be moved radially on the belt tensioner side at a predetermined force . in the embodiment shown in fig2 in which the individual parts of the first and second coupling mechanisms as well as the torsion bar 30 are mounted in each other , the torsion bar 30 is thus also indirectly radially yieldingly mounted on the belt tensioner side . alternatively , however , it is also possible , as shown in fig3 to provide for a separate mounting for the torsion bar 30 by elongating the torsion bar extension 102 axially so far outwards that it is accommodated in a radially yielding bearing plate 70 shown in fig4 in a bushing 72 formed there in one piece . the bearing plate 70 is preferably manufactured from plastic , attached to the housing 10 and has several recesses 120 as well as an uppermost recess 120a . the ratchet wheel 22 is rotatably mounted on the external surface shell of the bushing 72 . the mounting of the belt reel 12 directly on the housing 10 can even be dispensed with on the belt tensioner side , since the belt reel 12 is indirectly held firmly in position by means of the inner wheel 32 , the torsion bar 30 and the bearing plate 70 . in both embodiments , therefore , the torsion bar 30 is mounted coaxially to the outer ring 40 in idle state , when the belt reel is not under stress and no tensioning is taking place , so that the external coupling toothing of the inner wheel 32 do not touch the internal coupling toothing of the outer ring 40 . this is illustrated in fig5 . fig6 shows the situation in the belt retractor with the normal blocking function when the pawl 16 engages in an appropriate toothed gear of belt reel 12 . the normal blocking function of the belt retractor is effected by a pulling movement in belt webbing 14 . when the belt webbing 14 is pulled upwards , this results in a torque in the inner wheel 32 , which partly supports itself on the pawl 16 and thus leads to a radial upward movement of the inner wheel 32 until its external coupling toothing supports itself in the internal coupling toothing of the outer ring 40 . the recesses 120 permitting this movement are also indicated in fig6 . when the inner wheel 32 is moved upwards , it is compressed so that an upper recess 120a even disappears in some cases . the successive sequences during activation of the belt tensioner drive unit are indicated by the numbered arrows in fig7 . when the belt is tensioned in the direction of arrow 1 , torque acts on the circumference of the cable reel 20 via the draw cable 18 in a familiar manner . through the resulting rotation of the cable reel 20 , first the pawls 24 of the ratchet wheel 22 are moved to engage with the internal coupling toothing of the inner wheel 32 , so that the cable reel 20 , the ratchet wheel 22 , the inner wheel 32 and the torsion bar 30 are fixedly coupled to each other . the rotation of the cable reel 20 is transmitted to the belt reel 12 by means of the torsion bar 30 . this belt reel is driven in winding direction 2 so that the loose belt is pulled out of the safety belt system and the belt webbing 14 is tensioned . after tensioning is completed , the two ratchet wheels 22 and 32 remain coupled to each other , so that the torsion bar 30 is still connected to the cable reel 20 in such a way that they cannot rotate in relation to each other . during belt tensioning , the force of the belt tensioner via the engaged first coupling mechanism produces a counterforce in accordance with arrow 3 in the belt webbing 14 , which leads to a radial movement of the torsion bar 30 on the belt tensioner side and thus of the inner wheel 32 in accordance with arrow 4 upwards against the restoring force occurring through the bearing plate 70 in the course of its yielding deformation . in fig4 it can easily be seen that the movement of the torsion bar 30 leads to an elastic deformation of the bearing plate 70 , which leads to the uppermost recess 120a disappearing in some cases through opposite walls being pressed against each other . this is also shown in fig6 to 8 . in the embodiment shown in fig2 the torsion bar 30 is also pressed upwards in the direction of the arrow when the belt is tensioned , causing the inner wheel 32 to be pushed upwards as well until its external coupling toothing strike the internal coupling toothing of the outer ring 40 . during this movement there is a deformation of the inner wheel 32 in the region of the recesses 110 and of the belt reel in the region of recesses 111 . although the coupling toothings engage with each other after the movement of the inner wheel 32 , the inner wheel can still rotate in the direction of the arrow 2 , since the saw - toothings allow a rotating movement in only one direction , i . e . in the opposite direction to the arrow 2 . during the short phase between the tensioning process and the subsequent forward movement of the occupant , the internal and external coupling toothing remain engaged , i . e . the second coupling mechanism remains in the locked position which it had adopted during the tensioning process . as soon as a forward movement of the occupant takes place , a pull effect takes place in the belt webbing 14 in the direction of the arrow 5 , which leads to a rotation of the inner wheel 32 in the direction of the arrow 6 . the outer ring 40 is also engaged directly , that is , without any time delay , through the coupling toothing . this causes the outer ring to rotate in the direction of arrow 6 together with its radial cam 42 until the latter is located above the pawl 16 , so that the pawl 16 cannot reach its lock - in position during the forward movement . this is shown in fig8 . the forward movement causes a high load level in the safety belt system , and a correspondingly high torque acts on the belt reel 12 through the belt webbing 14 . however , since the torsion bar 30 is interposed between the belt reel 12 and the inner wheel 32 , the torsion bar 30 can rotate and become plastically deformed . this plastic deformation uses up energy and the load peaks occurring in the belt webbing 14 are largely absorbed . through appropriate dimensioning and selection of material , the threshold at which plastic deformation of the torsion bar 30 begins as well as its further behaviour and the resulting damping effect can be adjusted practically infinitely . when the load on the belt webbing 14 is then removed , the coupling mechanisms disengage . the outer ring 40 is also turned back to its initial position by the spring located between the limit stop 46 and its limit stop part 44 , thus enabling the retracting function as well as the automatic blocking device . a further advantage of the shown belt retractor is that the torsion bar 30 , which acts as a force limiter , is only twisted to the extent that it also acts as a force limiter when prior tensioning has taken place .