fig1 schematically illustrates a drive and a locking device , according to the present disclosure , for a sliding door having two leaves 8 , 8 ′. an electric motor 2 acts on a drive planetary gear set or drive transmission 3 , which sets a spindle 5 in rotation . a spindle nut 6 is mounted on the spindle 5 so as to be longitudinally displaceable but rotationally fixed . spindle nut 6 is connected to door leaf 8 by a fixed connection or connecting leaf 7 . symmetrically thereto , door leaf 8 ′ is connected to a connecting leaf ( not shown ) and another spindle nut ( not shown ) is connected to the drive . an end position of door leaves 8 , 8 ′ is illustrated in fig1 . a remaining door gap is closed off by rubber seals or the like ( not shown ). locking elements 12 , 12 ′ are arranged on each respective door leaf 8 , 8 ′ and move into a region of pivotable locking fingers 11 , 11 ′ which are rotationally fixedly arranged on a locking shaft 10 . the locking shaft 10 supports a gearwheel 9 which is operatively connected to a locking planetary gear set or locking transmission 4 . locking transmission 4 is connected to the drive transmission 3 by planet gears 13 . for example , if motor 2 is activated in an opening direction , it is not possible to move the door leaf 8 by engagement between the locking element 12 and the locking finger 11 . the result is that any rotation of the spindle 5 is prevented by fixed connection or connecting leaf 7 and the spindle nut 6 . as a result , it is also not possible for an outer wheel of the drive transmission 3 to be set in rotation . a motor torque sets the planet gears 13 in rotation , such rotation being transmitted to the locking transmission 4 . with a fixed transmission ratio of the locking transmission 4 , the gearwheel 9 is set in rotation , and with it the locking shaft 10 and the locking finger 11 . an identical operation applies to door leaf 8 ′. again , for example , as a result of the locking finger 11 pivoting out of locking element 12 , the door leaf 8 is released , resulting in the drive transmission 3 being set in motion and with it the spindle 5 , and the opening movement of the door begins . in order to limit the rotation of the locking shaft 10 to a practicable amount , stops are provided , and this may also ensure that full motor torque is available to provide drive after the unlocking process . the present disclosure is not limited to twin - leaf doors . for single - leaf doors , the second locking element 12 ′ can be provided on the vehicle body or on a wall of the vehicle body . during a closing process , the operations take place in the reverse order . when the door leaves 8 , 8 ′ have reached the end position as shown , the spindle 5 can be rotated no further and the locking mechanism 1 is locked by a torque dividing arrangement in the drive transmission 3 . fig2 , further illustrating the embodiment of fig1 , shows a connecting link 14 in which the locking element 12 is integrally formed . a purpose of the connecting link 14 is to prevent locking in those cases in which the movement of a door leaf 8 , 8 ′ is prevented , for example as a result of trapped persons or objects , in a position which does not correspond to the closed position . the connecting link 14 also prevents the locking axle or shaft 10 from pivoting , and the resulting reaction torque , which corresponds to the motor torque , can , for example , be used to detect an incidence of persons or objects being trapped . the locking device and the arrangement of the drive for twin - leaf doors in a region of a main closing edge has a functional advantage , and also an advantage that the important and relatively bulky components are provided at a point of the doorway or portal that is most accessible and where there is the greatest availability of space . this facilitates inspections , adjustments and repairs . the embodiment of fig1 and 2 shows a sliding door . it is possible to use the locking device or arrangement , according to the present disclosure , with swing and sliding doors in which the drive serves both to guide the door leaves 8 , 8 ′ longitudinally and to impart a swinging - out movement out of the plane of the portal . a brake or the like can be provided on the locking transmission 4 . the brake may be engaged at a very beginning of the opening movement so that the swinging - out movement takes place as a result of the reaction torque on the motor housing 2 a whereupon the brake is released , the locking action is released and , after unlocking is complete , the opening movement of the door leaves 8 , 8 ′ begins . it is not necessary for an engagement of the locking fingers 11 to be restricted by connecting link 14 to the closed end position . it is possible to detect the position of the door leaves 8 , 8 ′ in another way and to prevent the engagement by the brake on the locking transmission 4 in all positions other than the closed end position . this is advantageous for swing and sliding doors in which a brake as noted above is already provided . as briefly indicated above , it is not necessary for two planetary gear sets 3 , 4 to be used in order to provide the torque dividing arrangements . however , transmissions 3 , 4 are components that have robustness , compactness and large step - up or step - down transmission ratios which can be easily obtained within wide limits . fig3 to 8 show another embodiment of the present disclosure in which the very action of the door leaves entering the closed end position provides the locking action . in this embodiment , a simple sliding door is shown , although this embodiment can also include swing and sliding doors . thus , it is only necessary to match or refer to those elements of the locking device which interact with actuating elements on the door leaves to an oblique movement direction of the door leaves upon reaching the closed end position . in order to be distinguished from the first embodiment of fig1 and 2 , the reference symbols in fig3 - 8 have three digits , beginning at 101 . the locking device comprises a motor 113 which drives a sun gear 101 of a planetary gear set . the planetary gear set has an internal gear 104 which is rotationally fixedly connected to a gearwheel 105 having an outer toothing which itself meshes with a gearwheel 106 which in turn sets a spindle 107 in rotation . one nut 108 for each door leaf 109 is seated on the spindle 107 so as to be rotationally fixed . the nut 108 is displaced along the spindle or axle 107 as a result of the rotation of the spindle 107 , and in this way driving its respective door leaf 109 and displacing the latter between an open position and a closed position . door drives of this type are widely known and require no further explanation here . fixedly connected to the door leaves 109 are locking bolts 110 which , during the closing end movement of the door leaves 109 , pass by relatively short prongs and come into contact with relatively long prongs of latches 103 , and pivot the latches 103 into the closed position ( see fig6 ) counter to a force of springs 119 ( see fig6 ) which push the latches 103 into the open position ( fig5 ). in this embodiment , the springs 119 are coil springs which are loaded under tension . it is possible to provide rotary springs about pivot axes of the latches 103 , or one tension spring which can engage at corresponding points of those ends which are remote from prongs of the latches 103 . as a result of the pivoting movement of the latches 103 , as shown in fig5 and 6 , the movement of a locking element or lever 102 is permitted in a direction of the arrow f ( see fig6 ). the locking lever 102 is connected to a planet annulus of the planetary gear set ( see fig3 ). during a closing of the doors , after the latches 103 have pivoted , the locking lever 102 is pivoted into the position illustrated in fig7 in which it bears either against a housing of the planetary gear set or , by a shoulder , against a rear side of one of the latches 103 . when the locking lever 102 reaches its end position , the door drive is thus blocked and cannot be opened by any opening force , no matter how large , acting on the door leaves 109 . this is only possible by activating the motor 113 in the opening direction . since the motor torque is not capable of moving the door leaves 109 or their locking bolts 110 out of the prongs of the latches 103 , the planet gear , and therefore its part embodied as a locking lever 102 , rotates in the direction of the arrow f ′ in fig7 until the position illustrated in fig6 is reached . a stop of the planetary gear set 111 ( see fig3 ) then comes into contact with a catch 112 of the housing or vehicle body , and the full motor torque is then transmitted to the internal gear 105 and therefore via the gearwheel 106 to the spindle 107 . that initiates the opening of the doors with assistance from the spring 119 , which acts in the opening direction , of the latches 103 . the embodiment of fig3 - 8 can be modified in various ways . the prongs can be mounted differently or else can have a common pivoting point and can vacate the space for the locking lever 102 by a correspondingly angled design . the fact that other spring arrangements can be selected has already been explained further above . the design of the locking bolts 110 can be altered in various ways . for example , where the closing end movement of the door leaves 109 runs obliquely for the swing and sliding doors . it is possible to provide a design in the form of rollers to reduce friction , or to provide a resilient design etc . the force division or torque division of the motor 113 in the form of a planetary gear set , and the simple and robust design of the planet annulus , provide a compact and durable construction which also allows an emergency opening device . that is an essential prerequisite in many applications , to be easily attached by direct action on that part of the planet annulus which is designed as a locking lever 102 . the planet annulus need not directly support the locking lever or even be integrally formed with the latter even though this constitutes a simple and robust construction . it is also possible to provide , instead of the locking bolts 110 on each door leaf 109 , a contact track having a recess , on which contact track a roller , which is arranged on the end of the locking lever 102 , runs until it passes into the recess and thus allows the locking lever and therefore the planet annulus to pivot . in the last two possible embodiments , it is mechanically favorable and often requested by clients that the respective open / closed state is also maintained in the event of drive power being lost . this can be provided by a compression spring acting “ from the outside ” on the projecting part of the planet annulus . the compression spring comes to rest , in one of the two end positions , at the right , and in the other end position , at the left of the straight connecting line between its mounting point , which is fixed to the vehicle body , and the rotational axis of the planet annulus . there are of course other possibilities ; for example , a tension spring can engage on an end face of the planet annulus and run “ inward ”, or a spring can engage on another component of the drive . although the present disclosure has been described and illustrated in detail , it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation . the scope of the present disclosure is to be limited only by the terms of the appended claims .