drum 17 which narrow gap can serve to compensate for any manufacturing tolerances as shown in fig2 formed on the peripheral edge of the lower end face of the cable drum 17 is a radially protruding circumferential protrusion 23 which in the illustrated position of the cable drum 17 bears against the inner peripheral edge of the seal 30 fig1 or slightly overlaps the latter and thus completes the sealing of the worm wheel 10 with respect to the gear housing section 6 as shown in fig2 according to the invention the cable drum 17 engages directly in the worm wheel 10 by means of the claws 19 20 according to the invention no additional damping elements for example deformable rubber blocks are thus required in order to dampen the driving torque of an electric motor this simpler and more cost effective design is a direct consequence of the fact that according to the invention on account of the considerably smaller gear ratio of the worm gear and of the correspondingly smaller diameter of the cable drum 17 compared to the previously known prior art the maximum driving torque of an electric motor according to the invention can be selected to be considerably smaller fig3 shows in a perspective exploded view the worm wheel and the cable drum of fig2 as shown in fig3 the two recesses 13 14 lie on diametrically opposite sides of the through opening 16 each of the recesses 13 14 is formed by two peripheral walls running concentrically with respect to the through opening and by two side walls which connect said peripheral walls to one another and extend.