therein the motor shaft is extended to form a gear shaft along the inner surface of the gear wheel 1 spring elements 1 1 in the form of substantially tangentially extending segments are provided for stop absorption purposes in particular these spring elements 1 1 absorb a hard stop of the closing part which is to be driven when it reaches its end position along their end faces these segments merge integrally with the gear wheel 1 furthermore these segments can be elastically pushed in a radially outward direction into recesses 1 5 that are located between their tangentially formed end face junctions the degree of the elastic deformation is defined by limit stops 1 2 which are preferably integrally formed during injection molding as may be seen particularly in fig2 and fig4 the carrier 2 is inserted into the inner opening of the gear wheel 1 in order to facilitate an operational rotary drive of the carrier 2 the carrier 2 has cams 2 1 on its outer circumference which engage in its drive position with radially outwardly pointing indentations 1 3 in the gear wheel 1 these indentations 1 3 are arranged between the tangential end face side spring elements 1 1 such that in the absence of stop counter forces a positive rotary drive between the gear wheel 1 and the carrier 2 is ensured if the closing part runs against an obstacle or in particular against a limit stop e g in an upper closed position or a lower open position of a motor vehicle window the normal force sufficient for the positive rotary drive is exceeded when there is a relative movement between the.