11 34 is not central to the corresponding through bore 12 40 and or if one of the grooves is in the form of a cam for example then the transmission ratio between the first part 1 and the second part 66 of the transmission device can be defined arbitrarily within wide limits as a function of the rotational angle of the rotary elements 2 30 for low power ranges of the driving engine a relatively high transmission ratio can be selected for example and for high power ranges a relatively low transmission ratio can be selected with the apparatus shown as an example in fig1 and 2 the core 64 of the second part 66 of the transmission device and hence the control device as well can be adjusted by the control motor 130 in the regulated operating state both in the direction of the arrow 270 and in the opposite direction in the apparatus shown in fig4 and 5 an adjustment of the bowden cable core 64 of the second part 66 of the transmission device and hence of the control device 6 by the control motor is intended only in the direction of the arrow 270 in order to adjust the control device 6 via the control motor 130 for instance in the direction of the arrow 270 the third rotary element 80 must be rotated in a direction indicated by a further arrow 271 until the bearing face 96 comes to rest on the stop face 51 and the second rotary element 30 is rotated counter.