Spring drive for a switching apparatus

A spring drive for a switching apparatus for medium voltage and high voltage, said spring drive comprising:

• a switch-on spring which is coupled eccentrically to a rotatably mounted switch-on shaft for driving the switch-on shaft in a rotation direction to switch on the switching apparatus,
• a large wheel which is connected to the switch-on shaft,
• a small wheel which interacts with said large wheel and can be driven by means of a drive device in order to stress the switch-on spring by rotation of the switch-on shaft in the rotation direction from an initial position in which the switch-on spring is at least partially relieved of stress, via a deadpoint position in which the switch-on spring is stressed, and
• a latching device which supports the switch-on shaft in a supported position which follows the deadpoint position in the rotation direction and releases the switch-on shaft to switch on the switching apparatus,
• the large wheel comprising a first tooth system having a gap at a point which is arranged adjacent to the small wheel when the switch-on shaft is supported on the latching device, the large wheel and the small wheel forming a wheel pair, the small wheel comprising a second tooth system, each tooth of said second tooth system comprising flanks converging toward one another radially on an outer side to a common edge for preventing mutual blocking of the large wheel and the small wheel after release of the switch-on shaft by the latching device,
• wherein flanks of a first tooth on the large wheel, which trails behind the gap in the rotation direction, converge toward one another radially on an outer side to a common tooth edge, and
• the first tooth trailing behind the gap has an involute shape on the flank which is loaded during switch on, and the flank which is unloaded during switch on has a flat flank part which converges toward the common tooth edge and is inclined with respect to a radial straight line through a center of the tooth.