Tensioning mechanism for tensioning an accumulator spring of a spring stored energy mechanism, the tensioning mechanism comprising - a tensioning gear which is coupled to the accumulator spring, - an intermediate shaft which is coupled to the tensioning gear, - an intermediate gear which can be driven by a tensioning motor, - a freewheel which is coupled to the intermediate gear, characterized by - a dog clutch which couples the freewheel to the intermediate shaft in order to tension the accumulator spring, decouples it from the intermediate shaft in the tensioned state of the accumulator spring, and has a first clutch block which is coupled fixedly to the intermediate shaft so as to rotate with it and a second clutch block which is connected to the freewheel, - the first clutch block being able to be displaced between two end positions along a rotational axis of the intermediate shaft, and having a plurality of first dogs which face the second clutch block and are arranged around the intermediate shaft, - the second clutch block having a plurality of second dogs which face the first clutch block, - and, in an intermediate position of the first clutch block which lies between the two end positions, each second dog protruding into an intermediate space between two first dogs which are adjacent with respect to it, having a stop face for one of said two first dogs which are adjacent with respect to it, on which stop face a side face of said first dog bears in the case of a rotation of the first clutch block with respect to the second clutch block in a first rotational direction about the rotational axis, and forming a ramp for the other of the two first dogs which are adjacent with respect to it, on which ramp said first dog can slide in the case of a rotation of the first clutch block with respect to the second clutch block in a second rotational direction about the rotational axis, which second rotational direction is opposed to the first rotational direction, - a coupling element which is connected to the first clutch block, is guided through a transverse opening in the intermediate shaft, which transverse opening runs perpendicularly with respect to the rotational axis of the intermediate shaft, and can be displaced in the transverse opening parallel to the rotational axis of the intermediate shaft between a first position which defines a first end position of the first clutch block and a second position which defines the second end position of the first clutch block. - a tensioning gear which is coupled to the accumulator spring, - an intermediate shaft which is coupled to the tensioning gear, - an intermediate gear which can be driven by a tensioning motor, - a freewheel which is coupled to the intermediate gear, - a dog clutch which couples the freewheel to the intermediate shaft in order to tension the accumulator spring, decouples it from the intermediate shaft in the tensioned state of the accumulator spring, and has a first clutch block which is coupled fixedly to the intermediate shaft so as to rotate with it and a second clutch block which is connected to the freewheel, - the first clutch block being able to be displaced between two end positions along a rotational axis of the intermediate shaft, and having a plurality of first dogs which face the second clutch block and are arranged around the intermediate shaft, - the second clutch block having a plurality of second dogs which face the first clutch block, - and, in an intermediate position of the first clutch block which lies between the two end positions, each second dog protruding into an intermediate space between two first dogs which are adjacent with respect to it, having a stop face for one of said two first dogs which are adjacent with respect to it, on which stop face a side face of said first dog bears in the case of a rotation of the first clutch block with respect to the second clutch block in a first rotational direction about the rotational axis, and forming a ramp for the other of the two first dogs which are adjacent with respect to it, on which ramp said first dog can slide in the case of a rotation of the first clutch block with respect to the second clutch block in a second rotational direction about the rotational axis, which second rotational direction is opposed to the first rotational direction, - a coupling element which is connected to the first clutch block, is guided through a transverse opening in the intermediate shaft, which transverse opening runs perpendicularly with respect to the rotational axis of the intermediate shaft, and can be displaced in the transverse opening parallel to the rotational axis of the intermediate shaft between a first position which defines a first end position of the first clutch block and a second position which defines the second end position of the first clutch block.