22 which is arranged at the tip of the first pivoting lever 8 i e at that end which is directed toward the second pivoting lever 18 when the first pivoting lever is located in the work position illustrated in fig1 in the same manner the second pivoting lever has a first opening 23 in its locking plate 24 the first pivoting lever 8 has a second opening 25 the second pivoting lever 18 has a second opening 26 arranged at both second openings 25 26 is a hydraulic cylinder 27 28 each which acts parallel to the pivot axes 9 19 i e perpendicularly of the plane of the drawing in the illustrations of fig1 and 2 when the first pivoting lever 8 has been moved into the work position and the second pivoting lever 18 has been moved into the parking position the first opening 21 of the first pivoting lever 8 and the second opening 26 of the second pivoting lever 18 are in alignment as can be seen in fig3 the cylinder 28 can then push a bolt 29 into the openings so that the first pivoting lever 8 and the second pivoting lever 18 are locked together this means that the first pivoting lever 8 is indirectly secured relative to the frame 2 the two pivot axes 9 19 and the locking point.