Patent-family-84569761

A measuring motor (2) is described comprising a star member (3) having a first number of outer teeth (17) and an inner bore (15), a ring member (4) having a second number of inner teeth (18), wherein the first number is smaller than the second number, a first plate and a second plate, wherein the star member (3) forms a first sealing zone with the first plate and a second sealing zone with the second plate, and the star member (3) is arranged to rotate and orbit around an axis of the ring member (4) and together with the ring member (4) and the plates forms pressure chambers.

In such a measuring motor leakages on the output side of the measuring motor should be reduced.

To this end the star member (3) comprises a ring groove (20) in at least one of the first sealing zone and the second sealing zone, wherein the groove (20) is connected to the inner bore (15) via a leakage path (21) and to at least one of the pressure chambers (8) at a time via a connection arrangement.