The patent literature about DC permanent magnet torque motor at home and abroad mainly focuses on the design of motor structure and slot number, and its development trend is to make this kind of torque motor more compact in structure and larger in torque. Among them, U.S. Pat.No. US5990584 (publication date:1999-1-23) designed a permanent magnet DC torque motor, the stator of which was installed in a cantilever on a base and nested in a cup-shaped rotor. Its permanent magnet is wrapped inside the rotor, and the stator core is directly wound into a net with coils, which can be processed into sheet or thin plate shape. The pole piece has a shortened gap between the surface of the electrode shoe and the rotor magnet. The pole piece expands axially and laterally, and the expanded part of the axial pole piece can provide all the magnetic flux of a given motor without increasing the amperage of the current.
Domestic utility model 952 18685.3 (published date:1996.12.18) also relates to a large torque DC motor. The rotor adopts double positive slots, single-layer windings and at least six commutators, so that the magnetic axis intersection angle between rotor and stator magnetic field is less than right angle (30 ~ 45. It has the characteristics of large starting torque, easy processing, labor and material saving, convenient manufacturing and maintenance, reliable work, strong overload capacity and long service life.