Hydrodynamic retarder

A hydrodynamic retarder comprising:

• a primary blade wheel and a secondary blade wheel mounted for rotation relative to one another about a common axis, each of said primary and secondary blade wheels including an outer annular semi-toroidal blade ring and an inner annular semi-toroidal blade ring, the outer annular semi-toroidal blade rings facing one another and cooperating to define an outer toroidal working circuit capable of being filled with a working fluid, the inner annular semi-toroidal blade rings facing one another and cooperating to define an inner toroidal working circuit disposed within the outer toroidal working circuit and capable of being filled with a working fluid, the outer annular semi-toroidal blade rings including blades inclined in a first direction relative to an axial plane, the inner annular semi-toroidal blade rings including blades inclined in a second direction relative to an axial plane;
• primary shaft means connected to said primary blade wheels for rotation therewith;
• secondary shaft means connected to said secondary blade wheel for rotation therewith;
• working fluid means for selectively filling and emptying said inner and outer toroidal working circuits with a working fluid suitable for coupling said primary blade wheel to said secondary blade wheel for the transfer of energy therebetween;
• the facial surface area and the blade size and inclination of the outer annular semi-toroidal blade rings being selected with respect to the facial surface area and the blade size and inclination of the inner annular semi-toroidal blade rings such that the energy transfer of the outer toroidal working circuit is approximately equal to the energy transfer of the inner toroidal working circuit, and the energy transfer between said primary and secondary blade wheels is approximately equal in both directions of relative rotation.