Image Number 3 for United States Patent #4982819.
A hydrodynamic retarder suitable for use as a supplementary brake on trucks consists of a rotor wheel 20 fixed to an output shaft and a stator wheel 21. Movable blades 24 are attached to edges of blades 30 of the stator wheel 21 facing toward the rotor wheel 20. The movable blades 24 are biased by spring members to prevent air flowing into the stator wheel 21, but allow working oil to flow into the stator wheel 21. The movable blades 24 and spring members are provided internally of a torus defined by the stator wheel and provide an efficient hydrodynamic retarder of reduced weight and cost.