Variable displacement hydrostatic pump and neutral return mechanism therefor

A variable displacement hydraulic device of the type including a fluid displacement mechanism and means operable to vary the displacement of the displacement mechanism in response to rotation of a control shaft about its axis of rotation, from a neutral position to a first operating position, and from the neutral position, in an opposite direction, to a second operating position;

• control means operatively associated with said control shaft to rotate said control shaft between said first and second operating positions;
• a neutral centering mechanism operable to return said control shaft to said neutral position in the absence of actuation movement by said control means;
• said neutral centering mechanism being characterized by:
• (a) said control shaft defining a reference plane oriented generally perpendicular to an axis of rotation defined by said control shaft;
• (b) means defining first and second fixed stop surfaces disposed transversely adjacent said control shaft;
• (c) first and second substantially identical actuator members disposed about said control shaft, and being arranged generally in a mirror image relative to each other, about said reference plane, said first and second actuator members defining first and second movable stop surfaces, respectively, disposed to be in engagement with said first and second fixed stop surfaces, respectively, when said control shaft is in said neutral position;
• (d) spring means biasing said first actuator member counter-clockwise, biasing said first movable stop surface toward engagement with said first fixed stop surface, and biasing said second actuator member clockwise, biasing said second movable stop surface toward engagement with said second fixed stop surface;
• and
• (e) means operable to transmit counter-clockwise rotation of said control shaft into counter-clockwise rotation of said first actuator member, in opposition to the biasing force of said spring means, and means operable to transmit clockwise rotation of said control shaft into clockwise rotation of said second actuator member, in opposition to the biasing force of said spring means.