Neutral shifting mechanism for hydrostatic transmission

In a hydrostatic transmission comprising a radial piston pump and a radial piston motor coaxially positioned about a pintle, a shifting assembly comprising:

• a first annular track ring disposed around said pump;
• a second annular track ring disposed around said motor;
• and
• control means coupled to said first and second track ring for shifting and locking said hydrostatic transmission, said control means having a first position wherein circles defined by said second track ring and said pintle are concentric, and a second position wherein circles defined by said second track ring and said pintle are eccentric, said control means engaging said second track ring to secure said second track ring in said first position so that said radial piston motor provides a minimal resistance against rotation while in said first position, said control means for moving said first track ring to provide a continuously variable transmission while in said second position;
• wherein said second track ring defines a hole receiving a rod of said control means, said hole being elongated to allow said second track ring to vary its position between said first position and said second position, said second track ring also defining a slot, said rod having a cam structured and arranged to lock said second track ring in said first position and in said second position, said rod capable of rotating and moving said cam into and out of said slot thereby moving said second track ring and changing the location of said rod with respect to said elongated hole.

A hydrostatic transmission, comprising:

• a conduit means for fluid communication;
• a hydraulic pump coupled to an input shaft and in fluid communication with said conduit means, said hydraulic pump including a first rotatable cylinder unit comprising a plurality of first radial cylinders disposed about a first axis of rotation, a plurality of first pistons disposed within said first cylinders, each said first piston having an associated first slipper;
• a first track ring disposed around said first cylinder unit and guiding said first slippers, said first track ring determining the relative position of said first slippers with respect to said first axis of rotation;
• a hydraulic motor coupled to an output shaft and in fluid communication with said conduit means, said hydraulic motor including a second rotatable cylinder unit comprising a plurality of second radial cylinders disposed about a second axis of rotation, a plurality of second pistons disposed within said second cylinders, each said second piston having an associated second slipper;
• a second track ring disposed around said second cylinder unit and guiding said second slippers, said second track ring determining the relative position of said second slippers with respect to said second axis of rotation;
• a first control means coupled to said first and second track rings for moving said first track ring and changing the relative eccentricity of circles defined by said first track ring and said first axis of rotation;
• and
• a second control means coupled to said first and second track rings for shifting said second track ring and changing the relative position of circles defined by said second track ring and the axis of rotation of said second cylinder unit between a concentric position and an eccentric position;
• said first control means pivoting said first track ring about an axis defined by said second control means, said second control means being fixed in position relative to said first axis of rotation, and said second control means pivoting said second track ring about an axis defined by said first control means, a portion of said first control means fixed in position relative to said second axis of rotation.