Hydraulic motor having multiple speed ratio capability

A rotary fluid pressure device comprising a housing defining a fluid inlet port and a fluid outlet port;

• fluid pressure operated displacement means associated with said housing and including a first internally-toothed ring member, and a first externally-toothed star member eccentrically disposed within said first ring member for relative orbital and rotational movement therein, to define a plurality N+1 of expanding and contracting first fluid volume chambers in response to said orbital and rotational movements;
• commutating valve means cooperating with said housing to provide fluid communication between said inlet port and said first expanding volume chambers and between said first contracting volume chambers and said outlet port in response to one of said orbital and rotational movements;
• and shaft means for transmitting said rotational movement of said first star member;
• characterized by:
• (a) said fluid pressure operated displacement means including a second internally-toothed ring member, and a second externally-toothed star member eccentrically disposed within said second ring member for orbital and rotational movement therein, to define a plurality N+1 of expanding and contracting second volume chambers in response to said orbital and rotational movements;
• (b) connection means for connecting said second star member to said first star member for common orbital and rotational movement therewith;
• and
• (c) selector valve means operably associated with said first and second ring members and operable in a first low speed position to permit fluid communication to each of said first volume chambers and its corresponding second volume chamber, and a second high speed position in which said commutating valve means permits communication of pressurized fluid to only one of said first and second volume chambers and permits fluid communication between each of the other of said first and second volume chambers and a fluid recirculation chamber.