Hydraulic motor or pump with constant clamping force between rotor and port plate

A hydraulic piston motor or pump that comprises:

• a rotor defining an odd-numbered plurality of axially extending cylinders in each of which is disposed an associated piston, said rotor having a surface defining an annularly arranged plurality of uniformly spaced cylinder ports, each cylinder port being associated with one of said pistons and cylinders and being in fluid communication therewith;
• means operable with said rotor for causing said pistons to move in reciprocating fashion in said cylinders, said movement corresponding to compression and decompression strokes of said pistons;
• a port plate defining a flat surface facing said surface of said rotor, said flat surface defining two arcuate ports spaced from each other over two angular ranges and at least one fluid exchange port positioned in one of said angular ranges, said port plate being adapted for fluid communication with said rotor such that said cylinder ports successively register with said arcuate ports and said at least one exchange port as said rotor rotates, such that at substantially the same time as each of said cylinder ports begins to register with one of said arcuate ports during the decompression stroke of its associated piston another of said cylinder ports begins to register with the other of said arcuate ports during the compression stroke of its associated piston, and such that said at least one exchange port is separated from said arcuate ports by distances ensuring that none of said cylinder ports simultaneously registers with an arcuate port and said at least one exchange port, said port plate being positioned with respect to said rotor such that each of said cylinder ports registers with said at least one exchange port after it departs from registration with said one arcuate port but before its associated piston completes its decompression stroke.

A hydraulic piston motor or pump that comprises:

• a generally cylindrical rotatable member defining an odd-numbered plurality of axially extending cylinders in each of which is disposed an associated piston, said member having a surface defining an annularly arranged plurality of cylinder ports of uniform circumferential spacing, each cylinder port being associated with one of said pistons and cylinders and being in fluid communication therewith:
• means operable with said member for causing said pistons to move in reciprocating fashion in said cylinders, said movement corresponding to compression and decompression strokes of said pistons;
• a non-rotating port plate adapted for fluid communication with said rotatable member, said port plate defining a first flat surface facing said surface of said rotatable member and a second surface facing away from said rotatable member, said first surface defining two arcuate ports spaced from each other over two angular ranges, said first surface further defining at least one fluid exchange port positioned in one of said angular ranges, said port plate being adapted with respect to said rotatable member such that said cylinder ports successively register with said arcuate ports and said at least one fluid exchange port as said members rotates, such that at substantially the same time as one cylinder port begins to register with one of said arcuate ports during the decompression stroke of its associated piston, another of said cylinder ports begins to register with the other of said arcuate ports during the compression stroke of its associated piston, and such that said at least one fluid exchange port is separated from said arcuate ports by distances ensuring that none of said cylinder ports simultaneously registers with an arcuate port and said at least one fluid exchange port, said port plate being positioned with respect to said member such that each cylinder port registers with said at least one fluid exchange port after it departs from registration with said one arcuate port but before its associated piston completes its decompression stroke.