A variable displacement fluid machine comprising:
- an externally lobed first wheel mounted for rotation in a casing and at least partially received within an internally lobed second wheel eccentrically mounted with respect to said first wheel for rotation in said casing, the lobes of said first wheel engaging the lobes of said second wheel so that rotation of one of said wheels induces rotation of the other of said wheels and forms displacement chambers which progressively decrease and increase in volume on rotation of said wheels, a third wheel mounted for rotation in said casing and longitudinally adjacent said second wheel and concentric with said first wheel, said first wheel being longitudinally displaceably received into an axially extending passage in said third wheel, said passage being internally profiled to sealingly engage the lobed periphery of said first wheel and to close one end of said displacement chambers;
- said casing having two radially inwardly directed and circumferentially spaced sealing sections which are disposed longitudinally between said second and third wheels;
- the third wheel having a sealing surface which sealingly abuts said sealing sections and said third wheel sealingly abutting said second wheel radially inwardly of said sealing sections to form a nonrotatable outlet chamber and a nonrotatable inlet chamber which are sealed from each other and which are adjacent to and communicate with said displacement chambers, said outlet chamber communicating directly with displacement chambers which contract during rotation of said first and second wheels and said inlet chamber communicating directly with displacement chambers which expand during rotation of said first and second wheels;
- a fluid inlet port in the casing which communicates with the inlet chamber and a fluid outlet port in the casing which communicates with the outlet chamber;
- first and second control chambers provided in said casing and communicating with longitudinally opposed ends of the first wheel, said control chambers being subjected to variable fluid pressure by a control means to move said first wheel longitudinally, and a seal longitudinally slidably and sealingly engaging the lobed interior surfaces of said second wheel and sealingly engaging a second end of said first wheel received within said second wheel to close the end of each of said displacement chambers longitudinally remote from said inlet and outlet chambers whereby longitudinal displacement of said first wheel by varying the fluid pressure in the control chambers varies the capacity of the displacement chambers.