Fluid delivery devices using a pair of meshed external gears, in spite of no reciprocating component for fluid delivery enabling low rotational vibration, the high noise due to the trapping phenomenon, and the teeth bouncing contact due to undesired large backlash heretofore afforded in the gear manufacturing process, restrict the employments in the industrial field requiring quiet environment such as electric motor vehicles or room services. Accordingly, a gear pump or motor or a gear refrigerating compressor comprising a shaft gear and a driven gear meshed rotatably within a gear chamber formed with a housing and opposite side walls, which delivers fluids from a inlet chamber to a outlet chamber; a backlash of the meshed gears having fluid-leak-tight clearance; a closed chamber provided in a internal portion of at least a side wall; an opening provided on a side wall from which a communication passage extends to a closed chamber; and at least a elastic disc capsule contained in the closed chamber, comprising a pair of concaved elastic disc plate abutted and sealed against each other with gas inside, of which occupying volume varies elastically subject to the fluid pressure therein enabling to absorb or expel the squeezed fluid in the trapped interstice during the trapping period of the interstice, whereby the fluid entrapped in the interstices isolated by the fluid-leak-tight backlash suppressing the pressure transmission inwardly or outwardly, whereof volumetric variation during the trapping period is compensated by the compression or expansion of the elastic disc capsule, suppressing pressure pulse and air bubble generation and eliminating the teeth bouncing contact, achieving a low noise, low vibration and high efficiency gear pump or motor or refrigerating compressor.

The invention relates to a rotary piston engine (2) which operates as a pump, condenser or motor for a liquid or gaseous medium. The rotary piston engine (2) has a first gear (4) having a first central axis (I), a second gear (6) arranged opposite the first gear (4) and having a second central axis (II), and a drive shaft (8) having a third central axis (III) and a sliding plane (10, 12) fixedly connected to the drive shaft (8). The first central axis (I) and the second central axis (II) enclose an angle (3) which is not equal to 180. The third central axis (III) and at least one central axis (I, II) from the group comprising the first central axis (I) and second central axis (II) enclose an angle (1, 2) which is not equal to 0 or 90. The sliding plane (10, 12) and the central axis (I, II) are perpendicular to each other. The first gear (4) has a first end face (14) having a first has toothing (16) that h at least one first tooth (18), and the second gear (6) has a second end face (20) having a second toothing (22) that has at least one second tooth (24), wherein a first number of first teeth and a second number of second teeth differ from each other. The first tooth (18) and the second tooth (24) engage with each other in such a way that a working chamber (26) is formed by means of a meshing of the teeth (18, 24). A volume formed by means of the at least one working chamber (26) is changed by the meshing of the teeth (18, 24). The at least one working chamber (26) is delimited by a conically shaped inner wall (30) of a housing (28). The at least one working chamber (26) can be connected to a supply flow (40) and an outlet flow (42) for the medium. According to the invention, a component (4, 6) from the group comprising the first gear (4) and second gear (6) is coupled to the housing (28) such that a rotation of the drive shaft (8) causes only the components (4, 6) to tumble. The respective other components (4, 6) from the group comprising the first gear (4) and second gear (6) is coupled to the sliding plane (10, 12) such that the respective other component (4, 6) rotates and tumbles by means of a rotation of the drive shaft (8).