US3857326A - Rotary hydraulic machines - Google Patents

Abstract

A rotary hydraulic machine includes a plurality of pistons slidable in radial bores in a rotor which is mounted in a housing. A cam ring surrounds the rotor and has an internal cam surface engaged by the outer ends of the pistons. The cam ring is rotatable about an axis which is eccentric with respect both to the axis of the internal cam surface and the axis of the rotor. Means are provided for rotating the cam ring.

Description

- United States Patent 1191 Blandford Dec. 31, 1974 ROTARY HYDRAULIC MACHINES 3,122,104 2/1964 Byers, Jr. 91/482 3 196 B 9 47 [751 Gemge Alva Blandmrd, 31113519 111973 P1139 32; 91/472 Com/entry, England 3,626,810 12/1971 Morey 91/492 3,641,881 2/1972 Hashemi... 91/492 [73] Assgnee' P? Aemspace 3,657,971 4/1972 Freeman..... 91 /487 Birmingham, England [22] Filed: Aug 16, 1972 FOREIGN PATENTS OR APPLlCATIONS 51,532 10/1942, France 91/497 [21] App]. No.: 281,239

Primary Examiner-William L. Freeh [30] Foreign Application Priority Data Attorney, Agent, or Firm-Holman 8L Stern Aug. 17, 1971 Great Britain 38469/71 [57] ABSTRACT [52] US. Cl. 91/492, 91/497 A rotary hydraulic machine includes a plurality of [51] Int. C1 F04b 13/06 tons shdable 1n rad1a1 bores 1n a rotor which 1s [58] Field of Search 91/475, 492, 483

mounted 1n a housmg. A cam rmg surrounds the rotor and has an internal cam surface engaged by the outer [56] References Clted ends of the pistons. The cam ring is rotatable about an UNITED STATES PATENTS axis which is eccentric with respect both to the axis of 2,392,754 I/ 1946 Mercier 91/497 the internal cam surface and the axis of the rotor.

Ferris et a1 i Means are provided for rotating the cam ring 2,749,844 6/1956 Weisenbach et a1... 91/475 2,847,938 8/1958 Gondek 91/483 4 Claims, 5 Drawing Figures PATENTEU I974 3.857, 326

SHEET 10F 3 FIGJ PATENTEU UEE3 1 I974 SHEET 2 BF 3 IOOO 0 3V wmnmmwmm zoammmmzouw FIG S FRACTION OF FULL STROKE ROTARY HYDRAULIC MACHINES This invention relates to rotary hydraulic machines (i.e., pumps and motors) and has as an object to provide such a machine in a convenient form.

A machine according to the invention comprises a housing having an inlet and an outlet, a rotor mounted within the housing, a plurality of pistons Slidable in radial bores in the rotor, the said bores successively communicating, in use, with the inlet and the outlet, a cam ring surrounding the rotor and having an internal cam surface engageable by the pistons, the cam ring also having an external surface of revolution which engages a corresponding surface within the housing and the cam ring being rotatable within the housing about the axis of said outer surface which is eccentric with respect both to the axis of the cam surface and the axis of the rotor, and means for rotating the cam ring within the housing.

An example of a machine according to the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is alongitudinal section through a pump;

FIG. 2 is a section on line 2-2 in FIG. 1;

FIGS. 3 and 4 show diagrammatically the effects of cam ring movements, and

FIG. 5 shows a graph of precompression pressures in pumps according to the invention.

The pump has a housing having an inlet 11 and an outlet 12. Journalled in housing 10 is a rotor 13having a plurality of radial bores 14 (only one of which is shown) arranged in two rows A, B. Slidable in the bores 14 are pistons 15.

Inlet 11 opens into the space within the housing 10 surrounding the rotor 13, via a chamber 16 in which is a centrifugal impeller 17 secured to the rotor 13. Within the housing 10 are a pair of port plates 18, shown more clearly in FIGS. 3 and 4, having kidney ports 18a with which ports 19 in the rotor 13 successively communicate in use. Kidney port s 18a communicate with the outlet 12.

Surrounding the rotor 13 are a pair of cam rings 20, 21 respectively associated with the rows A,B, of bores 14. Cam rings 20, 21 have part cylindrical outer surfaces 20a, 21a which engage corresponding surfaces in the housing 10 and whose respective axes 22, 23 are the axes of rotation of the respective cam rings 20, 21. Axes 22, 23 are equispaced on opposite sides of the axis of the rotor 13. Cam ring 21 only is shown in FIG. 2, the relative position of cam ring 20 being indicated. Cam rings 20, 21 have respective inner cam surfaces 24, 25 engaged by the pistons, the respective inner cam surfaces 24, 25, being eccentric with respect to the respective axes 22, 23. The eccentricity of the cam surfaces 24, 25 is equal to the displacement of the axes 22, 23 from the rotor axis. In one angular position of the cam rings 20, 21 i.e. that shown in FIG. 2, the cam surfaces 24, 25 are concentric with the rotor 13.

Over a part of their outer surfaces, the cam rings 20, 21 are provided with gear teeth 26. The teeth 26 of both rings are engaged by rack teeth 27 on a stem 28 which extends through bore 29 in the housing 10 transtons 30, 31 being such that the cam rings are capable of approximately 50 rotation. The rings '20, 21 are initially set up so that the axes of the cam surfaces 24, 25 are coincident with the rotor axis for a given position of the stem 28. I

In use, with the surfaces 24, 25 eccentric to the rotor, the pump operates in a known manner to draw liquid in through inlet 11 and to discharge it under pressure through outlet 12. The strokes of the pistons 15 are variable by rotation of the rings 20, 21.

FIG. 3 shows the arrangement of port plate 18 and kidney port relative to the axis of the rotor 13 and the axis of rotation 22 of the cam ring 20 when it is required that cam ring 20 shall be rotated in a clockwise direction to increase the stroke of the pump. The axis of cam surface 24 is movable clockwise from a position 40, in which it is coincident with the rotor axis, to a position 41, in which the cam surface 24 has moved to the position indicated at 24a, the top dead centre point 42 on surface 24 moving along line 43. For a clockwise direction of rotation of rotor 13, inward movement of pistons 15 starts at an angular position of rotor 13 corresponding to the location for the time being of point 42. Clockwise movement of cam ring 20 decreases the angle between this rotor position and the rotor position at which ports 19, 18a intercommunicate.

Inward movement of pistons 15 is effective to compress the fluid only after the whole of the associated ports 19 is covered bythe port plate 18. Before ports 19 reach this position, inward movement of pistons 15 discharges fluid back to low pressure. It will be seen that in the arrangement of FIG. 3 movement of cam ring 20 by a substantial amount anticlockwise from its full stroke position 41 causes pistons 15 to discharge some of the fluid to low pressure, as aforesaid. The angle over which precompression of the fluid takes place does not, therefore, substantially alter during variation of the pump stroke. In addition, as pump stroke increases, the precompression stroke, that is the distance travelled by pistons 15 to precompress fluid after ports 19 have been shut off and before ports 19 communicate with port 18a, also increases. In these circumstances, however, by virtue of increased total swept volume of pistons 15, the volume swept by pistons 15 during precompression also increases. It can be arranged that the volume swept during precompression remains, over a significant part of the variation in pump stroke, a substantially constant fraction of the fluid volume which is within the bores 14 as ports 19 are shut off. FIG. 5 shows curves of the precompression pressure achieveable, plotted against the stroke of the pump for two values of the eccentricity of cam surfaces 24, 25 relative to the respective axes 22, 23. Curve A corresponds to an eccentricity of 0.50 inch and curve B to an eccentricity of 0. l 87 inch. The precompression pressure within bores 14, as ports 19 communicate with port 18a thus remains substantially constant over these parts of the pump stroke variation.

It will be understood that the above description applies equal to the cam ring 21 associated with the pistons 15 in row B.

FIG. 4 shows an arrangement in which the cam ring 20 is rotated anticlockwise to increase pump stroke, the rotor 13 moving clockwise, as before. In this case an increase in pump stroke results in an increase in the angle between top dead centre and the position at which ports 18a, 19 intercommunicate.

Since the ports 19 are covered by the port plate 18 during inward movement of pistons 15, in all conditions of pump stroke, the precompression angle'increases with increasing pump stroke. Moreover, as stroke is reduced there is an increasing amount of outward movementof pistons 15 while ports 19 are covered by plate 18. This outward movement causes initial decompression or sucking of fluid in the bores 14, tending to decrease the precompression pressure as pump stroke decreases. The combined effects of increased precompression angle and decreased sucking as pump stroke increases cause a substantial increase in precompression pressure. The arrangement shown in FIG. 4 is not, therefore, suitable if a substantially constant precompression pressure is required over a significant part of the pump stroke variation.

I claim:

1. A rotary hydraulic machine comprising a housing having an inlet and an outlet, a rotor mounted within the housing, a plurality of pistons slidable in radial bores in the rotor, thesaid bores successively communicating, in use, with the inlet and the outlet, a port plate fixed in the housing and engaged by the rotor to act as a valve to control communication between said bores in the rotor and the inlet and outlet, said rotor including ports communicating respectively with the bores and opening onto a face of the rotor which is engaged by said port plate, said port plate having a kidney-shaped port spaced from the edge of the port plate in the path of movement of the rotor ports thereover, by a distance greater than the width of each of said rotor ports, and a cam ring surrounding the rotor and having an internal cam surface engageable by the pistons, the cam ring also having an external surface of revolution which engages a corresponding surface within the housing, and the cam ring being rotatable within the housing about the axis of said outer surface, said outer surface being eccentric with respect both to the axis of the cam surface and the axis of the rotor, and means for rotating the cam ring within the housing, the cam ring being positioned so as to provide movement of said piston while said ports are shut, whereby, in use, there is a period in each revolution of the rotor when each port is shut off by the port plate so that liquid in the associated bore is subjected to a change of volume and pressure, said machine further including two cam rings arranged with the areas of their external surfaces equally spaced from the axis of the rotor, said axes lying in a common plane and which the rotor has two rows of radial bores slidably containing pistons engaged with the internal cam surfaces of the cam rings respectively.

2. A rotary hydraulic machine as claimed in claim 1 in which said means for rotating the cam ring comprises teeth on said external surface of the cam ring and a toothed gear element engaged with said teeth and movable relative to the housing.

3. A rotary hydraulic machine as claimed in claim 2 in which said tooth gear element comprises a rack longitudinally movable in a bore in the body.

4. A rotary hydraulic machine as claimed in claim 2 in which said toothed element is a rack which extends in a direction parallel to said common plane but perpendicular to said axis and engages the teeth on both cam rings.

Claims (4)

1. A rotary hydraulic machine comprising a housing having an inlet and an outlet, a rotor mounted within the housing, a plurality of pistons slidable in radial bores in the rotor, the said bores successively communicating, in use, with the inlet and the outlet, a port plate fixed in the housing and engaged by the rotor to act as a valve to control communication between said bores in the rotor and the inlet and outlet, said rotor including ports communicating respectively with the bores and opening onto a face of the rotor which is engaged by said port plate, said port plate having a kidney-shaped port spaced from the edge of the port plate in the path of movement of the rotor ports thereover, by a distance greater than the width of each of said rotor ports, and a cam ring surrounding the rotor and having an internal cam surface engageable by the pistons, the cam ring also having an external surface of revolution which engages a corresponding surface within the housing, and the cam ring being rotatable within the housing about the axis of said outer surface, said outer surface being eccentric with respect both to the axis of the cam surface and the axis of the rotor, and means for rotating the cam ring within the housing, the cam ring being positioned so as to provide movement of said piston while said ports are shut, whereby, in use, there is a period in each revolution of the rotor when each port is shut off by the port plate so that liquid in the associated bore is subjected to a change of volume and pressure, said machine further including two cam rings arranged with the areas of their external surfaces equally spaced from the axis of the rotor, said axes lying in a common plane and which the rotor has two rows of radial bores slidably containing pistons engaged with the internal cam surfaces of the cam rings respectively.

2. A rotary hydraulic machine as claimed in claim 1 in which said means for rotating the cam ring comprises teeth on said external surface of the cam ring and a toothed gear element engaged with said teeth and movable relative to the housing.

3. A rotary hydraulic machine as claimed in claim 2 in which said tooth gear element comprises a rack longitudinally movable in a bore in the body.

4. A rotary hydraulic machine as claimed in claim 2 in which said toothed element is a rack which extends in a direction parallel to said common plane but perpendicular to said axis and engages the teeth on both cam rings.

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