POSITIVE DISPLACEMENT HYDRAULIC MACHINES

Abstract: A positive displacement hydraulic machine is disclosed. The machine comprises a casing (10) in which there are formed overlapping bores (16) adapted to receive two gears for rotation in mesh with each other. One or more end covers (14) are provided which are located on the casing (10) by means of an integral non-circular spigot (56) which is a direct interference fit into the adjacent ends of the overlapping bores (16).

Description: POSITIVE DISPLACEMENT HYDRAULIC MACHINES This invention relates to positive displacement hydraulic machines of the kind comprising a gear pump or motor having a body in which there are formed overlapping bores within which two gears are disposed for rotation in mesh with each other. The body is adapted to accommodate the gears with minimal radial clearance at the tips of their teeth and minimal axial clearance at their end faces. The body comprises a casing•with two end covers in which there are mounted bearings for supporting two parallel shafts carrying respective gears, at least one of the covers being separate from the casing to enable the machine to be assembled and being secured to the casing as by set-screws. One end of one of the shafts projects from the body and constitutes the power input in the case of a pump and the power output in the case of a motor. It is essential for efficient high pressure performance that the bearings are assembled and held in accurate alignment. This has usually been achieved hitherto by fitting dowels between the casing and the or each separate end cover but these complicate the manufacturing and assembly procedures. It has also been proposed, in GB 2247923A, to locate the or each separate end cover accurately on the casing by forming a peripheral non- circular spigot on the adjacent end face of the casing which is a close fit in a peripheral mating recess formed in the cover. This complicates the manufacturing procedure by requiring additional accurate machining of both the casing and the cover. It is an object of the present invention to achieve accurate alignment in a simpler manner. The invention comprises a positive displacement hydraulic machine comprising a body in which there are formed overlapping bores adapted to receive two gears for rotation in mesh with each other and one or more end covers adapted to be located on the casing by means of an integral non- circular spigot which fits directly into the adjacent ends of the overlapping bores. Preferably, the spigot has an end profile which comprises portions of two overlapping circles smoothly interconnected by arcs to form a waisted shape approximating to a figure of eight. Whilst the spigot may be a close clearance fit in the adjacent ends of the overlapping bores, preferably it is an interference fit therein. Preferably, also, radius means are provided between the inner end face of the cover and the spigot formed thereon, and chamfer means for accommodating the radius means and facilitating press-fitting of the cover into the casing are provided at the adjacent ends of the overlapping bores. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is an end elevation of the open end of a gear pump casing with one integral end cover; Figure 2 is an enlargement of the area circled at 2 in Figure 1; Figure 3 is a section on the line 3-3 in Figure 1; Figure 4 is an end elevation of the inner face of a separate end cover for the casing; and Figure 5 is a section on the line 5-5 in Figure 4. Referring now to the drawings, a gear pump body comprises a casing 10 with an integral end cover 12 and a separate end cover 14. As shown in Figure 1, overlapping parallel bores 16 formed in the casing 10 with their centre-lines in a plane 18 are intersected by parallel troughs 20 and 22 formed symmetrically about a plane 24 perpendicular to the plane 18, the trough 20 being deeper that the trough 22. An inlet port 26 having its centre-line in the plane 24 communicates with the trough 20, and an outlet port 28 likewise having its centre-line in that plane communicates with the trough 22. The casing 10 has a flat end face 30 in which there are formed four tapped holes 32 and an asymmetrical groove 34. Parallel blind bores 36 which are not quite co-axial with the overlapping bores 16 are formed in the casing 10 for the purpose of accommodating bearings for one end of the shafts carrying the gears which are disposed, in use, in the bores 16. Chamfer means 38 are provided at the open ends of the overlapping bores 16 and are discontinuous at respective points on the bores (one of which points is best seen in Figure 2), the discontinuities comprising circumferentially short (say 1 millimetre) integral projections 40 and 42. As shown in Figure 4, the separate end cover 14 has a non- circular spigot 50 formed on its inner end face 52, the end profile of the spigot comprising portions of two overlapping circles 54 smoothly interconnected by arcs 56 to forma waisted shape approximating to a figure of eight. These portions are a light interference fit of, say, 50 microns directly into the open ends of the overlapping bores 16 formed in the casing 10. Radius means 58 small enough to be accommodated within the space defined by the chamfer means 38 are provided between the inner end face 52 of the cover 14 and the spigot 50 formed thereon. The cover 14 has formed in it four clearance holes 60 adapted to be aligned with the four tapped holes 32 formed in the casing 10. Parallel bores 63 and 64 which are adapted to be accurately aligned with the parallel bores 36 are formed in the cover 14 for the purpose of accommodating bearings for the other end of the shafts carrying the gears which are disposed in the overlapping bores 16. The bore 62 is blind but the bore 64 passes completely through the cover 14 to enable one end of the associated shaft to project from the gear pump body so as to constitute the power input, the bore 64 being adapted to house oil seal means. The pump is assembled by mounting the bearings in the bores 36, 62 and 64 and the oil seal means in the bore 64, locating one end of the shafts in the bearings mounted in the bores 36, placing an O-ring in the groove 34, fitting the cover 14 over the other end of the shafts, and inserting four set-screws through the holes 60 into engagement with the holes 32. Tightening of the set-screws causes the spigot 50 to make a press fit into the adjacent ends of the overlapping bores 16, facilitated by the chamfer means 38, so that the bores 32, 62 and 64 are both accurately and firmly aligned; the O-ring in the groove 34 is compressed to seal the joint between the flat end face 30 of the casing 10 and the inner end face 52 of the cover 14; and the projections 40 and 42 are deformed so as to block the arcuate leakage paths from the outlet side to the inlet side of the pump which would otherwise exist between the chamfer means 38 and the radius means 58. The end profile of the spigot 50 needs not conform to the preferred shape described and illustrated herein but it must make close clearance fit, or, preferably, an interference fit with the open ends of the overlapping bores 16 in the casing 10. The projections 40 and 42 can be provided on the radius means 58 instead of on the chamfer means 38. The invention is equally well applicable to a hydraulic gear motor as to a gear pump.

Claims: CLAIMS : 1. A positive displacement hydraulic machine comprising a body in which there are formed overlapping bores adapted to receive two gears for rotation in mesh with each other and one or more end covers adapted to be located on the casing by means of an integral non-circular spigot which fits directly into the adjacent ends of the overlapping bores. 2. A machine according to claim 1 in which the spigot has an end profile which comprises portions of two overlapping circles interconnected by arcs to form a waisted shape. 3. A machine according to claim 1 or claim 2 in which the the spigot is an interference fit in the adjacent ends of the overlapping bores. 4. A machine according to any preceding claim in which the inside corner where the base of the spigot meets the end cover is radiussed and the outside corner where the overlapping bores meet the casing is correspondingly truncated so as to accommodate the radius and facilitate press-fitting of the cover into the casing. 5. A positive displacement hydraulic machine as described herein with reference to and as illustrated in the accompanying drawings.

Inventors: PEACH RICHARD GUY, SYKES JEREMY ARTHUR, WYNN BARRY, PEACH, RICHARD, GUY, SYKES, JEREMY, ARTHUR, WYNN, BARRY
Applicants: BROWN DAVID HYDRAULICS LTD, PEACH RICHARD GUY, SYKES JEREMY ARTHUR, WYNN BARRY, DAVID BROWN HYDRAULICS LIMITED, PEACH, RICHARD, GUY, SYKES, JEREMY, ARTHUR, WYNN, BARRY
Application year: 1996
Main classification: F04C2
IPC codes: F04C2