GB2118259A

GB2118259A - Alignment of bearing surfaces in two-part casings

Info

Publication number: GB2118259A
Application number: GB08307769A
Authority: GB
Inventors: Ian Trevor Bristow
Original assignee: Hobourn Eaton Ltd
Current assignee: Hobourn Eaton Ltd
Priority date: 1982-04-05
Filing date: 1983-03-21
Publication date: 1983-10-26
Also published as: GB8307769D0

Abstract

Two casing parts 14, 15 which abut axially and which provide respective bearing surfaces for a shaft have respectively four bosses 21 and four lugs 20 for fixing screws 23. Alignment of the bearings is provided for by cutting the bearing surface in part 14 and cutting radially outwardly-facing cylindrically curved surfaces 26 at the outer edge portions of the bosses 21 adjoining the axial abutment face of the casing part 14 without altering the position of part 14 relative to the cutting centre between the two cutting operations, and by cutting the second bearing surface in part 15 and cutting radially inwardly- facing cylindrically-curved surfaces 29 adjacent the outer edge portions of the lugs 20 adjoining the axial abutment face of part 15 without altering the position of part 15 relative to the cutting centre between the two cutting operations, the surfaces 26 and 29 having substantially the same diameter and preferably engaging each other in an interference fit. <IMAGE>

Description

SPECIFICATION Alignment of bearing surfaces in two-part casings This invention relates to a method of securing alignment of bearing surfaces in two-part casings, and has a particularly useful but by no means exclusive application in casings for rotor pumps, sometimes known as N(N + 1) type pumps. Where the axial length of the pump is not of critical concern, the axial length of the bearings for the drive shaft can be selected to provide a substantial tolerance on the alignment of the bearing surfaces in the two parts without imposing undue loads on the bearings, but if the axial space available is limited, and it becomes necessary to reduce the bearing length, then a reduced tolerance on alignment becomes an important factor in keeping the loads on the bearings within acceptable limits.

According to this invention there is provided a method of forming two aligned cylindrical bearing surfaces in the respective parts of a two-part casing, which parts are to fit together axially, comprising cutting in one of the parts one of the bearing surfaces and a circumferentially discontinuous radially-outwardly facing locating surface at the outer edge of the part which is to fit against an edge of the other part, without altering the position of said one part relative to the cutting centre between the two cutting operations, and cutting in said other part the second bearing surface and a circumferentially discontinuous radially inwardly facing surface at said edge of the other part without altering the position of said other part between the two cutting operations, said locating surfaces of the two parts being circumferentially disposed for mutual engagement and having substantially equal diameters.

The locating surfaces on the two parts determine the relative radial positions of the two parts, and the tolerances on the diameters of these two parts determine the tolerance on the alignment of the bearing surfaces.

Preferably, the diameters of the locating surfaces are such as to produce an interference fit between the two parts.

In preferred embodiments of the invention, one or both of said parts have a plurality of circumferentially spaced lugs or bosses and said locating surfaces are cut on the radially outer portions of said lugs or bosses.

In one arrangement according to the invention, te portion or portions of said other part in which the radially inwardly facing locating surface is formed project axially beyond the said locating surface on said one part and are deformed into radially putwardly facing grooves on said one part.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows diagrammatically in axial section a rotor pump, Figure 2 is an external side elevation of the pump and illustrates one application of the invention to the pump of Fig. 1, Figure 3 is an end view of the pump of Fig.

2, Figure 4 is a fragmentary sectional view on the line 4-4 of Fig. 3, and Figure 5 is a view corresponding to Fig. 4 of a modification.

Referring first to Fig. 1 the lobed inner rotor 10 of a rotor pump is secured on the pump shaft 11 and drives the surrounding eccentrically disposed lobed outer rotor 1 2 to produce a pumping action in the known manner. The two rotors are accommodated in a cylindrical chamber in a first casing part' 1 4 and the chamber is closed off by a second casing part in the form of an end plate 1 5. The pumping action gives rise to a force on the shaft at right angles to the shaft axis, and bearing surfaces 16, 1 7 for the shaft to take this force are formed respectively in the end portion 1 8 of casing part 14 and in the end plate 1 5.

Referring now to Figs. 2 and 3, the end plate 1 5 has four circumferentially spaced lugs 20 which are respectively axially aligned with four bosses 21 on the outer surface of the casing part 14 and which are relatively flimsy. Screws 23 extend through holes in one diametrically opposite pair of lugs and engage in threaded holes in the associated bosses 21. Holes extend through the other two lugs and the aligned bosses and are for accommodating bolts to secure the pump to a mounting on, say, an internal combustion engine.

To ensure the alignment of the two bearings for the shaft 11, the bearing surfaces 16, 1 7 and surfaces for locating the casing part 1 4 and end plate 1 5 relative to each other are formed by a method according to the invention. The casing part 14 is secured with respect to a cutting centre and the cylindrical bearing surface 1 6 is cut, and with the position of the casing part unchanged a discontinuous radially-outwardly facing locating surface is formed by cutting a shoulder 25 on each of the bosses at its radially outer edge adjoining the end plate 15, each shoulder providing an arcuate radially-outwardly facing locating surface 26 centred on the axis of the bearing surface 16.

Similarly bearing surface 1 7 in the end plate 1 5 is cut with the end plate fixed in position relative to the cutting centre, and without changing these rel;ative positions a flat axially facing surface 28 is machined over the whole of the annular face of the end plate and outward beyond the annular face to a position a short distance from the tips of the lugs 20, so that each lug provides a short, cylindrically curved, radially-inwardly facing surface 29 centred on the axis of the bearing surface 17, and these inwardly facing surfaces together form a discontinuous locating surface which is an interference fit with the complementary locating surface on the bosses.

Owing to the relatively flimsy form of the lugs 20, their interference fit with the bosses 21 does not lead to any distortion of the casing part 1 4 or end plate 1 5 or any other part of the pump.

In a modification illustrated in Fig. 5, the end plate 1 5 is secured to the casing part 1 4 by deforming an axial extension 30 of the outer edge portion of the lug beyond the position of the interference fit into a radiallyoutwardly facing groove 31 in the complementary boss.

Claims

1. A method of forming two aligned cylindrical bearing surfaces in the respective parts of a two-part casing, which parts are to fit together axially, comprising cutting in one of the parts one of the bearing surfaces and a circumferentially discontinuous radially-outwardly facing locating surface at the outer edge of the part which is to fit against an edge of the other part, without altering the position of said one part relative to the cutting centre between the two cutting operations, and cutting in said other part the second bearing surface and a circumferentially discontinuous radially inwardly facing surface at said edge of the other part without altering the position of said other part between the two cutting operations, said locating surfaces of the two parts being circumferentially disposed for mutual engagement and having substantially equal diameters.

2. A method as claimed in claim 1, wherein the diamters of the locating surfaces are such as to produce an intereference fit between the two parts.

3. A method as claimed in claim 1 or claim 2 wherein one or both of said parts have a plurality of circumferentially spaced lugs or bosses and said locating surfaces are cut on the radially outer portions of said lugs or bosses.

4. A method as claimed in any one of claims 1 to 3, wherein the portion or portions of said other part in which the radially inwardly facing locating surface is formed project axially beyond the said locating surface on said one part and are deformed into radially outwardly facing grooves on said one part.

5. A method of forming two aligned cylin drical bearing surfaces in the respective parts of a two-part casing substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.