US2348881A - Method of and apparatus for the - Google Patents

Description

May 16, 1944. H. BLOOD 2,348,831

MBTLLIOD OF AND APPARATUS FOR THE GENERATIVE .FORMATION OF SURFACES 0F OVATE SECTIONS Filed Feb. 19. 1941 ,s Sheets-Sheet 1 giwwm Harold L.Blood.

5 Sheets-Sheet 2 ERATIVE VATE SECTIONS H. L. BLOOD APPARATUS FOR THE GEN METHOD 0F AND FORMATION OF SURFACES OF 0 Filed Feb. 19, 1941 May 16, 1944.

y 1944. H. BLOOD METHOD OF AND APPARATUS FOR THE GENERATIVE FORMATION OF SURFACES OF OVATE SECTIONS Filed Feb. 19, 1941 5 Sheets-Sheet 5 Patented May 16, 1944 UNITED- STATES PATENT OFFICE METHOD OF AND "APPARATUS FOR THE GENERATIVEv FORMATION OF SURFACES OF OVATE SECTION Harold L. Blood, Worcester, Mass, assignor to The Heald Machine Company,

Worcester,

10 Claims.

The present invention relates: to the direct. generation (i. e., without resort to copying from a master or pattern). by machining, boring, grinding or the. like, of. exterior or interior surfaces that are. slightly ovate. or noncircular in cross section. Examples of. such surfaces are the. cylinder bores required for certain fluidmotors, pumps, compressors etc.. of the rotary type. viz: those. wherein. the usual. eccentrically-mounted rotor or drum has a diametrally slidable vane or piston. of substantially one-piece or constantlength construction. Ihe operation of such a vane requires. a cylinder bore of approximately the sectional contour defined by a symmetrical limacon curve which. is equi-metrical in all directions through. a point corresponding to the center of the eccentric drum or rotor, namely. the curve which is traced. by the ends of a series of equallength chords all passing through the same interior point, and whose perpendicular bisectors pass through. the. center of the inscribed circle.

For the formation of a bore surface of such curvature, it has heretofore been proposed to eccentrically rotate the cylinder in a lathe with its drum or rotor axis in alignment with. the lathe axis,v thus. to'obtain, by the horizontal. component of the cylinders eccentric motion, the reciprocation of a cutting, tool which engages the cylinder bore in the horizontal plane. of. said. lathe axis. Theoretically, this previously proposed method will cause the, desired non-circular curvature to be described. by the tool. point. on the eccentrically-rotating worksurface; but-in the practice of this method, great. difficulties are encountered in the cutting action. of. the tool.. One. of these difiiculties stems. from the off-center rotation of the work, which compels. the point of cutting to constantly shift between positions far above and far below the cylinder bore axis; these changes. of cutting level,. relative to: the concave. surface ofthe work, involve such extreme variations in the rake and clearance angles of the tool thatno uniformity of. cutting action is obtainable. Another difficulty of this previously proposed method is the relatively great amplitude: of reciprocatory tool travel, over a. distance which is double the eccentricity of thebore and drum axes, and thus, far in excess. of? the actual departure. of the desired curve from its inscribed.- circlethis involving periodically such rapid feeding movements of the tool into the surface of the rotating work that excessive. cuttingpressures and rapid tool Wear are inevitable.

It has. also been proposed to. hold thework. from rotation, and. to. machine its bore to the. desired 65,

non-circular cross-section by a rotary and slidably-mounted cutting tool which, in revolving. about an axis corresponding to that of the cylinders eccentric rotor or drum, is constrained to slide in and out, togive the tool pointa noncircular path of the desired curvature; But hereagain there are wide variations in the rake and clearance angles of the tool; moreover the tools cutting poi-nt. is compelled. to pass very rapidly over certain: portionsof the work surface and very' slowly over other portions: of the work. surface, so that no uniformity of cutting actiorr is obtainable. 1

My invention overcomes all. these difficulties;

- by machining or cutting the work bore to the;

desired. ovatesection: in a. manner which permits. the relative: rotation between tool and workpiece to take: place on. the true. axis of the workpiece. bore, and which. allows the tool to have an abso-- lutely' uniform cutting speed with no appreciable variations in its? rake and; clearance angles; moreover, the. reciprocation. of the tool is of. very small: amplitude, at notime exceeding. the maximum. departure of the desired section from its inscribed vcirclez. Other and. further objects and. advantages of my invention will more fully appear from the following detailed description, taken: in.

connection with the; accompanying illustrative drawings, in which Fig. 1. is. a. sectionalview showing: the essential elements of. a vane type. pump or compressor, when a constant-length: vane is used.

Fig. la is a view similar to Fig; 1, showing. a. slightly different vane construction.

Fig. 2 is a diagram illustrating the nature of the sectional contour required for a cylinder bore adapted to accommodate a van-e of the typeshow-n by Fig.1".

Fig. 2a is a similar diagram for a cylinder bore adapted to accommodate a vane of the type shown by Fig. 1a.

Fig. 3 is a schematic view, illustrating the principles of my generative method, as. applied to the machining. of. the; contour represented. by Fig.. 2.

Fig, 4 is a. view in front elevation of a. boring machine: organization arranged in. accordance with: my invention to: generate the desired. surface. contour.

Fig. 5 is a top plan view of themachine of Fig. 4.

Fig. 6 is a larger scale: fragmentary end elevation of said machine, as viewed from the right Fig. 4.

Fig. 7 is a sectional View, on the line 1-1 of Fig. 6.

Fig. 8 is a large scale front elevation of the tool head of said machine.

Fig. 9 is an end elevation of said head as viewed from the left, Fig. 8.

Like reference characters refer to like parts in the different figures.

I have shown very simply in Fig. 1, the elements of a vane type pump or ompressor having the conventional eccentric rotor or drum A, but the latters vane instead of being the well-known variable-length device for operation in a cylinder chamber of circular cross section, is a constantlength vane B slidable diametrically in said rotor. Such a constant-length vane B requires for its operation a cylinder chamber or bore whose interior boundary surface is slightly non-circular in cross section, the same being typified, for example, by the curve D (Fig. 2) of the'limacon order,

such as would be traced or generated by the terminal points a and b of a succession of equallength chords L, L,- etc. (corresponding to the length of the vane), all passing through the same point P (the center of the eccentric rotor) which is at a fixed distance R. from the center C of the inscribed circle E; as shown in Fig. 2, each chords perpendicular bisector Z passes through said center C.

My improved method-of generating the substantial equivalent of this cross-sectional contour D is depicted diagrammatically by Fig. 3, wherein the point P represents a crank which follows a circular path of radius R about a center C; this crank is shown in engagement with a suitable slot s of a lever f, pivoted to rock, in response to said cranks rotation, about a fulcrum point b; the lever 7 provides at its other end a plane surface-g, which is at a distance in from fulcrum point D. Cooperating with surface g is an arcuate surface J, provided by a slidably mounted bar 112. carrying a cutting tool whose point is indicated at t-the arrangement providing a spring 12 or the like by which to maintain contact of surface J with surface 9. The tool it is shown in operative relation to the bore W of a piece of work (such as a pump cylinder of the type shown by Fig. 1) which isrevolved about the axis of its bore at the same angular speed a that imparted to the crank P.

- The arcuate surface J, Fig. 3, is struck from a center oraxis J onsuch a radius (70) that the sum of the distances hand k is equal to one half the length and are identical, since Therefore in the angular position of parts shown by Fig. 3, the distance X between points I) and of the crank P and work W, will be caused,

by the movements of bar m in response to rolling of surface 9 on surface J, to vary its distance from the work center 0 in nearly the same proportion as the terminal point b of chord L varies its distance from center C in tracing the curve D,. Fig. 2.

The cross-sectional contour generated in the bore of rotating work W by the tool t may vary slightly from the curve D, because of the fact that the fulcrum point '0' is fixed rather than movable. But the error or deviation is wholly negligible in practice. Actually the angle Cb'P' has the same value as shown in Fig. 3 at four different points in each revolution of the crank, and at each of these points, as demonstrated above, the distance from o to t exactly equals the distance from C to b. This'equality also prevails each time the angle CbP' passes through zer0making six points wherethe correspondence isexact. At intermediate points the differ ences between the angle Cb'P' and CbP are so slight that the deviation from curve D of the contour produced by tool t is negligible, being well within practical working tolerances.

The adaptation of the principles above set forth to a machine for generating a surface of revolution having the desired non-circular crosssection, is shown by Figs. 4 to 9 inclusive. As shown in Figs. 4 and 5, said machine Provides a suitable base I, having longitudinal ways, not shown, for the support of a reciprocatory'table or slide 2. A bridge 3 spanning said ways and said table, supports a head or mounting 4 wherein is suitably journalled a work-rotating spindle 5; the latter carries at one end a suitable holder 6 in which the work W is chucked, and at the other end a pulley 1 which may be connected as shown by a belt 8 to a drive pulley 9 on the shaft I0 of a motor or other prime mover, employed for the rotation of the work W.

The bridge 3 also carries a suitable bracket ll, having spaced bearing portions l2 and I3 wherein are rotatably mounted the sleeves I4 and I5. Slidably received in' these rotatable sleeves is the polygonal end portion IE or an elongated shaft l6, said end portion l6 being slidable endwise through a gear I! mounted thereon and meshing with a gear 18 of the same size on spindle 5 -any suitable means, such as a fixed housing l9 secured to head 4, being employed to hold the gear II against shifting endwise with shaft'wlfi, thus to insure the latter's rotation at the same speed as spindle 5. a This provision for endwise movement of shaft l6 grows out ofthe fact that its other end is supported andcarried by the reciprocatory table 2; the latter having mounted thereon asuitable bracket 20, providing a housing 2| in axial 'alin'ement with said'shaft and containing bearings 22 (Fig. '7) for the reduced end 23of said shaft. Beyond said bearings the shaft has an eccentric pin or crank extension 24, the latter entering and being turnable in a block 25 which is held on said crank by a nut 25'.

The bracket'ZD provides suitable housings 26 and 21 for'bearings 28 and 29 in which is Journalled, below shaft l6, 2. rock shaft 30, the latter having an intermediate cut-away portion 3| wherein is secured a hardened pad 32 whose fiat working surface, facing downwardly, is on a diameter of said shaft; that is, the shaft axis is contained by said surface, and the latter, at the middle of said shafts rocking movement occupies the horizontal plane of. said axis. Secured to rock shaft 30, as by apin 33 is the hub 34 of a yoke member 35, the latter extending upwardly around the crank 24, and providing interior parallelguide surfaces 36 and 31 (the latter on a cap 38) in opposed relation. The block 25 has. end surfaces (shown by broken lines in Fig. 6) which are in sliding contact with these guide surfaces 36 and 3|-whereby at each revolution of shaft |6,.said block 25, under the infiuence of crank 24, gives yoke 35 and with it the attached shaft 30 a back and forth rocking movement, similar to that of lever f in the diagram of Fig. 3. Also by analogy with Fig. .3, the center-to-center distance between shafts I6 and 30 and the radius of crank 24 are so chosen and proportioned as to be in the ratio to b R (Fig. 2) of the curve to be generated.

The bracket 20 of table 2 also supports a trunnion shaft39, parallel to the rock shaft 30 and offset therefrom a definite distance as hereinafter described. Mounted for rocking movement about the axis 43 of shaft 33 is a bell-crank member 4|, having a generally horizontal portion 42 whose free end underlies the rock shaft 30, and having a generally upright portion 43, for the support of a tool, as hereinafter described, adapted to operate in the bore of work W during the latters rotation by'the work spindle 5. The portion or arm 42 has secured thereto, as by suitable bolts 41, an upwardly extending post 44, carrying at the 'top a hardened-wear pad 46 whose convex upper surface, struck from an axis 45, is contacted by the flat under surface of wear pad' 32' on rock shaft 30. Such contact is maintained by a spring 48 here shown as seated on bracket 20 and thrusting upwardly against the arm 42. The minimum distance between the axis 45 and the axis of shaft 30 is made equal to one-half the chord length of the curve (Fig. 2) required to be generated. The axis 40 is equidistant from the axis of work rotation and from the axis of rock shaft 30; that is to say, as shown in Fig. 6, an are 49 struck from 40 as a center will pass through the axis of shaft 33 (about which rocks the yoke 35) and also through the axis (shown by point 50, Fig. 6) of the workspindle 5. As previously stated, the upright arm 43 of rockable member 4| supports the tool which, by movement of table 2 to the left, Fig. 1, is traversed from one end to the other of the bore of the rotating work W, to generate the desired surface of non-circular cross-section along the full length or depth of said bore.

The point of said tool is indicated in Fig. 6 by numeral the distance of said tool point 5| from work bore axis 50 determines and establishes the spacing (see X Fig. 3) of axis 45 from rocker axis 35, and as this spacing changes slightly, in response to rolling of surface 32 on surface 46, so will the tool point 5| vary its distance from work axis 50, since the triangles 30, 40, 45 and 50,40, 5| remain equal, for any given setting or adjustment of the machine, and always swing together.

It will be understood that the tool point 5|, in addition to its above-described in and out movements relative to work center 50, is caused by table 2 to traverse the bor of the work, thus to impart the desired cross-sectional contour all the way along said bore. The back and forth travel of the table 2 may, of course, be effected by any suitable means, such as the usual fluid-pressure actuated devices, not shown, whose controls are indicated at 2', Fig. 4.

As shown in Figs. 8 and 9, the tool-supporting arm 43 may be equipped with two tools 52 and 53, the former for a roughing operation and the latter for a subsequent finishing operation, these two operations being performed with a single chucking of the work W. The tools 52 and 53 are arranged 180 apart in a head 54, the latter beingmovable between two different positions-to dispose selectively either the tool 52 or the tool 53 in theworking position represented at 5|,-Fig. 6. To this end, the tool carrying head 54 is mounted on a shaft 55, the latter extending through andbeing supported by the arm 43 and the latters attached overhanging bracket 56. A collar 5'! secured to shaft 55 keeps the opposing faces of head 54iand bracket 56 in close contact. The head 54Lprovides index holes 58 and 59 which are'180" apart, and which, by turning of shaft 55 are selectively registrable with a pin Gil. slidably mounted in the bracket 56, and pressed toward said-head by a spring 3|. Entrance of pin 69 into hole 58, as shown in Fig. 8, looks the head 54 in the angular position which makes the roughing tool-52 operative; when it is desired to operate with finishing tool 53, the pin 5! is retracted by means of its handle 52, this allowing the shaft 55 to be turned, by its handle 63, through I", to aline the other hole 59 with pin 55, for locking the head in the angular position where said finishing tool 53, instead of the roughing tool 52, is operatively associated with the work, in the position 5| of Fig. 6.

Fig. in shows the same pump arrangement as Fig. 1, except that the constant-length vane B has convex, rather than chisel-point, ends. The method and means for generating the interior boundary surface D of the pump chamber is the same as above described for the surface D of Fig. 1, except as affected by the need to take account of the radius of curvature of the convex ends of the vane.- This may be done by utilizing for the cutting operation a grinding wheel or milling cutter having a radius of curvature substantially equal to that of the ends of the vane. Or, a close approximation of the desired contour, by a cutting tool of the type shown at t in Fig. 3, can be obtained, as shown in Fig. 2a, if the tool point be set out a distance equal to the vane-end radius, from the curve or contour D which is traced, as heretofore described, by a constant-length chord L (the distance between the vane-end centers). The difference in Fig. 2a between the contours'D and D is due tothe angle of contact a between the end of the vane and the'surface D.

- I claim:

1. Apparatus of the class described, for cutting a workpiece bore to a non-circular section approximating the curve traced by the ends of equal-length chords passing in different direc-

Images