US3232237A - Cam and method of generating same - Google Patents

Description

F. B. BURT CAM AND METHOD OF GENERATING SAME Feb. 1, 1966 5 Sheets-Sheet 1 Filed July 6, 1962 INVENTOR. FARLOW B BURT.

Mys /214i ATTORNEY.

Feb. 1, 1966 F. a. BURT CAM AND METHOD OF GENERATING SAME 5 Sheets-Sheet 2 Filed July 6, 1962 INVENTOR. FARLOW B. BURT,

Rim/1M A TTORNEY.

Feb. 1, 1966 F. B. BURT 3,

CAM AND METHOD OF GENERATING SAME Filed July 6, 1962 5 Sheets-Sheet 5 INVENTOR.

FARLOW B. BURT.

aid/4M A T ORA Y Feb. 1, 1966 F. B. BURT 3,232,237

CAM AND METHOD OF GENERATING SAME Filed July 6, 1962 5 Sheets-Sheet 4.

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INVENTOR MAM A TTOR NEY.

FARLOW B. BURT.

Feb. 1, 1966 F. B. BURT CAM AND METHOD OF GENERATING SAME Filed July 6, 1962 5 Sheets-Sheet 5 INVENTOR.

FARLOW B. BURT.

A TTOR NE Y,

3,232,237 CAM AND METHUD F GENERATING SAME Farlow B. Burt, Winter Park, Fla, assignor to The Bendix Corporation, South Bend, Ind, a corporation of Delaware Filed an 6, 1962, Ser. No. 208,137 2 Claims. or 103-136) The present application is a continuation-in-part of my copending application Serial No. 18,113, filed March 28, 1960, now abandoned, which in turn is a division of my then copending application Serial No. 635,747 filed January 23, 1957, now Patent No. 2,958,264, issued Novemher 1, 1960.

The present invention relates to positive displacement types of hydromechanical devices, such as pumps and motors of the sliding vane type; and more particularly to the cooperating camming surface on which the vanes slide; and further to a unique method of making such a part.

An object of the present invention is the provision of a new and improved cam configuration for a hydromechanical device and which cam has a plurality of lobes and valleys positioned radially about an axis of rotation with the tips of the lobes being uniformly machined to provide cylindrical surfaces of fixed radius from the axis of rotationthe lobes and valleys being preferably formed by a continuous repeating sinusoidal configuration, and the cylindrical surfaces having a length of from two to five degrees.

Another object of the invention is the Provision of a new and improved method of generating the preferred cam surface mentioned above by means of apparatus in which the rotatable cutting element is positioned radially with respect to the blank while the center of the cutting element and blank are rotated relative to each other to provide a cylindrical surface of fixed radius, and thereafter the sinusoidal valleys are formed by relative radial reciprocating movement between the cutting element and blank until the remaining sections of the cylindrical surface are machined to a predetermined length.

Further objects and advantages will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments described with reference to the accompanying drawings forming part of this specification, in which:

FIGURE 1 is a perspective view of apparatus embodying principles of the present invention;

FIGURE 2 is a cross-sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is a side view of a cam member finish machined according to the preferred cam configuration;

FIGURE 4- is a fragmentary side view of a portion of FIGURE 3 better illustrating a refinement in its contour;

FIGURE 5 is a fragmentary schematic view exaggerating the relationship between the desired cam configuration and cutting element to more fully depict the principles of the invention;

FlGURE 6 is a fragmentary schematic view exaggerating the relationship between a preferred form of gearing which strangely enough closely approximates a desired corrective phase shifting movement in the above apparatus; and

FIGURE 7 is a cross sectional view of the vane type ited States Patent 0 'ice pump described in Patent 2,985,110 but which includes the cam body member of the present invention.

As indicated above, the present invention relates to the part of a vane type hydromechanical device, be it a pump or a motor, against which the vanes slidingly abut during operation of the device to alternately expand and contract the chambers to which pressure fluid and exhaust is communicated. These members against which the vanes slide are commonly called cams by the men skilled in the art, and will be hereinafter so designated.

There is shown in the drawings apparatus which is specifically designed to machine the cam configuration illustrated in FIGURES 3 and 4 of the drawings. The cam body member C shown in these views is specifically designed for use in sliding vane cam pumps of the type described in the Burt, Sung and Farron application Serial No. 623,144, filed November 19, 1956, now Patent No. 2,985,110. In this type of pump, a cylindrical rotor member 8 is mounted within the central opening 10 of the cam, in sliding sealing engagement with the radially innermost projecting parts or lobes 12 of the cam. The rotor carries a plurality of vanes 13 which are biased radially outwardly into engagement with the cam surface 14, to sweep liquid out of the space defined by the valleys, or cam depressions, and the rotor through suitable passages in the rotor member. For a more complete description of the construction and operation of the pump for which the cam member C is designed, reference may be had to the above mentioned application.

The specific pump of which cam member C is a part is intended for use in hydraulic power steering systems where substantially pulse free flow is required at rotor speeds tan ing from to 4000 r.p.m. and at pressures in excess of 1000 p.s.i. Numerous problems are involved in designing pumps for these conditions. One of these problems is presented by leakage from a high pressure valley to a low pressure valley through the clearance between the separating lobe and rotor; and another of these problems is presented by the dynamic forces of the vanes which tend to'separate them from the cam surface. The specific cam contour used in the cam member C is a sinusoidal one conforming to the equation R=r +e cos at). For a more detailed description of this contour and of the problems of designing pulse free pumps, reference may be had to the above referred to application.

In his work with such pumps, applicant has found that a great reduction in leakage between the cam surface and rotor can be accomplished by means of a cylindrical contour in the tip of each lobe without harmfully affecting the pulse-free operation of the pump. These cylindrical contours should be confined to the tips of the lobes; and should extend over an arc of from about 2 to about 5 degrees,

The method and apparatus used by applicant to machine the cam contour previously described may best be understood by reference to FIGURE 5 of the drawings, wherein the pertinent angles and distances are shown exaggerated to better illustrate the relationship involved. The desired finished machined contour is generally indi cated at 15 and the periphery of a rotatable cutter of predetermined diameter for machining the contour is indicated at 16. There is also shown at 18 a line all points on which are spaced radially inwardly from the line 15 towards the center 0 of the blank a distance R which corresponds to the radius of the cutter 16. Relatively simple means could be provided for moving the center of the rotatable cutter along line 18; but were this to be done, the cutter would not be tangent to the desired contour as seen by the dot-dash line 20, but would dig out too much metal at some spots and not enough at others. In order for the above described cam contour to be able to develop substantially pulse free discharge, the cam contour must be machined to an accuracy approaching a few ten thousandths of an inch. This can only be obtained by correcting for the above-stated inaccuracy involved in the use of a rotatable cutter.

The applicant has theorized that the above errors could be eliminated were means to be provided which, it kept in phase relationship with the angle of rotation of the blank, would move the center of the cutter along a path which is a fixed radical distance from the desired cam contour (i.e. along the line 18); and further has theorized that by suitably changing the phase relationship between the cutter and the blank, the periphery of the cutter could be made tangent to the desired contour at all times. A preferred method of accomplishing these results will now be explained with reference to FIGURE 5 of the drawings. Assume for the time being that a suitable means is used to provide radial movement between the cutter and the blank, and that a further means is provided which, when rotated in direct proportion to said first means, moves the center of the cutter along the line 18. Referring to FIGURE 5, the equation for the desired cam contour 15 will be:

r =radius of any point of the cam defined by angle r =mean base circle for the cam e=maximum variation above and below the base circle n=number of lobes =the angle between any particular radius and an arbitrary reference line through a center of a valley.

For a cutter of radius R, the radius of curve 18 at any given point would be r =r R+e cos 11.

It will be seen that if the cutter is moved in and out on its radius in phase with its position about the cam its center would be at 22 at the angle shown in FIG- URE 5. If the center 22 were moved radially inwardly to the point 24, the cutter would be tangent to the desired contour at the point T. Point 24 is the distance S from the center 0; and if the cutter were moved out of phase by the angle 0, it would have a radius equal to S. Therefore to be tangent, the means moving the cutter radially would have to have moved an angle proportional to ,B when the cutter had moved 5. By means of polar coordinates:

also from the law of sines Constructing a normal from point 24 to the radian en sin nu F=a cos xix R a sin x O=arc sin 5 and x should approach 77 times the theoretical of Equation 6.

By cut and try methods applicant was able to establish that, when r =1.25, R=.375, 71:6, e"'.023, R-1 for the gear, and the a value of the theoretically desired conin the slide plate F and the top plate 48 of the frame, respectively, to receive the electric motor E and permit lateral movement thereof relative to the blank C.

The slide F is adapted to be reciprocated generally according to a desired sinusoidal function by an eccentric tour. G and a scotch yoke structure 72 fixed to the slide plate A tabulation of data indicating the accuracy with which F. The scotch yoke structure 72 is formed by means of the S value provided by the gearing approaches the theoa pair of blocks 74 and 76, adjacent sides of which are retically required S value for a perfect contour is as folsuitably recessed to receive opposite sides of a cylindrical lows; rotor 78. The blocks 74 and 76 are confined into tight Assuming values of on as indicated, 10 engagement With opposite sides of the rotor 78 by means RSln (so-r "F Rsin(90 1 will? angle "utput S 111 (90) m of gears angle of cos :5 IL-0.23 cos x S1.25-.375 ha S S gears It will be seen that the maximum error is less than 2 of a cross-bar 8t and through bolts 82 and 84 which exten thousandths of an inch and is therefore acceptable. 25 tend through openings in opposite side spacer members Apparatus embodying the above principles is. shown in $6 and 88 and are threaded into the end Of the slide plate FTGURES l and 2 of the drawings. The apparatus gen- F. The spacer members 86 and 8-8 are of a length which orally comprises a frame A on which is journalled a turn- Will provide a tight fit between the rotor 73 and the blocks table B for supporting and rotating an annular blank C 74 and 76 to overcome lost motion in the reciprocating to be machined. The blank is machined by a rotatable 3O strhctilre- The reciprocating cycle of the cutter D y be cutter D carried by a high speed electric motor E, which fed radially oiltwtiftiiy ihtQ the blank y 1.1163118 0f 11 and in turn is mounted on a slide F adapted to be reciprocated wheel- 90 and rod which is threaded into 21 pp so that the cutter moves in a straight line which passes block 4 and the end of which is adapted to abut he through the center of the blank. The slide F is moved block The Support block 94 is fixed to Slide F y back and forth by means of the eccentric G which in turn 35 bolts and the end of the rod 92 adjacent the and i ot t d by means f gearing H hi h id h wheel hi) is slidably received in an opening 98 in a guide proper lead and lag to and in-andout movement of the I Silltahiy fiXBd t0 the The block 4 slide to maintain the cutter tangent to the desired concarrying the hiOtOT E has been preylousty described a tour, as di d b being adjustably fixed to the slide plate F by means of The turntable B for supporting and rotating the blank Slotted hoihs 65 bolts 64; and y threading thfi fOd C comprises a bottom plate 36, the under surface of 92 lhwardiy against block 1 the i f y he Which is accurately machined to revolve on a correspondreiatlva to the Shde Plate dltli Indicator 10 i urf 32 i d into the top f f a m. is shown mounted on the block 54 with its sensitive elet l plate 34 of h frame A A f i plate 3 recgssed ment 1n engagement w1th the support block 94 such that i i upper f tovreceive the bottom end f the cutter the depth or cut of the cutter D can be readily determined. D and to provide chip space is suitably fastened to the a practlchl h f the bolts 64 may b8 tightened a plate 30; and the blank C is adapted to be clamped there- Point wherein incnon bfitween the hlock and Slide to by the bolts 33. The turntable assembly B is rotated Plate F sufficlent to hold the F t cutting engage by means of a shaft (it suitably journalled in the frame ment Wlm the thank and f' Sun Perm1t thfi block to A; d th bottom d f haft 49 j Coupled to the be moved relat1ve to the s l1de by means of the threaded put shaft 42 of a gear reducer 44 having an input shaft rod 92 t t further adiusitment of the bolts 46 adapted to be driven by dan elgctric motor (not The cylmdncal rotor 78 is mounted eccentncally on h the end of a shaft 11% by a distance 2 which 1n the The blank 0 n usually be rough machined to an present mstance is equal to 0.023 inch. The shaft 104 internal diameter approaching the desired distance between 1S Suitably tournaned m the,frame A and dnvfin at opposite lobes of the finished cam. The rotatable cutting t Whlch 1s generfany 51X tunes h the blanjk element D adapted to machine the finished contour is 15 rotated to Provide a F SIX h and SIX rotatably supported from the electric motor E which in The shaft m4 duvet from? h 106 turn is supported from the slide structure F about to by means P h fl later to h described and the if b described. h top plate 3 f the frame is machined 6O shaft 106 is suitably ournalled 1n the frame A and d11ven parallel to the machine surface 32 to provide a suitable at a rate six times that of the Shaft 40 by mums of gears surface on which the slide structure F reciprccates. Oppo- 108 and 11h fixed to t shafts 49 l f site side edges of the slide F are beveled for sliding en- The gear mearis H adapted to pl'owde t gagement With a pair of ways 50 and 52 which in turn by means of which the cutter ht is h i f are bolted to the top plate 43 in a manner assuring that tangent t t desire/d h Cohtcilf, lltihlhg the p lpi the cutter D Will move radially across the centerline of the p h y described with Thfhrence 9 IGURE oi t turntable B. The electric motor E is supported from the drawingg m H Comprises t cyhh-ihlcai slide F by means of blocks 54 and 55, the adjacent ends gears h h hflvlhg a Pitch filametfif Q two inches of which are suitably recessed to receive opposite sides of whlhh 1S mountefi its respective. Shaft eqcwtflcfliiy of the electric motor E; and the electric motor is clamped y a distance which In the PF 'Q Instance is equal to therebetwfifin by means f h hi b lt 62 Th 0. l061nc-hes. The gear 112wh1ch 1s fixed to the shaft 106 block 54 is in turn adjustably positioned upon the slide 0 COIFCSPOIId generally to the left-hand gear dehlct'id F by maans of a p lity of bolts 64 which extend through in FIGURE 6; and the gear 114 fixed to the shaft 164 slotted holes 66 in the block 54 and are threaded into the will correspond to that shown 1n the rlght-hand slde of the slide plate F. Suitable openings 68 and 70 are provided same figure.

In the preferred method of operating the apparatus above described, a gear blank C finished to a rough internal diameter will be bolted to the turntable B. The cutter D will be positioned within the opening of the blank C, and the gear 112 will be removed from the shaft 104 so that the slide F will not be reciprocated relative to the blank. The hand wheel 90 will be turned to gradually advance the rotating cutter D radially into the blank C until its internal diameter corresponds to the desired distance between the cylindrical surfaces 116 in opposite lobes of the finished cam. Once this diameter has been accurately machined the gear 112 is inserted upon the shaft 104 and the eccentric means G suitably rotated to provide reciprocatory movement of slide structure F. Prior to the time that the slide structure F is reciprocated relative to the blank, the motor E will be moved radially inwardly a sutficient distance such that the cutter D will not engage the surfaces of the blank about to be machined when the reciprocation of the slide structure is started. Thereafter the rod 92 is threaded inwardly until the reciprocatory cycle is moved outwardly to a point where the cutter D begins to engage the blank during the radially outermost portion of its cycle. Engagement of the cutter D during its outermost extremity of radial movement begins to form the valleys in the blank C; and by gradually advancing the rod 92 into the support member 94, these valleys will be deepened until all that remains of the original cylindrical internal surface are the sections which are to be left in the tips of each of the lobes. These cylindrical surfaces 116 will be from 2 to 5 degrees in length. It will be seen that the chordal length of the cylindrical surfaces 116 will be gradually reduced as the machining of the cam progresses. The cylindrical surfaces 116 provide a mark which can readily be seen by the operator; and when this mark has decreased to approximately 50 or 60 thousandths of an inch (which can be judged by eye, by a skilled machinist) the machining of the cam is complete. By this simple expedient the sinusoidal surfaces can be accurately machined to the desired depth. The apparatus shown in the drawings can be used to machine external cams as well as internal cams; and by suitably alternating the eccentric G and gearing H the same principles can be used to form cams having a configuration other than the sinusoidal one of the cam shown in FIGURE 3.

While the invention has been described in considerable detail, I do not Wish to be limited to the particular methods and constructions shown and described, and it is my intention to cover hereby all novel adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

Iclaim:

1. The fluid pressure chamber forming cam member of a vane type positive displacement fluid handling device comprising: a body member having a continuous fluid pressure chamber forming slide vane camming surface of generally predetermined width extending about an axis of rotation, said camming surface having spaced apart portion which project farthest out of said body member to form lobes and also having valleys between said lobes which recede into said body member to form said pumping chambers, the outermost surface of each lobe having a cylindrically contoured section therein with its center of curvature coincident with said axis of rotation and subtending an arc of from 2 to 5 degrees, and each of said cylindrically contoured surface sections being spaced at the same radial distance from said axis of rotation.

2. The fluid pressure chamber forming cam member of a vane type positive displacement fluid handling device comprising: a body member having a continuous fluid pressure chamber forming slide vane camming surface of generally predetermined width extending about an axis of rotation and conforming generally to the equation r =r +e cos 11 where r =radius of any point of the cam defined by angle r =mean base circle for the cam e=maximum variation above and below the base circle n=number of lobes =the angle between any particular radius and an arbitrary reference line through a center of a valley the portions of said surface which project farthest out of said body member forming lobes, the outer most portion of each lobe having a cylindrically contoured section over an arc of from 2 to 5 degrees, and the center of curvature of each cylindrically contoured section coinciding with said axis of rotation.

References Cited by the Examiner UNITED STATES PATENTS 2,174,664 10/1939 Korany 12316 2,730,076 1/1956 Hogue 103121 2,845,872 8/1958 Farron et a1 '103136 2,992,616 7/1961 Rineer 103-121 FOREIGN PATENTS 1,006,314 1/ 1952 France.

DONLEY'J. STOCKING, Primary Examiner.

JOSEPH H. BRANSON, JR., KARL I. ALBRECHT,

Examiners.

Claims (1)

1. THE FLUID PRESSURE CHAMBER FORMING CAM MEMBER OF A VANE TYPE POSITIVE DISPLACEMENT FLUID HANDLING DEVICE COMPRISING: A BODY MEMBER HAVING A CONTINUOUS FLUID PRESSURE CHAMBER FORMING SLIDE VANE CAMMING SURFACE OF GENERALLY PREDETERMINED WIDTH EXTENDING ABOUT AN AXIS OF ROTATION, SAID CAMMING SURFACE HAVING SPACED APART PORTION WHICH PROJECT FARTHEST OUT OF SAID BODY MEMBER TO FORM LOBES AND ALSO HAVING VALLEYS BETWEEN SAID LOSS WHICH RECEDE INTO SAID BODY MEMBER TO FORM SAID PUMPING CHAMBERS, THE OUTERMOST SURFACE OF EACH LOBE HAVING A CYLINDRICALLY CONTOURED SECTION THEREIN WITH ITS CENTER OF CURVATURE COINCIDENT WITH SAID AXIS OF ROTATION AND SUBTENDING AN ARC OF FROM 2 TO 5 DEGREES, AND EACH OF SAID CYLINDRICALLY CONTOURED SURFACE SECTIONS BEING SPACED AT THE SAME RADIAL DISTANCE FROM SAID AXIS OF ROTATION.

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