US2985110A

US2985110A - Pump construction

Info

Publication number: US2985110A
Application number: US623144A
Authority: US
Inventors: Farlow B Burt; Sung Chien-Bor; John R Farron
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1956-11-19
Filing date: 1956-11-19
Publication date: 1961-05-23
Anticipated expiration: 1978-05-23

Description

May 23, 1961 F. B. BURT ET AL PUMP CONSTRUCTION Filed NOV. 19, 1956 /Z MT /4 5 Sheets-Sheet 1 TETSE F. B. BURT ET AL 2,985,110

PUMP CONSTRUCTION May 23, 1961 Filed Nov. 19, 1956 3 Sheets-Sheet 2 IIIII 2 32 Z 60 T 4 5 L 5 42 If 1 E- E Fl/PZOWB. @599 CHEM-180A sa/v JOHN R. FARRfON 4 rramvir &

y 23, 1961 F. B. BURT ET AL 2,985,110

PUMP CONSTRUCTION Filed Nov. 19, 1956 3 Sheets-Sheet 3 START/N6 1/: 0; cum z NTOR mflawawmr oww-aom .50/V6 JOHN e. FZIERO/V KTTMA/f) United States Patent PUMP CONSTRUCTION Farlow B. Burt, South Bend, Ind., and 'Chien-Bor Sung, and John R. Farron, Oak Park, Mich., assignors to The Bendix Corporation, a corporation of Delaware Filed No 19, 1956, 'Ser. No. 623,144

6 Claims. (Cl. 103-136) The present invention relates to positive displacement pumps and fluid pressure motors, particularly of the type having radially movable fluid displacement members, capable of operating at high speeds and pressures efficiently and with a minimum of vibration and noise.

There has recently been developed a type of positive displacement pump having a more uniform discharge rate than has been achieved heretofore. The type of pump to which we refer utilizes a plurality of sliding vanes which project out of one of two relatively movable members into engagement with a cam surface on the other of the relatively movable members-and which vanes seal off fluid confined between the members to force the same out of the discharge of the pump. The cam surface of the type of pump to which we refer is designed in such a way that the total vane pumping area, or area of the vanes engaging the fluid being pumped, is a constant at all times. Reference to the work of one of the early workers in this field may be had by referring to the Ephraim W. Hogue Patent 2,730,076.

The Ephraim W. Hogue patent discloses the use of a sinusoidal configuration of cam surface which provides a constant sum total of pumping vane area at all times. The patent teaches that relatively movable parallel members lying in a single plane and employing sinusoidal cam surfaces will produce a constant instantaneous rate of pump displacement. The patent further suggests that the same is accomplished when the pumping surfaces extend around an axis of rotation as is necessary in any practical pumping adaptation of the principle. It has been found that all pumps having pumping members which are relatively movableabout an axis of rotation, do not of necessity produce a constant rate of displacement even though they achieve constant projected vane or fluid displacing areafor the reason that the movement arm of each vane from the axis of rotation to the center of its projected vane area is constantly changing as it slides over the cam surface. A full treatment of this subject will be given later on in the body of the specification.

Still other problems exist in the design of a commercially acceptable pump utilizing the teachings of this patcut, when the pump is to operate at high speeds (say in the order of 2500 r.p.m. or more) and at high pressures (say in the order of 1000 p.s.i.). We have found, as will later be shown, that the degree with which constant instantaneous displacement is achieved by pumps of this design using rotatable elements increases generally as the number of vanes and the number of repetitive cam segments increases. We have also found that the forces involved in holding the vanes into sliding contact with their cam surfaces increases greatly as the number of vanes and repetitive cam segments distributed around the axis of rotation increases. It is a well known requirement of the type of pump with which we are concerned that the number of repetitive camscgments be greater than the number of vanes in order that valves will not be required in the inlet and outlet ports for the pumping chambers. It has been found that leakage between the pump chambers increases as the number of cam segments approaches the number of vanes, and decreases as the number of cam segments exceeds the number of vanes Very close clearances are required in pumps construeted to develop these high pressures; and provision of these extremely close fits requires extreme accuracy of construction and assembly.

An object of the present invention is therefore the provision of a new and improved positive displacement fluid pressure machine of the above described type which will have substantially pulse free operation and which will operate efiiciently at the above referred to high speeds and pressures.

Another object of the invention is the provision of a new and improved positive displacement fluid pressure machine capable of fulfilling the above stated object and still be a commercially acceptable unit in that it is relatively simple in construction, reliable and eflicient in its operation over extended periods of time, and can be economically manufactured and assembled with very close tolerances. 7

Another object of the present invention is the provision of a new and improved fluid pressure machine of the type having a rotor member and a stator member providing cooperating fluid confining surfaces radially disposed relative to each other, one of which surfaces is a surface of revolution and the other of which surfaces is a continuous cam surface providing substantial fluid sealing engagement with the other of said surfaces at equally spaced intervals, said members being journalled for rotation relative to each other solely by abutment of the surface of revolution with the lobes of the continuous cam surface. The machine will preferably further include an arrangement whereby the members are hydraulically balanced relative to each other to prevent radial oscillation relative to each other, and thus further improve the efficiency of the machine.

A further object of the invention is the provision of a new and improved fluid pressure machine as set forth in the object immediately above and in which the rotor is driven by a shaft flexibly connected to the rotor in a manner permitting the rotor to center itself substantially unrestrainedly relative to the stator during operation of the machine.

A more specific object of the invention is the provision of a new and improved fluid pressure machine, and more especially a pump, having a sinusoidal type of cam surface in which varying moment arm considerations are corrected for, and in which the provisions of the above objects are incorporated.

A still more specific object of the invention is the provision of a new and improved fluid pressure machine, and more especially a pump, according to the above objects and in which the rotor member is driven by a sectionalized drive shaft-one section of which is journalled in the stator and an intermediate section of which is connected to said rotor and said first section of the drive shaft in a manner accommodating eccentricity between said rotor and said drive shaft.

Inaddition to the above objects, the provision of a drive shaft of the type set forth immediately above is believed novel in pumps generally.

The invention resides in certain constructions and combinations and arrangements of parts; and further objects and advantages will become apparent to those skilled in the art to which the invention relates from the following description ofthe preferred embodiments described with reference to the accompanying drawings forming a part of this specification, and in which:

Figure 1 is a longitudinal sectional view of a pump embodying principles ofv the present invention;

- Figure 4 is a diagram depicting the various distances and angles involved' in the formula of the camming contour used in the pump of Figure 1.

Referring to Figure 1, there is shown therein a positive displacement sliding vane-cam type pump embodying principles of the present invention and having a type of cam surface later to be described in detail. The pump generally comprises a casing or stator member A conveniently formed from an annular center section 10, and opposite

end closure members

12 and 14 bolted together to provide an internal chamber 16. The center section is provided with a continuous internal cam surface 18 formed from a number of repeating cam sections that provide a number of lob'es 20 and valleys 22 spaced around the axis of rotation 24 of the pump. A cylindrically shaped rotor member B having a Width corresponding to that of the center sect-ion 10 of the stator is positioned in the chamber 16 and is of such a diameter as to provide substantial fluid sealing engagement with respect to each of the lobes 20. A plurality of vanes 26 equal in width to that of the rotor B are positioned in equally spaced radially extending slots 28 in the rotor member B in a manner permitting centrifugal force to bias the vanes outwardly into engagement with the cam surface 18. The

rotor member B is rotated, as by the shaft 30, to cause each vane to sweep and displace fluid from each of the valleys 2. The pump shown in the drawing is adapted to be rotated counterclockwise as seen in Figure 2, and the rluid displaced from the valleys or pumping chambers 22 passes through a plurality of radial passages 32 positioned immediately forward (counterclockwise) of the vanes 26, to transverse drillings 34 in the rotor, and then on to

annular collector grooves

36 and 38 in the

stator sections

12 and 14 respectively and to the discharge connection 40 of the pump. Each of the radial passages 32 are conveniently made by means of a number of radial drillings spaced across the Width of the rotor member B with their sides opening into the slots 28 to distribute discharge pressure across the width of the vanes. Each of the vanes 26 is provided with a V-shaped edge which provides a substantially line contact with respect to the cam surface 18, and the transverse drillings 34 intersect the bases of the slots 28 in which the vanes are held, such that the pumps discharge pressure is continually used to hold the vane in engagement with the cam surface 18. As the fluid in the portion of each pumping chamber 22 ahead of each vane is being forced out of the pump discharge 40 by the vanes, fluid from the pump suction connection 42 is added to the portion of the pumping chambers behind the vanes through the internal chamber 44 of the rotor and radial drillings 46.

The pump shown in the drawing is used to develop hydraulic pressures in excess of 1000 p'.s.i. for use in power steering applications in automotive vehicles. The pump is driven directly from the engine of the vehicle and so must operate at speeds ranging up to 8000 to 10,000 r.p.m. In order for the rotor to effectively seal off adjacent pumping chambers 22 which are respectively at pump suction and discharge pressures, clearances of from 2 to 3 ten thousandths of an inch must be maintained between the rotor member B and the lobes 20 of the cam surface. These clearances should furthermore be maintained evenly around the rotor member to insure that adequate lubrication will exist between the rotor and stator members, and to prevent shifting of the rotor member to one side of the internal chamber 16 from doubling these clearances adjacent the opposite side of the rotor member. Prior to the present invention the construction and assemblyof a pump meeting the above standards is believed to be highly impractical commercially, if not impossible.

The pump shown in the drawing utilizes a sinusoidal type of configuration of cam surface, later to be described in detail, which among other things provides smooth in and out acceleration of .the vanes, such that centrifugal force will hold the vanes into engagement with the cam surface 18. It' is a further propertyfiofthis type of configuration that combinations of three vanes to every four lobes or multiples thereof, and combinations numerical greater than 3 vanes to 4' lobes, provides a pump of constant instantaneous theoretical displacement. The

' pump shown employs two sets of a 2 vane-3 lobe comthis fact, however, particular advantages are achieved by a combination of 2 vanes and 3 lobes, and these advantages will now be described in detail.

It has been found that a cam surface formed with the type of configuration mentioned above and having an even number of vanes and lobes, produces forces on opposite sides of a cooperating rotor which will exactly equal and oppose each other. Only combinations of 6 vanes-8 lobes, and numerically higher ratios (as for example 8 vanesl0 lobes, 4 vanes-10 lobes, l0 vanes-l2 lobes, etc.) Will satisfy these conditions exactly. The problem is further complicated in that the force tending to separate the vanes from the cam surfaces increases as the number of lobes positioned around the axis of the pump increases; and the forces also increase as the depth of the cam valleys are increased. A particularly advantageous solution to the over-all problem has been found to be achieved by a 4 vane-6 lobe combination utilizing the above type of cam configuration constructed in a manner later to be explained.

According to further principles of the invention, the rotor member B is permitted to float unrestrainedly within the internal chamber 16, and is journalle'd solely by the engagement of rotor member B with the peaks of the cam lobes 20. This obviates the necessity of positioning bear-. ing means for the rotor accurately with respect to the cam surface 18. A further refinement of the invention is provided by a shaft flexibly connected to the rotor in a manner which Will accommodate slight angular movement of the shaft. By use of such an arrangement, drive shaft bearing means need not be accurately centered with respect to the rotor member thereby further simplifying the construction and assembly of the pump.

The flexible shaft construction of they embodiment shown in Figure 1 comprises a sectionalized shaftone section 50 of which is jcurnalled in the stator member and an intermediate section 52 of which is connected between section 50 and the rotor member B in a manner permitting angular movement of the intermediate section relative to the rotor member. 'The shaft section 50 is a generally tubularly shaped member rotatably received in an axially extending opening 54 through the end closure member 14. The shaft section 50 is further journalled with respect to the stator by means of an anti-friction bearing 56 fitted between the shaft section and the side:

Walls of a counterbore 58 in the outer end of the closure member. Leakage past the shaft section 50 is prevented by a cup shaped seal 60 fitted into a smaller counterbore 62 in the bottom of the counterbore 58-which seal is held in place by a retaining washer 64. The retaining washer is abutted by the anti-friction bearing 56, and the assembly is locked in place by a snap ring 66 seated in a groove in the outer end of the counterbore 58.

- Rotation of the driven shaft section 50 is transmitted to the rotor member B by the spool shaped intermediate shaft section 52 having splines or teeth at its opposite ends. An internalspline 68 is broached into the tubular section 50 inwardly ofthe anti-friction bearing; and a similar female spline 70 is provided in the rotor member B. Opposite ends of the intermediate shaft section 52 engage with the

splines

68 and 70 respectively, and the splined connections are made in such a way as to permit slight angular movement of the intermediate shaft section. The outer end of the intermediate shaft section 52 is abutted by a plug 72 which seals off the end of the section 50 and prevents outward movement of section 52; and inward movement of the section 52 is prevented by a snap ring 74 retained in a groove in the shaft section 52, and which abuts the rotor member B. The shaft section 50 is driven by a pulley (not shown) keyed to the end of the shaft section and held in place by a screw threaded into the plug 72.

Operation of the embodiment shown in Figure 1 is believed to be self evident from the above description of the device. Suffice it to say that fluid from the pump suction 42 passes to the internal rotor chamber 44, through radial drillings 46 to the portions of the pumping chambers 22 situated immediately behind (clockwise of) the rotating vanes 26. The portions of the pumping chambers 22 in front of (counterclockwise of) the rotating vanes 26 is forced out through they radial passages 32, .through the. transverse drillings 34 to the

collector grooves

36 and 38, and thence to the discharge connection 40. Very close clearances aremaintained between the cam lobes 20 and the rotor member B to effectively seal olf each pumping chamber 22 from its adjacent pumping chambers. A similar close fit between the rotor member B and the

end closure members

12 and 14 eflectively seals off the

collector grooves

36 and 38 from the pump section; and leakage past the shaft section 50 is prevented by the cup shaped seal 60. As previously indicated, the rotor member B is journalled for rotation with respect to the stator member A solely by sliding engagement with the lobes 20 of the cam surface 18; and eccentricity problems of the drive shaft are compensated for by means of the intermediate splined shaft section 52.

A second embodiment of the invention is shown in Figure 3. This embodiment is identical with the embodiment described above, excepting that a drive shaft 80 having a reduced diameter section 82 is used which is relat-ively stilf in torsion but flexible in bending. The inner end of the shaft is splined to the rotor member B, and the outer end of the shaft is sealed off and journalled in a manner similar to that of the previous embodiment.

The sinusoidal configuration of cam surface used in the pumps described above can be defined by the equation:

' r=R +e sin n Expressing the pumping volume of a chamber defined by a vane positioned somewhere in a valley, with reference to the point at which the lobe contacts the rotor in terms of polar coordinates, it can be shown that:

The volume displaced per unit of time is therefore:

dV cit Where more than one vane and repeating cam surface is evenly spaced around the axis of rotation, the summation equation for the instantaneous displacement of all the vanes is:

5 k ab k=m 1,C R e cos n(0+- e 2(k1)1r d0 0 cos 271(6- m dt where m1=the number of vanes, n=the number of lobes, and k=any particular vane.

For a more detailed derivation and explanation of these equations, reference may be had to the John R. Farron and Chien-Bor Sung application Serial No. 380,406, now Patent No. 2,845,872.

It will be seen from the above equations that the first term of the summation equation is always equal to a constant, and that the total instantaneous displacement of the pump will only be constant if the last two terms of the equation are consta-nt.

For the type of pump wherein m=n1, the second termof the summation equation is constant for all combinations greater than 1 vane =2 lobes; but the last term of the equation is only constant for 3 vane4 lobe, and'combinations greater than this amount. The 2 vane-3 lobe combination (or 4 vane-6 lobe as used in the pumps described above) does not satisfy the equations to produce a constant displacement pump.

Applicants have further found that by tailoring the commercially acceptable pumps of the above stated type should have values of under 0.08, and most preferably below 0.04. The pump shown in the drawing has proven very successful, and has an e value equal to 0.023 inch, and an R equal to 1.25 inches-giving an b ratio of 0.0184.

It will be apparent that the objects heretofore enumerated as well as others have been accomplished, and that there has been provided a new and improved positive displacement pump capable of operating at extremely high speeds and pressure without appreciable noise or vibration. While the invention has been shown and described as embodied in a pump, it is not so limited. Other types of positive displacement fluid pressure machines, as for example motors, may be built embodying principles of the invention; and some of the principles might be used in machines other than those of the positive displacement type.

While the invention has been described in considerable detail, we do not wish to be limited to the particular constructions shown or described; and it is our intention to cover hereby all adaptations, modifications, and uses thereof which come Within the practice of those skilled in the art to which the invention relates.

We claim:

1. In a fluid pressure machine of the positive displacement type the combination of a rotor member and a stator member spaced concentrically about an axis of rotation and providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam surface having a pumping contour which is uninterrupted and continuous to form equally spaced lobes and valleys which lobes provide substantial sealing engagement with said one surface at equally spaced intervals to provide a. plurality of fluid chambers; a plurality of sliding vanes carried by the member having said surface of revolution, said vanes projecting out of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; all points of said cam surface being spaced relative to said axis at distances defined by the formula r=R +e cos 116; where:

r=the distance between any point on the cam surface to the axis about which relative rotation is produced,

R =the radius of the base circle of the cam,

e=rnaximum deviation of cam surface from the base circle,

n=the number of repetitive cam cycles employed in the cam surface,

6=the angle at which I; is taken relative to a reference plane;

there being four vanes and six fluid chambers, and said members being supported for rotation relative to each other solely by the journaling action of said surface of revolution upon the tips of said lobes.

2. In a fluid pressure machine of the positive displace ment type the combination of a rotor member and a stator member spaced concentrically about an axis of rotation and providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam surface having a pumping contour which is uninterrupted and continuous to form equally spaced lobes and valleys which lobes provide substantial sealing engagement with said one surface at equally spaced intervals to provide a plurality of fluid chambers; ,a plurality of sliding vanes carried by the member having said surface of revolution, said vanes projecting out of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; all points of said cam surface being spaced relative to said axis at distances defined by the formula r=R +e cos n; where there being four vanes and six fluid chambers; said members being supported for rotation relative to each other solely by the journaling action of said surface of revolution upon the tips of said lobes; and said members being rotated relative to each other by a non-rigid shaft connected to the rotor in a manner permitting the rotor to center itself substantially unrestrainedly relative to said stator during operation of the machine. 7

3. In a fluid pressure machineof the positive displacement type the combination of a rotor member and a stator member spaced concentrically about an axis of rotation and providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam surface having a pumping contour which is unina a n-a 8 terrupted and continuous to form equally spaced lobes and valleys which lobes provide substantial sealingengagement with said one surface at equally spacedintervals to provide a plurality of fluid chambers; a plurality of sliding vanes carried by the member having said, surface of revolution,,said vanes, projectingvout of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; all points of said cam surface being spaced relative to saidaxis at distances defined by the formula r=R +e cos n0; where;

r=the distance between any point on the cam surface to the axis about which relative rotation is produced, R =the radius of the base circle of the cam, e=maximum deviation of cam surface from the base circle, 7 n=the number of repetitive cam cycles employed in the cam surface, 0=the angle at which r is taken relative to a reference plane;

there being four vanes and six fluid chambers; said members being supported for rotation relative to each other solely by the journaling action of said surface of revolution upon the tips of said lobes; and a sectionalized shaft having an intermediate and an outer section, means journaling-said outer section on said stator member, first spline means forming a loose driving connection between one end of said intermediate section and said rotor and second spline means forming a loose driving connection between the other end' of said intermediate section and said section to thereby accommodate eccentricity between said rotor and said outer section of said shaft.

4. In a fluid pressure machine of the positive displacement type the combination of a rotor member and a stator member spaced concentrically about an axis of rotation and providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam: surface having lobes and valleys which lobes provide substantial sealing engagement with said one surface at equallyspaced intervals tovprovide a plurality of fluid chambers; means for producing relative rotation between said rotor and stator members; a plurality of sliding vanes carried by the member having said surface of revolution, said vanes projecting out of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; all points of said cam surfacebeingspaced relative to said axis at distances defined by the formula r=R -+e cos n0; where:

there being four vanes and six fluid chambers; and the ratio of e/R being less than approximately 0.04, said members being supported for rotation relative to each other solely by the journaling action of said surface of revolution upon the tips of said lobes; and said rotor member being rotatably driven relative to said stator member by a sectionalized drive shaft having an intermediate and a driven section, means journaling the driven section on said stator member, first spline means forming a loose driving connection, between one end of said intermediate' section and said rotor and second spline means forming a loose driving connection between the other end of said intermediate section and said driven section to thereby accommodate eccentricity between said rotor and said driven sect-ion of said drive shaft.

5. In a fluid pressure machine of the positive displacement type: the combination of a rotor member and a stator member providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam surface having a pumping contour which is uninterrupted and continuous to form equally spaced lobes and valleys which lobes provide a substantial sealing engagement with said one surface at equally spaced intervals to provide a plurality of fluid chambers; a plurality of sliding vanes carried by the member having said surface of revolution, said vanes projecting out of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; said members being journaled for rotation relative to each other solely by abutment of said surface of revolution with said lobes at said equally spaced intervals.

6. In a fluid pressure machine of the positive displacement type: the combination of a rotor member and a stator member providing cooperating fluid confining surfaces radially disposed relative to each other, one of said cooperating surfaces being a surface of revolution and the other of said cooperating surfaces being a continuous cam surface having a pumping contour which is uninterrupted and continuous to form equally spaced lobes and valleys which lobes provide a substantial sealing engagement with said one surface at equally spaced intervals to provide a plurality of fluid chambers; a plurality of sliding vanes carried by the member having said surface of revolution, said vanes projecting out of said surface of revolution into engagement with said cam surface; means for introducing fluid to and for removing fluid from said fluid chambers on opposite sides of said vanes; said members being journaled for rotation relative to each other solely by abutment of said surface of said surface of revolution with said lobes at said equally spaced intervals; and a sectionalized shaft having an intermediate and an outer section; means journaling said outer section on said stator member; first spline means forming a loose driving connection between one end of said intermediate section and said rotor; and second spline means forming a loose driving connection between the other end of said intermediate section and said outer shaft section to thereby accommodate eccentricity between said rotor and outer section of said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 917,466 Lees Apr. 6, 1909 1,687,523 Staude Oct. 16, 1928 1,978,922 Wemp Oct. 30, 1934 1,989,900 Vickers Feb. 5, 1935 2,372,335 Newell Mar. 27, 1945 2,411,606 Wilson Nov. 26, 1946 2,501,947 Johnson Mar. 28, 1950 2,650,753 Howard et al. Sept. 1, 1953 2,730,076 Hogue Jan. 10, 1956 2,738,660 Gail Mar. 20, 1956 2,786,421 Prendergast Mar. 26, 1957 2,825,287 Ostwald Mar. 4, 1958 2,845,872 Farron et al. Aug. 5, 1958 FOREIGN PATENTS 602,448 Great Britain May 27, 1948 754,427 Great Britain Aug. 8, 1956