US 3636821 A
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O United States Patent ns1 3,636,82 1 Rystrom [451 Jan. 25, 1972  VARIABLE DISPLACEMENT DEVICE 2,956,895 10/ 1960 Wahlmark ..92/256 2,980,077 4/l96l ...92/255  lnventor: Charles H. Rystrom, 696 Oak St., Winnet- 3,274,896 9/1966 ...9l/498 ka, Ill. 60093 3,366,0l7 l/l968 ...92/178  Filed: Selm lo 1969 3,435,774 4/l969 Parrett ..91/501 [2l] Appl. No.: 856,694 Primary Examiner-William L. Freeh Attorney-F idler, Bradley & Patnaude  U.S. Cl ..91/504, 91/475  im. ci .Fo4b1/zo,Foib 13/04  ABSTRACT  Field of Search ..92/255-259, [78; A positive displacement hydraulic device such as a pump or 91/499, 504 motor includes a plurality of hydraulically balanced ball piston actuators and pistons which are controllably reciprocated in  Y References Cited cylinder bores by a tile plate having a circular groove in which the piston actuator balls roll, the groove having a pair of UNITED STATES PATENTS diametrically opposed depressions disposed opposite to the 2,617,360 11/1952 Barker ..91/501 x respective 'ende i the Pert Plate 2,749,844 6/1956 Weisenbach et al ..91/475 3 Claims, 8 Drawing Figures VARIABLE DISPLACEMENT DEVICE The present invention relates to positive displacement hydraulic pumps and motors, and it relates more particularly to such devices employing hydraulically balanced ball piston actuators and to hydraulic pumps and motors having auxiliary depressions in the tilt plate to reduce noise.
Hydraulic pumps of the types using motor driven pistons have, in the past, had an objectionably high-noise level. The noise comes from two main sources-high compression and release of the hydraulic fluid in the cylinders as they pass from the inlet to the outlet ports in the valve or port plate, and cylinder block blowot, a condition wherein the cylinder block chatters against the port plate due to unbalanced forces acting thereon and which is often caused by whipping of the piston actuator mechanisms.
An object of this invention is to provide a new and improved variable displacement hydraulic device which operates at a relatively low-noise level.
Another object of this invention is to provide means for minimizing cylinder block blowoff in a hydraulic pump or molOl.
A further object of this invention is to provide a hydraulically balanced ball actuator arrangement for use in pumps and motors.
A still further object of this invention is to provide means for eliminating compression of fluid in the cylinders of a hydraulic pump or motor.
Briefly, the above and further objects may be realized in accordance with the present invention by providing a pump or motor of the axial piston type wherein the pistons and piston actuators which are preferably solid balls, are located within and guided by the cylinder bores in the cylinder block or rotor, and a tilt plate having a plurality of depressions for interrupting axial displacement of the pistons at the'ends of their strokes as they pass from the pressure to the suction ports of the port or valve plate.
The invention, both as to its organization and method of operation, together with further objects and advantages thereof` will best be understood by reference to the following detailed description taken in connection with the accompanying drawings, wherein:
FIG. 1 is a cross-sectional view of a variable displacement hydraulic fluid translating device embodying certain features of the present invention;
FIG. 2 is an end view of the device of FIG. 1 taken from the left-hand side thereof as viewed in FIG. l and showing the inlet and outlet ports thereof;
FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1 showing the arcuate ports in the port plate;
FIG. 4 is a sectional view taken along the line 4-4 in FIG. l showing the face of the tilt plate;
FIG. 5 is an enlarged view of the device of FIG. l;
FIG. 6 is a greatly enlarged view of a portion of the tilt plate taken along the line 6-6 in FIG. 4;
FIG. 7 is an alternative embodiment of the piston assembly illustrated in FIG. 5; and
FIG. 8 is still another alternative embodiment of the piston assembly illustrated in FIG. 5.
Referring now to the drawings, and particularly to FIGS. l and 2 thereof, a hydraulic pump or motor 10 includes a mainhousing member or casing 12 which is secured to a valve or port plate 14 by means of a plurality of bolts 16 to define a chamber 18 into which a main shaft 20 extends. The inner end of the shaft 20 is journaled in a bushing 22 mounted in a suitable recess in the port plate 14. A ball bearing assembly 24 supports the other end of the shaft 20 within the housing 12 and a suitable seal 26 is interposed between the shaft 20 and the housing 12 to seal off the chamber 18. For the same reason, an O-ring 28 is compressed between the housing l2 and the port plate 14. A cylinder block or rotor 30 is attached to the shaft 20 by means of a spline 32 and a tilt plate 34 is carried by means of a pair of conventional trunnions (not shown) mounted in the housing 12. As is explained more fully piston assembly in the hereinafter, the tilt plate 34 is pivotable in the plane of the drawing about the centerline 36 and is resiliently biased into the illustrated position by means of a coil spring 38 mounted within the chamber 18 near the top thereof between a shoe 40 which fits into a recess 42 in the tilt plate and a button 44 which is attached to the end of a threaded rod 46 which extends through a threaded hole in the housing 12 and over the end of which is mounted a capnut 48 which cooperates with a sealing washer 49 to prevent undesired leakage from the chamber 18. The chamber 18 may, however, be ported to the atmosphere by means not shown. The spring pressure on the tilt plate can thus be adjusted by removing the nut 48 and rotating the rod 46. A plurality of cylinder bores 40 are drilled in the cylinder block 30 and receive respective ones of an equal number of piston assemblies 52 which are described more fully hereinafter in connection with FIG. 5. The bottom (left as viewed in FIG. l) of each of the cylinder bores 50 is in communication with the face of the port plate I4 by means of a port 54 which extends through an annular boss 56 on the rear face of the cylinder block. The adjacent face of the port plate 14 is provided with a pair of arcuate ports 58 and 60 which respectively connect to the inlet and outlets 62 and 64 provided in suitable bosses 65 and 66 in the port plate 14. Between the arcuate ports 58 and 60 are a pair of lands 68 and 69 whose arcuate length is greater than the arcuate dimension of each of the ports 54 in the cylinder block 30 so that as the ports 54 travel between the passageways 58 and 60 and thus travel across the land areas 68 and 69 their associated cylinder bores 50 are completely isolated from both the inlet and outlet ports 58 and 60 in the port plate 14.
Mounted on and forming a part of the tilt plate 34 is an annular ring or plate 70, which may be made of hardened tool steel and having therein a shallow annular groove 72 in which the piston assemblies ride and which thus controls the axial reciprocation ofthe piston assemblies in the cylinder bores 50. As best shown in FIGS. 4 and 6, shallow, radially extending grooves 74 form very small depressions in the face of the tilt plate into which the pistons fall as their respectively associated ports 54 travel across the land areas 68 and 69. Where these land areas are located at the top and bottom of the pump, as illustrated in the drawings, the transverse grooves forming the depressions 74 are likewise located at the top and bottom of the plate 70. In other words, the depressions 74 are located directly opposite to the land areas which separate the inlet and outlet ports 58 and 60 at the right-hand face of the port plate 14.
Referring now to FIG. 5 for a more complete description of the piston assemblies 52, each of the piston assemblies includes an imperforate ball 76 which fits snugly but movably in a counterbore 78 at the right-hand end of the associated cylinder bore 50. A sleevelike piston 79 is fitted into the lower part of the bore 50 and is provided with a plurality of round bottom piston grooves 80. A shoe 81 which is slightly rockable in the piston 79 is sealed thereto by means of an O-ring 82. A coil spring 84 is compressed between a button 86 at the bottom of the bore 50 and a shoulder 88 within the sleeve 79 to resiliently urge the entire piston assembly into engagement with the tilt plate assembly.
The shoe 8l which is preferably an investment or precision casting has a longitudinal passageway 89 extending therethrough and a recess 90 adjacent to the surface of the ball and defined by an annular seat 92 which has a small radius of approximately 0.015 inch on its outer edge as it leads into the ball equal to that of the ball 76 and which seats on the surface of the ball 76 in a manner permitting rotation of the ball as it travels along the groove 72 in the tilt plate during rotation of the cylinder block 30. The seat 92 has a concave portion of about 0.047 inch whose radius is equal to that of the ball and adjacent to the concave portion and forward thereof toward the tilt plate 70 is a small convex radius of approximately 0.015 inch to provide a lead in for the ball. The effective area of the recess 90 if equal to that of the bore 50 whereby there is no hydraulic pressure forcing the shoe 8l against the ball. The
only frictional force exerted between the seat 92 and the ball 76 is that caused by the spring 84 which may have a relatively low spring constant and yet maintain the ball 76 in engagement with the tilt plate 70. Hence, the ball 76 rotates rather freely as it rolls along the groove 72 thus increasing the efficiency of operation of the device. A relief hole 93 is drilled into the counterbore 78 to prevent entrapment of hydraulic fluid behind the ball 76.
In the embodiment ofthe piston assembly illustrated in FIG. 7, the generally cylindrical sleeves 79 of FIG` l has been replaced with a hemispherical piston 79 which may be half of a ball bearing through which longitudinal bore and counterbore have been provided by means of an E.C.M. machine. A centrally apertured, conical button 94 fits into the left-hand end of the hemisphere 79 and a coil spring 9S urges the entire piston Q, ssembly into engagement with the tilt plate 70. Since the piston 79' cannot bottom in the cylinder bore 50, the need for a relief counterbore at the bottom is eliminated.
In the embodiment of FIG. 8 the piston comprises a pair of back-to-back mounted hemispheres 96 and 97 which replace the single hemisphere 79' of FIG. 7 and the button 94 of FIG. 7 is replaced with a somewhat longer button 98, the shank of which extends completely through the hemisphere 94 into the hemisphere 97.
OPERATION While the hydraulic fluid translation device l of the present invention finds application as either a pump or a motor, its operation will be described hereinafter as a pump, it being understood that those skilled in the art will thereby readily understand its operation as a motor.
With the inlet and outlet ports 62 and 64 connected in a suitable pumping loop or circuit, and the shaft connected to a suitable drive source whereby it is driven in a counterclockwise direction as viewed from the right-hand side of FIG. 1, as the particular piston assembly 52 which is disposed at the bottom moves upwardly, the ball 76 thereof rolls along the groove 72 in the tilt plate and under the force ofthe spring 84 it moves outwardly of the cylinder bore S0 thereby drawing hydraulic fluid from the inlet 62 through the passageway 58 in the port plate 14 and through the port S4 to fill the void created by the piston S2 moving outwardly of the cylinder bore. When this particular piston assembly has reached the top of the chamber I8, it is at the fully extended position and at this time it rides down along a sinusoidal-shaped surface portion 99 of the depression or groove 74 and onto the flat or planar bottom of the groove 74. With balls 76 having a diameter of seven-eighths of an inch this entire groove 74 may have a cross-sectional width of five thirty-seconds of an inch, the flat portions being 0.052-inch wide. At this same time, the port 54 is passing across the land area 68 and since the piston is now axially stationary within the bore S0 there is no force exerted on the fluid within the cylinder bore S0. As the piston assembly now crosses the land area 68 and the port 54 moves into communication with the outlet 60, the piston assembly moves axially into the bore 50 thereby forcing the fluid previously drawn therein into the outlet port 60 and thus out of the outlet 64, When the piston assembly 52 again reaches the bottom of the chamber I8 it will have completed one cycle of reciprocation as it travels into the lower depression or groove 74 just before the port 54 passes onto the land area 69.
lt will be understood that the number of bores 50 and associated piston assemblies 52 which are used may vary from one application to another but for most purposes nine such bores and associated assemblies will be used. Where, however. the device is to be used as a reversing pump, an even number, such as eight pistons should be used, the spring 38 replaced with hydraulic cylinders, and the pivot axis of the trunnions moved from the location indicated at 36 in FIG. l to the longitudinal axis of the shaft 20. Also, it will be understood that the spring 38 and the associated parts, which are conventional in these types of devices, may be re laced with hydraulic or other means for varying the angle o the tilt plate, thereby to vary and automatically adjust the strokes of the piston assemblies to compensate for the changing load conditions.
lnasmuch as the piston assemblies 50, including the ball piston actuators 76 are located within the bores 50 and the balls 76 provide the only variable mechanical force on the pistons, there is no angular thrust exerted on the cylinder block whereby it is at all times angularly balanced to minimize deflection of the shaft 20 and axial movement of the cylinder block relative to the port plate.
What is claimed is:
1. A variable pressure hydraulic fluid energy translating device of the type including a port plate having a plurality of spaced arcuate ports therein separated by land areas,
a cylinder block rotatable with respect to said port plate and having a plurality of bores opening into said port plate for sequential communication with said ports during rotation of said cylinder block, and
an angularly adjustable tilt plate for controlling the stroke of a plurality of piston assemblies reciprocably mounted in said bores,
said piston assemblies each including a freely rotatable ball disposed in and rolling around a circular groove in the face of said tilt plate as said cylinder block rotates, characterized by a plurality of radial grooves in said tilt plate extending below the bottom of said circular groove and respectively positioned along said circular groove opposite said land areas for permitting said piston assemblies to move into said radial grooves when said bores are disconnected from said ports.
2. A device according to claim 1 wherein said cylinder block is provided with a plurality of connec'tor ports connecting said bores to said port plate,
said connector ports having an arcuate length less than the arcuate length of said land areas, and
said radial grooves each have a width less than the arcuate length of said connector ports.
3. A device according to claim l wherein said bores are counterbored,
said balls are disposed in the counterbores, and
said piston assemblies each comprise a generally cylindrical sleeve and a pair of hemispheres.