US2850986A

US2850986A - Axial hydro-dynamic machine having opposed pistons

Info

Publication number: US2850986A
Application number: US545242A
Authority: US
Inventors: Adolf R Grad
Original assignee: Oilgear Co
Current assignee: Oilgear Co
Priority date: 1955-11-07
Filing date: 1955-11-07
Publication date: 1958-09-09
Anticipated expiration: 1975-09-09

Description

Sept'.` 9; 1958 Y A. R. GRAD Y I 2,850,986

l-DIIAI..V HYDRO--lDYNAMlICv MACHINE HAVING OPPOSED PISTONS mea Nov. '1. 195s I -8 sheets-sheet 1 ADOLF R. GRAD BVM/,f

ATTORNEY Septt 9, 1958 A. R. GRAD 2,850,985

AXIAL HYDRO-DYNAMIC MACHINE HAVING `OPPOSED PISTONS Filed Nov. 7, 1955 I a'lsheets-sheet 2 INVENTOR ADO LF R. GRAD ATTORNEY Sept." 9, 1958 Axnu. HYDRO-DYNAMIC MACHINE HAVING oPPosED PIsToNs :medl Nov. 7. 195s `:s sheets-shea s ADOLF RGRAD ATTORNEY A. R. GRAD 21,850,986

Sept- 9,1958 A. RGADf 2,850,986

AXIAL HYDRO-DYNAMIC MACHINE HAVING oPPosEp pIs'roNs ADO LF R. GRAD BYWW ATTORNEY Sept. 9. 1958 A. R. GRAD 2,850,986

AXIAL HYDRO-DYNAMIC MACHINE HAVING OPPOSED PISTONS Filed Nov. '7, 1955 8 Sheets-Sheet 5 24 SYM); l

ATTORNEY Sept. 9, 1958 A. R. GRAD 2,850,986

Axw. HYDRO-DYNAMIC MACHINE HAVING oPPosEn PIsToNs FiledNov. '7. 1955 8 Sheets-Sheet 6 y i I \7 g og LL m ,Q //////f\ L\\\\ E mfsi im ADOLF R. GRAD BWW ATTORNEY Sept. 9. 195s A. R. GR@ 2,850,986

TTTTTT EY SPf- 9 1958 A. R. GRAD 2,850,986

AXIAL HYDRO-DYNAMIC MACHINE HAVING OPPOSED PISTONS Filed Nov. 7. 1955 8 Sheets-Sheet 8 a@ mw www?! ATTORNEY AXIAL HYDRO-DYNAMIC MACHINE HAVING OPPSED PSTONS Adolf R. Grad, Milwaukee, Wis., assignor to The Gilgear Company, Milwaukee, Wis., a corporation of Wisconsm Application November 7, 1955, Serial No. 545,242

11 Claims. (Cl. 103-162) This invention 'relates to hydrodynamic machines of the axial type which will function as `pumps when driven mechanically and will function as motors when supplied with motive liquid. Since the function of a motor is substantially opposite to the function ofa pump, a machine embodying the invention will be referred to herein 'as a pump in order to simplify the description, but it is to be understood that the invention is equally applicable to motors, and that the term pump as used herein is intended to mean either a pump or a motor.

The type of pump to which the invention relates in particular has its pistons and'cylinders arranged vin a rotatable cylinder barrel around and parallel to `theaxis thereof, rotation of the cylinder causes the -pistons to be reciprocated by a swash plate when that'plate is inclined 'to the cylinder barrel axis, and the swash plate is carried by a cradle which may be tilted to vary the displacement of the pump. Such a pump -is disclosed in application Serial No. 388,163, tiled October 26, 1953, now Patent No. 2,804,828, of which this application is a ycontinuation in part.

The cradle is tiltable upon trunnions .carried by the pump casing, and the swash plate is rotatably supported upon the cradle and is rotated with the cylinder barrel. The pumping reactions are transmitted through the swash plate and the cradle to the casing and, `when the pump is of large capacity and is creating a high pressure, the resultant of the 'pumping reactions is tremendous and causes deflection of the cradle regardless of how heavy the cradle is made. The deflection of the cradle is slight, but it is sutlicient to cause some wear between the kswash plate and the cradle when the pump is creating very high pressures.

The present invention hasfas an object to provide a pump of the above type in which dellection of the cradle is avoided.

Another object is to provide a pump having a longer stroke than is possible in the prior pumps because of deflections of the cradles thereof.

Another object is to split the phase of an axial pump in order to provide better delivery characteristics and to reduce the noise level.

Another object is to provide a pump which may be driven at a speed considerably higher than the speed at which a conventional pump of the same capacity must be driven, thereby enabling the user to employ a high speed electric motor for driving the pump.

Another object is to provide a pump which may be` made in very large capacities and operated at very high pressures.

A pump constructed according to the invention has the advantage that it may be fully tested on a test stand having a capacity only one-half that of the pump.

Another advantage is that the majority of the parts of a large pump embodying the invention and the majority of the parts of a pump having one-half the capacity of the large pump are identical, thereby reducing tooling andy inventory costs.

rates Patent O ice Other objectsand advantages will appear from .the following description of the embodiment of the invention shown somewhat schematically inthe accompanying drawings in which the views areas follows:

Figs. land 1A taken together constitute a central, vertical, longitudinal sectionthrou'gh apurnp in which the invention is embodied, the plane vof the View being indicated by the line 1 1 of Fig. 3.

Fig. 2 is a central sectional plan view taken on the irregular line 2 2 of Fig. 3, but with the pump casing and the end portions of the pump omitted.

Fig. 3 is a vertical transverse section taken on the line 3 3 of Fig. l.

Fig. 4 is a section takenon the liner 4 4 of Fig. l, but with the pump casing omitted.

Fig. 5 is a face viewof one `ofthevalves 'which control the flow of liquid to and from the pumping cylinders, the plane of the view being indicated by the line 5 5 of Fig. l.

Fig. 6 is a section taken through the valve of Fig. 5 and portions ofthe adjacent parts, the view being taken on the line 6 6 of Fig. 5, but drawn to a larger scale.

Fig. 7 is a transverse section taken on the line 7 7 of Fig. Vl.

Fig. 8 is a sectional plan View showing the connections between the main fluid passages ofthe pump, the view being taken on the line 8 8 of Fig. 3, but with vcertain portions omitted.

Fig. 9 is a sectional view taken through a swash plate and through one ring of the universal joint which transmits rotary motion from a cylinder barrel to the swash plate, the View being taken in the plane indicated by the line 9 9 of Fig. l, but drawn to a larger scale.

Fig. l0 is an enlarged longitudinal section through one of the piston and piston rod assemblies shown in Fig. 1.

Fig. ll is a diagram illustrating the hydraulic circuits of the pump.

The pump has its mechanism arranged within and supported by a suitable casing shown as including a body 1, a block 2 which is fixed lto and closes the right or rear end of body 1, a block 3 which is xed to and closes the front or left end of body 1, and an end head 4 which is fixed to block 3 and carries a bearing 5 for a drive shaft 6 which extends through body 1 and is journaled ina pair of bearings 7 carried by blockY 2. The right end of the shaft 6 is reduced in diameter and has lfixed thereon the driven gear of a gear pump 8 which supplies liquid for control purposes as will presently be explained.

Shaft 6 has fixed for rotation therewith two cylinder barrels 9 and I'a which are arranged opposite hand to each other. Cylinder barrel v9 has a plurality of cylinders 10 formed therein parallel to shaft 6 and equally spaced in a circular row concentric with shaft 6. Each cylinder 10 has a piston 11 fittedftherein and an elongated cylinder port 12 `extending therefrom through the end of the cylinder barrel.

Cylinder barrel 9a is identical to cylinder barrel 9 and is similarly provided with identical cylinders 10a, pistons 11a and ports 12a. However, cylinder barrel 9a is rotated one-fourth of a cylinder space in respect to cylinder barrel 9 in order to split the phase ofthe pump. That is, there are an odd rnumber of cylinders in each cylinder barrel and one cylinder barrel is angularly displaced far enough from the other to prevent any two cylinders from opening't'o the valve ports 'at the same instant. In order to simplify the drawings, Figs. 1 and 1A show a cylinder 10 and a cylinder 10a in the plane indicated by the line 1 1 of Fig. 2 but actually that plane passes through only a small portion of cylinder 10a.

Each piston 11 is connected by a piston rod 15 to a swash plate 16, and each piston 118L is connected by a piston rod EL to a swash plate 16a. The swash plates are caused to rotate with the cylinder barrels and will effect reciprocation of the pistons when shaft 6 is rotated and the swash plates are inclined to the axis of shaft 6 as will presently be explained.

Reciprocation of the pistons causes liquid to be alternately drawn into and discharged from the cylinders. The valve for controlling the flow of liquid to and from the cylinders in each of the two cylinder barrels and the passages for such iiow are substantially the same as in the pump shown in application Serial No..388,163 to which reference may be had for details of construction.

As shown, flow of liquid into and out of the several cylinders 10 is controlled by an annular flat valve 17 which engages the end of cylinder barrel 9 and extends around shaft 6. The contacting surfaces are made at and smooth to provide a substantially liquid tight joint between valve 17 and cylinder barrel 9. Rotation of valve 17 is prevented such as by means of the one or more pins 18 which extend through valve 17 and into block 2.

Valve 17 has two arcuate ports 19 and 20 (Fig. 5) formed in the face thereof upon the same radius as cylinder ports 12 each of which registers with ports 19 and alternately as cylinder barrel 9 rotates. The adjacent ends of ports 19 and 2i) are spaced apart a distance equal to or slightly greater than the length of a cylinder port 12. The portions of the valve face between the ends of

port

19 and 20 constitute seals or bridges which prevent a cylinder port 12 from establishing communication between the two valve ports as the cylinder port moves from one valve port to the other.

Valve port 19 communicates with a plurality of oblong holes 21, four being shown, and valve port 20 communicates with an equal number of oblong holes 22. Each hole 21 communicates with a hold-up motor 23 and each hole 22 communicates with a hold-up motor 24 all of which are arranged within valve 17.

The hold-up motors are all alike and, as shown in Fig. 6, each includes a cylinder 25 which is formed in A valve 17, a tubular piston 26 which is tted in cylinder 25, an annular sealing member 27 which is arranged between piston 26 and block 2, and a spring 28 arranged between piston 26 and the end wall of cylinder 25 to initially urge valve 17 against cylinder barrel 9, piston 26 against member 27 and member 27 against block 2. The contacting surfaces of member 27 and block 2 are made flat and smooth and the contacting surfaces of member 27 and piston 26 are made spherical and smooth to provide substantially liquid tight joints therebetween while permitting valve 17 to adjust itself to the end of cylinder barrel 9.

Valve 17 is adapted to be intermittently urged against cylinder barrel 9 by a plurality of balancing motors 29 one of which is `shown in Fig. 2 behind each of the bridges between the adjacent ends of

valve ports

19 and 20. The hold-up motors and the balancing motors hold valve 17 in contact with cylinder barrel 9 and compensate for variations in the force which tends to move valve 17 away from cylinder barrel 9 as is well known and fully explained in application Serial No. 388,163.

Each hold-up motor 23 and each hold-up motor 24 register respectively with a hole 30 and a hole 31 found in block 2. As shown in Fig. 7, the four holes 31 communicate with a passage 32 which is found in block 2 and communicates with a passage 33. Likewise, the four holes 30 communicate with a passage 34 which is found in block 2 and communicate with a passage 35.

The flow of liquid into and out of the several cylinders 10a is controlled by a flat valve 17a which is identical to valve 17 and has identical hold-up and balancing motors. The hold-up motors in valve 17a communicate with passages 32a and 34a which are found in block 3. Valve 17a and the passages in block 3 have not been shown in detail because views showing the same would j be substantially duplicates of Figs. 5, 6, and 7. Therefore, corresponding parts and passages which appear in the drawings have been indicated by corresponding reference numerals with the exponent a added to the numerals applied to valve 17a and the passages in block 3. As best shown in Fig. 8,

passages

33 and 35 extend from passages 32a and 34a, respectively, through casing body 1 and block 2 for connection to opposite sides of an external circuit which has been represented by portions of two

pipes

36 and 37.

Passages

32 and 34 have been shown in Figs. 7 and 1l as having the lower ends thereof closed and passages 32a and 34a have been shown in Fig. 1l as having the lower ends thereof controlled by an automatic suction valve, but a suction valve may be arranged at either or both ends of the pump. Such valves are well known and in extensive use.

As indicated in Fig. 11, a valve body 40 is attached to the bottom of block 3 and provided with an axial bore 41 having formed in the wall thereof two annular grooves or

ports

42 and 43 with which passages 32a and 34a communicate respectively. Communication between

ports

42 and 43 is controlled by a valve 44 which is fitted into bore 41 and has two ducts 45 and 46 extending axially into it from its opposite ends and then extending radially outward into communication with

ports

42 and 43 respectively.

Bore 41 communicates at a point between

ports

42 and 43 with one end of a channel 47 the other end of which is connected to the outlet of a check valve 48 and the inlet of a low pressure resistance valve 49. A channel 50 connected to the inlet of the check valve 48 and a channel 51 connected to outlet of resistance valve 49 extend into a supply liquid contained in a reservoir 52 upon which the pump ordinarily is mounted.

The arrangement is such that, when valve 44 is in the position shown and the pump discharges into passages 34 and 34S', the discharged liquid will tend to iiow through body 40, channel 47 and resistance valve 49 into reservoir 52, but the resistance of valve 49 will cause pressure to -rise and liquid to flow through duct 46 into the end of bore 41 and move valve 44 against the other end of bore 41 in which position valve 44 blocks port 43 and prevents the pump from discharging into reservoir 52. Then when the pump is reversed, valve 49 will cause pressure to rise and liquid to flow through duct 45 into the end of bore 41 and move valve 44 to the position shown, in which position it blocks discharge from the pump into reservoir 52. When the liquid returned to the pump from the external circuit is in excess of the volume required to supply the pump, the excess is exhausted through valve body 40 and resistance valve 49 into reservoir 52 and, when the pump requires more liquid than is returned to it from the external circuit, it will draw liquid through body 40, channel 47, check valve 48 and channel 50 from reservoir 52 regardless of the position of valve 44.

As shown in Figs. l and 2, swash plates 16 and 16HL are rotatably supported, respectively, by two reaction members or cradles 54 and 54a which are swingable in a horizontal plane to vary the angle between the swash plates and the cylinder barrels and thereby vary the displacement of the pump, swinging of the cradles being permitted by tapered openings 55 and 55a which extend through cradles 54 and 54a respectively and through which shaft 6 passes.

Cradle 54 has an integral central horn 56 and two

integral arms

57 and 58 which are arranged diametrically opposite each other and are pivotally supported by two trunnions 59 and 60 respectively. Trunnion 59 is carried by the lower wall of casing 1 and by a web 61 which is formed integral with casing 1. Trunnion 60 is carried by the upper wall of casing 1 and by a web 62 which is formed integral with casing 1. Trunnions S9 and 60 are ordinarily provided with anti-friction bearings which have been omitted from the drawings in order to simplify the views.

Cradle 54 also includes a flat annular wear plate 63 which extends around the base of horn 56 and is engaged by an annular thrust bearing 64 which is xed for rotation with swash plate 16. Horn 56 has fixed thereon a bearing 65 on which swash plate 16 is journaled.

Except for the means for swinging the cradles upon their trunnions, cradle 54a and the means for mounting it are the same as, but are arranged opposite hand to cradle 54 and its mounting means. Therefore, further description thereof is deemed unnecessary since corresponding parts have been indicated by corresponding reference numerals the exponent a added to the numerals applied to cradle 54a and its mounting means.

The adjacent ends of cradles 54 and 54a are provided, respectively, with rolling contact faces 66 and 66a which firmly engage each other so that pumping reactions transmitted through swash plate 16 to cradle 54 are opposed by equal and opposite pumping reactions transmitted through swash plate 16a to cradle 54a, thereby preventing the cradles from being deected by the pumping reactions. Contact faces 66 and 66a have equal radii and are concentric with the trunnions of the respective vcradles so that they remain in firm contact with each other throughout the swinging movements of the cradles.

The piston and piston rod assemblies comprise pumping piston 11 or 11a piston rods 15 or 158L and the associated parts are all alike and a description of one will sufiice for all. As shown in Fig. l0, each piston 11 has formed in its outer end a spherical seat 68 which is complementary to and engaged by a spherical head 69 forming one end of piston rod 15 the other end of which is formed into a spherical head 70 which forms a part of a ball and socket joint 71 as will presently be explained. Head 69 is nearly as large in diameter as cyl-V inder to provide between it and piston 11 bearing surfaces which are of maximum area to thereby permit very high pumping forces to be transmitted therethrough and thereby enable piston 11 to create very high pressures in cylinder 10.

Piston 11 has a recess 72 of varying diameters extending into it from its inner end and a bore 73 extending from recess 72 through seat 68. Piston rod 15 has a spherical seat 74 formed within head 69 concentric with seat 68, an opening 75 extending from seat 74 through head 69 and a bore 76 extending from seat 74 through head 70.

Head 69 is held in Contact with seat 68 by a pin 77 having a spherical head 78 the surface of which is complementary to and in contact with seat 74. Pin 77 extends through opening 75 and bore 73 into recess 72 and has a cannelure 79 formed in the portion which extends into recess 72. When connecting piston 11 and piston rod to each other, head 78 is urged against seat 74, head 69 is urged against seat 68 and then a plug 80 of suitable metal is upset or swaged into the inner end portion of recess 72 and into cannelure 79 thereby preventing any relative axial movement between piston 11 and rod 15 while permitting rod 15 to gyrate relatively to piston 11 as cylinder barrel 9 rotates. Also, the end of pin 77 has no tendency to move radially relatively to the piston as is the case in the prior piston and rod assemblies of this type.

ln order to provide liquid for lubrication and hold-up purposes, pin 77 has a passage 81 extending axially therethrough and controlled by a check valve shown as comprising a plug 82 which is fixed in recess 72 and has a passage 83 extending therethrough, a ball 84 which normally closes the end of passage 83, a piston 85 which is fitted in recess 72 and has one or more passages 86 extending through its head end, and a spring 87 which urges piston S5 against ball 84 and ball 84 against plug 82. The arrangement is such that, when pressure is created in cylinder 1t?, it will raise ball 84 away from its seat, and then liquid can low from cylinder 10 through

passages

83, 86 and 8l into bore 76 and create pressure therein and, when cylinder 5.9 opens .to the low pressure valve port, spring 87 will urge ball 84 to its seat and preventy escape of liquid from bore 76 into cylinder 10 Also, if the pump case is not filled with liquid, checkv valve` S487 will prevent piston 11 during its suction stroke from drawing any air into cylinder 10 through the above described passages and through the lit between wear plate 63 and thrust bearing 64.

Ball and socket joint 71 includes a socket 90 `which is closely fitted upon the spherical head 70 of piston rod 15 and is arranged within a pocket 91 formed in `swash plate 16. Socket 90 is retained in pocket 91 in any suitable manner such as by means of a retainer ring 92 which has one end in contact with a shoulder formed upon socket 90 and its other end in contact with a snap ring 93 fitted in a suitable groove'formed in the wall of pocket 91.

Socket 90 has a central hole 94 extending therethrough to providey communication between the bore 76 in rod 15 land a hole 95 which extends kthrough swash plate 16 and communicates with a hole 96 which extends through thrust bearing 64 into communication with an elongated recess or pressure chamber 9'7 formed therein.

When pressure is rst created in cylinder 10, it will cause liquid to llow therefrom through the previously described passages into bore 76 in rod 15 and from bore 76 through

holes

94, 95 and 96 into pressure chamber 97. The pressure in chamber 97 will cause liquid to seep therefrom and spread over the contacting faces of thrust member 64 and wear plate 63 to form a lubricating lilm therebetween and the pressure will extend into that film. It has previously been stated that all of the pistons and piston rod assemblies are alike and it is to be understood that a pressure chamber is arranged in the same radial plane with each assembly. As indicated in Fig. 9, the pressure chambers in each thrust bearing are arranged in a circular row and spaced from each other.

As fully explained in application Serial No. 388,163, thearea of each chamber 97 and the area of the surrounding lilm into which pressure can extend form a balancing area which is so proportioned that the force exerted by the liquid therein is just slightly less than the force exerted -by the liquid upon the piston in the same radiall plane.

When the pump is performing useful work, each cylinder will communicate with a high pressure valve port and the piston in that cylinder'will be advanced and will eject liquid from the cylinder during one-half of each revolution of the cylinder barrels, and it will communicate with a low pressure port and the piston in that cylinder will be retracted and will draw liquid into the cylinder during the other half of each revolution of the cylinder barrels. The instant that a cylinder opens to the high pressure port, the pressure therein will act upon the end of the piston in that cylinder and also act upon the balancing area for that piston. The instant a cylinder opens to a low pressure port, pressure acting upon the piston in that cylinder and upon the balancing area for that piston will drop. The swash plates and the piston and piston rod assemblies are thus substantially hydrostatically balanced.

If it were not for this several check valves 82-87, each time a piston was retracted it would suck liquid out of the interior of that piston and piston rod assembly, thereby reducing the total volume of liquid delivered by the pump and causing momentary delays in establishing hydrostatic balance of' the piston and piston rod assemblies.

Rotary motion is transmitted to swash plates 16 and 16a from cylinder barrels 9 and 9EL through universal joints which are radially 4outward from the connections between the swash plates and the piston rods instead of being radially inward therefrom as is the common practice in the prior pumps of the same general type. Since the two universal joints are identical and are connected to the swash plates and to the cylinder barrels by identical means, a description of one will sufice for both as like parts have been indicated by like reference numerals with the exponent a added to the reference numerals applied to the universal joint and the connecting means through which rotary motion is transmitted from cylinder barrel 9a to swash plate 16a.

As shown in Figs. l, 2, and 9, swash plate 16 has two U shaped arms 100 formed integral with its outer peripheral portion at diametrically opposite points and connected by two pins 101 to a ring 102 at diametrically opposite points. A second ring 103 is connected to cylinder barrel 9 in the same radial plane in which ring 102 is connected to swash plate 16. As shown in Fig. 1, ring 103 is connected at diametrically opposite points by two pins 104 to the bifurcated outer ends of two plungers 105 which are slideable in bores 106 formed in cylinder barrel 9. Plungers 105 are urged outward by light springs 107. As shown in Fig. 2, rings 102 and 103 are pivotally connected to each other by two pins 108 which are spaced 90 from

pins

101 and 104 and are arranged in the same transverse plane as trunnions 59 and 60.

The arrangement is such that cylinder barrel 9 when rotated will rotate ring 103 through plunger 105 and pins 104, ring 103 will rotate ring 102 through pins 108, ring 102 will rotate swash plate 16 through pins 101 and. thrust bearing 64 will rotate with swash plate 16. If cradle 54 and swash plate 16 are inclined to the axis of cylinder barrel 9, ring 103 will pivot upon pins 104 and ring 102 will pivot upon

pins

101 and 108 to compensate for the angle between the axes of rotation of cylinder barrel 9 and swash plate 16.

The pump has been shown with swash plates 16 and 16e in their neutral positions, that is, normal to shaft 6 in which position of the swash plates, pump displacement is zero. When the pump is driven and the swash plates are inclined to shaft 6, the pump will deliver liquid in a direction and at a rate determined by the direction and distance that the swash plates are inclined from their neutral positions. Swash plates 16 and 16B' may be tilted by swinging cradles 54 and 54B upon their trunnions either manually or mechanically in any suitable manner.

As shown in Figs. l and 4, two intermeshing seg' mental gears 112 and 112u are fixed to cradles 54 and 54B, respectively, and a segmental gear 113 is fixed upon the arm 58 of cradle 54 and meshes with a rack 114 which is formed upon a piston rod 115 having a piston 116 (Fig. 3) fixed upon one of its ends. Piston 116 is fitted in a cylinder 117 which is carried by casing 1. The other end of piston rod 115 is tixed to the hub 118 of a piston 119 fitted in a cylinder 120 which is carried by casing 1 and has its outer end closed by a head 121. The inner ends of

cylinders

117 and 120 communicate with the interior of casing 1 so that the inner faces of

pistons

116 and 119 are never subjected to pressure.

Hub 118 has an axial bore 122 extending therethrough, a port 123 leading from bore 122 into communication with the outer end of cylinder 120 and at least one drain duct 124 leading from bore 122 into communication with the inner end of cylinder 120. Flow of liquid into and out of the outer end of cylinder 120 is controlled by a rotary valve 125 which is fitted into bore 122 and in end head 121 and has its outer end portion reduced in diameter and provided with a lever 126 for rotating it.

Valve 12S has a diagonal drain groove 127 and a diagonal pressure groove 12S formed in its peripheral surface.

Grooves

127 and 128 are arranged upon opposite sides of port 123 and are spaced apart a distance equal to the width of port 123 so that a slight rotary movement of valve 125 in one direction or the other will cause port 123 to communicate with one or the other of

grooves

127 and 128. Groove 127 extends to the inner end of valve 125 so that it is always connected to the exhaust. Groove 12S communicates with a passage 129 which is formed within valve 125` and communicates with an annular groove or port 130 which is formed in end head 121. The servo-motor mechanism including the follow-up valve just described is of a well known type and is similar to that illustrated and described in Patent No. 2,499,633.

, Liquid for operating the above described servo-motor mechanism is supplied by gear pump 8 which, as indicated in Fig. 1l, draws liquid from reservoir 52 and discharges it into a branched supply channel 131 which is connected to cylinder 117 and to port 130. Liquid discharged by gear pump 8 in excess of, requirements is exhausted through a relief valve 132 which enables pump 8 to maintain a constant low pressure in channel 131.

The arrangement is such that when valve 125 is rotated in a direction to open groove 127 to port 123, the liquid continuously supplied to cylinder 117 will cause piston 116 to move rod 115 and piston 119 toward the left in respect to Fig. 3 and piston 119 to eject liquid from cylinder through port 123, groove 127, bore 122 and duct 124 to exhaust. Piston 119 will move a linear distance proportional to the angular distance through which valve was rotated and then port 123 will move out of communication with groove 127 and further movement will cease. Conversely, when valve 125 is rotated in a direction to open groove 128 to port 123, liquid will flow from channel 131 through port 130, passage 129, groove 128 and port 123 into cylinder 120 and cause piston 119 to move rod 115 and piston 116 toward the right in respect to Fig. v3 and piston 116 to eject liquid from cylinder 117 into channel 131 because the effective area of piston 119 is approximately twice that of piston 116. Movement will continue until port 123 moves out of communication with groove 128 at which time piston 119 will have moved a linear distance proportional to the angular distance through which valve 125 was rotated.

Rack 114 being formed upon or fixed to piston rod 115, it will move with rod 115 and will cause gear 113 (Fig. 4) to rock cradle 54 on trunnions 59 and 60 and gears 112 and 112a `will rock cradle 54a upon trunnions 59 and 60zt to change the angle between swash plates 16 and 16a and the axis of the cylinder barrels and thereby change the displacement of the pump.

The pump illustrated and described herein may be modified various ways without departing from the scope of the invention which is hereby claimed as follows:

1. A pump, comprising a casing, two axially aligned cylinder barrels rotatably supported in said casing with each having a plurality of cylinders arranged therein around and parallel to the axis of rotation, means for rotating said cylinder barrels in unison, two swash plates arranged between the adjacent ends of said cylinder barrels, two pairs of trunnions carried by said casing and arranged between the adjacent ends of said cylinder barrels, a reaction member rotatably supporting each of said swash plates and journaled upon said trunnions, said members being swingable in opposite directions upon said trunnions to vary the angle between said swash plates and the axis of said cylinder barrels, means for rotating said swash plates in unison with said cylinder barrels, pistons fitted in said cylinders, piston rods connecting said pistons to said swash plates and effecting reciprocation of said pistons in response to said cylinder barrels and said swash plates being rotated and said swash plates being inclined to the axis of said cylinder barrels, valve means engaging said cylinder barrels to control the flow of liquid to and from said cylinders, and an arcuate contact face arranged upon each of said reaction members andengaging the contact face on the other member to thereby cause the pumping reactions from the pistons in one cylinder barrel to be counterbalanced by the pumping reactions from the pistons in the other cylinder barrel.

2. A pump according to claim 1 and including displacement varying means carried by said casing, means connecting said displacement varying means to one of said reaction members to enable it to swing said member upon its trunnions, and gears connecting said reaction members to each other.

3. A pump, comprising a casing, two axially aligned cylinder barrels rotatably supported in said casing with each having a plurality of cylinders arranged therein around and parallel to the axis of rotation, means for rotating said cylinder barrels in unison, two swash plates arranged between the adjacent ends of said cylinder barrels, two pairs of trunnions carried by said casing and arranged between the adjacent ends of `said cylinder barrels, a reaction member rotatably supporting each of said swash plates and journaled upon said trunnions, said members being swingable in opposite directions upon said trunnions to vary the angle between lsaid swash plates and the axis of said cylinder barrels, two annular universal joints extending around said swash plates with each connecting a swash plate to the adjacent cylinder barrel to rotate it therewith, pistons fitted in said cylinders, piston rods connecting said pistons to said swash plates and effecting reciprocating of said pistons in response to said cylinder barrels and said swash plates being rotated and said swash plates being inclined to the axis of said cylinder barrels, at valves engaging the far ends of said cylinder barrels to control the flow of liquid to and from said cylinders, and an arcuate contact face arranged upon each of said reaction members and engaging the contact face on the other member to thereby cause the pumping reactions from the pistons in one cylinder barrel to be counterbalanced by the. pumping reactions from the pistons in the other cylinder barrel.

4. A pump according to claim l and-including means for swinging said reaction members in unison upon said trunnions to thereby vary the displacement of said pump, said means comprising a pair of intermeshing gears connecting said members to each other, a third gear carried by one of said members, hydraulic servo-motor means carried by said casing, a rack carried by said servo-motor means and meshing with said third gear, and means for supplying motive liquid to said servo-motor means including a valve for controlling the ow of liquid thereto and therefrom.

5. A pump, comprising a casing, a drive shaft journaled in said casing, two cylinder barrels spaced from each other and xed upon said shaft to rotate therewith, each of said cylinder barrels having a plurality of cylinders arranged therein around and parallel to said shaft, two swash plates arranged between the adjacent ends of said cylinder barrels, two pairs of trunnions carried by said casing and arranged between the adjacent ends of said cylinder barrels, a reaction member rotatably supporting each of said swash plates and journaled upon said trunnions, means for swinging said members in opposite directions upon said trunnions to vary the angle between said swash plates ad said shaft and thereby vary the displacement of said pump, means for rotating said swash plates in unison with said cylinder barrels, pistons fitted in said cylinders, piston rods connecting said pistons to said swash plates and effecting reciprocation of said pistons in response to said cylinder barrels and said swash plates being rotated and said swash plates being inclined to the axis of said cylinder barrels, at valves engaging the far ends of said cylinder barrels to control the flow of liquid to and from said cylinders, and in arcuate contact face arranged upon each of said reaction members and engaging the contact face on the other member to thereby cause the pumping reactions from the pistons in one cylinder barrel to be counterbalanced by the pumping reactions from the pistons in the other cylinder barrel.

6. A pump according to claim 5 in which said casing includes a body portion and two blocks which are fixed to the opposite ends of said body portion and contain high and low pressure passages, said valves are supported by said blocks and control communication between said cylinders and said passages, and said body portion has formed therein two passages which connect the passages in one block with the corresponding passages in the other block.

7. In a pump of the class described having a casing, a cylinder barrel arranged within said casing and rotatable upon a stationary axis, a reaction member restrained from axial movement by said casing and inclined to said axis when the pump is functioning, a swash plate carried by said member and rotated in unison with said cylinder barrel, a socket carried by said swash plate and having an internal spherical surface, a hydraulic thrust bearing arranged between said swash plate and said member and having a pressure chamber formed therein and communicating with the interior of said socket, the combination of a piston fitted in said cylinder and having a spherical seat formed in its outer end, a piston rod having a first spherical head formed upon one end thereof and fitted in said seat, a second spherical head formed upon the other end of said piston rod and fitted in said socket to form therewith a ball and socket joint, said piston rod having an internal spherical seat formed therein concentric with the outer spherical surface of said first head and a bore extending therethrough from said internal seat into communication with the interior of said socket, said piston having a recess extending into it from its inner end and a bore extending from said recess through its outer end and said rst piston rod head having an opening extending therethrough from said internal seat, a pin extending from said internal seat into said recess and having an axial passage extending therethrough to permit pressure in said cylinder to extend through said passage and the bore in said rod into said socket and from said socket into said pressure chamber, a spherical head formed upon said pin and engaging said internal seat, and means arranged in said recess and engaging said pin for holding the head of said pin in contact with said internal seat and said iirst piston rod head in contact with the spherical seat in said piston.

8. A combination as set forth in claim 7 including a check valve arranged in said recess to prevent escape of liquid from the interiors of said piston and said pist0n rod into said cylinder and to prevent air being sucked when case is empty of oil.

9. A combination as set forth in claim 8 in which said check valve includes a valve seat xed in said'recess to close the end thereof and having a duct extending therethrough, a valve normally engaging said seat and closing the inner end of said duct, a piston fitted in said recess and having a passage extending therethrough, and a spring engaging said piston to urge it against said valve and said valve against said seat.

10. A combination as set forth in claim 7 in which said pin has a cannelure formed in its peripheral surface and arranged within said recess and a metal plug is swaged into said cannelure and against the end of said recess to hold the head of said pin in contact with the spherical seat in said piston.

11. A combination as set forth in claim 10 including a check valve arranged in said recess to prevent escape of liquid from the interior of said piston and said piston rod into said cylinder and to prevent air being sucked when case is empty.

References Cited in the le of this patent UNITED STATES PATENTS