The invention is related to positive displacement motors and pumps having rotating or reciprocating pistons. The invention is particularly related to variable-delivery piston pumps for hydraulic systems. b) BACKGROUND ART.

Mos of variable-delivery pumps belong to three basic types: vane pumps, radial piston pumps and axial piston pumps. A vane pump has a cylindrical rotor with two or more vanes which slide in slots spaced equidis tantly and radially aro _. und the rotor. The slots are sometimes inclined at a certain angle to radial directions in the rotor. The mechanism is confined within a track ring by closely fitting end plates, the rotor being e centrically placed. As the rotor rotates the centrifugal force maintains the vanes always in contact with the track ring. Due to the eccentricity between rotor and track ring the volume dle_ fined by two adjacent vanes varies from a minimum to a maximum in half turn of ..the rotor. In the subsequent half turn this volume decreases reaching again the minimum. As the volume i _ creases fluid is admitted through as inlet port in the track ring. As the volume decreases fluid is discharged through an opposite outlet port. Variable delivery is obtained by alter ing the degree of eccentricity of the rotor and the track ring. It is possible by moving either the rotor or the track ring to give a step less ly variable delivery from zero to a maximum as well as to invert the direction of the fluid flow. A radial piston pump resembles a ^' vane pump where the vanes were sμbstituted by pistons within bores equidis tantly and radially disposed in a rotor or cylinder block. As in a vane pump, the cylinder block rotates so that the pistons are thrown outwards by centrifugal force, their outward stroke being limited by their outer ends coming against a track or guide ring. During the rotation a reciprocating action is produced in the pistons when the cylinder block is located eccentrically within the guide ring. The pistons move in sequence to the outer ends of

their respective cylinders, drawing in fluid through an inle valve port located in a fixed shaft on which the cylinder bloc rotates. On reaching a. position of maximum displacement of th piston the inner end of the cylinder passes to a outlet valv port also in the fixed shaft in an opposite position to the i let valve port. From this point, as the rotation continues , th piston moves towards the center of the cylinder block dis charging its fluid contents in the outlet valve port .A variable delivery is produced in similar manner as in vane pumps by altering the relative eccentricity of the rotating cylinder block and the guide ring. There is another entirely different form of radial piston pump where the cylinder block is statio ary . In this type of pump the reciprocation of the pistons is achieved by an eccentrically mounted bearings on the driving shaft. The pistons are kept in contact with the bearings by action of springs. To alter delivery the eccentricity of the bearings can be varied by a mechanism passing through the center of the driving shaft. In this pump each cylinder has its own suction and delivery valves both of the spring-loaded ball type.

An axial piston pump has a cylinder block with bores equally spaced about the periphery of a circle concentric with the driving shaft. This is actually a more compact arrangement than in a radial piston pump. To actuate' in the pistons a mor complex mechanism is necessary. This mechanism is generally a circular plate inclined with respect to the driving shaft. Th pistons are linked to this plate, commonly called swashplate, by connecting rods and universal joints. As the cylinder bloc rotates apertures leading to the cylinders are brought opposit the suction and ^{^} delivery ports in a valve plate placed in contact with the cylinder block. The inclination of the swas plate is such that the cylinders are filled with fluid when i contact with the suction port and discharged when in contact with the delivery port. By tilting the swashplate to differen positions a _^ variable delivery is given.

Pumps which have rotary valves attain lower pressures than pumps with seated valves. Radial piston pumps of the stationar

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. cylinder block type, for instance, which have seated valves

2 are made, for pressures as high as 425 kg/cm (about 6,055 p.s.i.) whereas in radial piston pumps with rotating cylinder blocks, which have rotary valves, pressure is limited to about

5 210 kg/cm (about 3,000 p.s.i.) . Axial piston pumps, which hav ee 2 rotary valves, have maximum working pressure about 280 kg/cm

(about 4,000 p.s.i.). Vane pumps, in which vanes act as rotary

2 valves, are made for pressures up to 140 kg/cm (about 2,000 p.s.i.). All pressures above mentioned refer to continuous 0 working pressures. Peak pressures are in general higher than continuous pressures. The maximum working pressure attained by a pump depends essentially on its internal leakage. Rotary valves in general cause more leakage than seated valves, since the effect of fluid pressure in the pump chamber is to separate 5 the sealing surfaces. On the other hand, in seated valves the higher the pressure in the pump chamber, the greater is the sealing effect. Another source of leakage is the great number of moving parts. Unless they are machined to a high degree of precision as to fit perfectly in the parts where they move 0 severe internal leakage occurs. Compactness is another quality dependent on the number of parts of a pump. Although vane pumps are quite compact- its mechanism to vary the delivery is rather voluminous. Radial piston pumps, however, lack entirely in compactness as can be inferred in the description above. 5 More compact piston pumps are axial piston pumps, but they still lack in compactness and are less simple than radial pumps. A lower number of moving parts implies in a simpler and more compact pump and compactness as well as simplicity are certainly desirable qualities. 0 c) DISCLOSURE OF THE INVENTION.

This invention relates to a variable-delivery piston pump operating on entirely different principles to existing pumps of the variable- -delivery type. The invention provides a simpler and more compact variable-delivery piston pump when compared to existing 5 pumps of same type.

According to the present invention principles as well as parts will be described taking as reference Figures 1 to 3, which are

diagramatic illustrations of a pump ^' in three different stage of a pumping cycle. For the sake of clearness a few parts of the pump were omited in Figures 1 to 3. However, Figures 4 t 6, which are drawings illustrating a preferred embodiment fo the invention show the parts which are missing in Figures 1 3. Whenever necessary an appropriate mention will be done referring to these drawings and parts.

Referring now in more detail to Figures 1 to 3 the pump co prises a cylinder, which also serves as case for the pump, having near each end two internal inlet/outlet ports,so term since they can have one, other or both functions depending the mode of operation of the pump. These inlet/outlet- ports (12) (13) (14) (15) are arranged in such a manner that two of th (12) (14) are simmetrically disposed along a circle close to end and perpendicular to the axis of the cylinder; the other two(13)(15) are disposed in a similar way in the other end a well as are symmetrical to the former ones (12) (14) . Two inle outlet ports (12) (13) , at a same side of the cylinder, are co nected by a tube having in its central part an opening whic serves as inlet or outlet for the fluid. The other two ^' (14) (15), at the other side- of the cylinder, are connected in similar way. Figure 5 shows the cylinder incorporating the tub (16) (17) connecting the two pairs of inlet/outlet ports(12)-(1 (14)-(15) as well as open tubes (18)(19) serving as inlet and outlet f the fluid.

Within the cylinder are two rotary cylinders (2) (3) each on having a truncation in one of its ends. They are placed a certa distance apart and fixed on the driving shaf (9) in such a w that the truncations are facing each other in a symmetrical disposition. Between the two rotary cylinders (2) (3) is place a reciprocating pisttjn(l) with truncations at both ends. The truncations form parallel faces inclined to the axis of the reciprocating piston(l) at a same angle as the truncations i the rotary cylinders (2) (3) . The reciprocating piston(l) has central bore through which the driving shaf (9) passes leavi a very small clearance between them. The length of the recip eating piston(l) is such that it can rotate on the driving sha

(9). While rotating it reciprocates between the rotary cylinders (Z)- . (3) though it cannot reciprocate only without being hiήder_ ed by the rotary. cylinders (2) (3) . When inside the cylinder the rotary cylinders (2) (3) in conjunction with the reciprocating piston(l) define two pressure chambers (7) (8) in the pump. Pressure chamber(7) communicates alternately with the two inlet/ outlet ports (13) (15) through a drilled passage (5) in the rotary cylinder(3). Identically, pressure chamber(8) communicates al ternately with the two inlet/outlet ports (12) (14) through a drilled passage(4) in the rotary cylinder(2). Passages (4) (5) are opposite related to the driving shaft (9). As the driving shaft(9) rotates reciprocating piston(l) is prevented to rotate by a guide pin(6) entering in a lengthwise slot(lθ) on its side. The guide pin(6) can be moved to any position between the points (20) (22) indicated in Figure 1, the movement being govern ed by a lever which passes. through a semicircular aperture in the cylinder. In Figures 4 to 6 this lever(ll) is seen in a position corresponding to the intermediate position(21) in Figure 1. Referring now to Figures 1 to 3 as representing different stages of a pumping cycle the pump principles are described as follows. As the rotary cylinders(2)(3) rotate driven by the driving shaft(9) in the direction indicated by the arrow in the rotary cylinder (2). they force the reciprocating piston(l) to a back and forth movement in the cylinder. During the rotation, rotary cylinder(3) which in Figure 1 is defining a minimum volume for the pressure chamber(7) forces the reciprocating piston(l) to move to the right since i cannot turn by effect of guide pin(6). he .force is exerted through the border contact of both truncated surfaces in the rotary cylinder(3) and reciprocating piston(l). The borders of both parts must be shaped as to allow a fairly good contact between them. Pressure chamber (8), on the other hand, has a maximum volume defined by the rotary cylinder (2) and the reciprocatingpiston(1) . In this situation, passage(5) is commuting from the inlet/outlet port (15) to the inlet/outlet port(13) while passage(4) is commuting from the inlet/outlet port(12) to the inlet/outlet port(14). After a quarter turn,in

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Figure 2, the reciprocating piston(l) was displaced to the righ forced by the rotary cylinder(3). The volume in the pressure chamber(7) increased and fluid entered through the inlet/out let port(13) while in the pressure chamber(8) the volume de^ creased, discharging -fluid through the inlet/outlet port (14). In the following quarter turn, this process continues until a situation as showed in Figure 3 is reached. In this Figure, the volume in the pressure chamber(7) is maximum and the volume in the pressure chamber(8) is minimum. Passage(5) is now commuting from the inlet/outlet port(13) to the inlet/ outlet port(15) and passage(4) is commuting from the inlet/ou_ let port (14) to the inlet/outlet port(12). As the rotation continues pressure chamber(7) discharges its fluid contents i the inlet/outlet port(15). while pressure chamber(8) sucks flui from the inlet/outlet port(12). This process continues until reaching again the situation depicted in Figure 1. The second half turn briefly described above corresponds to the passage from Figure 3 to Figure 1. In this second half turn it is the rotary cylinder(2) which forces the reciprocating piston(l) t move to the left in Figure 3, in a similar way as described for the first half turn.

In a full turn of the driving shaft(9) pressure chamber(7)suck fluid from the inlet/outlet port(13) discharging it in the i let/outlet port(15) while pressure chamber(8) sucks fluid fro the inlet/outlet port(12) discharging it in the inlet/outlet port(14). Since the inlet/outlet port(12) is connected to the inlet/outlet port(13) as well as the inlet/outlet port(14) is connected to the inlet/outlet port(15), fluid enters the pum through the opening(lδ) and leaves it through the opening(19) (see Figure 5).

In the description above the guide pin(6) was settled in the position(20) in Figure 1. Supposing now that it is settled in any other position between positions (20) (21) , the latter bein an intermediate position between the extreme positions (20) (22 a dephasing occurs in the process such that when passage(5) i commuting from the inlet/outlet port(15) to the inlet/outlet port(13) the pressure chamber(7) has not yet reachedthe minimu

volume. Similarly, when passage (4) is commuting from the inlet/ outlet port(12) to the inlet/outlet port(14) the pressure chamber(8) has not yet reached the maximum volume. A minimum volume as well as a maximum volume only occur when the passages (4) (5) .and the guide pin(6) are on a same plane. This can be seen in the cross-sectional views in Figures 1 and 3. In such a situation, the pressure chamber(7) continues discharging its fluid contents in the inlet/outlet port(13) while the pressure chamber(8) continues drawing in fluid from the inlet/outlet port(14) till the passages (4) (5) and the guide pin(6) be on a same plane as described above. At this point, the volume in the pressure chamber(7) reaches the minimum while in the pressure chamber(8) it reaches the maximum. Then chamber (7) starts draw ing in fluid from the inlet/outlet ρort(13) . while pressure chamber(8) starts discharging fluid in the inlet/outlet port (14) . Af er this reversal of functions both pressure chambers when reaching the respective opposite inlet/outlet ports still continue their functions, until an equivalent situation as above is reached, i.e., passages (4) (5) and guide pin(6) are on a same plane, although they have commuted to inlet/outlet ports (14) (13) , respectively. Thus, the net amount of fluid sucked through the inlet/outlet ports (12) (13) as well as the net amount of fluid discharged through the inlet/outlet ports (14) (15) depend on the position of the guide pin(6), that is, on the dephasing introduced in the pumping cycle. It has to be noted that, since the dephasing is the same for the two pressure chambers, when drawing in or discharging fluid through their respective inlet/outlet ports, the amount of fluid which enters the pump varies depending on the position of guide pin(6),but it always equals the amount of fluid which leaves the pump.

For the guide pin(6) settled in the position(21) the amount of fluid sucked from a particular inlet/outlet port equals the amount discharged in the same inlet/outlet port. In this case, the net amount of fluid displaced in each inlet/outlet port becomes zero and consequently the pump gives a null flow, aJL though still rotating in the same direction and with the same speed.

For the guide pin(6) settled in any position between the ^" po_ sitions (21) (22) the pump works in a similar way as for any sition between the positions (20) (22) . However, in this case the _. flux is reversed when compared to the preceding case. 5 For the guide pin(6) settled in the position(22) the flux is maximum and also reversed regarding the case where the guide ρin(6) is in the position(20) .

Thus, changing the position of the guide pin(6) the delive can be varied from the maximum capacity of the pump to zero

10 well as the direction of flow can be reversed while maintaini the same direction of rotation of the driving shaft(9). The principle of operation of this pump permits a wide range of variation in the shape and relative position of its con stituent parts, provided that the basic principle 6f introduci

15 a dephasing in the pumping cycle be maintained. While the i vention has been described and illustrated with respect to certain preferred embodiment which can give satisfactory resul various other changes and modifications may be made without departing from the spirit and scope of the invention.

20 d) BRIEF DESCRIPTION OF DRAWINGS

The description of the invention is given with reference to t accompanying drawings, which are briefly described as follow Figure 1, in the left, is a schematic illustration of a giv stage in a pumping cycle embodying the principles of the

25 present invention;

Figure 1, in the right, is a longitudinal cross-sectional vi of Figure in the left taken along the passages (4) (5) ; Figure 2, in the left, is a schematic illustration of a sub_ sequent stage a quarter turn after the stage depicted in Figu

30 1;

Figure 2, in the right, is a longitudinal cross-sectional vi of Figure 2 in the left taken along the passages (4) (5) ; Figure 3, in the left, is a schematic illustration of a sub_ sequent stage a half turn after the stage depicted in Figure

35.Figure 3, in the right, is a longitudinal cross-sectional vi of Figure 3 in the left taken along the passages (4) (5) ;-

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; _. ' Figure 4 is a side view of a pump according to a preferred em bodiment of the present invention; >• Figure 5 is a upper view of the pump in Figure 4; and

Figure 6 is a longitudinal cross-sectional view taken along 5 the plane, parallel to the Figure 5 and passing by the axis of the driving shaft(9). e) BEST MODE OF CARRYING OUT THE INVENTION

Due to its simple conception and low number of components the present invention can be easily carried out employing well known

10 techniques and materials commonly employed in the fabrication of pumps of similar type. It will be understood by those skilled in the art that most of the details as well as the appropriate techniques and materials necessary to carry out this invention will depend on a particular embodiment of the pump and oh its

15 particular use. Nevertheless, a few suggestions are giving aim ing to point some important details which were not evinced in the description of the invention.

A low cost pump can be fabricated using mild steel for the case or cylinder as termed in the description of the invention. The

20 rotary cylinders as well as the reciprocating piston can be made of hardened steel and the borders of the truncations must be appropriately shaped to define a fairly good contact area between the actuating parts. A suitable material allied to a proper shape will prevent excessive wear. The assembly comprising

25 the rotary cylinders and the reciprocating piston must be fitted within the cylinder with a high degree -of accuracy to avoid too much internal leakage under high pressures. Although cylinder and rotary cylinders contact in a large area forming an extensive oil seal, some external leakage is likely to occur. Thus ap_

30 propriate seals must be fitted to the driving shaft to withhold hydraulic pressure.

In a pumping cycle the rotary cylinders a.nd consequently the driving shaft are submitted to a considerable alternating axial thrust which depends on the working pressure in the pump. In

35 this case, appropriate bearings must be placed between the rotary cylinders and the end plates.

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f) INDUSTRIAL APPLICABILITY

This invention is intended to be applied in hydraulic system as a pump of the variable-delivery type. There are many apρl cations for hydraulic systems. In particular, hydraulic systems are used in the operation of. machine tools where, depending o the particular cutting operation, there are certain optimum values of feed and speed of tool and work that must be combined to. produce economically a piece. The invention fulfills the condition of applicability in machine tools since it is a variable-delivery pump that can give stepless infinitely-variabl speed control. In addition it can change the direction of driv as easily as it can vary the speed. The invention is also suite for entirely automatic hydraulic operated machines since the variation of delivery is quickly and easily attained. In general, this invention can be applied to any hydraulic syste where variable delivery allied to compactness and simplicity are mostly required.

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