EP0016209A1 - Axial reciprocating piston pump with control and inversion of flow - Google Patents

Abstract

Variable flow piston pump suitable for use in hydraulic systems where variable flow rates are required. The invention includes a cylinder having internal inlet and outlet ports (12, 13, 14, 15); two rotary cylinders (2, 3), fixed on a drive shaft (9), which are truncated at one end and which have passages (4, 5) for the fluid; an alternating piston (1) which is truncated at both ends and free for an alternative action but is prevented from turning by a pilot spindle (6). When the rotary cylinders (2, 3) rotate, the reciprocating piston (11) is actuated to pump fluid alternately through the passages (4, 5) and the inlet and outlet ports (12, 3, 14, 15). A variable flow is obtained when the pilot spindle (6) is moved which causes a phase shift of the pumping cycle. The pump provides infinitely variable flow without steps, the direction of flow being variable.

Description

AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW. a) TECHNICAL FIELD.

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.

Most 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 equidistantly and radially around 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 ec 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 defined 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 increases 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 altering 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 lessly 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 equidistantly 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 inlet valve port located in a fixed shaft on which the cylinder block rotates. On reaching a. position of maximum displacement of the piston the inner end of the cylinder passes to a outlet valve port also in the fixed shaft in an opposite position to the inlet valve port. From this point, as the rotation continues, the piston moves towards the center of the cylinder block discharging 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 stationary. 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 more complex mechanism is necessary. This mechanism is generally a circular plate inclined with respect to the driving shaft. The pistons are linked to this plate, commonly called swashplate, by connecting rods and universal joints. As the cylinder block rotates apertures leading to the cylinders are brought opposite the suction and delivery ports in a valve plate placed in contact with the cylinder block. The inclination of the swashplate is such that the cylinders are filled with fluid when in contact with the suction port and discharged when in contact with the delivery port. By tilting the swashplate to different positions a variable delivery is given.

Pumps which have rotary valves attain lower pressures than pumps with seated valves. Radial piston pumps of the stationary cylinder block type, for instance, which have seated valves are made, for pressures as high as 425 kg/cm² (about 6,055 p.s.i.) whereas in radial piston pumps with rotating cylinder blocks, which have rotary valves, pressure is limited to about 210 kg/cm² (about 3,000 p.s.i.) . Axial piston pumps, which have rotary valves, have maximum working pressure about 280 kg/cm²

(about 4,000 p.s.i.). Vane pumps, in which vanes act as rotary valves, are made for pressures up to 140 kg/cm² (about 2,000 p.s.i.). All pressures above mentioned refer to continuous 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 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 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. 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. 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 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 stages 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 to 6, which are drawings illustrating a preferred embodiment for the invention show the parts which are missing in Figures 1 to 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 comprises a cylinder, which also serves as case for the pump, having near each end two internal inlet/outlet ports, so termed since they can have one, other or both functions depending on the mode of operation of the pump. These inlet/outlet ports (12) (13) (14) (15) are arranged in such a manner that two of them (12) (14) are simmetrically disposed along a circle close to an end and perpendicular to the axis of the cylinder; the other two(13)(15) are disposed in a similar way in the other end as well as are symmetrical to the former ones (12) (14). Two inlet/outlet ports (12) (13), at a same side of the cylinder, are connected by a tube having in its central part an opening which 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 tubes (16) (17) connecting the two pairs of inlet/outlet ports (12)-(13) (14)-(15) as well as open tubes (18) (19) serving as inlet and outlet for the fluid.

Within the cylinder are two rotary cylinders (2) (3) each one having a truncation in one of its ends. They are placed a certain distance apart and fixed on the driving shaft (9) in such a way that the truncations are facing each other in a symmetrical disposition. Between the two rotary cylinders (2) (3) is placed a reciprocating pistton(1) with truncations at both ends. These truncations form parallel faces inclined to the axis of the reciprocating piston(1) at a same angle as the truncations in the rotary cylinders (2) (3) . The reciprocating piston(1) has a central bore through which the driving shaft (9) passes leaving a very small clearance between them. The length of the reciprocating piston(1) is such that it can rotate on the driving shaft (9). While rotating it reciprocates between the rotary cylinders (2) (3) though it cannot reciprocate only without being hiήdered by the rotary cylinders (2) (3). When inside the cylinder the rotary cylinders (2) (3) in conjunction with the reciprocating piston(1) 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 alternately 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(1) is prevented to rotate by a guide pin(6) entering in a lengthwise slot(10) 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 governed by a lever which passes through a semicircular aperture in the cylinder. In Figures 4 to 6 this lever(11) 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(1) 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(1) to move to the right since it cannot turn by effect of guide pin (6). The force is exerted through the border contact of both truncated surfaces in the rotary cylinder(3) and reciprocating piston(1). 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 reciprocating piston(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 Figure 2, the reciprocating piston(1) was displaced to the right forced by the rotary cylinder(3). The volume in the pressure chamber(7) increased and fluid entered through the inlet/outlet port(13) while in the pressure chamber(8) the volume decreased, 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/outlet port (14) to the inlet/outlet port(12). As the rotation continues pressure chamber(7) discharges its fluid contents in the inlet/outlet port(15). while pressure chamber(8) sucks fluid 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(1) to 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 )sucks fluid from the inlet/outlet port (13) discharging it in the inlet/outlet port(15) while pressure chamber(8) sucks fluid from 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 pump through the opening(18) 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 being an intermediate position between the extreme positions (20) (22), a dephasing occurs in the process such that when passage (5) is commuting from the inlet/outlet port(15) to the inlet/outlet port (13) the pressure chamber (7) has not yet reached the minimum 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 drawing in fluid from the inlet/outlet ρort(13). while pressure chamber(8) starts discharging fluid in the inlet/outlet port(14) . After 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, although still rotating in the same direction and with the same speed. For the guide pin(6) settled in any position between the positions (21) (22) the pump works in a similar way as for any position between the positions (20) (22). However, in this case the flux is reversed when compared to the preceding case. 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 delivery can be varied from the maximum capacity of the pump to zero as well as the direction of flow can be reversed while maintaining 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 constituent parts, provided that the basic principle of introducing a dephasing in the pumping cycle be maintained. While the invention has been described and illustrated with respect to a certain preferred embodiment which can give satisfactory results, various other changes and modifications may be made without departing from the spirit and scope of the invention. d) BRIEF DESCRIPTION OF DRAWINGS

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

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

Figure 2, in the right, is a longitudinal cross-sectional view of Figure 2 in the left taken along the passages (4) (5); Figure 3, in the left, is a schematic illustration of a subsequent stage a half turn after the stage depicted in Figure 1; Figure 3, in the right, is a longitudinal cross-sectional view of Figure 3 in the left taken along the passages (4) (5); Figure 4 is a side view of a pump according to a preferred embodiment 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 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 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 on its particular use. Nevertheless, a few suggestions are giving aiming 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 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 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 appropriate seals must be fitted to the driving shaft to withhold hydraulic pressure.

In a pumping cycle the rotary cylinders and consequently the driving shaft are submitted to a considerable alternating axial thrust which depends on the working pressure in the pump. In this case, appropriate bearings must be placed between the rotary cylinders and the end plates. f) INDUSTRIAL APPLICABILITY

This invention is intended to be applied in hydraulic systems as a pump of the variable-delivery type. There are many apρlications for hydraulic systems. In particular, hydraulic systems are used in the operation of machine tools where, depending on 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-variable speed control. In addition it can change the direction of drive as easily as it can vary the speed. The invention is also suited 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 system where variable delivery allied to compactness and simplicity are mostly required.

Claims

CLAIMS 1. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW which consists in a variable-delivery piston pump comprising a cylinder, said cylinder having internal inlet/outlet ports (12) (13) (14) (15) which are disposed simmetrically in the cylinder, two rotary pistons (2) (3) fixed on a driving shaft (9) a certain distance apart, said rotary pistons (2) (3) having truncations which are simmetrically facing each other and having passages (4) (5) which are opposite related to the driving shaft (9), such passages communicating truncated faces to inlet/outlet ports (12) (13) (14) (15), a reciprocating pistons (1)between the rotary cylinders (2) (3) , said reciprocating piston(1) having two parallel truncated faces and an axial bore in which passes the driving shaft (9), a guide pin(6) entering a slot in reciprocating piston(1), said guide pin(6) preventing reciprocating piston(1) to rotate but permitting its reciprocation which is provoked by the rotary cylinders (2) (3)which alternately force the reciprocate piston(1) to an axial reciprocation producing a pumping effect, the fluid passing through passages (4) (5) and inlet/outlet ports (12) (13) (14) (15) in a proper sequence of a pumping cycle which can be dephased by moving the guide pin(6) through a semicircular aperture in cylinder, provoking variation in the magnitude and direction of flow.

2. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW, according to claim 1, characterized by having two rotary cylinders (2) (3) truncated at one end forming an angle to the driving shaft (9) which is equal to the angle of the truncations in the reciprocating piston(1), the rotation of said rotary cylinders (2) (3) being driven by driving shaft (9).

3. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW, according to claim 1, characterized by having two rotary cylinders (2) (3) with passages (4) (5) which are distribution holes serving for the communication between the pressure chambers (7) (8) and the inlet/outlet ports (12) (13) (14) (15) in the cylinder, said communication following an appropriate sequence during a pumping cycle in which the reciprocating piston(1) has an axial reciprocating movement by effect of rotation of the rotary cylinders (2) (3) which are driven by driving shaft(9).

4 . AXIAL REC IPROCATING PISTON PUMP WITH C ONTROL AND INVERS ION

OF FLOW, according to claims 1 and 2, characterized by the rotary cylinders(2) and (3) having the function of defining and varying the volumes of pressure chambers (8) and (7) during rotation of the driving shaft (9) as well as the function of communicating passage(4) of the pressure chamber(8) with the inlet/outlet ports(12) and (14), alternately, and passage(5) of the pressure chamber (7) with the inlet/outlet ports (13) and (15), alternately, being inlet/outlet port(12) connected to inlet/outlet ρort(13) and inlet/outlet port(14) to inlet/outlet port(15) .

5. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW, according to claim 1, characterized by having a cylinder, within said cylinder a reciprocating ρiston(1) which is a cylinder with truncations at both ends in such way that the resulting faces form a same angle with the driving shaft(9), being or not being parallel one another depending on the relative disposition of the other parts necessary to the suitable operation of the pump, said reciprocating piston(1) being commanded by an external lever (11) which can be rotated in a semicircular aperture in the cylinder through which a guide pin(6) enters in a slot(10) in the reciprocating piston(1).

6. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW, according to claims 1 and 2, characterized by having the positioning of the guide pin(6) which commands reciproeating piston(1) the function of causing a steplessly variation in delivery and a change in the direction of flow without changing the direction of rotation and the speed of driving shaft(9).

7. AXIAL RECIPROCATING PISTON PUMP WITH CONTROL AND INVERSION OF FLOW, according to claims 1, 2 and 3, characterized by having the possibility of inversion in the direction of rotation and the control of delivery being done without change in the rotation of the constituting parts or in the frequency of the reciprocating piston(1).