Hydraulic system

Abstract

A hydraulic device (1) comprising a rotor (3, 9, 10, 11, 16-18, 23) and a port member (5) including a high pressure port (6) and a low pressure port (7). An outer surface (21) of the rotor faces an outer surface (22) of the port member (5) and is rotatable in a rotational direction about a rotation axis (19) relative to the port member (5). The rotor comprises a plurality of cylinders (11) angularly spaced apart from one another about the rotation axis (19) and a plurality of cooperating pistons (10) movable within each cylinder (11). The cylinders (11) communicate with respective open ends (25) at the outer surface (21) of the rotor, each of the open ends (25) alternately communicating with the high pressure port (6) and the low pressure port (7) under operating conditions. Every two consecutive cylinders (11) of the plurality of cylinders (11) are interconnected via a fluid displacement member (26). The fluid displacement member has a first opening (27) communicating with one of the two consecutive cylinders (11), a second opening (28) communicating with the other of the two consecutive cylinders (11), and a closure element (29) freely movable between the first and second openings (27, 28) and configured to substantially block either the first opening (27) or the second opening (28) when, under operating conditions, the pressure in the cylinder (11) communicating with the second opening (28) is higher or lower, respectively, than the pressure in the cylinder (11) communicating with the first opening (27). A flow resistor (30) is provided in the rotor (3, 9, 10, 11, 16-18, 23) at a position away from each open end (25), and a first opening (27) and a second opening (28) of each of two fluid displacement members (26) communicating with one cylinder (11) are in fluid communication with that cylinder (11) on the opposite side of the flow resistor (30).

Description

[Technical field]

[0001] The present invention relates to a hydraulic device comprising a rotor and a port member including a high pressure port and a low pressure port, an outer surface of the rotor faces an outer surface of the port member and is rotatable in a rotational direction about a rotation axis relative to the port member; the rotor comprising a plurality of cylinders angularly spaced apart from one another about the axis of rotation and cooperating pistons movable within each of the cylinders; the cylinders communicating with respective open ends at the outer surface of the rotor, each of the open ends alternately communicating with the high pressure port and the low pressure port under operating conditions; Each two consecutive cylinders of the plurality of cylinders are interconnected via a fluid displacement member; The fluid displacement member is a first opening communicating with one of the two consecutive cylinders; a second opening communicating with the other of the two consecutive cylinders; a closure element freely movable between the first and second openings and configured to substantially block either the first opening or the second opening when, under operating conditions, the pressure in the cylinder communicating with the second opening is higher or lower, respectively, than the pressure in the cylinder communicating with the first opening. Pertaining to something. [Background technology]

[0002] Such a hydraulic device is known from NL 1016738. The known hydraulic device has a rotor connected to a swash plate, which during rotation of the rotor moves pistons in respective cylinders between bottom dead centre and top dead centre. Under operating conditions, a part of the cylinders communicates with a high pressure port and another part of the cylinders communicates with a low pressure port. Each cylinder is connected to a successive, adjacent or neighbouring cylinder via a fluid displacement member. The fluid displacement member is provided with a closure element freely movable between a first opening and a second opening of the member. Under operating conditions, if the pressure of hydraulic fluid in a cylinder communicating with the second opening is higher than the pressure of hydraulic fluid in a cylinder communicating with the first opening, the closure element can move to the first opening to substantially block the first opening, and if the pressure in a cylinder communicating with the first opening is higher than the pressure in a cylinder communicating with the second opening, the closure element can move to the second opening to substantially block the second opening. During the movement of the closure element from the first opening to the second opening or vice versa, a limited volume of hydraulic fluid flows between two consecutive cylinders.

[0003] Under operating conditions, when one of the open ends on the rotor's outer periphery moves between the high pressure port and the low pressure port, i.e., along the sealing land of the port member, the position of the piston in the cylinder changes while the open end is closed by the sealing land, thereby changing the pressure of hydraulic fluid in the cylinder communicating with that open end. This pressure change, called commutation, can lead to increased noise and vibration if the pressure at the high pressure port is different from the pressure in the cylinder when the corresponding open end begins to communicate with the high pressure port and / or if the pressure at the low pressure port is different from the pressure in the cylinder when the corresponding open end begins to communicate with the low pressure port. Known hydraulic systems counteract excessive pressure differences with fluid displacement members, also called shuttles, that can transfer excess hydraulic fluid between successive cylinders.

[0004] For example, consider the case where one of the open ends moves from the low pressure port to the high pressure port, the open end being closed by a sealing land between the low pressure port and the high pressure port. When the piston in the cylinder communicating with the open end under consideration moves in the direction from bottom dead center to top dead center, the pressure in the cylinder communicating with the open end under consideration rises during the movement. The successive cylinders communicating with the low pressure port remain at a lower pressure, whereby the closure element of the fluid displacement member interconnecting these cylinders substantially blocks one of the first and second openings of that member, whereby no hydraulic fluid flows to the successive cylinders, or only a limited amount of hydraulic fluid flows to the successive cylinders. The other successive cylinders already communicating with the high pressure port, as their open ends move along the sealing land, initially have a higher pressure than the cylinder communicating with the open end under consideration, so that the closure element of the fluid displacement member interconnecting these cylinders also substantially blocks one of the first and second openings of that member. During the movement of the open end under consideration along said seal land, when the pressure in the corresponding cylinder exceeds the pressure of said high pressure port (equal to the pressure in the successive cylinder already in communication with said high pressure port), the closure element of the fluid displacement member interconnecting these cylinders will move from one of said first and second openings to the other of said first and second openings. During this movement, hydraulic fluid will flow from the cylinder in communication with the open end under consideration to the fluid displacement member, displacing the closure element of that member, so that further pressure increase is avoided.

[0005] If the open end under consideration begins to communicate with the high pressure port before the closing element of the fluid displacement member interconnecting the successive cylinders substantially blocks the other of the first and second openings (in which case both successive cylinders communicate with the high pressure port), the pressure in the cylinder communicating with the open end under consideration will balance with the pressure at the high pressure port, thus avoiding a strong pressure difference. If the closing element already substantially blocks the other of the first and second openings before the open end under consideration begins to communicate with the high pressure port, the pressure in the cylinder communicating with the open end under consideration will rise further than the pressure of the high pressure port. Since the pressure in the cylinder reaches the pressure of the high pressure port faster as the pressure of the high pressure port decreases, the distance between the first and second openings should be such that the travel distance of the closing element is sufficient to avoid an undesirable pressure difference at the relatively low pressure of the high pressure port.

[0006] A similar effect occurs as the open end moves from the high pressure port to the low pressure port. Summary of the Invention

[0007] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an improved hydraulic system.

[0008] This object is achieved by a hydraulic device according to the invention, characterized in that a flow resistance is provided in the rotor, at a position away from each open end, and a first opening and a second opening of each of two fluid displacement members communicating with a cylinder are in fluid communication with that cylinder on the opposite side of the flow resistance.

[0009] The advantage of the present invention is that the closure element of the fluid displacement member is biased to a predetermined position before the open end of the rotor reaches the seal land between the low pressure port and the high pressure port. Under operating conditions, successive cylinders communicating with the low pressure port produce a flow of hydraulic fluid causing a pressure drop across the respective flow resistance in a direction from the corresponding open end to the cylinder, while successive cylinders communicating with the high pressure port produce a flow of hydraulic fluid causing a pressure drop across the respective flow resistance in a direction from the corresponding cylinder to the open end. Since the first opening and the second opening of each fluid displacement member communicate with two successive or adjacent cylinders on opposite sides of the corresponding flow resistance, the closure elements of the fluid displacement members interconnecting two successive cylinders communicating with either the low pressure port or the high pressure port will be biased in the same direction. As a result, when an open end communicating with a cylinder arrives at a seal land, the closure element of the fluid displacement member interconnecting that cylinder with a successive cylinder arriving at the seal land later will always substantially block either the first opening or said second opening of that member, thereby providing an opportunity to start compression or expansion at the seal land in a fixed reference state of the fluid displacement member, thereby preventing said closure element from being positioned, for example, depending on centrifugal forces.

[0010] It is noted that when the closure element of the fluid displacement member substantially blocks the first or second opening, the flow of fluid through the first or second opening, respectively, is minimized. This means that the first or second opening is completely closed or only a small amount of fluid still flows through the first or second opening. In the latter case, the flow of fluid will usually be much smaller than the flow of fluid through the first and second openings when the closure element moves between the first and second openings.

[0011] In a practical embodiment, each of the cylinders communicates with the corresponding open end through a passage in which the flow resistance is provided. The cross-sectional area of ​​the passage may be smaller than the cross-sectional area of ​​the respective cylinder. The passage and the fluid displacement member may be formed as a rigid unit.

[0012] The flow resistance may be formed by a local constriction of the passageway.

[0013] In one embodiment, the first opening of each fluid displacement member communicates with the corresponding cylinder through a first aperture in the passageway and the second opening of each fluid displacement member communicates with the corresponding cylinder through a second aperture in the passageway. In a more specific embodiment, considering one of the fluid displacement members, the first opening of that member is in fluid communication with a first aperture of the passageway corresponding to a first one of the cylinders and the second opening of that member is in fluid communication with a second aperture of the passageway corresponding to a successive cylinder following the first one of the cylinders under operating conditions.

[0014] Preferably, the first aperture is at a greater distance from the open end than the second aperture, since in this embodiment the flow resistance may be formed by the length of the passage between the first and second apertures, thereby providing a simple flow resistance such that local constriction of the passage is omitted.

[0015] Each of the fluid displacement members may comprise a linear channel between the first aperture of one of the two successive passages and the second aperture of the other of the two successive passages, the channel having a cylindrical portion between the first and second openings, such that the closure element moves within the cylindrical portion.

[0016] In a practical embodiment, the closure element is a ball, and the first and second openings are surrounded by respective seats cooperating with the ball, such that when the ball is pressed against the seat at the first opening, the flow of fluid through the first opening is substantially prevented, and when the ball is pressed against the seat at the second opening, the flow of fluid through the second opening is substantially prevented. This is a simple but effective configuration of the fluid displacement member. The ball may be made of ceramic. Furthermore, the ball of the fluid displacement member may be smaller than the diameter of the cylindrical portion between the first and second openings, as long as the ball substantially blocks the first or second opening when pressed against the corresponding seat. Nevertheless, alternative shapes of the closure element and / or the seat are conceivable, such as, for example, a small piston. In an alternative embodiment, the closure element fits tightly within the cylindrical portion between the first and second openings. In this case, the corresponding seats at the first and second openings as described hereinbefore may be omitted because a tightly fitting closure element will automatically substantially block the first and second openings when the closure element is in its respective opposite end position within the cylindrical portion. As described hereinbefore, the closure element may allow minimal leakage through the first or second opening when it substantially blocks the first or second opening, respectively.

[0017] The cylindrical portion has a centre line which lies in a plane extending tangentially to the axis of rotation at the rotational position in which it is located or is inclined to that plane at an angle of less than 45°, preferably less than 25°, to minimise the effect of centrifugal forces on the closure element which may act against displacement of the closure element due to pressure differences across the flow resistance.

[0018] In a preferred embodiment, the imaginary extension of the channel in the direction from the rotor towards the port member passes through the open end of the passage where the second aperture is located, as this provides the opportunity to drill the channel through the open end, so that the drilling of a separate hole that subsequently needs to be partially closed and sealed can be omitted.

[0019] In certain embodiments, the outer surfaces are in a common plane; the axis of rotation extends perpendicular to the outer surface(s); the centerlines of the cylinders extend parallel to the axis of rotation; The high pressure port and the low pressure port are arcuate about the axis of rotation.

[0020] In a more particular embodiment, the rotation axis is a first rotation axis, The rotor has a shaft rotatable about a second axis of rotation and a flange extending perpendicular to the second axis of rotation; the plurality of pistons are fixed to the flange at equal angular distances about the second axis of rotation; the cylinders being separate sleeves resting on a barrel plate in which the passages are disposed; The second axis of rotation intersects the first axis of rotation at an acute angle such that rotation of the shaft causes each of the pistons to reciprocate within the associated cylinder. Such an arrangement is called a floating cup hydraulic system, since the position of the cylinder on the barrel plate is determined by the actual position of the associated piston. In this embodiment, the channel may have an imaginary extension in the direction from the port member towards the cylinder, which extension passes through the inlet of the passage on the opposite side of the member from the open end, as this provides an opportunity to drill the channel through the inlet.

[0021] In one embodiment, the outer surface of the port member having a first seal land between the low pressure port and the high pressure port through which the cooperating piston of an open end passes and reaches bottom dead center, and a second seal land between the low pressure port and the high pressure port through which the cooperating piston of an open end passes and reaches top dead center, A length of each of the first and second seal lands, measured in the rotational direction, is greater than a length of each of the open ends.

[0022] The distance, measured in the direction of rotation, between an edge of the first seal land adjacent the low pressure port and a position at which the piston reaches bottom dead centre at the first seal land may be half the length of each open end, and / or the distance, measured in the direction of rotation, between an edge of the second seal land adjacent the high pressure port and a position at which the piston reaches top dead centre at the second seal land may be half the length of each open end, meaning that bottom dead centre and top dead centre are reached when the first and second seal lands start to close the corresponding passing open ends.

[0023] The length of the first seal land, measured in the direction of rotation, may be greater than the length of the second seal land because after leaving top dead center only dead volume in the cylinder must be expanded by the corresponding piston, whereas after leaving bottom dead center both the dead volume and the volume to be displaced by the piston must be compressed by the corresponding piston.

[0024] The hydraulic device may be a pump, a motor, or a transformer. [Brief description of the drawings]

[0025] The invention will now be described, by way of example only, with reference to highly schematic drawings showing embodiments of the invention. [Figure 1]1 is a cross-sectional view showing an embodiment of a hydraulic device according to the present invention. [Diagram 2] FIG. 2 is a front view of a port plate of the hydraulic device of FIG. 1. [Diagram 3] FIG. 2 is an enlarged perspective view of the barrel plate of the embodiment of FIG. 1. [Figure 4] FIG. 4 is a view similar to FIG. 3, but showing a part of it on an enlarged scale. [Diagram 5] FIG. 5 is an enlarged cross-sectional view of a portion of FIG. [Figure 6] FIG. 2 is a schematic diagram illustrating the function of the embodiment shown in FIG. [Figure 7] FIG. 7 is a diagram similar to FIG. 6, illustrating the function of another embodiment. [Figure 8] FIG. 8 is a diagram similar to FIG. 6, and is used to explain the function of yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] 1 shows the internal parts of a hydraulic device 1, such as a pump or hydromotor, which is mounted in a housing 2 in a known manner. The hydraulic device 1 comprises a shaft 3 rotatably supported in the housing 2. An opening is provided on one side of the housing 2 through which a toothed shaft end 4 of the shaft 3 projects from the housing 2. If the hydraulic device 1 is a pump, a motor can be connected to the toothed shaft end 4, and if the hydraulic device 1 is a motor, a driven tool can be connected to the toothed shaft end 4.

[0027] The hydraulic device 1 includes port members in the form of port plates 5 mounted in a housing 2 in a spaced apart relationship. FIG. 2 shows one of the port plates 5 in more detail. Each port plate 5 includes an arcuate high pressure port 6 and an arcuate low pressure port 7. Between the high pressure port 6 and the low pressure port 7 are first and second seal lands 8a and 8b. The port plates 5 have a fixed position relative to the housing 2 in their rotational direction, although in an alternative embodiment (not shown), the port plates 5 may be rotatable relative to the housing 2. A shaft 3 extends through a central through hole in each of the port plates 5.

[0028] The shaft 3 is provided with a flange 9. A plurality of pistons 10 are fixed to both sides of the flange 9 by press fitting, in this case 14 pistons 10 are fixed to each side. The pistons 10 shown in FIG. 1 are made of separate parts, but may be a single body. Each piston 10 cooperates with a separate cylinder 11 to form a compression chamber 12 with a variable volume. The hydraulic device 1 shown in FIG. 1 has 28 compression chambers 12. Each cylinder 11 has a cylinder bottom 13 and a cylinder jacket 14 extending from the cylinder bottom 13.

[0029] The cylinder bottom 13 of each cylinder 11 is supported by two barrel plates 16 which fit around the shaft 3 by respective ball hinges 17 and are coupled to the shaft 3 by keys 18. As a result, the barrel plates 16 rotate with the shaft 3 under operating conditions. Figure 3 shows one of the barrel plates 16 in more detail. It is noted that although the cylinder bottom 13 rests on the respective barrel plates 16, the cylinder bottoms 13 do not have a fixed position relative to the respective barrel plates 16.

[0030] FIG. 1 shows that the barrel plates 16 rotate about respective first axes of rotation 19 that are angled relative to a second axis of rotation 20. The shaft 3 is rotatable about the second axis of rotation 20, and the flanges 9 extend perpendicular to the second axis of rotation 20. The pistons 10 are disposed at equal angular distances about the second axis of rotation 20. The pistons 10 have centerlines that extend parallel to the second axis of rotation 20. The arcuate low pressure ports 7 and the arcuate high pressure ports 6 of each port plate 5 extend about the corresponding first axis of rotation 19. The angle between the second axis of rotation 20 and the respective first axis of rotation 19 is in practice approximately 9 degrees, but may be less or greater.

[0031] Rotation of the shaft 3 causes the barrel plates 16 and cylinders 11 to rotate about their respective first axes of rotation 19. Each cylinder 11 undergoes a combined translational and orbital motion about its associated piston 10. Each piston 10 moves relative to its associated cylinder 11 between bottom dead center BDC and top dead center TDC, thereby changing the volume of the corresponding compression chamber 12.

[0032] Each barrel plate 16 has an outer surface 21 oriented away from the flange 9 and facing an outer surface 22 of the associated port plate 5 (see FIGS. 1-3). The barrel plates 16 are biased against their respective port plates 5 by springs 23 mounted in holes in the shaft 3. The outer surfaces 21, 22 extend perpendicular to the respective first axes of rotation 19. Due to the inclination of the outer surface 22 of the port plate 5 relative to the flange 9, the barrel plates 16 pivot about ball hinges 17 while rotating with the shaft 3.

[0033] Considering one of the barrel plates 16, the cylinders 11 resting on it communicate with associated passages 24 in the barrel plate 16 via a central through hole in the bottom 13 of each cylinder. The passages 24 have respective open ends 25 on the outer surface 21 of the barrel plate 16, see Figures 3 and 4. In this case, each barrel plate 16 has 14 consecutive open ends 25 which communicate with 14 consecutive cylinders 11. Under operating conditions, the open ends 25 communicate alternately with high and low pressure lines (not shown) provided in the housing 2 via the high and low pressure ports 6 and 7, respectively.

[0034] Indeed, in the embodiment shown in FIG. 1, the shaft 3, barrel plate 16, piston 10, cylinder 11, ball hinge 17, key 18 and spring 23 may be considered parts of the rotor having an outer surface 21 facing the outer surface 22 of the respective port plate 5.

[0035] 3-5 show that each pair of consecutive passages 24 is interconnected via a fluid displacement member 26. This means that each pair of consecutive cylinders 11 is also interconnected via a fluid displacement member 26. Thus, each barrel plate 16 is also provided with 14 consecutive fluid displacement members 26. Each of the fluid displacement members 26 includes a channel between each pair of consecutive passages 24 and has a first opening 27 and a second opening 28 spaced apart from each other. The channel has a cylindrical portion between the first and second openings 27, 28. A closure element in the form of a ball 29 is freely movable between the first and second openings 27, 28. Although two balls are shown in one fluid displacement member 26 in FIGS. 3-5 for ease of illustration, in reality, each fluid displacement member 26 has a single ball 29.

[0036] 4, the first opening 27 communicates with the right passage 24 of the pair of continuous passages 24, and the second opening 28 communicates with the left passage 24 of the pair of continuous passages 24. The first and second openings 27, 28 and the ball 29 are configured such that, under operating conditions, the ball 29 substantially blocks the first opening 27 when the pressure in the passage 24 communicating with the second opening 28, i.e., the left passage 24 in FIG. 4, is higher than the pressure in the passage 24 communicating with the first opening 27, i.e., the right passage 24 in FIG. 4, while the ball 29 substantially blocks the second opening 28 when, under operating conditions, the pressure in the passage 24 communicating with the first opening 27, i.e., the right passage 24 in FIG. 4, is higher than the pressure in the passage 24 communicating with the second opening 28, i.e., the left passage 24 in FIG. 4.

[0037] As the ball 29 moves from the first opening 27 to the second opening 28, it displaces fluid towards the passageway 24 that communicates with the second opening 28, and as the ball 29 moves from the second opening 28 to the first opening 27, it displaces fluid towards the passageway 24 that communicates with the first opening 27. Thus, the greater the distance between the first and second openings 27, 28, the greater the volume of fluid displaced between each pair of successive passageways 24.

[0038] Considering one of the passages 24, it communicates with a first opening 27 and a second opening 28 of two consecutive fluid displacement members 26 located on opposite sides of the passage 24. The first opening 27 of one of the two consecutive fluid displacement members 26 is in fluid communication with the passage 24 through a first aperture 31 of that passage 24, and the second opening 28 of the other of the two consecutive fluid displacement members 26 is in fluid communication with the passage 24 through a second aperture 32 of that passage 24. The first aperture 31 is at a greater distance from the open end 25 of the passage 24 under consideration than the second aperture 32 (see Figures 4 and 5). The distance between the first aperture 31 and the second aperture 32 in the passage 24 forms a flow resistance 30 between the first aperture 31 and the second aperture 32 under operating conditions (the effect of which will be explained below). In another embodiment (not shown), each of the passages 24 is provided with a flow resistance in the form of a restriction in which the cross-sectional area of ​​the passage 24 is locally narrowed.

[0039] 4 shows by the arrows how the fluid displacement member 26 is manufactured by drilling a channel in the form of an elongated stepped hole between every two successive passages 24 by inserting a drill through the open ends 25 and drilling in the direction of the arrow. The advantage of this way of manufacturing is that the fluid displacement member 26 is located completely within the barrel plate 16, so no seals between the different parts are required.

[0040] FIG. 5 shows that the first opening 27 is close to the first aperture 31. The first opening 27 is surrounded by a seat cooperating with the ball 29, so that when the ball 29 is pressed against said seat at the first opening 27, the flow of fluid through the first opening 27 is prevented. Similarly, the second opening 28 is surrounded by a seat cooperating with the ball 29, so that when the ball 29 is pressed against said seat at the second opening 28, the flow of fluid through the second opening 28 is prevented. The seat at the second opening 28 is formed by the tapered end of a socket screw 32, which includes a through hole, which is screwed into the drilled hole after the ball 29 has been introduced into the cylindrical part of the stepped hole. Other construction designs are possible, for example a seat fixed by pressing, clamping or adhesive in the drilled hole is conceivable.

[0041] Each of the elongated stepped holes has a centre line that is slightly inclined with respect to a plane extending tangentially to the first axis of rotation 19 in the rotational position in which the cylindrical part of the fluid displacement member 26 is located. This means that the effect of centrifugal forces on the balls 29 is limited. The rotational speed of the shaft 3 therefore has a limited effect on the function of the fluid displacement member 26. It is noted that in the embodiment as shown in Figures 1 to 5, the elongated stepped holes can be drilled from the side of the barrel plate 16 opposite to that shown by the arrow in Figure 4, preferably via the inlets of the respective passages 24 located away from the open end 25, i.e. on the side of the barrel plate 16 on which the cylinder bottom 13 rests.

[0042] It is not necessary for the ball 29 to fit tightly within the cylindrical portion of the fluid displacement member 26, so long as the ball 29 contacts a seat in the first opening 27 or the second opening 28 to substantially impede fluid flow and minimize leakage.

[0043] The function of the hydraulic device 1 is illustrated in FIG. 6, which shows the port plate 5 including the high pressure port 6 and the low pressure port 7 in a linear manner for ease of illustration. Furthermore, only eleven pistons 10, cylinders 11, passages 24, flow resistances 30, open ends 25 and fluid displacement members 26 are shown. The passages 24 including the flow resistances 30 and open ends 25, the cylinders 11 and the fluid displacement members 26 are represented as parts of a unit moving along the linear port plate 5. The direction of movement of this unit relative to the port plate 5 is indicated by the arrow X in FIG. 6. Each of the pistons 10 passes through bottom dead center BDC and top dead center TDC while the corresponding open end 25 moves along the first seal land 8a between the low pressure port 7 and the high pressure port 6 and the second seal land 8b between the high pressure port 6 and the low pressure port 7. The length of each open end 25 in the moving direction X is smaller than the length of each of the first and second seal lands 8a, 8b in that direction, which means that the open end 25 is closed by one of the first and second seal lands 8 within a certain period of time while passing each of the first and second seal lands 8a, 8b.

[0044] Preferably, the distance between the edge of the first seal land 8a adjacent to the low pressure port 7 and the position where the piston 10 reaches bottom dead center BDC at the first seal land 8a is approximately half the length of the open end 25 in the direction of movement X, since the compression in each of the passing cylinders 11 starts substantially at bottom dead center BDC of the corresponding piston 10. Similarly, the distance between the edge of the second seal land 8b adjacent to the high pressure port 6 and the position where the piston 10 reaches top dead center TDC at the second seal land 8b is preferably approximately half the length of the open end 25 in the direction of movement X, since the expansion in each of the passing cylinders 11 starts substantially at top dead center TDC of the corresponding piston 10. FIG. 2 illustrates said half length by the angle α. Said half length is measured in the direction of rotation about the first axis of rotation 19.

[0045] Furthermore, the distance between the position at the first seal land 8a where the piston 10 reaches bottom dead center BDC and the edge of the first seal land 8a adjacent to the high pressure port 6 is greater than the distance between the position at the second seal land 8b where the piston 10 reaches top dead center TDC and the edge of the second seal land 8b adjacent to the low pressure port 7. These distances are measured in the direction of rotation and are shown as angles β1 and β2, respectively, in Figure 2. The reason that β1 is greater than β2 is that after leaving top dead center TDC only the dead volume in the cylinder 11 must expand, whereas after passing bottom dead center BDC both the dead volume and the stroke volume to be displaced by the piston 10 must compress.

[0046] When the open end 25 passes through and is closed by the first or second seal land 8a, 8b, the pressure in the cylinder 11 communicating with the open end 25 changes because the piston 10 is still moving during such period. When the open end 25 reaches the high pressure port 6 or low pressure port 7, the pressure in the cylinder 11 and the pressure at the high pressure port 6 or low pressure port 7 are preferably the same or close to each other to avoid excessive pressure differences that could cause noise generation. This is achieved by the fluid displacement member 26 between each pair of successive passages 24, as described below. The arrows on the piston 10 in FIG. 6 indicate the direction of movement of the piston 10 and the direction of hydraulic fluid flow through the passages 24 when the open end 25 communicates with the high pressure port 6 or low pressure port 7.

[0047] In FIG. 6 one of the pistons 10, its associated cylinder 11, passage 24 and open end 25 are designated by the reference numerals 10', 11', 24' and 25' respectively. In the situation shown in FIG. 6, the piston 10' approaches bottom dead center BDC and the cylinder 11' still communicates with the low pressure port 7 via the passage 24' and the open end 25'. The fluid displacement member 26 and its ball 29 on the left side of the passage 24' are designated by the reference numerals 26' and 29' respectively, while the successive fluid displacement member 26 and its ball 29 on the right side are designated by the reference numerals 26'' and 29'' respectively. The successive passages 24 of the passage 24' which cooperate with the fluid displacement member 26' are designated by the reference numeral 24'' and the successive passages 24 of the passage 24' which cooperate with the fluid displacement member 26'' are designated by the reference numeral 24''''. The further successive passages 24 of the passage 24''' are designated by the reference numeral 24''''.

[0048] In the condition shown in FIG. 6, fluid displacement member 26' prevents flow from passage 24' to passage 24'', by closing first opening 27 in the member, while fluid displacement member 26'' prevents flow from passage 24''' to passage 24' by closing first opening 27 in the member. Ball 29'' of fluid displacement member 26'' is held in position due to the increased pressure at high pressure port 6 communicating with passage 24'''. Ball 29' of fluid displacement member 26' is held in position due to the presence of flow resistance 30, in accordance with the present invention. Flow resistance 30 in passage 24' is designated 30' and flow resistance 30 in passage 24'' is designated 30''.

[0049] Since the open ends 25 communicating with the low pressure ports 7 also communicate with the cylinders 11 in which the pistons 10 move from top dead center TDC to bottom dead center BDC, under operating conditions, hydraulic fluid flows from the low pressure ports 7 to each cylinder 11 through the associated passages 24. This creates a lower pressure on the downstream side of each flow resistance 30, i.e., the side where the corresponding cylinder 11 is located, than on its upstream side, i.e., the side where the open ends 25 are located. As a result, as shown in FIG. 6, the arrangement of the fluid displacement members 26 interconnecting the open ends 25 communicating with the low pressure ports 7 urges the respective balls 29 of the fluid displacement members 26 upward against their respective first openings 27. In other words, the balls 29' of the fluid displacement members 26' are always already in a predetermined position before the open ends 25' reach the first seal land 8a.

[0050] It is noted that providing a distance between the first and second apertures 31, 32 along the passage 24 without locally narrowing the passage 24 may only cause a small pressure drop, but may be sufficient to displace the ball 29 of the fluid displacement member 26 due to the small weight of the ball 29. For example, the ball 29 has a diameter of 4 mm and a weight of 0.1 g.

[0051] Referring again to FIG. 6, if the open end 25' moves further in the moving direction X, the open end 25' will be completely closed by the first seal land 8a when the piston 10' in the corresponding cylinder 11' reaches the bottom dead center BDC. The pressure in the cylinder 11' will rise after the bottom dead center BDC as long as the open end 25' is closed. Due to the rising pressure, the first opening 27 of the fluid displacement member 26' remains blocked, but when the pressure in the cylinder 11' exceeds the pressure at the high pressure port 6, the ball 29'' of the fluid displacement member 26'' moves in the direction from the passage 24' toward the continuous passage 24''', and the pressure in the cylinder 11' does not rise any more or only rises a little. As a result, when the open end 25' starts to communicate with the high pressure port 6, the pressure in the cylinder 11' is substantially equal to the pressure at the high pressure port 6. The moving distance of the ball 29'' of the fluid displacement member 26'' depends on the pressure level at the high pressure port 6. If the pressure at the high pressure port 6 is relatively low, a relatively long travel distance is required since the cylinder 11 will already reach the low pressure level while the open end 25' is moving along the first seal land 8a.

[0052] As the open end 25' passes the first seal land 8a and travels along the high pressure port 6, the ball 29'' is either moved to the required position of the ball 29'' before the piston 10' reaches the second seal land 8b where the piston 10' passes top dead center TDC, or it automatically remains in the position of the ball 29''. On the downstream side of each flow resistance 30, i.e., the side where the open end 25 is located, the pressure is lower than on the upstream side, i.e., the side where the cylinder 11 is located. This biases the ball 29''' to a lower position as shown in FIG. 6. The ball 29''' thereby blocks the flow from the passage 24''' to the successive passage 24'''' by blocking the second opening 28.

[0053] It is important that each of the balls 29 of the respective fluid displacement members 26 have a predetermined position before the open ends 25 reach the respective first and second seal lands 8a, 8b. If, for example, the ball 29' in FIG. 6 is somewhere intermediate between the first and second openings 27, 28 before reaching the first seal land 8a, the ball 29' will be moved to the correct upper position first when closing the open end 25'. This will delay the onset of compression in the cylinder 11', resulting in an indefinite onset of compression in the cylinder 11' after the corresponding piston 10' has passed bottom dead center BDC.

[0054] The same effect as described herein when the open end 25 passes the first seal land 8a also occurs when the open end 25 passes the second seal land 8b and the piston 10 of the cylinder 11 communicating with the open end 25 passes the top dead center TDC. When the open end 25 is closed by the second seal land 8b and the piston 10 moves from the top dead center TDC towards the bottom dead center BDC, the pressure in the cylinder 11 decreases, whereby the ball 29 of the fluid displacement member 26 interconnecting the cylinder 11 and the successive cylinders 11 following it under operating conditions remains in the same position, i.e. closes the second opening 28. Meanwhile, the ball 29 of the other successive fluid displacement member 26 will be displaced towards the first opening 27 as soon as the pressure in the cylinder 11 becomes lower than the pressure of the low pressure port 7. The ball 29 moves to the first opening 27, i.e. the upper position in FIG. 6, before reaching the first seal land 8a, or automatically remains in its upper position.

[0055] FIG. 7 shows an alternative embodiment that functions similarly to the embodiment shown in FIG. 6, but with a different arrangement of the fluid displacement member 26. In this case, the open end 25 in communication with the low pressure port 7 urges the ball 29 of the corresponding fluid displacement member 26 upwards. FIG. 7 shows that when the open end 25' reaches the first sealing land 8a, the ball 29' of the fluid displacement member 26' blocks the first opening 27. Since the open end 25'' is already in communication with the high pressure port 6, the ball 29'' of the fluid displacement member 26'' is urged to a downward position and blocks the second opening 28 of that member. As soon as the open end 25' is closed by the first sealing land 8a, the piston 10' will start moving from bottom dead center BDC and the pressure in the cylinder 11 will start to rise. As a result, the ball 29' will immediately move downwards, blocking the flow from the passage 24' to the passage 24''. Subsequently, when the pressure in cylinder 11' exceeds the pressure at high pressure port 6, ball 29'' of fluid displacement member 26'' moves in a direction from passage 24' toward the continuous passage 24''', i.e., upward. However, as soon as open end 25' is in communication with high pressure port 6, due to the arrangement of fluid displacement member 26, ball 29'' is urged downward.

[0056] The opposite effect occurs with the second seal land 8b. Referring to Figure 7, the ball 29''' remains in a lower position until the piston 10''' reaches top dead center TDC, while the open end 25''' is closed by the second seal land 8b. After passing top dead center TDC, the ball 29''' moves immediately upward.

[0057] Because the ball 29 of the fluid displacement member 26 must immediately displace between the first and second openings 27, 28 after passing top dead center TDC or bottom dead center BDC to begin expanding or compressing, respectively, the first and second seal lands 8a, 8b in the arrangement of the fluid displacement member 26 as shown in FIG. 7 will be larger, measured in the direction of movement X, than those in the arrangement of the fluid displacement member 26 as illustrated in FIG. 6.

[0058] Figure 8 shows another alternative embodiment in which the hydraulic device 1 is applied as a motor. The passages 24 with the flow resistances 30 and the open ends 25, the cylinders 11 and the fluid displacement members 26 are represented as parts of a unit moving along a linear port plate 5 in a direction of movement Y opposite to the direction of movement X in the embodiment as shown in Figures 7 and 8. The function of the fluid displacement member 26 is equivalent to the embodiment as shown in Figures 6 and 7.

[0059] The invention is not limited to the embodiments shown in the drawings and described herein, but can be varied in different ways within the scope of the claims and their technical equivalents, for example, the hydraulic device can be a slipper type axial pump or motor with a cylinder in a block, or the hydraulic device can be a transformer.

Claims

1. A hydraulic device (1) comprising a rotor (3, 9, 10, 11, 16 - 18, 23) and a port member (5) including a high - pressure port (6) and a low - pressure port (7), wherein an outer surface (21) of the rotor faces an outer surface (22) of the port member (5) and is rotatable relative to the port member (5) in a rotational direction around a rotation axis (19), the rotor comprising a plurality of cylinders (11) arranged at angular intervals around the rotation axis (19) and a plurality of cooperating pistons (10) movable within respective ones of the cylinders (11), the cylinders (11) communicating with respective open ends (25) at the outer surface (21) of the rotor, each of the open ends (25) communicating alternately with the high - pressure port (6) and the low - pressure port (7) under operating conditions, each two consecutive cylinders (11) of the plurality of cylinders (11) being interconnected via a fluid displacement member (26), the fluid displacement member comprising a first opening (27) communicating with one of the two consecutive cylinders (11), a second opening (28) communicating with the other of the two consecutive cylinders (11), and a closing element (29) movable freely between the first and second openings (27, 28) and configured to substantially block either the first opening (27) or the second opening (28) when the pressure in the cylinder (11) communicating with the second opening (28) is respectively higher or lower than the pressure in the cylinder (11) communicating with the first opening (27) under operating conditions, in a hydraulic device, a flow resistance (30) is provided within the rotor (3, 9, 10, 11, 16 - 18, 23) at a position remote from each open end (25), the first opening (27) and the second opening (28) of each two fluid displacement members (26) communicating with one cylinder (11) are in fluid communication with that cylinder (11) on opposite sides of the flow resistance (30). A hydraulic device characterized by the above.

2. In the hydraulic device (1) according to Claim 1, each of the cylinders (11) communicates with the corresponding open end (25) through a passage (24) provided with the flow resistance (30). A hydraulic device characterized by the above.

3. In the hydraulic device (1) according to Claim 2, the flow resistance (30) is formed by a local narrowing of the passage (24). A hydraulic device characterized by the above.

4. In the hydraulic device (1) according to claim 2 or 3, the first opening (27) of each fluid displacement member (26) communicates with the corresponding cylinder (11) via a first aperture (31) in the passageway (24), and the second opening (28) of each fluid displacement member (26) communicates with the corresponding cylinder (11) via a second aperture (32) in the passageway (24). A hydraulic device characterized by this.

5. In the hydraulic device (1) according to claim 4, the first aperture (31) is at a greater distance from the open end (25) than the second aperture (32). A hydraulic device characterized by this.

6. In the hydraulic device (1) according to claim 5, each of the fluid displacement members (26) has a straight channel between the first aperture (31) of one of the two consecutive passageways (24) and the second aperture (32) of the other of the two consecutive passageways (24), and the channel has a cylindrical portion between the first and second openings (27, 28). A hydraulic device characterized by this.

7. In the hydraulic device (1) according to claim 6, the closing element is a ball (29), and the first and second openings (27, 28) are surrounded by respective seats that cooperate with the ball (29), such that when the ball (29) is pressed against the seat at the first opening (27), the flow of fluid through the first opening (27) is substantially blocked, and when the ball (29) is pressed against the seat at the second opening (28), the flow of fluid through the second opening (28) is substantially blocked. A hydraulic device characterized by this.

8. In the hydraulic device (1) according to claim 6, the cylindrical portion has a center line that lies in a plane extending tangentially to the rotation axis (19) at the rotational position where the cylindrical portion is located, or is inclined by an angle less than 45°, preferably less than 25°, with respect to that plane. A hydraulic device characterized by this.

9. In the hydraulic device (1) according to claim 6, the virtual extension of the channel in the direction from the rotor to the port member (5) passes through the open end (25) of the passageway (24) where the second aperture (32) is located. A hydraulic device characterized by this.

10. In the hydraulic device (1) according to claim 2 or 3, the outer surfaces (21, 22) are in a common plane, the rotating shaft (19) extends perpendicular to the outer surfaces (21, 22), the center line of the cylinder (11) extends parallel to the rotating shaft (19), the high-pressure port (6) and the low-pressure port (7) are arcuate around the rotating shaft (19) A hydraulic device characterized by this.

11. In the hydraulic device (1) according to claim 10, the rotating shaft is the first rotating shaft (19), the rotor has a shaft (3) rotatable around a second rotating shaft (20) and a flange (9) extending perpendicular to the second rotating shaft (20), the plurality of pistons (10) are fixed to the flange (9) at equal angular distances around the second rotating shaft (20), the plurality of cylinders are separate sleeves (11) placed on a barrel plate (16) provided with the passage (24), the second rotating shaft (20) intersects the first rotating shaft (19) at an acute angle, whereby when the shaft (3) is rotated, each of the pistons (10) reciprocates within the cooperating cylinder (11) A hydraulic device characterized by this.

12. In the hydraulic device (1) according to claim 1, 2 or 3, the outer surface (22) of the port member (5) has a first seal land (8a) between the low-pressure port (7) and the high-pressure port (6) where the cooperating piston (10) of the passing open end (25) reaches the bottom dead center (BDC), and a second seal land (8b) between the low-pressure port (7) and the high-pressure port (6) where the cooperating piston (10) of the passing open end (25) reaches the top dead center (TDC), the length of each of the first and second seal lands (8a, 8b) measured in the rotating direction is greater than the length of each of the open ends (25) A hydraulic device characterized by this.

13. In the hydraulic device (1) according to claim 12, The distance between the edge of the first seal land (8a) adjacent to the low-pressure port (7) and the position where the piston reaches the bottom dead center (BDC) on the first seal land (8a) is measured in the rotational direction and is half of the length of each open end (25), and / or the distance between the edge of the second seal land (8b) adjacent to the high-pressure port (6) and the position where the piston (10) reaches the top dead center (TDC) on the second seal land (8b) is measured in the rotational direction and is half of the length of each open end (25). Hydraulic device characterized by the above.

14. In the hydraulic device (1) according to claim 12, The length of the first seal land (8a) is measured in the rotational direction and is greater than the length of the second seal land (8b). Hydraulic device characterized by the above.

15. In the hydraulic device (1) according to claim 1, 2 or 3, The hydraulic device is a pump, a motor, or a transformer. Hydraulic device characterized by the above. is in fluid communication with the cylinder (11).

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