WO2020007559A1

WO2020007559A1 - Piston hydraulic device

Info

Publication number: WO2020007559A1
Application number: PCT/EP2019/064705
Authority: WO
Inventors: Federica Franzoni; Fabio Natali; Alessandro Sassi
Original assignee: Dana Motion Systems Italia S.R.L.
Priority date: 2018-07-05
Filing date: 2019-06-05
Publication date: 2020-01-09
Also published as: EP3591224A1; DE212019000338U1

Abstract

A piston hydraulic device comprises a cylinder block (12) having a plurality of cylinder assemblies (24) having a cylinder (26) and a piston (28), and being rotatable about a first rotation axis (A). A port plate (14) has a first port (38) and a second port (40). A plurality of first conduits (50) connects a respective cylinder (26) alternately to the first port (38) or the second port (40) relative to the angular position of the cylinder assembly (24) about the first rotation axis (A). At least one second conduit (52) connects between at least one first conduit (50) and an accumulator (54). At least one directional system (56) fluidly connects to at least one first conduit (50) and to the at least one second conduit (52). The at least one directional system (56) is configured to convey return fluid from the cylinder assembly (24) to the port plate (14) in a first operative condition and to divert return fluid from the cylinder assembly (26) to the accumulator (54) in a second operative condition.

Description

PISTON HYDRAULIC DEVICE

Technical Field

This disclosure relates to the field of piston hydraulic devices such as pumps or motors, particularly variable displacement piston hydraulic devices, and more particularly to the control of fluid displacement in the piston hydraulic devices.

Background

Piston hydraulic devices may be axial piston machines or radial piston. The Piston hydraulic devices may be operated as pumps or motors.

Variable axial piston hydraulic devices may be swash plate type devices or bent axis type devices. Swash plate type axial piston devices have a tiltable swash plate that controls the stroke of the piston within a rotating cylinder block. With bent axis type axial piston devices, the pistons are at an angle to the drive shaft and thrust plate.

In both the "swash plate" and the "bent axis" types, the devices comprise a cylinder block carrying the pistons. The cylinder block rotates about a first axis. The devices also comprise a transmission shaft that rotates around a second axis of rotation, also called the transmission axis. Through this shaft mechanical work that is carried out for the compression of fluid (in the case of the pumps) or mechanical work (in the case of the motors) is determined by the pressure of the operating fluid.

In the swash plate type device, the first and second axes coincide. The swash plate has a variable inclination to vary the stroke of the pistons between the dead points and, accordingly, the displacement of the machine. For varying displacement in the swash plate type device, the inclination of the plate is varied to change the stroke of the pistons.

In bent-axis type device, the first and the second axis are incident. The relative inclination of these axes is varied to vary the stroke of the pistons between the dead points and, accordingly, the displacement of the machine. For varying displacement in the bent-axis type device, the inclination of the cylinder block is varied.

The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of the prior art system.

Brief Summary of the Invention

The present disclosure describes a piston hydraulic device. The piston hydraulic device comprises a cylinder block having a plurality of cylinder assemblies, the cylinder block being rotatable about a first rotation axis wherein each cylinder assembly comprises a cylinder and a piston. A port plate has a first port and a second port. A plurality of first conduits connect a respective cylinder alternately to the first port or the second port relative to the angular position of the cylinder assembly about the first rotation axis. At least one second conduit connects between at least one first conduit and an accumulator. At least one directional system fluidly connects to at least one first conduit and to the at least one second conduit. The at least one directional system is configured to convey return fluid from the cylinder assembly to the port plate in a first operative condition and to divert return fluid from the cylinder assembly to the accumulator in a second operative condition.

Brief Description of the Drawings

The foregoing and other features and advantages of the present disclosure will be more fully understood from the following description of various embodiments, when read together with the accompanying drawings, in which:

Fig. 1 is a schematic illustration of a piston hydraulic device in a first embodiment according to the present disclosure wherein the directional control valves are in the first position;

Fig. 2 is a schematic illustration of a piston hydraulic device in a second embodiment according to the present disclosure;

Fig. 3 is a schematic illustration of a piston hydraulic device in a third embodiment according to the present disclosure wherein the directional control valves are in the first position;

Fig. 4 is a schematic illustration of a piston hydraulic device in the fourth embodiment according to the present disclosure;

Fig. 5 is a cross sectional view of a portion of a swash plate type axial piston hydraulic device according to the present disclosure; and

Fig. 6 is a cross sectional view of a portion of a bent axis type axial piston hydraulic device according to the present disclosure.

Detailed Description

This disclosure generally relates to a piston hydraulic device. The device is configured to have discrete variation of fluid displacement and energy recovery with respect to the return fluid leaving from a piston chamber.

Fig. 1 schematically illustrates a piston hydraulic device 10 (hereinafter referred to as “device”) in the first embodiment. Fig. 1 illustrates an axial piston hydraulic device 10. In an alternative embodiment, the device 10 may be a radial piston hydraulic device. The device 10 comprises a cylinder block 12, a port plate 14, a plurality of first conduits 50, at least one second conduit 52 and at least one directional system 56.

The cylinder block 12 comprises a plurality of cylinder assemblies 24. The cylinder block 12 is rotatable about a first rotation axis A (not shown). The cylinder block 12 is rotatably supported in the device 10. Cylinder block 12 is rotatably supported in a housing (not shown) of the device 10. The cylinder assemblies 24 are radially positioned in the cylinder block 12 relative to the first rotation axis A. The cylinder assemblies 24 are mutually angularly spaced about the cylinder block 12. The cylinder block 12 has first block surface 30 and a second block surface 32. First and second block faces 30, 32 are formed on opposite sides of the cylinder block 12. First and second block faces 30, 32 are parallel.

Each cylinder assembly 24 comprises a cylinder 26 and a piston 28. The cylinders 26 have respective openings 34 on the first block surface 30. Pistons 28 extend and retract in the cylinders 26. Pistons 28 extend from the openings 34. Cylinders 26 have a base 36. A cylinder conduit 48 extends from the base 36 to the second block face 32. Cylinder conduit 48 communicates with the cylinder 26. Fluid enters and exits the cylinder 26 through the cylinder conduit 48. Pistons 28 have a piston head 42 and a piston base 44. Piston head 42 is positioned external to the cylinder 26. Piston base 44 travels in the cylinder 26 during a stroke of the piston 28. Piston base 44 moves away from the base 36 of the cylinder 26 during an extraction stroke. Piston base 44 moves towards the base 36 of the cylinder 26 during a return stroke. Each piston 28 moves along the respective cylinder 26 in parallel to the first rotation axis A.

Base 44 of piston 28 defines a chamber 46 in the cylinder 26. The chamber 46 varies in volume as the piston 28 extends and retracts in the cylinder 26. Change in the fluid in the chamber 46 acts on the piston base 44. The chamber 46 varies in volume from a maximum volume which is reached when the piston 28 is at the top dead centre of an extraction stroke to a minimum volume which is reached when the piston 28 is at the bottom dead centre of a return stroke.

The port plate 14 has a first port 38 and a second port 40. Port plate 14 is supported in the housing (not shown) of the device 10. Port plate 14 is positioned adjacent the cylinder block 12. Port plate 14 is positioned so as to face the second block face 32. Cylinder block 12 is rotatable relative to the port plate 14. The first and second ports 38, 40 are angularly spaced relative to the first rotation axis A. The first and second ports 38, 40 are positioned in respective separate angular sectors of the port plate 14. In an embodiment, first and second ports 38, 40 are angularly extended on the port plate 14. The cylinders 26 are configured to be alternately fluidly connected to the first and second ports 38, 40 as the cylinder block 12 rotates relative to the port plate 14. The cylinder conduit 48 of respective cylinders 26 fluidly alternately connects with the first and second ports 38, 40. The first and second ports 38, 40 are configured to be connected to different operating fluid sources. The fluid sources are a high pressure fluid source or a low pressure fluid source.

The plurality of first conduits 50 alternately fluidly connects respective cylinder assemblies 24 to the port plate 14. The plurality of first conduits 50 alternately fluidly connects respective cylinder 26 to the first port 38 or the second port 40. The plurality of first conduits 50 alternately fluidly connects respective cylinder conduits 48 to the first port 38 or the second port 40. The plurality of first conduits 50 alternately fluidly connects respective cylinder conduits 48 to the first port 38 or the second port 40 relative to the angular position of the cylinder assembly 24 about the first rotation axis A. Each cylinder 26 alternately connects to the first port 38 or the second port 40 of the port plate 14 as the cylinder block 12 rotates about the first rotation axis A.

The at least one second conduit 52 is connected to at least one first conduit 50. The at least one second conduit 52 is connected to an accumulator 54. The at least one second conduit 52 is connected between the at least one first conduit 50 and the accumulator 54. The second conduit 52 is formed as an annular channel in cross section. The second conduit 52 is formed in the housing (not shown) of the device 10.

In an embodiment, the device 10 has a single second conduit 52 connected to the accumulator 54. In alternative embodiment, the device has a plurality of second conduits 52 each connected to a respective accumulator 54. The plurality of second conduits 52 are each connected to respective first conduits 50.

The at least one directional system 56 is fluidly connected to the at least one first conduit 50. The at least one directional system 56 is fluidly connected to the at least one second conduit 52. The at least one directional system 56 is configured to convey return fluid from the cylinder assembly 24 to the port plate 14 in a first operative condition. Return fluid exits the chamber 46 of the cylinder 26 as the piston 28 undergoes a return stroke. Return fluid flows into the at least one first conduit 50 from the cylinder assembly 24. The at least one directional system 56 is configured to divert return fluid from the cylinder assembly 24 to the accumulator 54 in a second operative condition. Return fluid moves from the at least one first conduit 50 to the at least one second conduit 52.

In the first embodiment, device 10 has a plurality of directional systems 56. The plurality of directional systems 56 are fluidly connected to the respective first conduits 50. The plurality of directional systems 56 are fluidly connected to a single second conduit 52. The plurality of directional systems 56 are interposed between the plurality of respective first conduits 50 and the accumulator 54. The plurality of directional systems 56 are each operatable independently.

In the second embodiment, as illustrated in Fig. 2, device 10 has a plurality of directional systems 56 that are each connected to respective second conduits 52. The plurality of directional systems 56 are each operatable independently. Each second conduit 52 is connected to a respective accumulator 54. The plurality of directional systems 56 are interposed between the respective first conduits 50 and the respective accumulators 54.

With respect to Fig. 1 and 2, the at least one directional system 56 is configured to fluidly disconnect the cylinder assembly 24 from the accumulator 54 in the first operative condition. Fluid is prevented to flow from the cylinder assembly 24 to the accumulator 54 during piston 28 retraction and extraction. The at least one directional system 56 is configured to fluidly connect the cylinder assembly 24 to the port plate 14. Fluid is permitted to flow from the cylinder assembly 24 to the port plate 14 during piston 28 retraction. Fluid is permitted to flow from the port plate 14 to the cylinder assembly 24 and during piston 28 extraction. The at least one directional system 56 is configured to fluidly disconnect the cylinder assembly 24 from the port plate 14 in the second operative condition at piston 28 retraction. Fluid is prevented to flow from the cylinder assembly 24 to the port plate 14 during retraction of the piston 28 and fluid is permitted to flow from the port plate 14 to the cylinder assembly 24 during extraction of the piston 28. The at least one directional system 56 is configured to fluidly connect the cylinder assembly 24 to the accumulator 54 in the second operative condition at piston 28 retraction. Fluid is permitted to flow from the cylinder assembly 24 to the accumulator 54 during retraction of the piston 28 and fluid is prevented to flow from the cylinder assembly 24 to the accumulator 54 at piston 28 extraction.

With reference to Figs. 1 and 2, the at least one directional system 56 comprises a first control valve 58, a second control valve 60 and a pilot valve 62. The first control valve 58 is positioned in the at least one first conduit 50 to control fluid flow between the cylinder assembly 24 and the port plate 14. The first control valve 58 controls the fluid flow between the cylinder 26 and the first port 38 or the second port 40. The second control valve 60 is positioned in the at least one second conduit 52 to control fluid flow to the accumulator 54. The second control valve 60 is positioned in the at least one second conduit 52 to control fluid flow from the at least one fluid conduit 50 to the at least second fluid conduit 52. The pilot valve 62 is fluidly connected to the first and second control valves 58, 60. The pilot valve 62 controls the actuation of the first and second control valves 58, 60.

The at least one second conduit 52 is connected to the at least one first conduit 50 between the first control valve 58 and the respective cylinder assembly 24. The point of connection of the at least one second conduit 52 and the at least one first conduit 50 is positioned between the first control valve 58 and the respective cylinder assembly 24. In an embodiment, the point of connection of the at least one second conduit 52 and the at least one first conduit 50 is positioned between the first control valve 58 and the cylinder conduit 48 of respective cylinders 26.

The first control valve 58 is actuatable to open in the first operative condition so as to permit fluid to flow between the port plate 14 and the cylinder assembly 24. The first control valve 58 is actuatable to close in the second operative condition so as to obstruct fluid flow from the cylinder assembly 24 to the port plate 14. In an embodiment, the first control valve 58 is a check valve.

The first control valve 58 is actuatable to open or to close. In the open condition, the first control valve 58 is actuated so as to remain open. The first control valve 58 permits fluid to flow from the port plate 14 to the cylinder assembly 24, during extraction of the piston 28, and permits fluid to flow from the cylinder assembly 24 and to the port plate 14, during retraction of the piston 28. In the closed condition, the first control valve 58 is actuated to close so as to operate as a check valve. The first control valve 58 permits fluid to flow from the port plate 14 to the cylinder assembly 24, during extraction of the piston 28. The force of the pressure of the fluid from the port plate 14 is sufficient to overcome the force holding the first control valve 58 in the closed position. The first control valve 58 prevents fluid to flow from the cylinder assembly 24 and to the port plate 14, during retraction of the piston 28.

The second control valve 60 is actuatable to close in the first operative condition so as to obstruct fluid flow from the cylinder assembly 24 to the accumulator 54. The second control valve 60 is actuatable to open in the second operative condition so as to permit fluid flow from the cylinder assembly 24 to the accumulator 54. In an embodiment, the second control valve 60 is a check valve.

The second control valve 58 is actuatable to close or to open. In the closed condition, the second control valve 60 is actuated to remain closed. The second control valve 60 prevents fluid to flow from the first conduit 50 through the second conduit 52 to the accumulator 54. Force of the pressure of the fluid from the port plate 14 or the cylinder assembly 24 is not sufficient to overcome the force holding the second control valve 60 in the closed position. Second control valve 60 prevents fluid to flow to the accumulator 54 from either from the cylinder assembly 24 or from the port plate 14. In the open condition, second control valve 60 is actuated to open so as to operate as a check valve. The second control valve 60 permits fluid to flow from the first conduit 50 through the second conduit 52 to the accumulator 54. Second control valve 60 permits fluid to flow to the accumulator 54 from the cylinder assembly 24. The force of the pressure of the fluid from the cylinder assembly 24, during retraction of the piston 28, is sufficient to overcome the force of holding the second control valve 60 in the closed position. The force of the pressure of the fluid from the port plate 14, during extraction of the piston 28, is not sufficient to overcome the force holding the second control valve 60 in the closed position.

The pilot valve 62 is connected to the first control valve 58 through a first pilot line 64. The pilot valve 62 is connected to the second control valve 60 through a second pilot line 66. The second pilot line 66 is connected to the first pilot line 64. A pilot signal is sent from the pilot valve 62 to the first and second control valves 58, 60 for the actuation thereof. The pilot signal is sent through the first and second pilot lines 64, 66. The first and second control valves 58, 60 are actuated by the same pilot signal. The pilot signal is provided by a pressure source (not shown). The pressure of the pilot signal may be selected as required.

The pilot valve 62 is actuatable between a first position 70 and a second position 72. In the first position 70, the first and second pilot lines 64, 66 are fluidly connected to the pressure source. The pilot signal is sent to the first and second control valves 58, 60 from the pressure source. The at least one directional system 56 is set to the first operative condition when the pilot valve 62 is actuated to the first position 70. The pilot signal actuates the first control valve 58 to remain open and actuates the second control valve 60 to remain closed.

In the second position 72 the first and second pilot lines 64, 66 are fluidly connected to a tank 68. The pressurized fluid is drained from the first and second pilot lines 64, 66 to the tank 68. The at least one directional system 56 is set to the second operative condition when the pilot valve 62 is actuated to the first position 72. The drop in pressure in the first and second pilot lines 64, 66 actuates the first control valve 58 to close and actuates the second control valve 60 to open. The first and second control valves 58, 60 operate as check valves.

The pilot valve 62 is actuatable between the first position 70 and the second position 72 through mechanical means. The mechanical means is electronically controlled. In an embodiment, the mechanical means is an actuation member 74. Actuation member 74 may be comprised in the pilot valve 62. A controller (not shown) may be operatively associated with the pilot valve 62 for switching between the first and the second positioned 70, 72.

In a further embodiment, the actuation member 74 may operate in conjunction with a return spring 76. The pilot valve 62 may be normally in the first position 70. The activation of the actuation member 60 may actuate the pilot valve 62 from the first position 70 to the second position 72. The deactivation of the actuation member 60 permits the return spring 62 to return the pilot valve 62 from the second position 72 to the first position 70. In an embodiment, the directional control valve 56 is a three way two position valve.

In an embodiment, the accumulator 54 is fluidly connected to a work tool (not shown). The fluid connection to the work tool is controlled by a normally closed two position valve 78. As required, the pressurized fluid stored in the accumulator may be released through the two position valve 78 for use in operations such as to operate the work tool. With respect to Fig. 2, the device 10 comprises a plurality of accumulators 54. Each accumulator 54 is connected to a respective second conduit 52. Each conduit is connected to a respective directional system 56.

In an embodiment, the accumulator 54 is connected to a pressure switch 80. The pressure switch 80 is set to activate at a predetermined pressure value. The predetermined pressure value may be set to correspond to the maximum pressure of the accumulator 54. When the pressure in the accumulator 54 reaches the predetermined pressure value, the pressure switch 80 sends a signal to an electric power unit (not shown) for activation of the actuation means 74. The actuation means 74 actuates the pilot valve 62 from the second position 72 to the first position 70 to thereby setting the directional system 56 to the first operative condition so as to prevent more oil being sent to the accumulator 54. With respect to Fig. 2, with a plurality of accumulators 54 the respective pressure switches 80 have the same predetermined pressure values. In an alternate embodiment, the respective pressure switches 80 may have different predetermined pressure values.

In respect to the device 10 acting as a motor and in the first operative condition, with the piston 28 retracted in the cylinder 26, the connection to a port 38, 40 with high pressure fluid permits pressurised fluid to flow to the chamber 46 so as to extract the piston 28. In the first operative condition fluid is permitted to flow through first conduit 50 by the first control valve 58 that is actuated to the open position. Fluid is prevented from flowing to the accumulator 54 through the second conduit 52 by the second control valve 60 that is actuated to the closed position.

With the piston 28 extracted in the cylinder 26, the connection to a port 38, 40 with low pressure fluid enables return fluid to flow from the cylinder 26 so as to allow the retraction of the piston 28. Second control valve 60 obstructs fluid from flowing to the accumulator 54. Fluid is permitted to flow through the first control valve 58 to the port plate 14 and out through either port 38, 40.

In respect to the device 10 acting as a motor and in the second operative condition, with the piston 28 retracted in the cylinder 26, the connection to a port 38, 40 with high pressure fluid permits pressurised fluid to flow to the chamber 46 so as to extract the piston 28. In the second operative condition fluid is permitted to flow through the first conduit 50 to the chamber 46 through the first control valve 58. The second control valve 60 is actuated to the open position. Fluid is prevented from flowing to the accumulator 54 through the second conduit 52 as the fluid pressure is not sufficient to overcome the second control valve 60.

In an embodiment, fluid may be prevented from flowing to the accumulator 54 when the pressure in the accumulator 54 is low and/or the pressure along the first conduit 50 is high. Fluid may flow through the second control valve 60 to the accumulator 54 if the fluid pressure in the accumulator 54 is low. Fluid may flow through the second control valve 60 to the accumulator 54 when pressure along the first conduit 50 is high. With reference to Figs. 3 and 4, the device 10 may further comprise a third pilot line 88 to prevent flow of high pressure fluid to the accumulator 54. The third pilot line connects the second control valve 60 to a respective first conduit 50. The third pilot line 88 connects to the first conduit 50 upstream from the first control valve 58. The third pilot line 88 connects to the first conduit 50 between the first control valve 58 and the port plate 14. Figs 3 and 4 operate as in Figs. 1 and 2 respectively with the exception of the third pilot line 88.

With reference to Figs, 1 and 2 with the piston 28 extracted in the cylinder 26, the connection to a port 38, 40 with low pressure fluid enables return fluid to flow from the cylinder 26 so as to allow the retraction of the piston 28. First control valve 58 prevents fluid from flowing to the port plate 14 and out through either port 38, 40. As the pressure in first conduit 50 rises, the pressure reaches a point to overcome the second control valve 60 so that fluid flows to the accumulator 54 through the second conduit 52.

In respect to the device 10 acting as a pump and in the first operative condition, with the piston 28 retracted in the cylinder 26, the connection to a port 38, 40 with the low pressure fluid permits pressurised fluid to flow to the chamber 46 so as to extract the piston 28. In the first operative condition fluid is permitted to flow through first conduit 50 by the first control valve 58 that is actuated to the open position. Fluid is prevented from flowing to the accumulator 54 through the second conduit 52 by the second control valve 60 that is actuated to the closed position.

With the piston 28 extracted in the cylinder 26 the connection to a port 38, 40 with the high pressure fluid enables return fluid to flow from the cylinder 26 so as to allow the retraction of the piston 28. Second control valve 60 obstructs fluid from flowing to the accumulator 54. Fluid is permitted to flow through the first control valve 58 to the port plate 14 and out through either port 38, 40.

In respect to the device 10 acting as a pump and in the second operative condition, with the piston 28 retracted in the cylinder 26, the connection to a port 38, 40 with the low pressure fluid permits pressurised fluid to flow to the chamber 46 so as to extract the piston 28. In the second operative condition fluid is permitted to flow through the first conduit 50 to the chamber 46 by the first control valve 58 that returns to the closed position. The second control valve 60 is actuated to the open position. Fluid is prevented from flowing to the accumulator 54 through the second conduit 52 as the fluid pressure is not sufficient to overcome the second control valve 60.

With the piston 28 extracted in the cylinder 26 the connection to a port 38, 40 with the high pressure fluid enables return fluid to flow from the cylinder 26 so as to allow the retraction of the piston 28. First control valve 58 prevents fluid from flowing to the port plate 14 and out through either port 38, 40. As the pressure in first conduit 50 rises, the pressure reaches a point to overcome the second control valve 60 so that fluid flows to the accumulator 54 through the second conduit 52.

Fig. 5 illustrates the device 10 as a swash plate type axial piston hydraulic device. Device 10 comprises a housing 82. A rotor 86 is coupled to the cylinder block 12. The rotor 86 is adapted to be coupled to a drive shaft or to a driven shaft (not shown). The rotor 86 is rotatably supported by the housing 82 around the first rotation axis A. A swash plate 84 is coupled to the housing 82. The rotor 86 is inserted passing through the swash plate 84. The swash plate 84 has ring conformation. The port plate 14 is coupled to the housing 82. In an embodiment, the at least one directional system 56 is coupled to the housing 82. In a further embodiment, a plurality of directional systems 56 are coupled to the housing 82. The cylinder block 12 is rotatably supported in the housing 82. Pistons 28 are movably positioned in the respective cylinders 26. Pistons 28 are coupled to the swash plate 84. Cylinder conduits 48 extend from the base 36 of respective cylinders 26.

The first conduit 50 extends from the cylinder block 12 through the housing 82. A portion of the first conduit 50 extends through the cylinder block 12. First conduit 50 extends from the respective cylinder conduit 48 through the cylinder block 12. A first conduit path 50A of the first conduit 50 extends through the cylinder block 12 to the housing 82. The first conduit 50 extends to the at least one directional system 56. A second conduit path 50B extends through the housing 72 to the first control valve 58. A first annular groove 50E is interposed between the first and second conduit path 50A and 50B. The first annular groove 50E is defined in the housing 72.

The first conduit 50 extends from the first control valve 58 back to the cylinder block 12. A third conduit path 50C extends through the housing 82 to the cylinder block 12. The first conduit 50 extends through the cylinder block 12 to the port plate 14. A fourth conduit path 50D extends through the cylinder block 12 to the port plate 14. A second annular groove 50F is interposed between the third and fourth conduit path 50C and 50D. The second annular groove 50F defined in the housing 82. Sealing gaskets (not shown) are interposed between the first and second annular groove 50E and 50F, the housing 82 and the cylinder block 12.

The second conduit 52 extends through the housing 82. A first conduit channel 52A of the second conduit 52 extends from the first control valve 58 to the second control valve 60. A second conduit channel 52B of the second conduit 52 extends from the second control valve 60 to the accumulator 54 (not shown).

A first pilot line 64 extends through the housing 82 from the first control valve 58 to the pilot valve 62 (not shown). The second control valve 60 is connected to the first pilot line 64 through the second pilot line 66 (not shown).

Fig. 6 illustrates the device 10 as a bent-axis type axial piston hydraulic device. Device 10 comprises a housing 82. A rotor 86 is coupled to the housing 72. The rotor 86 is adapted to bed to a drive shaft or to a driven shaft (not shown). The rotor 86 is rotatably supported by the housing 82 around a second rotation axis B inclined in respect of the first rotation axis A. The port plate 14 is coupled to the housing 82. In an embodiment, the at least one directional system 56 is coupled to the housing 82. In a further embodiment, a plurality of directional systems 56 are coupled to the housing 82. The cylinder block 12 is rotatably supported in the housing 82. Pistons 28 are movably positioned in the respective cylinders 26. Pistons 28 are coupled to the rotor 86. Cylinder conduits 48 extend from the base 36 of respective cylinders 26.

The first conduit 50 extends from the cylinder block 12 through the housing 72. A portion of the first conduit 50 extends through the cylinder block 12. First conduit 50 extends from the respective cylinder conduit 48 through the cylinder block 12. A first conduit path 50A of the first conduit 50 extends through the cylinder block 12 to the housing 82. The first conduit 50 extends to the at least one directional system 56. A second conduit path 50B extends through the housing 82 to the first control valve 58. A first annular groove 50E is interposed between the first and second conduit path 50A and 50B. The first annular groove 50E is defined in the housing 72.

In an embodiment, the device 10 is configured to operate as a hydraulic motor. In an alternate embodiment, the device 10 is configured to operate as a pump. The skilled person would appreciate that foregoing embodiments may be modified or combined to obtain the piston hydraulic device 10 of the present disclosure.

Industrial Applicability

This disclosure describes a piston hydraulic device 10 that has individually variable pistons. The piston hydraulic device 10 provides for the discrete variation in fluid displacement. The discrete variation of displacement is enabled without modifying the geometric configuration of the piston hydraulic device 10. The relative inclination of the various structures such as the swash plate 84 or the housing 82, are not varied to obtain the variation of displacement. Energy recovery is obtained by means of the directional system 56 that fluidly connects the piston assembly 24 to the accumulator 54. Energy is stored in the accumulator 54 in the form of pressurised fluid that may be used as required such as to operate a tool.

Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein.

Where technical features mentioned in any claim are followed by reference signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, neither the reference signs nor their absence have any limiting effect on the technical features as described above or on the scope of any claim elements.

One skilled in the art will realise the disclosure may be embodied in other specific forms without departing from the disclosure or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the disclosure described herein. Scope of the invention is thus indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

The disclosures in European Patent Application No. 18425052.0 from which this application claims priority are incorporated herein by reference.

Claims

1. A piston hydraulic device (10) comprising:

a cylinder block (12) having a plurality of cylinder assemblies (24), the cylinder block (12) being rotatable about a first rotation axis (A) wherein each cylinder assembly (24) comprises a cylinder (26) and a piston (28);

a port plate (14) having a first port (38) and a second port (40);

a plurality of first conduits (50) for connecting a respective cylinder (26) alternately to the first port (38) or the second port (40) relative to the angular position of the cylinder assembly (24) about the first rotation axis (A),

characterized in that the piston hydraulic device (10) further comprises

at least one second conduit (52) connected between at least one first conduit (50) and an accumulator (54);

at least one directional system (56) fluidly connected to at least one first conduit (50) and fluidly connected to the at least one second conduit (52) wherein the at least one directional system (56) is configured to convey return fluid from the cylinder assembly (24) to the port plate (14) in a first operative condition and to divert return fluid from the cylinder assembly (26) to the accumulator (54) in a second operative condition.

2. The piston hydraulic device (10) of claim 1 wherein the at least one directional system (56) is configured to fluidly disconnect the cylinder assembly (24) from the accumulator (54) and to fluidly connect the cylinder assembly (24) to the port plate (14) in the first operative condition.

3. The piston hydraulic device (10) of claims 1 or 2 wherein the at least one directional system (56) is configured to fluidly disconnect the cylinder assembly (24) from the port plate (14) and to fluidly connect the cylinder assembly (24) to the accumulator (54) in the second operative condition at piston (28) retraction.

4. The piston hydraulic device (10) of claims 1, 2 or 3 wherein the at least one directional system (56) comprises a first control valve (58) positioned in the at least one first conduit (50) to control fluid flow between the cylinder assembly (24) and the port plate (14), a second control valve (60) positioned in the at least one second conduit (52) to control fluid flow to the accumulator (54) and a pilot valve (62) fluidly connected to the first and second control valves (58, 60) to control the actuation of the first and second control valves (58, 60).

5. The piston hydraulic device (10) of claim 4 wherein the at least one second conduit (52) is connected to the at least one first conduit (50) between the first control valve (58) and the respective cylinder assembly (24).

6. The piston hydraulic device (10) of claims 4 or 5 wherein the first control valve (58) is actuatable to open in the first operative condition so as to permit fluid to flow between the port plate (14) and the cylinder assembly (24).

7. The piston hydraulic device (10) of claims 4, 5 or 6 wherein the first control valve (58) is actuatable to close in the second operative condition so as to obstruct fluid flow from the cylinder assembly (24) to the port plate (14).

8. The piston hydraulic device (10) of claims 4, 5, 6 or 7 wherein the second control valve (60) is actuatable to close in the first operative condition so as to obstruct fluid flow from the cylinder assembly (24) to the accumulator (54).

9. The piston hydraulic device (10) of claims 4, 5, 6, 7 or 8 wherein the second control valve (60) is actuatable to open in the second operative condition so as to permit fluid flow from the cylinder assembly (24) to the accumulator (54).

10. The piston hydraulic device (10) of any one of preceding claims 4 to 9 wherein the pilot valve (62) is connected to the first control valve (58) through a first pilot line (64) and the pilot valve (62) is connected to the second control valve (60) through a second pilot line (66) connected to the first pilot line (64).

11. The piston hydraulic device (10) of claim 10 further comprising a third pilot line (88) connects the second control valve (60) to a respective first conduit (50) between the first control valve (58) and the port plate (14).

12. The piston hydraulic device (10) of any one of preceding claims wherein a plurality of directional systems (56) are fluidly connected to the plurality of respective first conduits (50) and fluidly connected to the second conduit (52).

13. The piston hydraulic device (10) of any one of preceding claims wherein the accumulator (54) is fluidly connected to a work tool wherein the fluid connection is controlled by a normally closed valve (78).

14. The piston hydraulic device (10) of any one of preceding claims wherein the device (10) is a bent axis hydraulic device.

15. The piston hydraulic device (10) of any one of preceding claims 1 to 13 wherein the device (10) is a swash plate type hydraulic device.