FLUID-WORKING MACHINE AND OPERATING METHOD

Abstract

A fluid-working machine has a plurality of working chambers, e.g., cylinders, of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber to each manifold, and electronic sequencing means for operating said valves in timed relationship with the changing volume of each chamber, wherein the electronic sequencing means is arranged to operate the valves of each chamber in one of an idling mode, a partial mode in which only part of the usable volume of the chamber is used, and a full mode in which all of the usable volume of the chamber is used, and the electronic sequencing means is arranged to select the mode of each chamber on successive cycles so as to infinitely vary the time averaged effective flow rate of fluid through the machine.

Claims

1. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising: operating the valves of at least one of said working chambers in a partial motoring mode in which only part of the usable volume of the one working chamber is used.

2. The method according to claim 1, further comprising closing the valve linking said one of the working chambers to the high-pressure manifold and opening the valve linking said one of the working chambers to the low-pressure manifold a small fraction after the top dead center position of the piston of the at least one working chamber.

3. The method of claim 1, further comprising determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, and (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon a function of the error between the measured and demanded pressure.

4. The method of claim 1, further comprising determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, and (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon the time history of past systems responses to past decisions.

5. A fluid-working machine comprising: a plurality of working chambers of cyclically varying volume, said working chambers comprising cylinders within which pistons are arranged to reciprocate; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber of said working chambers to each manifold; and a controller having a configuration to operate the valves of at least one of the said working chambers in a partial motoring mode in which only part of the usable volume of the at least one working chamber is used.

6. The fluid-working machine according to claim 5, wherein: the controller has a configuration to close the valve linking the at least one working chamber to the high-pressure manifold, and open the valve linking the at least one working chamber to the low-pressure manifold, a small fraction in advance of the top dead center position of the piston of the at least one working chamber.

7. The fluid-working machine according to claim 5, wherein the controller is further configured to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon a function of the error between the measured and demanded pressure.

8. The fluid-working machine according to claim 5, wherein the controller is further configured to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) said partial motoring modes, wherein the sequence of modes of operation is based upon the time history of past systems responses to past decisions.

9. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising: determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) partial stroke modes in which only part of the usable volume of the chamber is used and (iii) full stroke modes in which all of the usable volume of the working chamber is used.

10. The method of claim 9, wherein the demand level is varied in use.

11. The method of claim 9, wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one in which valve actuations are delayed to almost the end of the stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

12. The method of claim 9, wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one that provides sufficient stability of valve operation at the low flow end.

13. The method of claim 9, wherein, in the partial stroke modes, valve actuations are delayed to almost an end of a stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

14. The method of claim 9, wherein the partial stroke mode is a part stroke motoring mode in which the transition from intake from the high-pressure manifold to intake from the low pressure manifold happens a small fraction after top dead center, wherein the small fraction is one in which valve actuations are such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

15. The method of claim 9, wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion.

16. A machine comprising: a plurality of working chambers of cyclically changing volume; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber to each manifold; and a controller having a configuration to: determine a mode of each working chamber on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) partial stroke modes in which only part of the usable volume of the working chamber is used and (iii) full stroke modes in which all of the usable volume of the working chamber is used.

17. The machine of claim 16, wherein the demand level is varied in use.

18. The machine of claim 16, wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one in which valve actuations are delayed to almost the end of the stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

19. The machine of claim 16, wherein the partial stroke modes comprise use of only a small fraction of the usable volume of the working chambers, and wherein the small fraction is one that provides sufficient stability of valve operation at the low flow end.

20. The machine of claim 16, wherein, in the partial modes, valve actuations are delayed to almost an end of a stroke such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

21. The machine of claim 16, wherein the partial stroke modes are part stroke motoring modes in which the transition from intake from the high-pressure manifold to intake from the low pressure manifold happens a small fraction after top dead center, wherein the small fraction is one in which valve actuations are such that a rate of change of working chamber volume will be at an acceptably low level to permit valve actuation.

22. The machine of claim 16, wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion.

23. A machine comprising: a plurality of working chambers of cyclically changing volume; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber to each manifold; and a controller having a configuration to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) idling modes, (ii) partial stroke modes in which only part of the usable volume of the working chamber is used and (iii) full stroke modes in which all of the usable volume of the working chamber is used.

24. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber to each manifold, the method comprising: determining a mode of each of the working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the fluid-working machine according to a demand level; and operating the valves of each of the working chambers to select the determined mode in one of (i) an idling mode, (ii) a partial stroke mode in which only part of the usable volume of the working chamber is used, and (iii) a full stroke mode in which all of the usable volume of the working chamber is used, wherein the sequence of modes of operation is tailored for one or more of the smoothest flow result, the most seamless change in audible noise, minimal pressure ripple, and optimum actuator motion.

25. A method of operating a fluid-working machine having a plurality of working chambers of cyclically changing volume, a high-pressure fluid manifold and a low-pressure fluid manifold, at least one valve linking each working chamber of said working chambers to each manifold, the method comprising: determining a mode of each working chamber of said working chambers on successive cycles of changing working chamber volume so as to vary the time averaged effective flow rate of fluid through the machine according to a demand level; and operating the valves of each of said working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) partial stroke modes in which only part of the usable volume of the chamber is used and (ii) full stroke modes in which all of the usable volume of the working chamber is used.

26. A machine comprising: a plurality of working chambers of cyclically changing volume; a high-pressure fluid manifold; a low-pressure fluid manifold; at least one valve linking each working chamber to each manifold; and a controller having a configuration to: vary the time averaged effective flow rate of fluid through the machine according to a demand level, and operate the valves of each of the working chambers to select the determined mode in accordance with an operation sequence which, in the successive cycles of changing working chamber volume, intersperses modes including at least (i) partial stroke modes in which only part of the usable volume of the working chamber is used and (ii) full stroke modes in which all of the usable volume of the working chamber is used.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0027] FIG. 1 is a schematic sectional view of the known fluid-working machine described above which can be adapted according to the present invention;

[0028] FIG. 2 is a pulse and timing diagram for the adapted machine when operating as a pump; and

[0029] FIG. 3 is a pulse and timing diagram for the adapted machine when operating as a motor.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0030] The machine described in EP-A-0494236 and shown in FIG. 1 can be adapted to provide a machine according to the invention without additional hardware to create a part-stroke mode. The adaptation consists of increasing the functionality and complexity of the microprocessor control algorithms.

[0031] At any one instant there are four possible states for any of the chambers 11: (1) intake from the low-pressure manifold, (2) exhaust to the low-pressure manifold, (3) intake from the high-pressure manifold and (4) exhaust to the high-pressure manifold.

[0032] Let “mode” denote a repeating cyclic sequence of transitions from one of these states to another. There are five distinct modes: full stroke pumping, part stroke pumping, full stroke motoring, part stroke motoring, and idling.

[0033] The difference between full and part stroking modes is the phase angle at which transitions are made from one of these states to the other relative to bottom and top dead centre of piston movement:

[0034] FIGS. 2 and 3 are timing diagrams for pumping and motoring respectively, showing piston position, the states of electronic gates for controlling the high-pressure and low-pressure valves, the positions of those valves and the cylinder pressure, all plotted against time. The shaded portions indicate active portions of the piston stroke. For example, the top half in FIGS. 2 and 3 shows HPV Gate On 30A, HPV Gate Off 30B, HPV at Open Position 31A, HPV at Shut Position 31B, LPV Gate On 32A, LPV Gate Off 32B, LPV at Open Position 33A, LPV at Shut Position 33B, High Cylinder Pressure 34A, and Low Cylinder Pressure 34B. The bottom half in FIGS. 2 and 3 shows HPV Gate On 35A, HPV Gate Off 35B, HPV at Open Position 36A, HPV at Shut Position 36B, LPV Gate On 37A, LPV Gate Off 37B, LPV at Open Position 38A, LPV at Shut Position 38B, High Cylinder Pressure 39A, and Low Cylinder Pressure 39B.

[0035] In the case of full stroke pumping mode, shown at the bottom right of FIG. 2, the transition from state (1) to state (4) happens at or near to bottom dead centre causing the full cylinder volume to be pumped into the high-pressure manifold.

[0036] In the case of part stroke pumping mode, shown in the top half of FIG. 2, the transition from state (1) to state (4) happens a small fraction in advance of top dead centre, causing only a small fraction of the cylinder volume to be pumped into the high-pressure manifold.

[0037] In both pumping modes the transition from state (4) to state (1) happens at or near to top dead centre.

[0038] In the case of full stroke motoring mode, shown in the bottom half of FIG. 3, the transition from state (3) to state (2) happens at or near to bottom dead centre, causing the full cylinder volume to be inducted from the high-pressure manifold. The transition from state (2) to state (3) happens at or near to top dead centre.

[0039] In the case of part stroke motoring mode, shown in the top half of FIG. 3, the transition from state (3) to state (1) happens a small fraction after top dead centre, causing only a small fraction of the cylinder volume to be inducted from the high-pressure manifold. The transition from state (1) to state (2) happens at bottom dead centre. The transition from state (2) to state (3) happens at or near to top dead centre of piston movement.

[0040] In the case of idling mode, shown at the bottom left of FIG. 2, the transition from state (1) to state (2) happens at bottom dead centre of piston movement. The transition from state (2) to state (1) happens at top dead centre of piston movement.

[0041] A sequence of mode changes on successive machine cycles mixing pumping or motoring modes with idling modes allows the time averaged effective flow rate into and out of the high-pressure manifold to be infinitely varied between full pumping flow, zero flow, and full motoring flow.

[0042] Since the machine has a plurality of chambers, and each chamber may be set in any of five states, then many instantaneous configurations are possible. Some physical limitations exist however, in that a chamber which has been selected for full-stroke operation cannot, on the same part of the cycle, be selected for part-stroke use.

Control Over the Full Range of Output

[0043] The flow control method described in EP-A-0361927 and EP-A-0494236, which used a displacement demand during an accounting interval, combined with a look-ahead algorithm, can be extended for use with the five-mode machine of the invention. At zero flow the machine is in a permanent idling mode. At low flows the operation sequence is composed of partial stroke and idling modes with the fraction of these two modes reflecting the demand level. As flow demand increases, the fraction of partial stroke modes relative to idling modes increases. At some stage the controller begins to use occasional full stroke modes interspersed with idle and part-stroke modes to continue the ramping up of flow. Starting from the other end of the range at full flow output, the machine is in permanent full stroke mode. As flow demand drops, idling modes are interspersed with full stroke modes, leaving regular gaps in the flow rate. This process continues until the ratio of full stroke modes to idling modes falls below a fixed or variable threshold, at which point the controller begins mixing idle modes, part stroke modes and full stroke modes. The mixture of modes of operation, where three modes are being employed in a sequence, is tailored for the smoothest flow result and/or the most seamless change in audible noise and/or minimal pressure ripple and/or optimum actuator motion. Several algorithms are possible to mix states over this range.

[0044] In the case of pressure control, the decision on the mixture of modes in the sequence is based upon some function of the error between the measured and demanded pressure, and optionally the time history of past system responses to past pumping/motoring decisions allowing for adaptive techniques to minimise pressure fluctuation in response to varying system parameters.

[0045] In the case of position or velocity control of an hydraulic actuator, the decision on the mixture of modes in the sequence is based upon some function of the error between the measured and demanded position or velocity, and optionally the time history of past system responses to past pumping/motoring decisions allowing for adaptive techniques to minimise position or velocity error in response to varying system parameters.

[0046] As alternatives to electromagnetic valves, valves operating by piezoelectric or magnetostrictive means could be used in the invention.

[0047] All forms of the verb “to comprise” used in this specification have the meaning “to consist of or include”.