U.S. patent application number 14/942567 was filed with the patent office on 2017-10-19 for fluid-working machine and operating method.
The applicant listed for this patent is Artemis Intelligent Power Limited. Invention is credited to Jonathan Paul ALMOND, Niall James CALDWELL, William Hugh Salvin RAMP EN, Uwe Bernhard Pascal STEIN.
Application Number | 20170298928 14/942567 |
Document ID | / |
Family ID | 9943932 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170298928 |
Kind Code |
A9 |
STEIN; Uwe Bernhard Pascal ;
et al. |
October 19, 2017 |
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.
Inventors: |
STEIN; Uwe Bernhard Pascal;
(Loanhead, GB) ; CALDWELL; Niall James; (Loanhead,
GB) ; RAMP EN; William Hugh Salvin; (Loanhead,
GB) ; ALMOND; Jonathan Paul; (Loanhead, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Artemis Intelligent Power Limited |
Loanhead |
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GB |
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|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20160169222 A1 |
June 16, 2016 |
|
|
Family ID: |
9943932 |
Appl. No.: |
14/942567 |
Filed: |
November 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12929497 |
Jan 28, 2011 |
9188119 |
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14942567 |
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10526444 |
Mar 1, 2005 |
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PCT/GB2003/003949 |
Sep 11, 2003 |
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12929497 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04B 49/225 20130101;
F04B 7/0076 20130101; F01B 25/10 20130101; F04B 49/243 20130101;
F04B 2201/02 20130101; F04B 49/065 20130101; F04B 49/12 20130101;
F04B 53/1082 20130101; F04B 2201/0807 20130101 |
International
Class: |
F04B 49/22 20060101
F04B049/22; F04B 49/06 20060101 F04B049/06; F04B 49/12 20060101
F04B049/12; F01B 25/10 20060101 F01B025/10; F04B 7/00 20060101
F04B007/00; F04B 49/24 20060101 F04B049/24; F04B 53/10 20060101
F04B053/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2002 |
GB |
0221165.4 |
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
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. application Ser. No.
10/526,444, filed Mar. 1, 2005, which in turn is a national phase
application of PCT/GB2003/003949 filed Sep. 11, 2003 which is based
on priority application GB 0221165.4, filed Sep. 12, 2002, the
entire contents of each of which are hereby incorporated by
reference in this application.
BACKGROUND TO THE INVENTION
[0002] This invention relates to a fluid-driven (motor) and/or
fluid-driving (pump) machine having a plurality of working chambers
of cyclically changing volume and valve means to control the
connection of each chamber to low and high-pressure manifolds. The
invention also relates to a method of operating the machine.
[0003] The invention has particular reference to non-compressible
fluids, but its use with gases is not ruled out. It has particular
reference to machines where the at least one working chamber
comprises a cylinder in which a piston is arranged to reciprocate,
but its use with at least one chamber delimited by a flexible
diaphragm or a rotary piston is not ruled out.
[0004] With most fluid working machines the fluid chambers undergo
cyclical variations in volume following a sinusoidal function. It
is known to provide flow rectifying seating valves, allowing fluid
to be admitted and exhausted from the working chamber, which valves
are electro-magnetically actuated such that pumping and motoring
strokes can be achieved. The chamber can be left to idle by holding
the valve, between the working chamber and the low-pressure sump,
in the open condition.
[0005] A shaft position sensor is used to provide the
micro-controller with chamber phase information while flow or
pressure demand inputs influence the rate at which chambers are
pumped, motored or left idle. The micro-controller drives
semiconductor switches, such as field effect transistors, which in
turn actuate the valves connecting the chambers to either the
high-pressure manifold or low-pressure sump.
[0006] Experience shows that varying the timing of the valves, such
that portions of the stroke are disabled, in order to vary machine
output creates a significant amount of audible and fluid borne
noise.
[0007] The development of electro-magnetically actuated; seating
valves working in conjunction with a varying fluid chamber volume,
such as described in EP-A-361927 and EP-A-0494236, permitted the
output of a fluid working machine having a plurality of working
chambers to be varied, in a time averaged way, by the rate of
selection of whole chambers as they became available at the ends of
each expansion or contraction cycle.
[0008] EP-A-0361927 described the use of this technique for a pump
in which shaft power was controllably converted to fluid power.
EP-A-0494236 continued the concept and, by introducing a new
mechanism for actuating the valves in a motoring cycle, developed
the machine to allow a controllable bi-directional energy flow.
[0009] A multi-piston hydraulic machine according to EP-A-0494236
is shown in schematic section in FIG. 1. In the side wall of each
cylinder 11 is a poppet valve 13 communicating with a high-pressure
manifold 14 and in the end wall of each cylinder is a poppet valve
15 communicating with a low-pressure manifold 16. The poppet valves
13 and 15 are active electromagnetic valves controlled electrically
by a microprocessor controller 20 feeding control signals, via
optoisolators 21, to valve-driving semiconductors 22.
[0010] Pistons 12 act on a drive cam 23 fast to an output shaft 24,
the position of the cam 23 being sensed by an encoder 25.
[0011] The controller 20 receives inputs from the encoder 25, a
pressure transducer 26 (via an analogue to digital converter 27)
and via a line 28 to which a desired output speed demand signal can
be applied.
[0012] The poppet valves 13, 15 seal the respective cylinders 11
from the respective manifolds 14, 16 by engagement of an annular
valve part with an annular valve seat, a 30 solenoid being provided
to magnetically move each said valve part relative to its seat by
reacting with ferromagnetic material on the said poppet valve, each
said poppet valve having a stem and an enlarged head, the annular
valve part being provided on the head and the ferromagnetic
material being provided on the stem.
[0013] In EP-A-361927 and EP-A-0494236, whole chambers were
selected on the basis that valve actuation could be done during the
instances of near zero flow. It was considered that delayed closure
of valves, occurring during times of significant flow, such that
part of the chamber displacement could be rejected, would result in
extremely high rates of change of flow and pressure, which in turn
would generate noise.
[0014] The approach of whole chamber selection works well for high
flow rates, seeing as the mechanical payload, driven by this type
of system, typically has a large momentum such that variations in
flow energy cause relatively small changes in its velocity and,
therefore, acceleration.
[0015] However, in practice it was found that whole chamber
selection during times of low flow demand resulted in large flow
variations, seeing as the fluid machine was idle for long instances
between active chambers. When a payload has a small velocity, as it
will when the actuating flow is low, the momentum will also be
minimal. If each actuated chamber is considered to be delivering a
quantum of energy to the payload, then the change in velocity will
be significantly higher when the initial energy is low.
SUMMARY OF THE INVENTION
[0016] The invention seeks to address this problem such that a
smooth actuating response can be achieved at the payload.
[0017] The present invention provides 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, 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 vary the time
averaged effective flow rate of fluid through the machine.
[0018] In a most preferred embodiment of the invention, the partial
mode comprises the use of only a small fraction of the usable
volume of the chamber.
[0019] Preferably, the machine is operable as both a pump and a
motor, each chamber having five selectable modes, namely idling
mode, partial motoring mode, full motoring mode, partial pumping
mode and full pumping mode.
[0020] Preferably, the working chambers comprise cylinders in which
pistons are arranged to reciprocate. If so, the partial pumping
mode preferably includes closing the valve linking the cylinder to
the low-pressure manifold and opening the valve linking the
cylinder to the high-pressure manifold a small fraction in advance
of the top dead centre position of the piston. The partial motoring
mode preferably includes closing the valve linking the cylinder to
the high-pressure manifold and opening the valve linking the
cylinder to the low-pressure manifold a small fraction after the
top dead centre position of the piston.
[0021] If valve actuations are delayed in this way to almost the
end of the stroke, then the rate of change of chamber volume will
be at an acceptably low level to permit valve actuation. This means
that a small fraction of a whole cylinder can also be selected by
the controller to add to the machine's output. The range over which
this is practicable is limited by stability of valve operation, on
the low flow end, and by machine noise on the higher end. In
practice this range is sufficiently limited that it is considered
to have added two distinct, low-flow, modes to the three-mode
machine, providing the above-mentioned range of five modes to the
controller at any time that a chamber comes to the position at
which an action can be taken.
[0022] The invention also provides 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-press fluid manifold, at least one valve linking each working
chamber to each manifold, comprising operating 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, wherein the
mode of each chamber is selected on successive cycles so as to vary
the time averaged effective flow rate of fluid through the
machine.
[0023] Preferably, the method comprises selecting the number of
chambers to be operated in each of said modes according to an
algorithm depending on the actual and required output of the
machine.
[0024] In a most preferred embodiment of the invention, the partial
mode comprises the use of only a small fraction of the usable
volume of the chamber.
[0025] The method may comprise a preliminary step of selecting
whether to operate the machine as a pump or a motor, and choosing
the algorithm accordingly.
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".
* * * * *