HYDRAULIC APPARATUS AND OPERATING METHOD

Abstract

A hydraulic apparatus has a plurality of pump modules each of which is formed by a plurality of working chambers having a common high pressure manifold. A connecting circuit switchably connects pump modules to first and second hydraulic circuit portions to allocate capacity as first and second demands for hydraulic fluid vary. In an apparatus which may have two or more connecting circuit outputs, valves may be controlled or working chamber pumping cycles made inactive to facilitate the reallocation of a pump module from one output to another, and a control strategy addresses pump module allocation when the demands for hydraulic fluid exceed available capacity.

Claims

1. An apparatus comprising: first and second hydraulic circuit portions, the first hydraulic circuit portion having a first hydraulic circuit portion input, and a plurality of valves configured to regulate the flow of hydraulic fluid from the first hydraulic circuit portion input to each of a first group of at least two hydraulic actuators, the second hydraulic circuit portion having a second hydraulic circuit portion input, and a plurality of valves configured to regulate the flow of hydraulic fluid from the second hydraulic circuit portion input to each of a second group of at least two hydraulic actuators, a prime mover, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising at least three working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold, wherein the working chambers are formed into a plurality of pump modules each pump module comprising a group of one or more of the working chambers and a high-pressure manifold which is common to each working chamber in the group, a hydraulic connecting circuit comprising a plurality of connecting circuit inputs, each of which is in fluid communication with the high-pressure manifold of a respective pump module, a first connecting circuit output in fluid communication with the first hydraulic circuit portion and a second connecting circuit output in fluid communication with the second hydraulic circuit portion input, the hydraulic connecting circuit configured to connect each said connecting circuit input to a said connecting circuit output and comprising a plurality of valves which are switchable to change the connecting circuit output to which a said connecting circuit input is connected, so that each pump module is connected to one hydraulic circuit portion at a time and that for some or all of the pump modules, the hydraulic circuit portion to which the respective pump module is connected may be changed, a controller configured to actively control at least the low pressure valves of the said working chambers to determine the net displacement of each working chamber during each cycle of working chamber volume, and also the said valves, such that the net displacement of the working chambers of each pump module which are connected to the first hydraulic circuit portion is controlled in response to a first demand for hydraulic fluid of the first hydraulic circuit portion, and the net displacement of the working chambers of each pump module which are connected to the second hydraulic circuit portion is controlled in response to an independent second demand for hydraulic fluid of the second hydraulic portion.

2. An apparatus according to claim 1, wherein the first hydraulic circuit portion comprises a first valve block portion and the second hydraulic circuit portion comprises a second valve block portion, the two valve block portions being part of a metal block within which valves are located, and each of the first and second valve block portions each comprises a port which functions as the first or second hydraulic circuit portion input respectively.

3. An apparatus according to claim 1, wherein the said valves are diverting valves which are electronically controllable to connect the high-pressure port of a pump module exclusively to either the first connecting circuit output or to the second connecting circuit output.

4. An apparatus according to claim 1, wherein the controller controls at least the low pressure valves of the working chambers to determine whether each working chamber undergoes either an active cycle, with a net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, or an inactive cycle, with no net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, for each cycle of working chamber volume.

5. An apparatus according to claim 1, wherein the apparatus comprises one or more further hydraulic circuit portions, each further hydraulic circuit portion having a respective hydraulic circuit portion input, and one or more further hydraulic actuators, wherein the hydraulic connecting circuit further comprises, for each further hydraulic circuit portion, a further connecting circuit portion in fluid communication with the respective hydraulic circuit portion input, wherein the plurality of valves of the hydraulic connecting circuit are switchable to connect the high pressure manifold of each respective pump module to one or another of the connecting circuit outputs at a time.

6. An apparatus according to claim 1, wherein the circuit portions each include at least one proportional valve which is controllable to divert a proportion of working fluid received by the hydraulic circuit portion to one or more actuators.

7. An apparatus according to claim 6, wherein at least one of the first and second hydraulic circuit portions further comprises a hydraulic conduit which provides a pathway for hydraulic fluid to flow from the hydraulic circuit portion input to at least one actuator of the hydraulic circuit portion not through proportional valves of the hydraulic circuit portion, and a controllable bypass valve which selectively allows flow of fluid through the hydraulic conduit such that the said at least one actuator is selectively provided with hydraulic fluid from the hydraulic circuit portion input via at least one of one or more proportional valves and the hydraulic conduit both.

8. An apparatus according to claim 1, wherein the apparatus is configured such that when a pump module is switched from being connected to one hydraulic circuit portion to another hydraulic circuit portion, the working chambers of the respective pump module are caused to carry out only inactive cycles while the valves are switched or the working chambers are not caused to start any active cycles.

9. An apparatus according to claim 1, wherein the high pressure manifold of some or all pump modules are connected to the first hydraulic circuit portion through a first valve and to the second hydraulic circuit portion through a second valve, wherein the controller staggers switching of the first and second valves, to avoid both being closed at the same time, typically wherein one of the first and second valves is a normally open valve and the other is a normally closed valve.

10. An apparatus according to claim 1, wherein the hydraulic connecting circuit comprises a conduit extending between the first and second connecting circuit outputs and having a plurality of fluid junctions along the length of the conduit, each junction connecting to a different connecting circuit input, and a plurality of blocking valves controllable to selectively block the conduit and thereby determine which connecting circuit inputs are connected to which connecting circuit outputs, wherein the conduit extends from the first connecting circuit output to the second output and back to the first connecting circuit output in a closed loop, with said junctions and blocking valves distributed around the loop.

11. An apparatus according to claim 1, wherein the hydraulic connecting circuit comprises a first manifold portion extending to the first connecting circuit output, a second manifold portion extending to the second connecting circuit output and a third manifold portion extending to a third connecting circuit output, connected to the input of a third hydraulic circuit portion comprising a third group of one or more actuators, and a switching manifold portion, wherein at least the first manifold portion, the second manifold portion, and the switching manifold portion are each selectively connectable to one or more said connecting circuit inputs through one or more valves, and wherein the hydraulic connecting circuit further comprises a manifold diverting valve which is controllable to connect the switching manifold portion to the first manifold portion or the third manifold portion.

12. An apparatus comprising: a plurality of hydraulic actuators, a prime mover, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising at least three working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold, wherein the working chambers are formed into a plurality of pump modules each of which has a respective high-pressure manifold which is common to the pump module, a hydraulic connecting circuit comprising a plurality of inputs, each of which is in fluid communication with the high-pressure manifold of a respective pump module, a plurality of connecting circuit outputs, each of which is in fluid communication with a different one or more of the hydraulic actuators, the hydraulic connecting circuit configured to connect each said connecting circuit input to a said connecting circuit output and comprising a plurality of valves which are switchable to change the connecting circuit output to which a said connecting circuit input is connected, so that each pump module is connected to one connecting circuit output at a time and thereby to the one or more of the hydraulic actuators which are in fluid communication with the respective connecting circuit output, a controller configured to actively control at least the low pressure valves of the said working chambers to determine the net displacement of each working chamber on each cycle of working chamber volume, such that the net displacement of the working chambers of each pump module which are connected to a respective connecting circuit output is controlled to meet a respective demand for hydraulic fluid by the one or more actuators in fluid communication with the respective connecting circuit output.

13. An apparatus according to claim 12, wherein the high pressure manifold of some or all pump modules are connected to a first connecting circuit output through a first valve and to a second connecting circuit output through a second valve, and wherein the controller staggers switching of the first and second valves, to avoid both being closed at the same time.

14. An apparatus according to claim 12, wherein the apparatus is configured such that when a pump module is switched from being connected to one connecting circuit output, the working chambers of the respective pump module are caused to carry out inactive cycles while the valves are switched.

15. A method of operating an apparatus, the apparatus comprising: first and second hydraulic circuit portions, the first hydraulic circuit portion having a first hydraulic circuit portion input, and a plurality of valves configured to regulate the flow of hydraulic fluid from the first hydraulic circuit portion input to each of a first group of at least two hydraulic actuators, the second hydraulic circuit portion having a second hydraulic circuit portion input, and a plurality of valves configured to regulate the flow of hydraulic fluid from the second hydraulic circuit portion input to each of a second group of at least two hydraulic actuators, a prime mover, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising at least three working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold, wherein the working chambers are formed into a plurality of pump modules each pump module comprising a group of one or more of the working chambers and a high-pressure manifold which is common to each working chamber in the group, a hydraulic connecting circuit comprising a plurality of connecting circuit inputs, each of which is in fluid communication with the high-pressure manifold of a respective pump module, a first connecting circuit output in fluid communication with the first hydraulic circuit portion and a second connecting circuit output in fluid communication with the second hydraulic circuit portion input, the hydraulic connecting circuit configured to connect each said connecting circuit input to a said connecting circuit output and comprising a plurality of valves which are switchable to change the connecting circuit output to which a said connecting circuit input is connected, so that each pump module is connected to one hydraulic circuit portion at a time and that for some or all of the pump modules, the hydraulic circuit portion to which the respective pump module is connected may be changed, the method comprising: actively controlling at least the low pressure valves of the said working chambers to determine whether each working chamber undergoes either an active cycle, with a net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, or an inactive cycle, with no net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, and also the said valves, such that the net displacement of the working chambers of each pump module which are connected to the first hydraulic circuit portion is controlled in respond to a first demand for hydraulic fluid of the first hydraulic circuit portion and the net displacement of the working chambers of each pump module which are connected to the second hydraulic circuit portion is controlled in response to an independent second demand for hydraulic fluid of the second hydraulic circuit portion.

16. A method of operating an apparatus, the apparatus comprising: a plurality of hydraulic actuators, a prime mover, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising at least three working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold, wherein the working chambers are formed into a plurality of pump modules each of which has a respective high-pressure manifold which is common to that pump module, a hydraulic connecting circuit comprising a plurality of inputs, each of which is in fluid communication with the high-pressure manifold of a respective pump module, a plurality of connecting circuit outputs, each of which is in fluid communication with a different one or more of the hydraulic actuators, the hydraulic connecting circuit configured to connect each said connecting circuit input to a connecting circuit output and comprising a plurality of valves which are switchable to change the connecting circuit output to which a said connecting circuit input is connected, so that each pump module is connected to one connecting circuit output at a time and thereby to the one or more of the hydraulic actuators which are in fluid communication with the respective connecting circuit output, the method comprising actively controlling at least the low pressure valves of the said working chambers to determine the net displacement of each working chamber on each cycle of working chamber volume, such that the net displacement of the working chambers of each pump module which are connected to a respective actuator is controlled to meet a respective demand for hydraulic fluid by the one or more actuators in fluid communication with the respective connecting circuit output, and changing the connecting circuit output and thereby the one or more hydraulic actuators to which a pump module is connected by switching one or more valves of the hydraulic connecting circuit.

17. A method according to claim 16, wherein the demand signals are regulated to avoid a sudden increase, exceeding a threshold, in the displacement of working fluid to a hydraulic circuit portion or a connecting circuit portion responsive to changing the hydraulic circuit portion or connecting circuit output to which a pump module is connected.

18. A method according to claim 16, wherein at least when a plurality of demands for hydraulic fluid, relating to respective hydraulic circuit portions or the one or more actuators in fluid communication with respective connecting circuit outputs, are such that the plurality of demands cannot be met concurrently, irrespective of which pump modules are connected to which hydraulic circuit portions or connecting circuit outputs, some or all of the plurality of demands are reduced proportionately by multiplication by a scaling factor so that they are in total at most the maximum rate of displacement which is possible concurrently by all but one of the pump modules which can be connected to an individual hydraulic circuit or connecting circuit output.

19. A method according to claim 18, wherein the scaling factor is, or is at most, the ratio of (a) the maximum rate of displacement which is possible concurrently by all but one of the pump modules which can be connected to an individual hydraulic circuit or connecting circuit output, to (b) the sum of the plurality of demands.

20. A method according to claim 16, wherein there are n demands for hydraulic fluid for respective hydraulic circuit portions, or for or more actuators connected to respective connecting circuit outputs, and when the n demands are such that irrespective of which pump modules are connected to which connecting circuit outputs, the n demands cannot all be met concurrently, then if one of then demands are for more than (100/n) % of the maximum displacement of the pump modules which can be connected to the respective hydraulic circuit portion or connecting circuit output, then the respective hydraulic circuit portion or connecting circuit output has pump modules capable of delivering at least (100/n) % of the maximum displacement connected thereto, wherein n=2.

21. A method according to claim 20, wherein if one of the demands is for below (100/n) % of the maximum displacement of the pump modules but above a threshold, each hydraulic circuit portion or connecting circuit portion has pump modules capable of delivering at least (100/n) % of the maximum displacement connected thereto, wherein if one of the demands is below the threshold, the demands are scaled down such that they sum to at most the maximum rate of displacement which is possible by all but one pump module which can be connected to any of the hydraulic circuit portions or connecting circuit outputs.

Description

DESCRIPTION OF THE DRAWINGS

[0107] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0108] FIG. 1 is a schematic diagram of a hydraulic apparatus according to the invention;

[0109] FIG. 2 corresponds to FIG. 1 with some additional detail;

[0110] FIG. 3 is a partially exploded view of a pump module and endplate;

[0111] FIG. 4 is a schematic diagram of a pump module;

[0112] FIG. 5 is a schematic diagram of a controller;

[0113] FIGS. 6A, 6B and 6C are graphs of flow demand (x axis) versus pressure (y axis) for two hydraulic circuit portions for a prior art machine without pumped flow merging, at low load (6A); a prior art machine with conventional pumped flow merging at high load (6B); and a machine according to the invention (without merging) at high load (6C);

[0114] FIG. 7 is a schematic diagram of a hydraulic apparatus with three hydraulic circuit portions;

[0115] FIG. 8 is a schematic diagram of an integer portion of the apportioning block showing the diverting valve arrangement;

[0116] FIG. 9 is a flow chart of an operating procedure for reallocating pump modules to hydraulic circuit portions;

[0117] FIG. 10 illustrates the changes with time in flow demand signal and maximum flow capacity for each of two hydraulic circuit portions, and diverting valve control signals and positions during a process of reallocating a pump module from hydraulic circuit portion 2 to hydraulic circuit portion 1;

[0118] FIG. 11 is a schematic diagram of an alternative diverting valve arrangement;

[0119] FIG. 12 is a schematic diagram of an alternative diverting valve arrangement;

[0120] FIG. 13 is a schematic diagram of an alternative diverting valve arrangement;

[0121] FIG. 14 is a schematic diagram of an alternative connecting circuit arrangement;

[0122] FIGS. 15A and 15B are schematic diagrams of further alternative connecting circuit arrangements;

[0123] FIG. 16 is a schematic diagram of a further alternative connecting circuit arrangement;

[0124] FIG. 17 is a schematic diagram of a pressure relief valve arrangement;

[0125] FIG. 18A is a plot, on the y-axis of maximum flow through a connecting circuit output (dashed line), and actual flow (solid line) for a given demanded flow (dotted line), over time (x-axis) when demand flow is ramped up linearly, without restricting the demand signals for individual outputs; the numbers represent the number of pump modules which are connected to a hydraulic circuit portion/connecting circuit output;

[0126] FIG. 18B corresponds to FIG. 18A while restricting the demand signals for individual outputs;

[0127] FIG. 19 is a schematic diagram of flow being met by first and second hydraulic circuit portions/connecting circuit outputs in a first approach;

[0128] FIGS. 20A, 20B and 20C are schematic diagrams of demanded flow for first and second outputs in a second approach, with the x axis representing demand in units of the capacity of an individual pump modules, with both first and second demands exceeding 50% of maximum displacement (FIG. 20A), with the second demand reduced to just under 50% of maximum displacement (FIG. 20B) and with the second demand further reduced (FIG. 20C), without demand restriction, and FIGS. 20D, 20E and 20F correspond to FIGS. 20A, 20B and 20C but with the demands being restricted.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

[0129] With reference to FIG. 1, an excavator 1 (being an example of a hydraulic apparatus) comprises an engine 2, which drives a plurality of pump modules 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, (being a plurality of pump modules) each of which comprises a number of working chambers in the form of piston cylinder units, PCUs, which are driven by the prime mover through a common rotating shaft 6. The working chambers within a given pump module are connected so as to provide a common output of hydraulic fluid through a respective high pressure manifold 8A, 8B, 8C, 8D, 8E, 8F, 8G, 8H to an apportioning block 10 which has inputs (the connecting circuit inputs) to receive fluid from each high pressure manifold, and outputs 12, 14 (connecting circuit outputs) which connect with or function as inlets 16, 18 (hydraulic circuit portion inlets) to first and second hydraulic circuit portions 20, 22. Pressure sensors 17, 19, measure the pressure at the inlets to the first and second hydraulic circuit portions. The first hydraulic circuit portion has a first valve block 24 and a first plurality of actuators (6, 28, 30), in this example a boom 26, a bucket 28 and a right track 30. A boom bypass valve 32 is configured to provide a selectable alternative path for hydraulic fluid from the inlet to the first hydraulic circuit portion to flow directly to the boom rather than through the first valve block. The second hydraulic circuit portion has a second valve block 26 and a second plurality of actuators (34, 36, 38), in this example a dipper 34, a slew function 36, and a left track 38. A dipper bypass valve 40 is configured to provide a selectable path for hydraulic fluid from the inlet to the second hydraulic circuit portion to flow directly to the dipper rather than through the second valve block. The first and second hydraulic circuit portions output fluid back to tank 42. A controller 50 controls valves which regulate the flow of fluid within each working chamber and valves within the apportioning block as will be described.

[0130] Features in FIG. 2 correspond to the features of FIG. 1, and FIG. 2 shows that within the apportioning block, for each pump module, there are first and second diverting valves 52, 54, which are controllable to connect the high pressure manifold (output, when pumping) of the pump module to either first or second apportioning manifold 56, 58 which extend through the apportioning block to respective outputs 12, 14 and inputs 16, 18 of the first and second valve blocks (the connecting circuit outputs). Furthermore pressure relief valves 55 connect each high pressure manifold to tank. The controller receives demand signal from sensor through inputs 49, receives pressure (and other feedback signals) through inputs 47, and transmits signals to the working chamber valves through signal lines 89, 93 and to the switchable valves of the apportioning block through control lines 51. Features which are custom to the present invention are shown within the dashed box 53 and the remaining features are known from existing hydraulic apparatuses such as excavators.

[0131] More detail is shown in FIG. 8 for a single integer portion of the apportioning block. In this example, the first and second diverting valve for each pump module are poppet valves which are controlled in tandem such that one is open and the other is closed, with both being switched between open and closed or vice versa at the same time (or with a short delay, to ensure that one is open at all times, to reduce the risk of hydraulic deadhead). Thus, they function as diverting valves. In some embodiments the first and second valves are formed with a single valve member which moves together under the control of a single valve control signal. In other embodiments, they are separate but controlled in tandem. For each pair of first and second valves, one is typically a normally open valve and the other typically a normally closed valve, which also reduces the risk of hydraulic deadheading, especially if the control signal is lost. This is shown in FIG. 8 where valve 52 is normally open and valve 54 is normally closed. However, they may be both normally open or normally closed.

[0132] Check valves 55, 57 are provided which open away from the switchable valve to block flow from the hydraulic circuit portion to which it is connected back into the high pressure manifold. This maintains isolation of the high pressure manifolds from each other and avoids fluid from a higher pressure manifold draining to a lower pressure manifold. In embodiments in which one or more pump modules may also function as a motor to receive hydraulic fluid back from the actuators of a hydraulic circuit portion, the check valves could be omitted (at least for the pump modules which may functions as motor). In this case arrangements using the configurations of FIG. 11 or 13 would be useful. It would also be possible to substitute the check valves with a pair of solenoid operated single blocking valves, or pilot operated check valves or to include a selectively openable bypass around the check valves.

[0133] A pressure relief valve 59 provides an outlet to a drain line 61 which connects to tank, for use in the event of excess pressure (e.g. during a deadhead event).

[0134] The controller is also connected to the pump modules and transmits control signals to regulate the displacement of the pump modules. As we will describe this can be achieved by sending active control signals to electronically controlled valves which regulate the flow of fluid into and out of the working chambers of the pump modules.

[0135] Accordingly, the controller can switch which pump modules are connected to which inputs of the hydraulic circuit portions and can regulate the net displacement of each individual pump module as we will describe further below.

[0136] The pump modules typically each contain a plurality of working chambers, for example n working chambers which are phased apart by 360°/n, where n is an integer such as 2, 3 or 4. The distributed phasing provides a relatively smooth output of fluid into the respective high pressure manifold. The allocation of working chambers to pump modules is typically fixed but is defined by the connection of the outputs of each working chamber in the pump module to the same high pressure manifold through conduits. Typically each working chamber in the same pump module is fixedly connected to the same shared high pressure manifold. The working chambers which form an individual pump module need not be discrete from the working chambers which form other pump modules, for example, working chambers from different pump modules may be interleaved along the shaft, which may be advantageous, for example to distribute torque along the shaft.

[0137] The number of working chambers in each pump module need not be the same. One approach to connecting working chambers to form pump modules is shown in FIG. 3 which shows connections being formed in a pump endplate 66 suitable for fitting to a pump housing 68 having a plurality of working chambers. FIG. 3 is a partially exploded view and the dashed lines show the centre lines of manifolds. The manifolds of the pump endplate and the pump housing mate. Conduits having manifolds 70A, 70B, 70C, 70D extend through the pump housing and connect internally to the high pressure outlets of each of a plurality of working chambers. Each working chamber is connected to one conduit. In an example a first pump module is formed in a group 72 of three adjacent bores 74 of the pump housing and these working chambers are connected to conduit 70A. The conduits extend from a group of bores, through the housing, along its axis, and intersect with the face of the machine housing where a port of the conduit mates directly with a matching port on the endplate. Within the endplate, the individual conduit manifolds 70A, 70B, 70C, 70D are connected internally to first, second and third pump module fluid manifolds 76A, 76B, 76C. Each conduit port is connected to one pump module fluid port, but a pump module fluid port may be connected to one or more conduit port. The pump module fluid manifolds are connected to separate input manifolds of the apportioning block and so function as the high pressure manifolds 8A, 8B, 8C of individual pump modules. Thus, pump modules are defined from respective pump modules. In this example, each conduit connects to the output of three working chambers and so each pump module has a multiple of three working chambers.

[0138] FIG. 4 is a schematic diagram of a portion of an electronically commutated hydraulic machine (ECM) implementing a pump module 4A. The ECM comprising a plurality of working chambers having cylinders 80 which have working volumes 81 defined by the interior surfaces of the cylinders and pistons 82 which are driven from a rotatable shaft 83 by an eccentric cam 84 and which reciprocate within the cylinders to cyclically vary the working volume of the cylinders. The rotatable shaft is firmly connected to and rotates with a drive shaft. A shaft position and/or speed sensor 85 determines the instantaneous angular position and/or speed of rotation of the shaft, and transmits this to the controller 50 through signal line 86, which enables the machine controller to determine the instantaneous phase of the cycles of each cylinder.

[0139] The working chambers are each associated with Low Pressure Valves (LPVs) in the form of electronically actuated face-sealing poppet valves 87, which have an associated working chamber and are operable to selectively seal off a channel extending from the working chamber to a low-pressure hydraulic fluid manifold 88, which may connect one or several working chambers, or indeed all of the working chambers in the pump module as is shown here, to the low-pressure hydraulic fluid manifold of the apparatus and to tank 42. The LPVs are normally open solenoid actuated valves which open passively when the pressure within the working chamber is less than or equal to the pressure within the low-pressure hydraulic fluid manifold, i.e. during an intake stroke, to bring the working chamber into fluid communication with the low-pressure hydraulic fluid manifold but are selectively closable under the active control of the controller via LPV control lines 89 to bring the working chamber out of fluid communication with the low-pressure hydraulic fluid manifold. The valves may alternatively be normally closed valves.

[0140] The working chambers are each further associated with a respective High-Pressure Valve (HPV) 90 each in the form of a pressure actuated delivery valve. The HPVs open outwards from their respective working chambers and are each operable to seal off a respective channel extending from the working chamber to a high-pressure hydraulic fluid manifold 91, which may connect one or several working chambers, or indeed all as is shown in FIG. 2, to the high-pressure hydraulic fluid manifold 8A of the pump module. The HPVs function as normally-closed pressure-opening check valves which open passively due to the pressure difference across the valve, and taking into account the force of a biasing member within the HPV). The HPVs also function as normally-closed solenoid actuated check valves which the controller may selectively hold open via HPV control lines 93 once that HPV is opened by pressure within the associated working chamber. Typically, the HPV is not openable by the controller against pressure in the high-pressure hydraulic fluid manifold. The HPV may additionally be openable under the control of the controller when there is pressure in the high-pressure hydraulic fluid manifold but not in the working chamber, or may be partially openable.

[0141] In a pumping mode, the controller selects the net rate of displacement of hydraulic fluid from the working chamber to the high-pressure hydraulic fluid manifold by the hydraulic pump by actively closing one or more of the LPVs typically near the point of maximum volume in the associated working chamber's cycle, closing the path to the low-pressure hydraulic fluid manifold and thereby directing hydraulic fluid out through the associated HPV on the subsequent contraction stroke (but does not actively hold open the HPV). The controller selects the number and sequence of LPV closures and HPV openings to produce a flow or create a shaft torque or power to satisfy a selected net rate of displacement. The above ‘selection’ by the controller is refreshed periodically, or continuously. The selection is refreshed, or updated, when pump modules are allocated to or deallocated from a particular part of the hydraulic circuit portion.

[0142] Some embodiments may include pump modules which are also capable of motoring, thereby regenerating energy from hydraulic fluid received back from the hydraulic circuit portions, and converting it into mechanical energy, for example when an actuator is lowered or when a wheel motor is operated as a pump in order to apply braking torque. In these cases, the working chambers of the pump modules are also adapted to motor in which case the controller actively controls the HPV as well as the LPV and can carry out a motoring mode of operation in which the controller selects the net rate of displacement of hydraulic fluid, displaced by the hydraulic machine, via the high-pressure hydraulic fluid manifold, actively closing one or more of the LPVs shortly before the point of minimum volume in the associated working chamber's cycle, closing the path to the low-pressure hydraulic fluid manifold which causes the hydraulic fluid in the working chamber to be compressed by the remainder of the contraction stroke. The associated HPV opens when the pressure across it equalises and a small amount of hydraulic fluid is directed out through the associated HPV, which is held open by the hydraulic machine controller. The controller then actively holds open the associated HPV, typically until near the maximum volume in the associated working chamber's cycle, admitting hydraulic fluid from the high-pressure hydraulic fluid manifold to the working chamber and applying a torque to the rotatable shaft.

[0143] As well as determining whether or not to close or hold open the LPVs on a cycle by cycle basis, the controller is operable to vary the precise phasing of the closure of the HPVs with respect to the varying working chamber volume and thereby to select the net rate of displacement of hydraulic fluid from the high-pressure to the low-pressure hydraulic fluid manifold or vice versa.

[0144] Arrows on the manifolds 86, 92 indicate hydraulic fluid flow in the motoring mode; in the pumping mode the flow is reversed. A pressure relief valve 94 may protect the hydraulic machine from damage.

[0145] In practice there are a number of pump modules such as that shown in FIG. 4, connected by a common shaft and a single controller that can transmit the control signals to the valves associated with each working chamber of each of the pump modules. The working chambers within a pump module need not be evenly spaced around the shaft and are typically interleaved with each other to distribute load along the shaft.

[0146] Although the working chambers which make up each pump module are fixed, the pump modules which provide flow to a hydraulic circuit portion can be changed dynamically using the diverting valves. For example, at one time there may be 4 pump modules connected to the first hydraulic circuit portion and 4 pump modules connected to the second hydraulic circuit portion. At another time there may be 6 pump modules connected to the first hydraulic circuit portion and 2 pump modules connected to the second hydraulic circuit portion.

[0147] FIG. 5 is a schematic diagram of the controller 50. The controller includes a processor circuit 100 in electronic communication with memory 102 which stores a database 104 of pump modules and which working chambers are fixedly associated with which pump modules, and a database 106 of which pump modules are currently connected to which hydraulic circuit portion. The controller receives demand signals 108 which are indicative of a demand for working fluid by each of the first and second hydraulic circuit portions and the shaft position and/or speed signal through signal line 86. The demand signal 108 could be a simple pressure signal, however as an alternate embodiment the demand signal might be in the form of an electronic joystick position signal, whilst an additional pressure signal is provided as an input to the controller. Output from the controller includes working chamber valve control lines 89, 93 (for controlling LPVs and, if required, HPVs) and valve switching control lines 110 which actuate the diverting valves 52, 54 within the apportioning blocks.

[0148] The demand signals may be relatively simple, for example a measurement of pressure at the hydraulic input to the respective hydraulic circuit, or more complex, for example signals representing both pressure and flow requirements of the respective hydraulic circuits. The controller may receive signals indicative of demand by individual actuators or from an operator of the apparatus through manual controls. This latter approach enables compatibility with pre-existing hydraulic apparatus.

[0149] During operation, the controller maintains the database of which pump modules are connected to which hydraulic circuit portion, starting from a default configuration. The controller also maintains accumulators (which are internal variables stored in the controller) 112 of the difference between demanded volume of hydraulic fluid and delivered volume of hydraulic fluid to each hydraulic circuit portion by pump modules connected to the respective hydraulic portion. As the rotatable shaft turns, decision points are reached at different times (shaft positions) for the various working chambers. At the decision point for a given working chamber, the controller determines which hydraulic circuit module the working chamber is connected to (which requires querying the database 104 of pump modules and which working chambers are fixedly associated with which pump modules, and the database 106 of which pump modules are currently connected to which hydraulic circuit portion) and the controller then updates the accumulator of the hydraulic circuit portion to which the working chamber is connected depending on the received demand for that circuit portion. The controller then compares the accumulator value with a threshold and if the accumulated demand exceeds the threshold, it schedules then transmits valve controls signals to cause the working chamber to carry out an active cycle in which the working chamber makes a net displacement of working fluid and subtracts the net displacement of working fluid from the value stored by the accumulator. Otherwise, it causes the working chamber to carry out an inactive cycle in which the working chamber makes no net displacement of working fluid (for example, the controller may transmit a signal to the LPV of the working chamber to hold the LPV open throughout a cycle of working chamber volume) and the accumulator is not modified. In this way, the controller makes decisions for each working chamber as to whether or not to carry out active cycles depending on the demand from the hydraulic circuit portion to which the working chamber is connected. The accumulators and demand signals may use any convenient units. In one known example, the demand is expressed as “displacement fraction” which is a fraction of the maximum possible displacement per revolution of the rotating shaft, referred to as F.sub.d. Target flow rate, in volumetric terms, is a product of F.sub.d and the speed of rotation of the rotatable shaft.

[0150] From time to time, the controller will determine that there is a requirement to reallocate a pump module from one hydraulic circuit module to another hydraulic circuit module in order to meet changing demand for hydraulic fluid. In this case, the controller transmits a control signal to the relevant valves in the apportioning module to switch the high pressure manifold of the pump module from one hydraulic circuit module to another hydraulic circuit module (the other hydraulic circuit module in embodiments with two hydraulic circuit modules) and it updates the database 106 of which pump modules are currently connected to which hydraulic circuit modules. Thus, in future, when a decision point is reached for each working chamber of the pump module which has been switched from allocation to one hydraulic circuit module to another hydraulic circuit module, the controller reads the value of the displacement accumulator of the new hydraulic circuit module and thus the demand for hydraulic fluid by the new hydraulic circuit module.

[0151] The moment in time that is chosen to reallocate a pump module is important, and the moment may be chosen in relation to the timing of the cycle of one or more working chambers, so as to minimise pulsation/ripple arising from those corresponding chambers. A forecast of flow, arising from the connected working chambers, can be used during this allocation process in particular to choose the moment in time to perform reallocation. Reallocation may be performed to increase flow provision, or simply flow capacity for some future time.

[0152] Notably, the controller may deliver hydraulic fluid with quite different pressure and flow rates to each hydraulic circuit portion at the same time. In a simple example, the pressure at the input to the hydraulic circuit portions is measured and the accumulator for each hydraulic circuit portion is incremented with time in proportion to the error between the measured pressure and a set point pressure. The error may also be integrated over time and added to the accumulator. The pressure set points may be different for each hydraulic circuit portion and may be rapidly varied in response to loads on the actuators, or proportional valve positions. For example in response to a significant increase in pressure set point, each allocated working chamber could carry out an active cycle until the revised pressure set points was obtained. Additionally, if an actuator increased the amount of flow it was absorbing, the many working chambers would need to undergo active cycles to maintain the pressure set point Furthermore, the hydraulic circuit portions may receive very different volumes of hydraulic fluid as the net displacement of working fluid by the pump modules connected to each hydraulic circuit portion are entirely independent although working chambers connected to each hydraulic circuit portion are driven by the same engine through the same shaft.

[0153] Although the controller is shown here as being implemented by a single processor one skilled in the art will appreciate that the function of the controller may readily be distributed between a plurality of processors and/or circuits.

[0154] The benefits of the invention can be seen from FIGS. 6A through 6C. FIG. 6A shows the operation of a conventional hydraulic machine, such as an excavator, having tandem pumps which drive first and second hydraulic circuit portions with respective groups of actuators, with a control valve block allowing selective combining of the flow from the tandem pumps, while the flow is not combined and at a relatively low demand level. The x-axis shows flow rate and is numbered in terms of the number of pump modules to deliver the required flow rate. I.e. a required flow rate on the x-axis between 3 and 4, will require no fewer than 4 pump modules (even for a required rate which is only marginally above 3). In this case it assumed that each pump module has the same number of working chambers, n, each of the same capacity and so m pump modules delivers the maximum flow output of m×n working chambers. Q.sub.max1 is the maximum flow rate which can be delivered using working chambers of one pump (equivalent to 4 pump modules) and Q.sub.max2 is the maximum flow rate which can be delivered using working chambers of two pumps (equivalent to 8 pump modules). The y-axis shows pressure. The area of portion 112 shows the power output (pressure×flow rate) for the first hydraulic circuit portion at output pressure P1 and flow rate Q.sub.demand1 The area of portion 114 shows the power output for the second hydraulic portion at output pressure P2, which is lower than P1, and flow rate Q.sub.demand2, which is higher than Q.sub.demand1 Similar total power outputs are provided to the hydraulic circuit portions but with quite different pressure and flow rate characteristics.

[0155] With reference to FIG. 6B, in a conventional excavator circuit, when one hydraulic circuit portion requires a greater flow rate of hydraulic fluid than can be met with one pump (Q.sub.max1), the control valve block combines the flow from both pumps so that the flow requirement can be met, but this means that the power output is determined by the product of the higher pressure requirement P1 and the total flow requirement. Thus, instead of a power requirement equal to the product of pressure required and flow requirement of the first hydraulic circuit portion 112, and also the product of the pressure required and flow requirement of the second hydraulic circuit portion 114, power is wasted, represented by portion 116. In practice this is dissipated by throttling fluid flow. This demonstrates that the conventional excavator arrangement is inefficient when one hydraulic circuit portion demands high-pressure low-flow and the other demands low-pressure high-flow.

[0156] FIG. 6C shows what may be achieved using the invention. In this example, the second hydraulic circuit portion has a flow requirement which requires 6 of 8 available pump modules, at relatively low pressure P2, and the first hydraulic circuit portion has a flow requirement which can be met by a single pump module of 8 available pump modules, albeit at relatively high pressure P1. The controller switches 6 of the pump modules to the second hydraulic circuit portion, allocating only 1 pump module to the first hydraulic circuit portion and so can deliver the appropriate flow requirement 112 to the first hydraulic circuit portion and the appropriate flow requirement 114 to the second hydraulic circuit portion without the wasted energy represented by portion 116. Accordingly, the invention has provided a method to efficiently meet the requirements of the first and second hydraulic circuit portions.

[0157] The controller uses demand signals from the various hydraulic circuit portions in order to determine the net displacement of working fluid of the working chambers in the pump module(s) connected to the respective hydraulic circuit portions and also to determine when to switch pump modules from one hydraulic circuit portion to another. The demand signals may be used for feedback control of displacement. For example, demand signals may comprise or be determined from a measure of pressure in the hydraulic circuit portion (at some or all of the input to the hydraulic circuit portion, at a conduit extending to an actuator, or at an output to tank of the hydraulic circuit portion, for example, across a throttle (orifice) at an output of the hydraulic circuit portion), and also signals from manual controls, such as a joystick position signal. The demand signals may be used for feedforward control. For example, a demand signal may be determined from a user interface (e.g. manually operable control such as a joystick position), or a demand calculated by the controller (e.g. in response to current or intended activities of the apparatus) or demand derived from spool valve commands within the hydraulic circuit portions (e.g. pilot valve pressures) and/or the position of proportional valves.

[0158] In a largely redesigned application, the actuators allocated to the first and second hydraulic circuit portions can be selected as required, for example the first portion may have the swing motor, dipper primary actuator, boom secondary actuator, and one side of the travel and the second portion may have the dipper secondary, boom primary, bucket, and the other side of the travel.

[0159] In a largely conventional application, where the invention is retrofitted to existing apparatus, the actuators are already allocated to hydraulic circuit portions.

[0160] FIG. 7 is a schematic diagram of an alternative system architecture in which there is a third hydraulic circuit portion 120. The third hydraulic circuit portion includes a hydraulic slew drive 122 (which may for example control slew of the vehicle body in an excavator). A further apportioning block 124 is in communication with the high pressure manifolds 8C, 8D, 8E, 8F of four (i.e. only some) of the pump modules and, as with the main apportioning block 10, it contains valves which are controllable by the controller to switch the pump modules to a respective hydraulic circuit portion input 126 (the input to the third hydraulic circuit portion). This third input is connected to the slew drive through a slew direction valve block 128 which regulates fluid flow to cause the apparatus to slew clockwise or anticlockwise as required. The switchable valves of the further apportioning block are controlled by the controller in concert with the switchable valves of the main apportioning block 10 so that the pump modules 4C, 4D, 4E, 4F which are connectable to the third hydraulic circuit portion are connected to only one of the three hydraulic circuit portions at any time. Thus, the output of pump modules 4A, 4B, 4G and 4H may be diverted to the first or second hydraulic circuit portions and the output of pump modules 4C, 4D, 4E and 4F may be diverted to the first, second, or third hydraulic circuit portions. The controller receives a demand signal for and maintains an accumulator for the third hydraulic circuit portion to thereby adapt the displacement of working fluid to the third hydraulic circuit portion to meet demand. The further apportioning block may be integrated with the main apportioning block.

[0161] As shown in FIGS. 1 and 2, within the hydraulic circuit portions, bypass valves (typically spool valves) 32 and 40, can be provided to selectively route hydraulic fluid directly to specific actuators (the boom in the case of boom bypass valve 32 and the dipper in the case of dipper bypass valve 40), bypassing the proportional valves in the main valve control blocks. This is advantageous because for actuators (such as the boom or dipper function) which may consume a particularly high volumetric flow rate of hydraulic fluid, the proportional valve may lead to an excessive loss of energy through throttling or even prevent sufficient hydraulic fluid from being supplied to these functions. This is especially useful when fitting the current invention into existing excavator apparatus, whereby the primary spool would throttle too much power, and the pressure drop would be too high. Existing excavator apparatus would service some actuators via a primary and secondary spool. To retrofit the present invention (e.g. to an excavator) the secondary spool for the actuators would be shut off. (If the present invention is designed in during manufacture rather than retrofitted, it does not need a bypass spool, and could just have one higher capacity spool.

[0162] In the embodiment of FIG. 7, the slew circuit can therefore be connected to one or more pump modules directly, without any proportional valve therebetween (as would be common in a conventional excavator). Furthermore, the pump modules connected to the slew actuators may be accurately controlled based on a demand signal concerning only the slew function. This arrangement is energy efficient (as it omits proportional valves and reduces or avoids throttling) and allows fine control of actuator movement (as the working chambers of the respective pump modules in direct fluid communication with the slew actuators are operated in displacement control mode).

[0163] One skilled in the art will appreciate that the third hydraulic circuit portion and any other further hydraulic circuit portions may be connected to any subset of, or even all of, the pump modules. However, it may not make sense due to maximum flow requirements on a specific actuator to allocate all pump modules to that actuator.

[0164] In the embodiment of FIGS. 1 and 2, there are 256 possible combinations of connection of pump modules to the first and second hydraulic circuit portions (254 of which provide at least some flow to both hydraulic circuit portions), although if the pump modules all have the same capacity, there are effectively 9 different choices as to how many pump modules are allocated to each hydraulic circuit portion.

[0165] In some embodiments, one or more of the pump modules is fixedly connected to one of the circuit portions, and respective fluid flow does not pass through apportioning valve. The working chambers of the fixed allocation pump modules are always controlled, along with the working chambers of any other pump modules currently connected to the same circuit portion, to together meet the demand for hydraulic fluid of that circuit portion.

[0166] In an example 8 pump modules can be connected as follows:

[0167] Pump module 1: Circuit portion 1 only

[0168] Pump module 2: Circuit portion 1 only

[0169] Pump module 3: Circuit portion 2 only

[0170] Pump module 4: Circuit portion 2 only

[0171] Pump module 5: Circuit portion 1 or 2

[0172] Pump module 6: Circuit portion 1 or 2

[0173] Pump module 7: Circuit portion 2 or 3 (which may be a swing or slew circuit, for example)

[0174] Pump module 8: Circuit portion 2 or 3 (which may be a swing or slew circuit, for example)

[0175] In this case circuit portion 1 may receive the output of up to 5 pump modules; circuit portion 2 may also receive the output of up to 5 pump modules and circuit portion 3 may receive the output of up to 2 pump modules. The inclusion of a number of pump modules which are fixedly connected/allocated to specific hydraulic circuit portions can reduce complexity and cost, but it also reduces the flexibility.

[0176] FIG. 9 is a flow chart of an operating procedure carried out by the controller to regulate the switching of pump modules from one hydraulic circuit portion to another. On an ongoing basis, the controller monitors the flow required by the first hydraulic circuit portion 150A and by the second hydraulic circuit portion 150B. The controller than periodically calculates 152A, 152B the number of working chambers/PCUs required to supply the required flow of fluid to the first and second hydraulic circuit portions. Then, with reference to databases 104, 106, the controller determines whether the working chambers which are part of the pump modules currently connected to each hydraulic circuit portion are sufficient to provide the required flow and whether they should be redistributed. If there is no requirement to change the allocation, then the procedure continues again from the beginning. Otherwise, the controller determines 154 that one or more pump modules should be reallocated, it decides 156 which pump module or modules should be reallocated and then updates the database 106 of which pump modules are allocated to which hydraulic circuit portions and sends valve control signals 158 to the diverting valves 52, 54 to implement the change. Details around this changeover procedure are described further below. When decision points as to whether to cause individual working chambers to carry out active cycles are reached in the future, the controller will automatically consider the demand and the demand accumulator for the hydraulic circuit portion to which the relevant working chambers are connected when determining whether the respective working chamber should undergo an active or an inactive cycle of working chamber volume.

[0177] The controller also considers limits for the torque, flow or power output of individual pump modules and these are dynamically varied as pump modules are reallocated from one hydraulic circuit portion to another.

[0178] When the total demand for fluid by all hydraulic circuit portions is within the overall capacity of the hydraulic machine, pump modules can be allocated to hydraulic circuit portions such that the total number of working chambers allocated to each hydraulic circuit portion will supply the demanded displacement, with rounding up as required.

[0179] If however the total demand for fluid by each hydraulic circuit portion exceeds the overall capacity of the hydraulic machine—or cannot be met given the number of working chambers in each pump module, the controller employs an alternative strategy.

[0180] In one strategy, when an overload criteria is met, the controller allocates pump modules having working chambers equal to one half of the total number available to the first hydraulic circuit portion and one half of the total number available to the second hydraulic circuit portion. Alternatively, one hydraulic circuit portion may be prioritised and be allocated sufficient working chambers to meet demand while the other hydraulic circuit portion is allocated the remainder of working chambers whose potential sum displacement is insufficient to meet demand. For example, it might be determined to prioritise a hydraulic circuit portion comprising steering actuators. There may be a default state of allocation of pumping module to hydraulic circuit portions to which the controller reverts where possible given immediate demand.

[0181] For example each hydraulic circuit portion may be allocated a proportion of working chambers equal to its current or time-averaged or predicted displacement demand as a fraction of the total current or time-averaged or predicted displacement demand, without rounding as required.

[0182] When it is determined that a pump module is to be reallocated from one hydraulic circuit portion to another, the pump module(s) to be reallocated may be selected taking into account one or more of: [0183] a preference for particular pump modules or a particular number of pump modules to be commoned, or [0184] a preference or requirement for a particular pump module or pump modules to be excluded from supplying fluid to one or more hydraulic circuit portions, or [0185] a requirement such as ensuring smooth flow of hydraulic fluid/reducing flow ripple (and therefore considering which pump module would, if connected to a particular hydraulic circuit module, give smoothest flow during the transition), minimising the number of diverting valve switching events (to minimise wear), distributing use (and therefore wear) among different pump modules, switchable valves etc. This may be a primary requirement.

[0186] In some embodiments pump modules are reallocated when a flow or displacement demand (by a hydraulic circuit portion) exceeds a threshold. This is especially useful where there are three or more hydraulic circuit portions. For example, when the demand signal is representative of a target flow rate (“flow domain” control), allocation of a further pump module to a hydraulic circuit portion may be triggered Q.sub.demand>Q.sub.n−1 (where Q.sub.demand is the flow demand, and Q.sub.n is the maximum flow associated with a number (n) of pump modules allocated to the respective hydraulic circuit portion). This control method seeks to retain an excess of potential displacement. E.g. If the flow demand Q.sub.demand is 65 litres per minute (LPM) and n=2 (where the maximum flow of one pump module is 60 LPM), then Q.sub.n−1 is 60, and the condition of the equation is met, and thus the number n should increase. In this example, a pump module would be allocated, increasing the total capacity of the pump modules allocated to the respective hydraulic circuit portion, and the condition of the equation would be false (65<120). The allocation, and the value of n, would remain constant until the triggering condition is again true. One skilled in the art can see the equation can be readily varied to make more conservative (e.g. Q.sub.demand>Q.sub.n−1.5), or to make less conservative (Q.sub.demand>Q.sub.n−0.5) The latter carries the risk that the demanded displacement by a hydraulic circuit portion may in course exceed that available from the pump modules connected to the respective connecting circuit output.

[0187] Alternatively, instead of providing a trigger in the flow domain, it may be that demand is signalled in terms of displacement fraction (Fd, the fraction of maximum possible displacement per rotation of the rotatable shaft). As the demand displacement fraction for a given hydraulic circuit portion approaches the maximum available displacement fraction, another pump module should be allocated to the respective hydraulic circuit portion. The threshold demand which triggers allocation of an additional pump module may be a predetermined fraction of the maximum displacement associated with the pump modules currently allocated to the respective hydraulic circuit portion. For example, for a threshold of 0.9, when displacement demand transitions from below 0.9 to above 0.9 of the maximum displacement by the working chambers of the pump modules connected to the hydraulic circuit portion, an additional pump module would be allocated and join the group. This would trigger a change in the Fd commanding the working chambers in the respective group of pump modules, since the total available displacement of the hydraulic circuit portion has changed.

[0188] A group of pump modules may exist as a ‘pool’ from which modules are selected for allocation for use. Pump modules surplus to requirement, are thus unselected/deallocated.

[0189] The physical state of the switchable valves (of the hydraulic connecting circuit) may mean that a pump module is connected to a hydraulic circuit portion, and if the respective working chambers operate in an idle mode, no pressurised fluid is communicated to or from the high pressure gallery and the respective working chambers. Thus the controller might deem such a pump module as ‘deallocated’ and so not contributing to meeting demand for the hydraulic circuit portion to which it is connected. In the same physical valve switching state, it may also be said that the pump module is ‘allocated’ (irrespective of the mode of the respective working chambers).

[0190] The reallocation of a pump module from one hydraulic circuit portion to another hydraulic circuit portion may be determined based on current demand (e.g. flow demand) or an estimate or a prediction of demand. The controller may predict future increases or decreases in demand, for example they may detect a standard or repeating demand cycle (for example a common sequence of movement of the various actuators of an excavator while it carries out a common tasks, for example, digging, lifting, rotating and then dropping matter). The controller may measure a particular gradient in demand. In response, the controller may reallocate one or more pump modules from one hydraulic circuit portion to another based on a predicted future demand, in advance of the demand occurring. The controller could take into account typical ramp rates or gradients of the demand signal. The controller may also take into account data from sensors (e.g. accelerometers, vibration sensors, tilt sensors), for example, it may be detected that the device is on a gradient, or moving, or not moving.

[0191] In any case, hysteresis may be provided, such that the transition (allocation, or de-allocation) between the number of pump modules connected to a hydraulic circuit portion is not triggered unnecessarily. An example of an unnecessary transition might be where it is caused by a temporary/dynamic oscillation in displacement demand around the (flow or displacement) threshold level, where the oscillation does not follow a longer term trend or steady state. The usual trigger level for requiring allocation of an additional pump module may be higher than the usual trigger level for permitting removal of a pump module to connect to another hydraulic circuit portion to create this hysteresis.

[0192] When a pumping module is switched from one hydraulic circuit portion to another hydraulic circuit portion it may be necessary for the controller to amend data concerning working chamber active cycle allocation and accumulated demand. In the example given above, accumulators are used to store accumulated unmet demand by hydraulic circuit portion in absolute units, for example units of volumetric flow rate, and are incremented proportionally to demand and decremented by the volume of fluid displaced by a working chamber when a working chamber carries out an active cycle.

[0193] FIG. 10 shows the controlled switching process when a pump module is reallocated from one hydraulic circuit portion to another (hydraulic circuit portion 2 to hydraulic circuit portion 1). The demand signals 201, 202, for hydraulic circuit portions 1 and 2 are expressed in terms of flow rate and vary with time. In this example, each hydraulic circuit portion initially has the same number of pump modules allocated to it, each having the same number of working chambers, each of which have the same capacity, thus the maximum flow rate 211, 212 which can be delivered to hydraulic circuit portions 1 and 2 respectively are initially the same as each other. The middle and lower traces illustrate the valve control signals 220, 230 and valve positions 222, 243 (open or closed) for the normally open and normally closed valves 52, 54 respectively for an individual pump module (for example pump module 4A) which is initially connected to one of the hydraulic circuit portions (e.g. portion 2).

[0194] At time ‘A’ the demand signal for the other of the hydraulic circuit portions (portion 1) exceeds a threshold and the controller makes a decision to reallocate one or more pump modules from hydraulic circuit portion 2 to hydraulic circuit portion 1, to increase the maximum possible flow to hydraulic circuit portion 1. (In some embodiments, demand falling below a threshold may trigger deallocation of a pump module from a hydraulic circuit portion, causing it to be reallocated to another hydraulic circuit portion, for example to distribute capacity evenly between hydraulic circuit portions). The determination of how many pump modules should be reallocated to hydraulic circuit 1 may take into account whether hydraulic circuit 2 will continue to be able to meet its demand without one or more pump modules, taking into account demand thresholds; the application of prioritisation logic, for example prioritising flow capacity of a hydraulic circuit portion that feeds steering actuators.

[0195] Once the controller has determined at time A that one or more pump modules should be reallocated from hydraulic circuit portion 2 to portion 1, at time B the controller sends commands to the diverting valves 52, 54 (commands may include starting a solenoid current to open or close a valve or stopping a solenoid current to allow a normally open valve to open or a normally closed valve to close). The diverting valves take time to move and reach their new state at time C. During this time the controller updated database 106(not shown) as to which pump modules are allocated to which hydraulic circuit portions. Thus the controller will begin to take into account the revised allocation of pump modules and therefore working chambers to hydraulic circuit portions when making working chamber displacement decisions.

[0196] Nevertheless, in some embodiments, during the period of time between sending the commands to the diverting valve, the controller causes working chambers of the pump module which is being reallocated to commence only inactive cycles with no net displacement of working fluid. This minimises flow during the switching process. It may be that the controller causes working chambers of the pump module which is switching to carry out only inactive cycles from time A, when the decision is made, because once a working chamber has been committed to carry out an active cycle by closure of the LPV, that cannot be stopped until the shaft has rotated by a predetermined angle and if it is desired to avoid any working chamber carrying out an active cycle during switching of the diverting valves, then a period of time is required first for working chambers to complete any active cycles which are currently underway. The controller may wait for working chambers within the pumping module which is to be switched to reach a particular state (phase) and or wait for the flow from the pumping module to fall below a particular threshold before activating the diverting valves.

[0197] It is possible for the timing of closure of LPVs to be synchronised with the timing of movement of diverting valves, to delay active cycles of working chamber volume until the diverting valves have finished reconnection of the pump module containing an individual working chamber between hydraulic circuit portions. Typically it is the timing of LPV closure which is varied as LPV closure is typically much quicker than the opening of closing of diverting valves.

[0198] It is also possible for the controller to carry out one or more active cycles of working chamber volume prior to a reallocation of a pump module from one hydraulic circuit portion to another to deliberately increase the pressure in the high pressure manifold of the pump module, for example to close to or at the pressure of the apportioning manifold/input to hydraulic circuit portion to which the pump module is to be connected. This can reduce transient pressure fluctuations.

[0199] In some embodiments, the switching of the diverting valves is staggered, i.e. it may be that the valve within a pair of valves as a unit (as shown in FIGS. 8,11) which is to be changed from closed to open is kept open until the other valve of the pair has opened; alternatively the valve which is to be changed from open to closed may be kept open until the other valve has closed. This reduces the risk of hydraulic deadhead.

[0200] Although the above example uses a normally open and a normally closed poppet valve, other switching mechanisms can be employed. For example, instead of the arrangement of FIG. 8, the arrangement of FIG. 11 uses a pair of double-blocking valves. In effect, the separate check valves of FIG. 8 have been incorporated into the diverting valves. Separate check valves are not required and it is especially important in this case to use the staggered opening/closing of valves when swapping a pump module between hydraulic circuit portions.

[0201] FIG. 12 shows a further diverting valve embodiment which corresponds to the arrangement of FIG. 8 except that it employs a single switchable valve 62 instead of pair of poppet valves 52,54. The switchable valve has a first position in which the high pressure manifold 8B of an individual pump module is connected to the first apportioning manifold 56 and thus to the first hydraulic circuit portion, a second position in which the high pressure manifold is connected to the second apportioning manifold 58 and thus to the second hydraulic circuit portion and an intermediate portion in which it is connected to both but through orifices. The spool valve is switched between the first and second positions by the controller, and passes through the intermediate position only briefly. It is preferable for the high pressure manifold to be connected briefly to both apportioning manifolds than neither to avoid hydraulic deadhead although in some embodiments the intermediate position is blocking. A spring biases the valve to normally open to the first hydraulic circuit portion and normally closed to the second hydraulic circuit portion. This switching arrangement would also be useful, for example, for diverting flow to a third hydraulic circuit portion as per the embodiments of FIGS. 7,8,11,12, and 13 at least.

[0202] It would also be possible to use a spool valve with multiple positions corresponding to different flow configurations where the spool valve controls pilot flow to hydraulically actuated valves which open or close to allow flow in from a high pressure manifold to one or other hydraulic circuit portion depending on valve position. Thus flow from the pumping modules need not pass through the single spool valve.

[0203] FIG. 13 shows an alternative diverting unit which employs a multi-position poppet valve 66, which could be pilot operated or actuated by a solenoid. As with the valve of FIG. 12 it has first and second positions in which a high pressure manifold is connected to one or the other apportioning manifold (and thereby to a respective hydraulic circuit portion). There is an intermediate position between the first and second positions where the high pressure manifold is connected to both apportioning manifolds but through throttles (and typically also check valves to prevent back flow to the high pressure manifold of the respective pump module). The valve passes very briefly through the intermediate position as it is switched from the first position to the second position, or vice versa, by the controller.

[0204] FIG. 14 is a schematic diagram of an alternative configuration of the connecting circuit which enables the switching of pumping modules between three different hydraulic circuit portions via manifolds 56, 58, 250 and so which can be used as an alternative to the connecting circuit of FIG. 7. The high pressure manifolds 8A—8H of pump modules 4A—4H may be switched between a first apportioning manifold 56 which is in communication with the first hydraulic circuit portion, a second apportioning manifold 58 which is in communication with the second hydraulic circuit portion and a third apportioning manifold 250 which is in communication with the third hydraulic circuit portion (used in this example for a slew function as per FIG. 7) with a plurality of diverting valves 252, which may take any of the forms described above and which are under the control of the controller, and a further diverting valve 254, also under the control of the controller. Any of the pump modules may be connected to the first apportioning manifold. With the further diverting valve 254 in the position shown, pump modules 4C through 4H may always be connected to the second apportioning manifold irrespective of the state of the further diverting valve, by switching the valves 252, associated with the respective pump modules, to position 2. When the further diverting is in the state shown, it connects switchable manifold portion 256 to the second apportioning manifold 58. In combination with this, pumps 4A and 4B, are selectively connectable to the switchable manifold portion through diverting valves 252 (in position 2), would in the positions shown be connected to the second apportioning manifold and so connected to the second hydraulic circuit portion. When the further diverting valve is switched to its alternative state (not shown), the switchable manifold portion is instead connected to the third apportioning portion. In combination with this, pumps 4A and 4B would be connected to the third hydraulic circuit portion (via the third apportioning portion) with an appropriate configuration of the diverting valves 252, to position 2. Pump modules 4A and 4B may therefore be switched simultaneously between the second and third hydraulic circuit portion by the controller actuating the respective further diverting valves. Alternatively the pump modules can be switched one at a time to or from the first hydraulic circuit portion and either the second or third hydraulic circuit portion depending on the position of the further diverting valve.

[0205] The further diverting valve may be located at a different position along the length of the first or second apportioning manifold. For example, if it was located at position 258 it might switch up to four pump modules between the first and third hydraulic circuit portions. If it was located at position 260 it might switch up to seven pump modules between the second and third hydraulic circuit portions.

[0206] With respect to FIG. 15A, a convenient location for the switchable valves (of the hydraulic connecting circuit/apportioning valves) is the endplate 66 of the hydraulic machine. In this case, conduits through the hydraulic machine which function as the high pressure manifolds 8A through 8D of pumps 4A through 4D connect to a ring conduit 270 in the endplate. This arrangement is convenient to form as the conduits extend at right angles to the plane of the endplate. First and second connecting circuit outputs 12, 14 from the hydraulic machine to the first and second hydraulic circuit portions respectively also extend from opposite ends of the ring conduit. Double blocking valves 272A through 272F under the control of the controller may be selectively closed. In use two of the double blocking valves are closed at any time to thereby define first and second apportioning manifolds in communication with the first and second connecting circuit outputs and so the first and second hydraulic circuit portions and with selected pump module high pressure manifolds. Thus, pump modules may be selectively connected to one or another of the hydraulic circuit portions but with the limitation that multiple pump modules connected to the same hydraulic circuit portions must be adjacent around the circumference of the ring conduit. Portions 274, 276 are connections between the ring conduit and the first and second connecting circuit outputs but may also communicate with conduits through the hydraulic machine which function as the high pressure manifold of a further pumping module, in which case there is a pumping module permanently connected to each of the connecting circuit outputs although the remaining pumping modules may be switched.

[0207] FIG. 15B illustrates an alternative in which instead of a ring conduit there is a C-shaped conduit 278 which communicates with conduits connected to four different pump modules. Any one of the double blocking valves 272A, 272B, 272C can be closed giving three different options whilst all others remain open. In a first option, with 272A closed, the pump module with high pressure manifold 276 is connected to the second output 14 and pump modules with high pressure manifolds 8A, 8B and 274 are connected to the first output. In a second option, with 272B closed, the pump module with high pressure manifold 276 and the pump modules with high pressure manifold 8A are connected to the first manifold and the pump modules with high pressure manifolds 8B and 274 are connected to the first output. In a third option with 272C closed, the pump module with high pressure manifold 276 and the pump modules with high pressure manifold 8A and 8B are connected to the first manifold and the pump module with high pressure manifold 274 is connected to the first output. The controller switches the double blocking valves are required to reallocate pumping modules.

[0208] In the embodiments of FIG. 15A and FIG. 15B, a third connecting circuit output, for a third hydraulic circuit portion, might be connected at any of the locations 8A, 8B, 8C, 8D.

[0209] In the embodiment of FIG. 16, the first apportioning manifold 56, extending to first output 12 and the first hydraulic circuit portion input 16 and second apportioning manifold 58, extending to the second output of the apportioning block and the second hydraulic circuit portion input 18 are connected together through 8 blocking valves 280, connected in series, with T junction connections to the high pressure manifolds 8A through 8H of 8 pump modules 4A through 4H between each blocking valve. The controller selects one blocking valve at a time to close, thereby splitting the pump modules between allocation to the first and second hydraulic circuit portion depending on the selected blocking valve.

[0210] In case of an overpressure event, the apparatus typically comprises pressure relief valves. One may be provided per pump module but in the embodiment of FIG. 17 the high pressure manifold of each of four pump modules is connected, in parallel, through check valves 280 to a single pressure relief valve 290. The check valves are all upstream of the pressure relief valve and perform the function of checking flow in the event that the pressure behind the pressure relief valve is higher than the high pressure manifold pressure. The embodiment of FIG. 17 may be provided within or separate to the apportioning block.

[0211] In the apparatus described above, problems may arise after a demand for working fluid cannot be met due to competing requirements for pump modules, when the pump modules connected to a connecting circuit output (and thereby to a hydraulic circuit portion and/or a group of one or more actuators) are as a result unable to meet the demand, and when, due to a further increase in demand associated with the connecting circuit output, or a decrease is other competing demands, one or more additional pump modules are connected to the same connecting circuit output, thereby increasing the maximum displacement to the connecting circuit output. When this additional capacity becomes available, the actual displacement to the connecting circuit output (and thereby to a hydraulic circuit portion and/or a group of one or more actuators) suddenly jumps, leading to vibrations, juddering or difficulties in machine control (especially by a human operator).

[0212] This is illustrated with reference to FIG. 18A which shows the actual flow (solid line) to a connecting circuit output as a demand for flow (dotted line) is increased linearly with time in an arrangement in which up to 8 pump modules of the same capacity are available for connection to a connecting circuit output. At time zero, 4 pump modules are connected to the connecting circuit output. In this example, there is already a sufficient demand for flow to one or more other connecting circuit outputs that when the demand exceeds the maximum capacity (dashed line) for 4 pump modules, at time t1, the actual flow remains at the maximum capacity of 4 pump modules and drops behind the demanded flow. As the demanded flow increases, at time t2, the demand, relative to other competing demands, is sufficient that the controller decides to connect a 5.sup.th pump module to the connecting circuit input, causing the capacity to increase in a step. At this point it can be seen that the solid line showing actual flow jumps suddenly as it becomes possible for the 5 pump modules, operating below maximum combined flow, to accurately meet the demand. It is this jump which can cause vibrations, juddering and control difficulties. As shown in FIG. 18A, the actual displacement will again be limited by capacity at time t3 and then jump up again at time t4 when a 6.sup.th pump module is allocated.

[0213] In a first approach, we have found that these jumps in displacement can be avoided by scaling down the demand signals by multiplying them by a scaling factor once the total demand exceeds a threshold.

[0214] The threshold is once the sum of the demand exceeds (a) the maximum displacement of all of the pump modules apart from one.

[0215] The scaling factor is such that the sum of the demands does not exceed (a) the maximum displacement of all of the pump modules apart from one. This is a fraction of the maximum possible displacement equal to (a) the maximum displacement of all of the pump modules apart from one divided by (c) the maximum displacement of all of the pump modules (assuming that all of the pump modules can be connected to either output).

[0216] In this example where there are 8 pump modules with the same maximum displacement, this has the effect that if the sum of the demands exceeds 7/8 of the maximum displacement, the sum of the scaled back demands does not exceed 7/8 of the maximum displacement.

[0217] The scaling factor is therefore (a) the maximum displacement of all of the pump modules apart from one divided by (b) the sum of the demands.

[0218] Once the demand is scaled in this way then, as shown in FIG. 18B, which shows a scaled down demand, not only do the scaled demands signals never exceed the available capacity, there are no sudden jumps in displacement as additional pump modules are connected to the connecting circuit output.

[0219] This applies especially when each connecting circuit output/hydraulic circuit portion is allocated a fraction of available pump modules which is proportional to the demand for hydraulic fluid for that output/hydraulic circuit portion, typically rounded up to the nearest integer.

[0220] With reference to FIG. 19, the effect of scaling by the said ratio is that effectively a displacement equal to the capacity of one of the pump modules is never used. In this image, the line labelled Output 1 is the scaled back demand signal for one of two connecting circuit outputs, the line labelled Output 2 is the scaled back demand signal allocated to the other of two connecting circuit outputs and the dashed line is unused capacity of the machine, which is the capacity of one pump module. At the precise position shown, 3 pump modules are connected to Output 1 and 5 pump modules are connected to Output 2 and the maximum displacement of either output is not exceeded. Although this does reduce maximum capacity, the discontinuities in displacement are avoided.

Worked Example—First Approach

[0221] A pump has 24 working chambers, grouped into 8 pump modules, each formed of 3 working chambers with a common high pressure manifold. Half of the working chambers and pump modules are located within one housing and half within another and the working chambers have a common shaft. The maximum displacement of each pump module is 24 cc per revolution of the rotatable shaft of the pump and so the total maximum displacement of the machine is 192 cc per revolution. The 8 pump modules can be connected through the connecting circuit to either of two connecting circuit outputs (or hydraulic circuit portions).

[0222] The capacity of one pump module is not used and demands are scaled back where required so that the sum of the demands cannot exceed 7/8×192=168 cc/rev (the threshold). This equates to multiplying the individual demands by 168 cc/rev divided by the sum of the demands when the demands are for more than the total displacement which can be output by all but one of the pump modules in combination.

[0223] In an example during operation, the demands for output are 100 cc/rev for output 1 and 150 cc/rev for output 2, 100 and 150 are 0.4 and 0.6 of the total demand. The sum of these demands is 250 cc/rev which exceeds the threshold of 168 cc/rev. Accordingly the demands are to be scaled down so that their sum is 168 cc/rev.

[0224] The total available pump capacity is divided proportionally between each service and the scaled back demands are 0.4×168 cc/rev=67.2 cc/rev and 0.6×168 cc/rev=100.8 cc/rev respectively. This equates to having multiplied the original demands (100 cc/rev and 150 cc/rev) by 168 cc/250 cc=0.672.

[0225] Next, calculate the number of pump modules required to connect to each output is calculated by rounding up the demand divided by the capacity of each pump modules, thus 67.2/24 cc/rev=2.8 which rounds up to 3 pump modules, and 100.8/24 cc/rev=4.2 which rounds up to 5 pump modules, respectively. As a check, these numbers should equal the total number of pump modules, 8.

[0226] This approach ensures that there is never a sudden increase in displacement arising from the connection of a new pump modules to an output. The scaled demand is never saturated.

[0227] In a further sophistication to the above method, illustrated with reference to FIGS. 20A through 20F, each connecting circuit output (whether to a hydraulic circuit portion and/or a group of one or more actuators) is allocated a minimum fraction of the available pump module capacity (or a minimum fraction of the available pump modules when they have the same capacity) equal to the reciprocal of the number of connecting circuit outputs. This applies when the demands are sufficiently high, e.g. for more than the total possible displacement, or where each demand exceeds the reciprocal of the number of connecting circuit outputs of the maximum possible displacement. Typically this second approach is only applied at higher demands than trigger the first approach and there can be a demand region in between where only the first approach is applied or there is a transition approach.

Worked Examples—Second Approach

[0228] In the following worked examples there are two outputs and eight pump modules, each of which has a capacity of 24 cc/rev.

[0229] In a first example illustrated in FIGS. 20A and 20D, the first demand (labelled output 1) and second demand (labelled output 2) are both for more than half of the available displacement, indeed the first demand alone is for the entire available displacement. Each of the two outputs is allocated 100/2%=50% of the available capacity and so allocated 4 pump modules, with the first and second demands scaled back to 50% of the total available displacement.

[0230] In a second example illustrated in FIGS. 20B and 20E, the first demand (output 1) is again for more than half of the available displacement but now the second demand (output 2) is for less than half of the available displacement. The first output is allocated 100/n=50% of the available capacity, and so allocated 8/2=4 pump modules. The second output is allocated the remainder of the capacity, and so is also allocated 4 pump modules. The dashed line in FIG. 20E shows a small amount of lost capacity.

[0231] In a third example illustrated in FIGS. 20C and 20F, the first demand (output 1) is still high, the second demand is sufficiently low as to not require 8/2=4 pump modules in order to be met. In this case, the second output is allocated a sufficient number of pump modules to enable the full second demand to be met (2 in this case) and the remainder (6) are allocated the remaining pump modules.

[0232] In more detail, the allocation in the third example can be calculated by the following approach.

[0233] Demand for Output 1=192 cc/rev (full pump capacity, would require all 8 pump modules)

[0234] Demand for Output 2=36 cc/rev (well under half pump capacity, can be achieved with 1.5 pump modules)

[0235] Demand Total=228 cc/rev

[0236] Output 1 demand is processed using the following algorithm:

IF (36 cc/rev<(0.5n−1)*24 cc/rev)[statement is true]

Output 1 displacement allocation=MIN(192 cc/rev,192 cc/rev−24 cc/rev−36 cc/rev)=132 cc/rev

ELSE

Output 1 displacement allocation=MIN(Output 1 Demand,equal fraction of maximum output capacity)

[0237] Output 2 demand is processed as follows:

IF (192 cc/rev<(0.5n−1)*24 cc/rev)[statement not true]

Output 2 displacement allocation=MIN(Output 2 demand,Total pump capacity-1−Output 1 demand)

ELSE

Output 2 displacement allocation=MIN(36 cc/rev,96 cc/rev)=36 cc/rev

[0238] Thus the demand for output 1 is scaled to 132 cc/rev and output 1 is allocated 6 pump modules and the demand for output 2 is maintained and output 2 is allocated 2 pump modules.

[0239] This, each output has been allocated pump modules capable of providing as a minimum an equal fraction of total displacement capacity when it has a demand for at least an equal fraction of the total displacement capacity, and may be allocated more if the other demands allow.

[0240] The benefits of implementing this second, guaranteed fraction approach (guaranteed half in the case of two outputs), in combination with the first approach is that the pump's full capacity can be used more of the time, resulting in faster operation (faster duty cycle times). It will also greatly reduce the number of switching cycles required from the connecting circuit valves, resulting in an increased service life of the system. The downside is some loss of controllability when compared with the first strategy.