Fluid working machine having first and second valve cylinder devices in fluid communication with each other via a common conduit

Abstract

The invention provides a fluid working machine comprising: a cylinder block (1) having an axial bore (4); a crankshaft (2) which extends within the axial bore (4) and is rotatable about an axis of rotation (3); and first and second valve cylinder devices (13) provided in the cylinder block (1) arranged about and extending outwards with respect to the axial bore (4), the first and second valve cylinder devices (13) being axially offset from each other, the first and second valve cylinder devices (13) being offset from each other about the axis of rotation (3), and the first valve cylinder device having an axial extent which overlaps the axial extent of the second valve cylinder device, wherein the first and second valve cylinder devices (13) comprise first valves (14) having respective first working fluid ports (48, 49), the said respective first working fluid ports (48, 49) of the first valves (14) of the first and second valve cylinder devices (13) being in fluid communication with each other via a common conduit (50, 52) extending within the cylinder block (1).

Claims

1. A fluid working machine comprising: a cylinder block having an axial bore; a crankshaft which extends within the axial bore and is rotatable about an axis of rotation; and first and second valve cylinder devices provided in the cylinder block arranged about and extending outwards with respect to the axial bore, the first and second valve cylinder devices being axially offset from each other, the first and second valve cylinder devices being offset from each other about the axis of rotation, and the first valve cylinder device having an axial extent which overlaps the axial extent of the second valve cylinder device, wherein the first and second valve cylinder devices comprise first valves having respective first working fluid ports, the said respective first working fluid ports of the first valves of the first and second valve cylinder devices being in fluid communication with each other via a common conduit extending within the cylinder block.

2. The fluid working machine according to claim 1 further comprising a third valve cylinder device provided in the cylinder block, the third valve cylinder device being axially offset from the first and second valve cylinder devices, and the second valve cylinder device being offset from the third valve cylinder device about the axis of rotation.

3. The fluid working machine according to claim 1 wherein the said common conduit intersects the said respective first working fluid ports of the first valves of the first and second valve cylinder devices.

4. The fluid working machine according to claim 1, wherein the said common conduit comprises a single straight drillway extending through the cylinder block.

5. The fluid working machine according to claim 1, wherein the said common conduit extends in a direction substantially parallel to the axis of rotation.

6. The fluid working machine according to claim 1, wherein the first and second valve cylinder devices are comprised in a first group of valve cylinder devices, the fluid working machine further comprising a second group of valve cylinder devices provided in the cylinder block adjacent the first group of valve cylinder devices, the second group of valve cylinder devices being spaced from the first group of valve cylinder devices about the axis of rotation.

7. The fluid working machine according to claim 6 wherein the second group of valve cylinder devices comprises a plurality of valve cylinder devices having first valves comprising respective first working fluid ports, the respective first working fluid ports of the first valves of the valve cylinder devices of the second group being in fluid communication with each other via a second common conduit extending within the cylinder block.

8. The fluid working machine according to claim 6 wherein the second group of valve cylinder devices comprises a valve cylinder device having an axial extent which overlaps with the axial extent of a valve cylinder device of the first group of valve cylinder devices.

9. The fluid working machine according to claim 1, further comprising respective pistons reciprocating in the first and second valve cylinder devices, wherein the crankshaft comprises a plurality of cams including first and second cams, and wherein the piston reciprocating in the first valve cylinder device is in driving relationship with the first cam and the piston reciprocating in the second valve cylinder device is in driving relationship with the second cam.

10. The fluid working machine according to claim 9 wherein the first and second valve cylinder devices are comprised in a group of valve cylinder devices, the cams of the crankshaft being rotationally offset from each other about the axis of rotation such that the pistons reciprocating in the said group of valve cylinder devices drive, or are driven by, cams of the crankshaft respectively at phases which are substantially equally spaced.

11. The fluid working machine according to claim 1, wherein a longitudinal axis of the common conduit is offset from the first valve cylinder device about the axis of rotation in a first rotational sense and offset from the second valve cylinder device about the axis of rotation in a second rotational sense opposite the first rotational sense such that the common conduit has a circumferential position which is disposed circumferentially between the circumferential position of the first valve cylinder device and the circumferential position of the second valve cylinder device.

12. The fluid working machine according to claim 1, wherein the first and second valve cylinder devices are provided in first and second housing bores of the cylinder block respectively, the first and second housing bores being axially offset from each other, the first and second housing bores being offset from each other about the axis of rotation, and the first and second housing bores having axial extents which overlap with each other.

13. The fluid working machine according to claim 2 wherein the said common conduit intersects the said respective first working fluid ports of the first valves of the first and second valve cylinder devices.

14. The fluid working machine according to claim 2, wherein the said common conduit comprises a single straight drillway extending through the cylinder block.

15. The fluid working machine according to claim 3, wherein the said common conduit comprises a single straight drillway extending through the cylinder block.

16. The fluid working machine according to claim 2, wherein the said common conduit extends in a direction substantially parallel to the axis of rotation.

17. The fluid working machine according to claim 3, wherein the said common conduit extends in a direction substantially parallel to the axis of rotation.

18. The fluid working machine according to claim 1, further comprising an additional conduit, wherein the common conduit has a first longitudinal axis and the additional conduit has a second longitudinal axis, wherein the first longitudinal axis and the second longitudinal axis are parallel to the axis of rotation, and wherein the second longitudinal axis of the additional conduit is radially closer to the axis of rotation than the first longitudinal axis of the common conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

(2) FIGS. 1a and 1b are exploded perspective and frontal views a cylinder block and a crankshaft of a fluid working machine;

(3) FIGS. 2a and 2b are exploded perspective and rear views the cylinder block and crankshaft shown in FIGS. 1a and 1b;

(4) FIGS. 3a and 3b are side views of the cylinder block and crankshaft of FIGS. 1a, 1b, 2a and 2b;

(5) FIG. 4 is a side sectional view of the cylinder block and crankshaft of FIGS. 1-3;

(6) FIGS. 5a-5d are frontal, perspective and respective side views of the crankshaft of FIGS. 1-4, FIGS. 5c and 5d showing the crankshaft at different stages of rotation;

(7) FIG. 6 is a plot of output versus time with respect to a group of piston cylinder devices of a fluid working machine comprising the cylinder block and crankshaft of FIGS. 1-5; and

(8) FIGS. 7a-7c are front, side and perspective views of the crankshaft, pistons and valve cylinder devices of a group of piston cylinder devices disposed about and extending away from the crankshaft of FIGS. 5a-5d, FIGS. 7a-7c also illustrating the common conduits fluidly connecting the low pressure valves within each group and the high pressure valves within each group respectively.

DETAILED DESCRIPTION

(9) FIGS. 1a and 1b are exploded front perspective and frontal views respectively of a (typically monolithic) cylinder block 1 and rotatable crankshaft 2 of a radial piston fluid working machine, which may be (for example) a hydraulic or pneumatic pump, motor or pump/motor (which is capable of operating as a pump and/or as a motor in different operating modes). FIGS. 2a, 2b are rear perspective and rear views respectively of the cylinder block 1 and crankshaft 2. FIGS. 3a, 3b are respective side views of the cylinder block 1 and crankshaft 2. The crankshaft is rotatable about an axis of rotation 3 (see FIG. 1a), and is provided in a central axial bore 4 extending through the cylinder block 1 in a direction parallel to the axis of rotation 3. The cylinder block 1 comprises four groups 5-10 of housing bores (formed by drilling drillways through the cylinder block 1 or by casting holes in the cylinder block 1 which are typically subsequently drilled) 12 sized and arranged to receive (and/or to help to define) respective valve cylinder devices 13, each of the valve cylinder devices comprising an integrated valve unit 14 in fluid communication with (and coupled to) a cylinder 15. It will be understood that the cylinders 15 may be omitted, and the housing bores 12 may alternatively define the cylinders of the valve cylinder devices 13.

(10) The housing bores 12 are disposed about the crankshaft 2 and extend (typically radially) outwards with respect to the crankshaft 2. The groups 5-10 of housing bores 12 are spaced from adjacent groups of housing bores about the axis of rotation 3. In the illustrated embodiment, the groups 5-10 of housing bores 12 are substantially identical. It will therefore be understood that the features of the first group 5 are also (in the illustrated embodiment) features of the other groups 6-10. Indeed, the valve cylinder devices of the first group are typically provided on the same planes as the corresponding valve cylinder devices of the other groups 6-10 (i.e. corresponding valve cylinder devices between groups have axial extents which (typically fully) overlap). Accordingly, only the first group 5 is described in detail below. However, in other embodiments there may be variations between groups, such as the number of housing bores (and thus the numbers of valve cylinder devices) per group and the configurations of the common conduits (see below).

(11) The first group 5 of housing bores 12 comprises first, second and third housing bores 12a, 12b, 12c. The first and third housing bores 12a, 12c are axially displaced from each other in a direction parallel to the axis of rotation 3, and aligned with each other along an alignment axis 16 (see FIG. 2a) which extends between the centres of the first and third housing bores 12a, 12c in a direction parallel to the axis of rotation 3. The second housing bore 12b is axially offset from the first and third housing bores 12a, 12c, and the second housing bore 12b is also offset from the first and third housing bores 12a, 12c in a clockwise direction as viewed in FIG. 1a about the axis of rotation 3 by an angle of approximately 30° (measured from the alignment axis to the centre of the second housing bore 12b about the axis of rotation 3). The second housing bore 12b has an axial extent, b, which overlaps with the axial extents a and c of the first and third housing bores 12a, 12c (see FIG. 1a), while the axial extents of the first and third housing bores 12a, 12c do not typically overlap. By axially offsetting the second housing bore 12b from the first and third housing bores 12a, 12c, offsetting the second housing bore 12b from the first and third housing bores 12a, 12c about the axis of rotation 3 and overlapping the axial extent b of the second housing bore 12b with the axial extents a, c of the first and third housing bores 12a, 12c, the group 5 of housing bores is provided with a space efficient nested arrangement. This allows a greater number of housing bores 12 (and thus valve cylinder devices) to be incorporated into a cylinder block 1 of a given axial length (i.e. a given length in a direction parallel to the axis of rotation). The second housing bore 12b also has an extent, x, about the axis of rotation which does not in this case overlap with the extents, y, z of the first and third housing bores 12a, 12c about the axis of rotation (although in other embodiments the extent, x, of the second housing bore 12b may overlap with the extents y, z of the first and/or third housing bores 12a, 12c about the axis of rotation).

(12) It will be understood that, within each of the groups 5-10, the valve cylinder devices 13 provided in the housing bores 12a, 12c are axially aligned and axially offset from each other and that the valve cylinder device 13 provided in housing bore 12b is axially offset from the valve cylinder devices 13 provided in the housing bores 12a, 12c and the valve cylinder device 13 provided in housing bore 12b is offset from the valve cylinder devices 13 provided in the housing bores 12a, 12c about the axis of rotation. The axial extent of the valve cylinder device 13 provided in housing bore 12b overlaps the axial extents of the valve cylinder devices 13 provided in the housing bores 12a, 12c, while the axial extents of the valve cylinder devices 13 provided in the housing bores 12a, 12c do not typically overlap. Indeed, typically, the cylinders 15 (where provided) of the valve cylinder devices 13 provided in the housing bores 12a, 12c are axially aligned and axially offset from each other, the cylinder 15 (where provided) of the valve cylinder device 13 provided in housing bore 12b is axially offset from the cylinders 15 of the valve cylinder devices 13 provided in the housing bores 12a, 12c, and the cylinder 15 of the valve cylinder device 13 provided in housing bore 12b is offset from the cylinders 15 of the valve cylinder devices 13 provided in the housing bores 12a, 12c about the axis of rotation 3. The axial extent of the cylinder 15 of the valve cylinder device 13 provided in housing bore 12b typically overlaps the axial extents of the cylinders 15 of the valve cylinder devices 13 provided in the housing bores 12a, 12c, while the axial extents of the cylinders 15 of the valve cylinder devices 13 provided in the housing bores 12a, 12c do not typically overlap.

(13) Integrated valve units 14 of the valve cylinder devices 13 comprise both low and high pressure valves. It will be understood that for pumps (or pump/motors operating in pumping mode), the low pressure valve acts as an inlet valve and the high pressure valve as an outlet valve; for motors (or pump/motors operating in motoring mode), the high pressure valve acts as an inlet valve and the low pressure valve as an outlet valve. The valve units 14 typically comprise a threaded end 14a which can be screwed into corresponding threads provided in radially outer (with respect to the axis of rotation 3) ends of the housing bores 12 to retain the valve units 14 in the housing bores 12. Additionally or alternatively threads may be provided on the outer diameters of the cylinders 15 (where provided) which instead mate with the threads of the housing bores 12.

(14) The valve units 14 also each comprise a valve head 14b provided at a second end of the valve unit 14 opposite the threaded end 14a at a radially outer (with respect to the crankshaft) end of the valve cylinder devices 13. The heads 14b of the valve units 14 of the valve cylinder devices 13 provided in the housing bores 12a, 12c are axially aligned and axially offset from each other, the head 14b of the valve unit 14 of the valve cylinder device 13 provided in the housing bore 12b is axially offset from the heads of the valve units 14 of the valve cylinder devices 13 provided in the housing bores 12a, 12c, and the head 14b of the valve unit 14 of the valve cylinder device 13 provided in housing bore 12b is offset from the heads of the valve units 14 of the valve cylinder devices 13 provided in the housing bores 12a, 12c about the axis of rotation 3. The axial extent of the head 14b of the valve unit 14 of the valve cylinder device 13 provided in housing bore 12b typically overlaps the axial extents of the heads 14b of the valve units 14 of the valve cylinder devices 13 provided in the housing bores 12a, 12c, while the axial extents of the heads 14b of the valve units 14 of the valve cylinder devices 13 provided in housing bores 12a, 12c do not typically overlap.

(15) As shown in FIG. 4, radially inner (with respect to the axis of rotation 3) ends of the cylinders 15 (or of the housing bores 12) comprise apertures which reciprocably receive pistons 24 in driving relationship with the crankshaft 2. The crankshaft 2 comprises first, second and third cams 30-34 (which in the illustrated embodiment are eccentrics) which are axially displaced from each other. The pistons 24 each comprise piston feet 24a resting on (and in driving relationship with) a respective cam 30-34 of the crankshaft 2. More specifically, via respective piston feet 24a, the first cam 30 is in driving relationship with the piston 24 reciprocating in the valve cylinder device 13 provided in the first housing bore 12a (of each of the groups 5-10); the second cam 32 is in driving relationship with the piston 24 reciprocating in the valve cylinder device 13 provided in the second housing bore 12b (of each of the groups 5-10); and the third cam 34 is in driving relationship with the piston 24 reciprocating in the valve cylinder device 13 provided in the third housing bore 12c (of each of the groups 5-10). The said pistons 24 cyclically reciprocate within a respective cylinder 15 (or housing bore 12) substantially in a radial direction with respect to the axis of rotation 3, thereby cyclically varying the volume of respective working chambers defined between the respective piston 24 and the cylinder 15 (or housing bore 12) in which it reciprocates. The pistons 24 are arranged such that when they drive, or are driven by, the respective cams 30-34 of the crankshaft 2, they rotate (and rock) about respective rocking axes parallel to the axis of rotation.

(16) The integrated valve unit 14 comprises a valve member which is engageable with a valve seat. The integrated valve unit 14 is typically an annular valve unit having valve inlets and valve outlets in the form of annular galleries provided in the perimeter of the annular valve unit 14 (see FIGS. 7a-7c described below). One or both of the low and high pressure valves of the integrated valve unit 14 are electronically actuatable (i.e. the opening and/or closing of the valves can be electronically controlled). A position and speed sensor may be provided which determines the instantaneous angular position and speed of rotation of the crankshaft 2, and which transmits shaft position and speed signals to a controller (not shown). This enables the controller to determine instantaneous phase of the cycles of each individual working chamber. The opening and/or the closing of the valves is typically under the active control of the controller. The controller thus regulates the opening and/or closing of the low and high pressure valves to determine the displacement of fluid through each working chamber (or through each group of working chambers), on a cycle by cycle basis, in phased relationship to cycles of working chamber volume, to determine the net throughput of fluid through each of the groups 5-10 according to a demand (e.g. a demand signal input to the controller). Thus, the fluid working machine typically operates according to the principles disclosed in EP 0 361 927, EP 0 494 236, and EP 1 537 333, the contents of which are incorporated herein by virtue of this reference.

(17) By spacing the groups 5-10 from each other about the axis of rotation 3, the radial extent of the crankshaft 2 can be reduced (compared to closely packing the groups around the crankshaft 2). This is explained as follows. There is a need for the piston feet 24a to be able to rest against the respective cam with which they are in driving relationship. Spacing the groups 5-10 from each other about the crankshaft 2 reduces the number of piston cylinder devices which can be provided around the crankshaft 2 and, because fewer piston feet need to rest on each cam 30-34, the surface areas of the cams 30-34 do not need to be as large and the radial extents of cams 30-34 can be reduced accordingly. In addition, the cylinder block 1 can be made mechanically stronger than a cylinder block in which the housing bores 12 are more closely packed because (strengthening) material is provided in the space between the groups about the axis of rotation 3.

(18) The first, second and third cams 30-34 are offset from each other about the axis of rotation 3 of the crankshaft 2 and they drive (in the case of a pump or a pump/motor operating in pumping mode) or are driven by (in the case of a motor or a pump/motor operating in motoring mode) the pistons reciprocating in the housing bores 12a, 12b, 12c. The second housing bore 12b of each group is offset from the first and third housing bores 12a, 12c of that group about the axis of rotation, and thus in order to provide a smooth output the cams 30-34 are not equally distributed (0°, 120°, 240°) about the axis of rotation. Rather, the second cam 32 in driving relationship with the second (offset) valve cylinder device 12b is also offset from a position equally spaced with respect to the first and third cams 30, 34 in order to provide the machine with groups of piston cylinder devices which work together driving or being driven at phases which are (substantially) equally spaced. For example, if the second housing bore 12b is offset from the alignment axis 16 of the first and third housing bores 12a, 12c by 30°, the second cam 32 may be offset from the first cam 30 by 90° about the axis of rotation in a first rotational sense (e.g. clockwise), the third cam 34 may be offset from the first cam 30 by 240° about the axis of rotation in the said first rotational sense, and the third cam 34 may be offset from the second cam 32 by 150° about the axis of rotation in the said first rotational sense. This enables the first, second and third cams 30-34 to drive or be driven by the pistons reciprocating in the housing bores 12a-12c at phases which are successively 120° apart (i.e. at phases which are equally spaced).

(19) The cams 30-34 and the piston feet 24a slidably bear against one another such that, when the cams 30-34 drive or are driven by the pistons 24 reciprocating in the housing bores 12a, 12b, 12c of the first group 5, each of the pistons 24 reciprocates in respective housing bores to generate a sinusoidal output 40-44 (see FIG. 6). As the cams 30-34 drive or are driven by the pistons 24 at phases which are equally spaced, the sinusoidal outputs 40-44 of the piston cylinder devices of the first group combine to provide a substantially smooth output 46. It will be understood that the output 46 is high pressure fluid in the case of a pump (or a pump motor operating in pumping mode), and mechanical torque in the case of a motor (or a pump-motor operating in motoring mode).

(20) FIGS. 7a-7c are front, side and perspective views of the crankshaft, pistons and valve cylinder devices of a group of piston cylinder devices disposed about and extending away from the crankshaft of FIGS. 5a-5d. In the illustrated embodiment, the valve units 14 of the valve cylinder devices 13 comprise working fluid inlets 48 and working fluid outlets 49. The valve units 14 are annular valve units and the working fluid inlets 48 and outlets 49 are annular galleries provided around the perimeter of the valve units (it will be understood that the inlets and outlets may be interchangeable when the fluid working machine is a pump-motor operable to function as a pump and/or a motor in different operating modes and that, in this case, the inlet/outlet terminology assumes that the fluid working machine is a motor or a pump-motor operating in motoring mode). The low pressure valves of the integrated valve units 14 coupled to the housing bores 12a, 12b and 12c of the first group 5 are in fluid communication with each other by a first common conduit 50 which intersects the outlets 49. It will be understood that, in order for the first common conduit 50 to intersect the outlets 49, the first common conduit 50 typically intersects the housing bores 12a, 12b, 12c in which the valve cylinder devices 13 of the first group 5 are provided. In addition, the high pressure valves of the integrated valve units 14 coupled to the housing bores 12a, 12b and 12c of the first group 5 are in fluid communication with each other by a second common conduit 52 which intersects the inlets 48. It will be understood that, in order for the second common conduit 52 to intersect the inlets 48, the second common conduit 52 typically intersects the housing bores 12a, 12b, 12c in which the valve cylinder devices 13 of the first group 5 are provided.

(21) The common conduits 50, 52 have longitudinal axes parallel to the axis of rotation 3 and are typically formed by single straight drillways extending through the cylinder block 1. The common conduit 50 extends between the low pressure valves of the piston cylinder devices of the first group 5, while the common conduit 52 extends between the high pressure valves of the piston cylinder devices of the first group. The longitudinal axes of the common conduits 50, 52 are offset from the first and third housing bores 12a, 12c of that group about the axis of rotation 3 in a first rotational sense (e.g. clockwise) and offset from the second housing bore 12b about the axis of rotation in a second rotational sense opposite the first rotational sense (e.g. anticlockwise) such that it has a circumferential position which is disposed circumferentially between the circumferential position of the second housing bore 12b and the circumferential positions of the first and third housing bores 12a, 12c. This is a space efficient arrangement which is made possible because the second housing bore 12b is axially offset from the first and/or third housing bores 12a, 12c and the second housing bore 12b is offset from the first and third housing bores 12a, 12c about the axis of rotation 3.

(22) By fluidly connecting the low pressure valves and the high pressure valves via respective (single) common conduits, fewer conduits need to be formed within the cylinder block 1, and importantly each conduit can be drilled in a single operation and thus manufacture is faster and less expensive. In addition, as the cams 30-34 drive, or are driven by, the pistons reciprocating in the housing bores 12 of each group at different phases, the common conduits 50, 52 can have smaller diameters than might otherwise be the case because they do not have to have capacity for the combined peak flows from or to all of the piston cylinder devices of that group.

(23) As the valve inlets and outlets are in the form of annular galleries, the orientation of the valve units 14 has little influence on the fluid communication of the valves with the common conduits 50, 52. However in alternative embodiments, the valve inlets/outlets may be directional (rather than annular galleries), for example the valve inlets and/or outlets may each comprise a single drilling (which may be perpendicular to the axis of rotation, for example). In this case, the valve units 14 need to be oriented and aligned with corresponding common conduits prior to securing in position, to ensure fluid communication therebetween.

(24) It may be that the second housing bore 12b of one or more of the groups 5-10 is canted with respect to the first and third housing bores 12a, 12c of that group such that the longitudinal axis of the second housing bore 12b (along which the piston reciprocating within the second housing bore 12b reciprocates) intersects with the longitudinal axis of the first and/or third housing bores 12a, 12c (along which the respective pistons reciprocate in the respective first and/or third housing bores) at the axis of rotation 3 when viewed along the axis of rotation. However, in some cases, the second housing bore 12b of one or more groups 5-10 may be canted with respect to the first and third housing bores 12a, 12c of that group such that the longitudinal axis of the second housing bore 12b intersects with the longitudinal axis of the first and/or third housing bores 12a, 12c at a point above the axis of rotation 3 (i.e. closer to the second 12b and first and/or third housing bores 12a, 12c than the axis of rotation 3 is to the second 12b and first and/or third housing bores 12a, 12c) when viewed along the axis of rotation. This allows more space to be provided for the common conduits 50, 52.

(25) The piston cylinder devices of each group 5-10 provide a number discrete service outputs, typically one per group. Accordingly, the common conduits 50, 52 typically extend to respective ports (not shown) provided at an end-plate (not shown) bolted to the front axial face 62 of the cylinder block 1. More specifically, one of the common conduits 50, 52 (which one depends on whether the fluid working machine is a pump, a motor or a pump motor operating in pumping or motoring mode) is connected to a source of fluid: a propel return, a common crankcase/tank or any other fluid source, while the other common conduit 50, 52 (again which one depends on whether the fluid working machine is a pump, a motor or a pump motor operating in pumping or motoring mode) is connected to a sink of fluid: propel out, work function out, universal out or any other fluid sink.

(26) It may be that more or less than three valve cylinder devices are provided in each group 5-10. It may be that there are more or fewer than four groups. In some embodiments, the second housing bore 12b of each group is offset from the first and third housing bores 12a, 12c of that group by an angle of (360/(m*n))° about the axis of rotation, where m is the number of groups and n is the number of housing bores per group (or, if different groups have different numbers of housing bores per group, it may be that n is the number of housing bores in the group with the greatest number of housing bores). In addition, to ensure that the pistons 24 of each group drive or are driven by the cams 30-34 at phases which are substantially equally spaced, the first and third cams 30, 34 may be offset from each other by an angle of 2*(360/(n))° in a first rotational sense (e.g. clockwise) and the second cam 32 may be offset from the first cam 30 in the said first rotational sense about the axis of rotation by an angle of ((360/(n))−α°) where a is the angle in degrees by which the second housing bore 12b is offset from the first and third housing bores 12a, 12c about the axis of rotation 3.

(27) The fluid working machine described above may be manufactured as follows. The cylinder block 2 is typically formed by casting or machining a central axial bore 4 through the centre of a monolithic billet of material, and the housing bores 12a-12c of each group are typically formed in the cylinder block 2 by drilling bores substantially radially through the billet with respect to the central axial bore 4, the bores being disposed about and extending outwards with respect to the axial bore 4. The housing bores 12a-12c may alternatively be cast in the billet with the central axial bore 4 before being subsequently drilled. As explained above, the first and third housing bores 12a, 12c of each group are axially offset from each other, and the second housing bore 12b is axially offset from the first and third housing bores 12a, 12c and the second housing bore 12b is offset from the first and third housing bores 12a, 12c about the central axial bore 4. The groups 5-10 of housing bores are spaced from each other about the central axial bore 4. In addition, the housing bores 12a-12c of each group are provided with a space-efficient nesting arrangement whereby the second housing bore has an axial extent which overlaps at least partly with axial extent of one, or the axial extents of both, of the first and third housing bores 12a, 12c.

(28) The common conduits 50, 52 are formed by drilling straight drillways through the cylinder block 2 between the housing bores 12a-12c of each group which extend parallel to the axial bore 4. A thread cutting tool is used to add the thread to the outer ends of the housing bores for mating with the corresponding thread on the integrated valve units 14. As described above, the longitudinal axes of the common conduits 50, 52 of each group are offset from the first and third housing bores 12a, 12c of that group about the axis of rotation 3 in a first rotational sense (e.g. clockwise) and offset from the second housing bore 12b of that group about the axis of rotation in a second rotational sense opposite the first rotational sense (e.g. anticlockwise) such that it is disposed circumferentially between the second housing bore 12b and the first and third valve housing bores 12a, 12c.

(29) Integrated valve units 14 are screwed into the respective housing bores 12a-12c of each group. Pistons 24 may be mounted to con-rods (which act as piston feet) coupled to (or resting on) the cams 30-34 of the crankshaft 2 such that the pistons 24 are in driving relationship with the cams 30-34, the crankshaft 2 is mounted in the axial bore 4 and the pistons 24 are reciprocably received by the housing bores 12a-12c of the respective groups 5-10. As explained above, the cams 30-34 of the crankshaft 2 are arranged (typically unevenly offset about the axis of rotation 3) such that they drive or are driven by the pistons 24 within each group at phases which are substantially equally spaced.

(30) It will be understood that, in some embodiments, the third housing bore 12c and associated valve cylinder device 13 and piston 24 may be omitted from each group 5-10. However, the third housing bore 12c and associated valve cylinder device 13 and piston 24 are preferably included in order to provide a substantially smooth output from each group 5-10.

(31) Further variations and modifications may be made within the scope of the invention herein described.

(32) Additional information, in particular additional features, embodiments and advantages of the present invention can be found in application PCT/EP2014/060897 that was filed at the European patent office as receiving office for a PCT-application on the very same date by the same applicants. The disclosure of said application is considered to be fully contained and incorporated in the present application by reference.