AU737023B2 - Rotary piston pump and method of operation - Google Patents

Description

WO 99/28629 PCTINZ98/00175 1 ROTARY PISTON PUMP AND METHOD OF OPERATION BACKGROUND OF THE INVENTION The present invention relates to a work unit such as a blower or compressor and particularly when acting as a supercharger, although as will be appreciated by persons skilled in the engineering arts, the present invention can find application in any work producing unit, whether this be a pump, compressor, motor, engine or the like. However, merely for simplicity and ease of description, the term "work unit" will be used throughout this specification. It is to be understood, however, that all types of work producing units are included within that term for the purposes of this specification.

To the present time, numerous proposals have been put forward for producing work output, many of which have succeeded in being commercially developed, but many of which have been found to be practically not feasible. The previous proposals which have reached commercial production have all, to a greater or lesser extent, suffered from various disadvantages in respect of their performance and/or cost and complexity. Many engines have suffered badly from exhaust emissions which no longer satisfy the strict clean air requirements of many jurisdictions to the extent that in some countries such as the United States of America, there is a substantial move towards electrically powered engines, solely because of the clean air regulations. This is despite the major disadvantages which are inherent in electrically powered units especially when used for transportation purposes.

Furthermore, many engines have been based on the Otto engine, which while it has proved a satisfactory power unit in the past, suffers from various disadvantages including the difficulty in providing a sufficiently clean exhaust emission and in effectively transmitting the power from the pistons to the crank shaft.

In the case of superchargers for automotive engines, these have been generally large and inefficient.

WO 99/28629 PCT/NZ98/00175 2 OBJECTS OF THE INVENTION It is an object of the invention to provide a work unit as hereinbefore defined and/or a method of operating a work unit which will overcome, or at least obviate, problems in work units, or methods of operating same to the present time, or which at least will provide the public with a useful choice.

Further objects of this invention will become apparent from the following description.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a work unit (as herein defined), including a housing, a shaft rotatable about an axis within said housing, at least one piston having a stationary orientation relative to said axis but which rotates with said shaft about said axis, the or each said piston being part cylindrical and being concentrically mounted relative to the, or a respective, part cylindrical recess provided in said shaft so that an external arcuate surface of said piston cooperates with an internal arcuate surface of said shaft recess as the piston and shaft move relative with one another, a recess in said piston which forms a chamber for at least part of a cycle of the work unit to receive a charge of a fluid, an internal arcuate surface of said housing being concentrically provided relative to the said axis, so that as the shaft rotates, the arcuate external surface of the piston can cooperate with the internal arcuate surface of said housing as work is performed.

According to a further aspect of the present invention, a work unit as defined in the paragraph immediately above has said piston recess with an additional recess to retain said charge of fluid for an expansion part of said cycle.

According to a further aspect of the present invention, a work unit is as defined in either of the paragraphs immediately above wherein the or a further recess of said piston is adapted to receive a charge of fluid in one WO 99/28629 PCT/NZ98/00175 3 cycle or part of a cycle and to transfer it to an opposite side of the housing on the next cycle or part of a cycle.

According to a further aspect of the present invention, there is provided a method of operating a work unit (as herein defined) including providing a housing and mounting a shaft to rotate about an axis within said housing, providing at least one part cylindrical piston and mounting the piston to rotate with the shaft while maintaining a stationary orientation relative to the axis, concentrically mounting the piston relative to a part cylindrical recess provided in the shaft so that an external arcuate surface of the piston can cooperate with an internal arcuate surface of the shaft recess as the piston and shaft move relative with one another, providing a recess in the piston which forms a chamber for at least part of a cycle of the work unit to receive a charge of fluid, further providing an internal arcuate surface for the housing concentric relative to the axis which can cooperate with the external arcuate surface of the piston as the piston moves relative to the housing with the shaft and work is performed.

According to a further aspect of the present invention, a method as defined in the paragraph immediately above includes providing the or each piston with a pair of said recesses, one of which is adapted to provide a portion of a fluid being exhausted to form part of a fluid which has been induced and to provide a portion of said fluid which has been induced as part of said fluid being exhausted.

According to a further aspect of the present invention, a work unit (as herein defined) and/or a method of operating a work unit (as herein defined) is substantially as herein described, particularly, but not exclusively, with respect to the accompanying drawings.

Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description given by way of example of possible embodiments thereof, and in which reference is made to the accompanying drawings.

WO 99/28629 PCT/NZ98/00175 RRIEF DESCRIPTION OF THE DRAWINGr FIGURE 1: FIGURE 2: FIGURE 3: FIGURES 4-15: shows diagrammatically a cross sectional view of a work unit operating as an engine according to one possible embodiment of the invention; shows diagrammatically an end view of an engine of Figure 1; shows diagrammatically an end view of an engine according to one possible embodiment of the invention including the gearing which may be utilised; show very diagrammatically the operation of an engine according to one possible embodiment of the invention; shows very diagrammatically the operation of a pump or compressor according to one possible embodiment of the invention; shows diagrammatically an exploded view of the pump or compressor of Figure 16; shows diagrammatically front and cross-sectional views of the pump or compressor of Figure 16 and 17; shows diagrammatically a side exploded view of the pump or compressor of Figures 16 to 18; and shows diagrammatically a front view of the gearing assembly of Figure 19.

FIGURE 16: FIGURE 17: FIGURE 18: FIGURE 19: FIGURE 20: WO 99/28629 PCT/NZ98/00175 DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION The present invention will initially be described with particular reference to its use in a two stroke rotary engine. However, as mentioned previously, this is by way of example only and it will be readily apparent to those skilled in the engineering arts that other work producing units such as pumps, compressors and the like could embody the present invention with any modifications which may be appropriate to suit a particular purpose.

An embodiment suitable for use as a pump or compressor is described in respect of Figures 16 to Referring to Figures 1 to 15 of the accompanying drawings and initially particularly with respect to Figures 1, 2 and 3, an engine referenced generally by arrow 50 has a main housing 5 and end housings 27. A main shaft 1 extends through the housing 5 between main shaft ends 2 and is provided with main shaft bearings 6. A pair of pistons 3 are in this embodiment (one, or more than two, pistons 3 could be used in other embodiments) are mounted diametrically opposite about the main shaft 1 on respective piston shafts 4 and with piston shaft bearings 7. Seals 8 and 9 are respectively provided for the main shaft 1 and the piston shafts 4.

The main shaft 1 is provided with gearing 10 which in this embodiment is connected through spur timing gear 12 with piston shaft gearing 11. A gear cover 14 provided with a gear cover seal 15 is secured in position by gear cover studs 13. Lubrication for the gearing is provided through oil lubrication inlet 16 with the lubrication oil then leaving through oil lubrication outlet 17 for filtering and return. The oil provides main bearing lubrication at 18 and gear lubrication at 19 with pipe 20 providing for lubrication to be directed to an oil centrifuge chamber 21 to provide rotor bearing lubrication at 22 utilising rotor centrifuge oil hole 23. Rotor centrifuge gas hole 24 allows the escape of any build up of gases and any oil which passes centrifuge hole 23 and seal 9. An oil collection gallery provides a sump from which oil can be recovered by means of scoop 26.

In the particular embodiment shown, the engine 50 has inlet ports 28 positioned adjacent outlet ports 29. Aperture 30 provides a gas bypass outlet through the end housings 27.

WO 99/28629 W09928629PCTINZ98/00175 6 As will be seen, therefore, the main shaft 1 in this embodiment has a pair of opposed radial cuts or part cylindrical recesses 55 in it to accommodate respective concentric part cylindrical pistons 3 which can rotate with the shaft 1 with a prescribed tolerance between the arcuate external surfaces of the pistons 3 and the recesses 55 as relative movement between those surfaces occur, the shaft 1 and the rotor pistons 3 all operating within the chamber defined within the main housing The pistons 3 are in the nature of rotors in that they have a rotational movement relative to the main housing 5 and there is rotational movement of the shaft 1 relative to the pistons 3. The pistons 3, however, themselves, as will become clear later in this description, have a stationary orientation relative to the axis of the shaft 1 and the housing 5, this being substantially horizontal in the disposition of the work unit 50 as shown in the drawings. The pistons 3 are each part cylindrical with arcuate diametrically opposed recesses 51, 52 and arcuate external surfaces R4 which can cooperate with the concentrically radiused arcuate internal surface R5 of the recesses or chambers 55 on opposed sides of the main shaft 1. The term "part cylindrical" is used throughout the specification to define a shape which is essentially cylindrical but has had portions removed or omitted. As the main shaft 1 rotates, the internal surface R5 sweeps past the surfaces R4 of the pistons 3 to work on the fluid contained within the chamber defined at any time between the respective piston 3 and the shaft 1. The chamber 5 on both of its opposite sides in the embodiment shown in Figure 2, itself has respective radiused arcuate surfaces R3 concentric relative to the axis of the shaft 1 so that, (see Figure 9 for example) the arcuate surface R4 of the piston 3 can sealably cooperate with the arcuate surface R3 in moving the fluid charge before it in the embodiment of Figure 2. Additional radiused surfaces R1 and R2 are provided on each side of the radius surface R3, and each side of the blades or projections 53, 54, to sealably engage with the edges or tips 48 of the rotor pistons 3 as they sweep around the internal surfaces R 1 and R 2 The blades or projections 53, 54 are required to sweep the chambers formed by the recesses 51, 52 as they move past. The radial relationship between the radii of recesses 51, 52, the radii, R1, R2, R3, the piston WO 99/28629 PCT/NZ98/00175 7 radius R4 and the spacing of the axes of shafts 2 and 4 is, therefore, important.

Assuming the spacing between the axis of shafts 2 and 4 is Xmm, then X R4 R3. The radii of the piston recesses 51, 52 will equal the distance and the respective centre of curvature will be displaced by the same distance.

The radii R1 and R2 will also equal the distance X with the center of curvature moved vertically and rotated by a few degrees relative to the axes defined by the piston tips or edges 48.

In the operation of the work unit 50, as an engine especially, the fluid charge as it ignites and expands will need to be retained as the top recess 51 sweeps past the blade 53. For that purpose, an additional recess 56 is shown in outline in Figures 1 and 2 extending axially and longitudinally of the piston 3 and its main recess 51.

Additionally, in this particular embodiment, the top surface of piston recess 51 is shown to extend deeper towards the shaft 4 so that a clearance is provided between the upper surface of the piston 3 as it passes the top blade 53. This again retains some volume in the top recess 51 despite the sweeping action of the top blade 53. The additional recess 56 can be of any shape or size extending to be within the boundary defined by the piston tips 48. It will be appreciated that no such additional recess 56 is required for the bottom piston recess 52.

The main shaft 1 has its main shaft ends 2 supported by bearings 6 within its end housings 27, the bearings 6 being lubricated and cooled by the lubrication channel 18.

The pistons 3 are mounted on the piston shafts 4 provided with the piston shaft bearings 7 and held by the main shaft ends 2.

The piston bearings 7 are lubricated and cooled by the oil fed by centrifugal action fed through a lubrication pipe 20, spun into the centrifuge chamber 21 and passing through the rotor centrifuge oil hole 23. The seal WO 99/28629 PCT/NZ98/00175 8 9, which may be of ceramic or othe.r material, can control the oil so that the oil flow is centrifuged out of the oil hole 23 to form the chamber from which any oil seepage can be centrifuged through gas hole 24, together with any blow by gas from within the housing 5. In this embodiment, the oil lubrication for the gearing may be derived from the main shaft gear to be spread to all the other gears and to be finally centrifuged to the gear box cover 14. All the oil may suitably enter the gear box through the oil inlet 16 to be collected in the oil collection gallery or sump 25 and to be picked up by the oil recovery scoop 26 and drawn out into the oil suction pipe 17.

It is envisaged that the induction of the engine will run vacuum to the oil reservoir to draw off oil through the scoop 26, although a separate vacuum pump could be provided, if necessary.

The engine 50 is shown provided with a spark plug 43 and a fuel injector 44. Of course, a plurality of spark plugs and fuel injectors may be used in alternative embodiments. In this particular embodiment, the engine may be liquid cooled through cooling ducts 46.

It will be appreciated that the engine 50 in this particular embodiment may operate as a two stroke engine being piston ported but firing twice for every rotation per cylinder instead of only once. Alternatively, the engine may fire as many times per cylinder as may be required. As will also be appreciated from the description herein below particularly, tuning for the induction and exhaust may be unnecessary in that the engine 50 operates with positive induction and the exhaust gases are swept out from the engine 50 by the pistons 3.

Most importantly, the present invention provides a non-reciprocating engine 50 and as will be appreciated by those skilled in the engineering arts, the engine 50 may, therefore, be considered as being an Otto engine, but with the main shaft 1 replacing the normal crank shaft and with the usual con rods and cylinders omitted. It will also be appreciated that as the main shaft 1 of the engine 50 may extend the entire length of the engine it may be driven or drive from either end. Additionally, as will be WO 99/28629 PCT/NZ98/00175 9 appreciated from the brief description of the lubrication of the engine 50, in a preferred embodiment, it is substantially an oiless engine in that the pistons 3 are not required to contact the shaft 1 or the inner surface of the housing 5, but instead can operate with prescribed clearances, relying on the fluid flow through the engine to effectively provide seals between the component parts. These clearances may be maintained as appropriate and by appropriate cooling of the engine 50 such as by liquid cooling through ports 46 in the present embodiment.

In that the engine 50 of present invention avoids any reciprocating action, mechanical loss is minimised. Additionally, as in a preferred embodiment, there are no piston rings required on the pistons 3, frictional loss is also minimised.

Furthermore, as will be appreciated from the description herein below particularly, as from each cylinder two firing strokes are provided for each revolution, and as with the firing in one embodiment a 2100 rotation can be achieved before exhausting, in the engine 50 of the illustrated embodiment 4200 of power can be achieved from firing for each revolution.

It will also be appreciated by those skilled in the engineering arts that the engine 50 can allow the cylinder pressure to maintain a squared position back to the main axis of the shaft 1 for most of the working or power stroke. In this regard, as the angle from the top of each of the pistons 3 back to the central axis decays, the pistons 3 uncover or expose the side of the piston 3 to enable the pressure to maintain a good angle for conversion of that pressure into mechanical work.

Referring now to Figures 4 to 15, the shaded portions of the drawings are intended to indicate very diagrammatically the charges of air, fuel/air or exhaust which result from an engine cycle.

In Figure 4, the pair of part cylindrical pistons 3 are each shown very diagrammatically mounted on their respective shafts 4 about the main shaft 1 with the main shaft 1 and the pistons 3 being able to rotate within the main housing 5. The pistons 3 are each shown provided with respective WO 99/28629 PCTINZ98/00175 radiused recesses or scallops 51, 52 on opposed sides of the rotor pistons 3. Each of the pistons 3 is held by gearing so as to maintain its substantially horizontal position or orientation relative to the axis of the shaft 1 and housing 5. The pistons 3 engage with prescribed clearances, with the respective concentric radiused part cylindrical recesses provided on opposed sides of the main shaft 1, and with the arcuate inner surfaces R1, R2, R3 of the housing In Figure 4, at the start of a cycle of the engine 50, a charge of air 31, shown shaded, has been induced through inlet 28 into the chamber defined by the recess 52 of the bottom piston 3 and the inner surface of the housing 5. It will be noted that adjacent the inlet port 28 and between the inlet port 28 and the exhaust port 29, is the projecting portion or blade 54 of the wall of the housing 5, this serving to provide a demarcation point between the induction and the exhaust parts of the cycle and assisting in defining the chamber into which the charge of air 31 is induced. In Figure the charge of air 32, again shown shaded, has increased in volume as the main shaft 1 rotates, in this case through 90 0 As the piston 3, with its consistent orientation, moves through the cylinder 47, the induced charge 32 provides a seal behind the piston 3.

In Figure 6, as the piston 3 moves towards the top of the housing the piston 3, with the shaft 1, creates a fresh air pocket 33, which as shown in Figure 7, is sealed from the cylinder 47 in which the rest of the charge of induced air remains, as a fuel injection 35 occurs from the fuel injector 44. At the top of the housing 5 is shown the further projecting portion or blade 53 of the inner wall of the chamber 5, in this case, adjacent the spark plug 43. The projecting portion or blade 53 defines a transition between the induction and firing and compression and exhaust sides of the engine.

In Figure 8 the charge of fresh air 33 is shown having now been transferred to the exhaust side of the engine 50 and the charge of fuel/air 36 is now being compressed as the other piston 3 pushes the charge 36 in front of it. In Figure 9 the fuel/air charge 37 has been further compressed while the fresh air charge 33 is continuing to be moved in front of the other piston 3. In Figure 10 a further charge of fresh air 33 is shown having WO 99/28629 PCT/NZ98/00175 11 been created by the upper rotor piston 3 while the compressed fuel/air charge 38 is ignited by the spark plug 43. At this time while the ignition is occurring the original fresh air pocket 33, as is shown in Figure 10, is being discharged through the outlet 29. It will be appreciated that the engine is therefore achieving a transfer of fresh air between the induction and exhaust sides of the engine and is thereby enabling a contribution to the exhaust of the fresh air. This will be substantially reducing, at least in respect of the relevant ratios, the unwanted components of the exhaust emissions.

Also, fresh air coming in contact with carbon monoxide and hydrocarbons in the exhaust produces an oxidation which will considerably reduce unwanted pollutants.

In Figure 11 the ignited charge 39, together with the second fresh air charge 33, are shown being moved through the right hand cylinder space 47 as the charge 39 expands. The object of good combustion chamber design is to create the condition in the cylinder for the air and fuel to be thoroughly mixed and then excited into a highly turbulent state so that the burning of the charge will be completed in the shortest possible time and to burn as completely as possible. The beginning of turbulence begins after the induction port is completely sealed and during the start of the compression phase, when the pocket of pressurized exhaust gas exits into the induction charge creating vortices that interact to cause viscous shear interaction which will speed up the rate of heat transfer and fuel mixing.

As compression continues and the ignition point is reached, see Figure the flame front is broken by the protruding portion or blade 53 that the combustion chamber passes through during the burning phase thus increasing the turbulence and the speed of the flame front travel thereby preventing overheating of the end mixture. It will be appreciated that the fresh air charge 33 in all these instances also assists in the cooling of the engine In Figure 12 the charge 40 as part of the power stroke now has the piston 3 at 900 while at the position shown in Figure 13 the top of the bottom piston 3 is shown capturing a pocket of exhaust gas 41 which in Figure 14 is then shown transferred to the induction side of the engine.

WO 99/28629 PCT/NZ98/00175 12 The remainder of the exhaust gas 42 can, as shown in Figure 1 5, then be swept out through the exhaust port 29 by the piston 3. It will be appreciated that the pocket 41 of the exhaust gas, being transferred to the induction side after the inlet port 28 is closed so as to not displace valuable induction air, is again contributing to a reduction in unwanted exhaust emissions in that the charge 41 will be fed back to be included in the next ignition charge. Furthermore the exhaust gas charge 41 will be able to contribute its thermal energy to the induction charge to improve the thermal efficiency of the engine 50. The three offending pollutants released by an engine in the atmosphere are CO, HC and NOx. As the chemically correct air-fuel mixture is introduced to combustion, carbon monoxide and hydrocarbon products of combustion are considerably reduced, but at the expense of oxides of nitrogen increasing. Further leaning of the mixture to around 20:1, while that brings about a reduction in the production of NOx, creates instability in combustion. By recycling the exhaust gas back through the engine, the stoichiometric values can be kept to assist with the reduction of CO and HC while at the same time reducing the production of NOx.

The recycling of exhaust gas through the engine 50 does not displace the full induction charge during the wide open throttle setting as in most other types of engines and the exhaust gas recycling is always proportional to the throttle settings. Testing has shown that NOx can be reduced by 88% with the recirculation of 15% or more of the exhaust gas.

As mentioned previously, although a pair of pistons 3 are shown in this embodiment, it is envisaged that in its various possible embodiments as envisaged by the applicant, a single piston 3 or more than two pistons 3 could be used.

Referring now to Figures 16 to 20, a further embodiment of the invention operates as a pump or compressor and is particularly suitable for use as a supercharger for an engine.

As is well known, superchargers are used in various types of engines to supply air or a charge of fuel at a higher than atmospheric pressure.

WO 99/28629 PCT/NZ98/00175 13 The present invention may have a cylinder or chamber with a volume less than the volume being displaced per rotation. This means, of course, that a pump or compressor of the present invention can be of a substantially small size with the ongoing benefits that this can, therefore, provide, particularly as in an automobile engine compartment, space is at a premium. It is envisaged that a supercharger according to the present invention could be, for example, no larger than a typical automobile alternator.

Referring firstly now to Figure 1 6 of the accompanying drawings, a pump or compressor according to one embodiment of the invention is shown very diagrammatically with its main shaft 100 extending through a housing 150 and with a pair of part cylindrical pistons 103 mounted on respective rotor shafts 104. Each piston 103 is mounted within a respective opposed radial cut or part cylindrical recess 155 provided in the main shaft 100 and is held in its stationary orientation relative to the axis of the shaft 100 engaging the arcuate surfaces of the recess 155 and/or the housing 150, with the appropriate working clearances, as the main shaft 100 is rotated.

Figure 16 illustrates diagrammatically the positioning of the pistons 103 relative to the main shaft 100 through one half of revolution of the main shaft 100. The sequence is illustrated from left to right and from top to bottom in Figure 16. It is seen that as each piston 103 moves relative to the main shaft 100, from an initial position shown at the top left hand illustration, the volume of fluid on each side of the housing 150 introduced through a respective one or more inlets 160 will be swept in front of a respective leading face of a piston 103 to exit through a respective one or more exhaust ports 161. A complete revolution of the main shaft 100 will, therefore, result in both sides of the housing 150 being swept by a respective piston 103. The pump or compressor is, therefore, displacing its capacity in half a revolution, so that in one revolution, it has displaced twice its capacity.

In Figure 17, one particular embodiment of the invention is shown diagrammatically in an exploded view with the pistons 103 positioned for rotation with the main shaft 100 and within a housing 150. One set of WO 99/28629 PCT/NZ98/00175 14 exhaust ports 161 are shown provided with the inlet ports 160 being diametrically opposite and an outlet pipe 200 and an inlet pipe 201 being able to be mounted either side of the housing 150. A front cover 202 is also shown provided with air flow ports 203, 204. A front shaft assembly 205 includes bearings 206 for the respective piston shafts 104 and is provided with appropriate bolt holes 207 to enable the front assembly to be bolted to the centre shaft 100.

At the bottom left hand corner of Figure 17, a diagrammatic representation of the front manifold 208 is shown.

In Figure 18, the front and side cross-sectional views show the front manifold 208 with the inlet and outlet pipes 201 and 200 and with the back manifold 209 extending around a gear assembly 210 with rotor gears 211 connected with respective pistons 103 and a main gear 212. Air seals may suitably be provided in the areas referenced generally by arrow 213.

As seen particularly in Figures 19 and 20, the piston gears 211 mesh with rotating spur gears 214 and with a stationary main gear 212. It will be appreciated that the gearing connecting the pistons with the main shaft in this and the earlier embodiments is not being used as a drive mechanism but merely to maintain the orientation of the pistons. This gearing, therefore, ensures that the pistons 103 will, as shown particularly in Figure 16, maintain a fixed disposition, substantially horizontal as shown, relative to the housing 150, as the main shaft 100 rotates. A main bearing is provided for the rear shaft assembly 216 and appropriate bearings provided for the shafts associated with the other gears. In Figure 19, a main bearing 215 displaced from its actual position is shown also provided for the front shaft assembly 205 including the drive shaft 217.

The ducting of the inlet and outlet fluid flow paths can be arranged as appropriate, so as to accommodate various types and sizes of engines for example. Where particular ducting and ports are required for a particular type of engine such as a V6 or V8, then the internal ducting of the housing 150 and the ducting of the front and back manifolds 208, 209 will be arranged accordingly.

WO 99/28629 PCT/NZ98/00175 Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope or spirit of the invention, as defined in the appended claims.

Claims (14)

1. A work unit (as herein defined), including a housing, a shaft rotatable about an axis within said housing, at least one piston having a stationary orientation relative to said axis but which rotates with said shaft about said axis, the or each said piston being part cylindrical and being concentrically mounted relative to the, or a respective, part cylindrical recess provided in said shaft so that an external arcuate surface of said piston cooperates with an internal arcuate surface of said shaft recess as the piston and shaft move relative with one another, a recess in said piston which forms a chamber for at least part of a cycle of the work unit to receive a charge of a fluid, an internal arcuate surface of said housing being concentrically provided relative to the said axis, so that as the shaft rotates, the arcuate external surface of the piston can cooperate with the internal arcuate surface of said housing as work is performed.

2. A work unit as claimed in claim 1 wherein said piston recess has an additional recess to retain said charge of fluid for an expansion part of said cycle.

3. A work unit as claimed in Claim 1, wherein the or a further piston recess is adapted to receive a charge of fluid in one cycle or part of a cycle and to transfer it to an opposite side of the housing on the next cycle or part of a cycle.

4. A work unit as claimed in any one of the preceding claims, wherein said internal surface of said housing includes at least one inwardly directed projection or blade which is positioned between one or more inlet and one or more outlet ports to extend into the piston recess as it moves relative thereto. A work unit as claimed in Claim 4 when operating as an engine, wherein said housing has at least one of said inwardly directed projections or blades positioned so as to be adjacent and in front of an ignition means so that a flame front can be disturbed by that said projection or blade.

WO 99/28629 PCTINZ98/00175 17

6. A work unit as claimed in any one of the preceding claims, wherein gearing interconnects said at least one piston and said shaft so as to synchronise their respective positions and to hold said piston(s) in said stationary orientation relative to the axis.

7. A work unit as claimed in any one of the preceding claims and in which at least one pair of said pistons is provided diametrically opposite one another and movable within respective said recesses in said shaft.

8. A work unit as claimed in any one of the preceding claims, wherein an edge or tip is defined on each side of said external arcuate surface of said piston, each of which edge or tip being engageable with a further respective internal arcuate surface of said housing.

9. A work unit as claimed in Claim 8 when dependent on Claim 4 or Claim 5, wherein one of said further internal arcuate surfaces is provided on each side of the or each projection or blade.

10. A work unit (as herein defined), as claimed in Claim 9 in which on opposite sides of said housing is one of said internal arcuate surfaces, said shaft has a pair of diametrically opposed part cylindrical recesses in each of which is movable a respective said piston, each said piston being provided with a pair of diametrically opposed said recesses, each of said pistons being mounted on a respective support shaft, said support shafts and said shaft being interconnected by respective gears to hold said pistons in said stationary orientation relative to said axis while enabling a respective said part cylindrical recess in said shaft to cooperate with respective external arcuate surfaces of said piston.

11. A method of operating a work unit (as herein defined) including providing a housing and mounting a shaft to rotate about an axis within said housing, providing at least one part cylindrical piston and mounting the piston to rotate with the shaft while maintaining a stationary orientation relative to the axis, concentrically mounting the piston relative to a part cylindrical recess provided in the shaft so that WO99/28629 PCT/NZ98/00175 18 an external arcuate surface of the piston can cooperate with an internal arcuate surface of the shaft recess as the piston and shaft move relative with one another, providing a recess in the piston which forms a chamber for at least part of a cycle of the work unit to receive a charge of fluid, further providing an internal arcuate surface for the housing concentric relative to the axis which can cooperate with the external arcuate surface of the piston as the piston moves relative to the housing with the shaft and work is performed.

12. A method as claimed in Claim 11 and further including providing for the or each piston, a pair of said recesses, one of which is adapted to provide a portion of a fluid being exhausted to form part of a fluid which has been induced and to provide a portion of said fluid which has been induced as part of said fluid being exhausted.

13. A method of operating a work unit (as herein defined) substantially as herein described with reference to Figures 1 to 3 and/or Figures 4 to and/or Figures 16 to 20 of the accompanying drawings.

14. A work unit (as herein defined) substantially as herein described with reference to Figures 1 to 3 and/or Figures 4 to 15 and/or Figures 16 to 20 of the accompanying drawings.