WO2012168696A2

WO2012168696A2 - A rotary power device

Info

Publication number: WO2012168696A2
Application number: PCT/GB2012/051221
Authority: WO
Inventors: Kambiz Morteza EBRAHIMI; Antonios PEZOUVANIS
Original assignee: University Of Bradford
Priority date: 2011-06-07
Filing date: 2012-05-31
Publication date: 2012-12-13
Also published as: GB201109505D0; WO2012168696A3

Abstract

A rotary power device comprising a stationary block; at least one cylinder defining a cylinder axis formed in the block; a piston slideably supported in the cylinder; a cylindrical crankshaft arranged to rotate about a crankshaft axis which is parallel to the cylinder axis; and a connecting rod attached at a first end to the piston and coupled at a second end to the crankshaft by at least one piston bearing; wherein the crankshaft comprises a curved annular track defining first and second axially spaced bearing surfaces for engagement with the piston bearing.

Description

A ROTARY POWER DEVICE

The present invention relates to a rotary power device and more specifically to the crank shaft design of a five stroke internal combustion engine. However, the invention is applicable to other forms of rotary machine comprising a piston and cylinder, such as a pump for example.

Conventional gasoline and diesel internal combustion engines typically use a four stroke cycle; the four strokes referring to intake, compression, combustion (power) and exhaust strokes that occur during two crankshaft rotations per working cycle of the engine. The working cycle begins at Top Dead Centre (TDC) when the piston is at its upmost position and furthest away from the axis of the crankshaft. A stroke refers to the full travel of the piston from Top Dead Centre (TDC) to Bottom Dead Centre (BDC).

During the intake or induction stroke, the piston descends from TDC to BDC, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close. With both intake and exhaust valves closed, the piston returns to TDC compressing the fuel-air mixture and increasing the cylinder pressure and temperature. This is known as the compression stroke. While the piston is close to TDC, the compressed air-fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting significant pressure from the combustion of the compressed fuel-air mixture drives the piston back down towards BDC with significant force. This is known as the power stroke, which is the main source of the engine's torque and power. During the exhaust stroke, the piston once again returns to TDC while the exhaust valve is open forcing the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s). The working cycle is then repeated. However, the four stroke Otto cycle' only provides a single power stroke for two turns of the crankshaft which is not ideal. Increased engine efficiency requires an increased expansion ratio whilst increased power density requires an increased compression ratio. However, the compression and expansion ratios are the same as defined and limited by the crankshaft design.

The 'Atkinson' cycle attempts to improve engine efficiency. The design of the crankshaft of 'Atkinson cycle' engines allows the expansion ratio to differ from the compression ratio with a longer power stroke than the compression stroke resulting in greater thermal efficiency. However, the power density of such an engine is sacrificed.

Furthermore, as described above, combustion of the air-fuel mixture occurs partly during the end of the compression stroke and partly during the start of the power stroke when the ignited fuel expands. This is undesirable as part of the combustion is being compressed which results in lost work due to the additional work required to compress part of the combustion and in addition this combustion part has not produced useful work in the expansion/power stroke. Also, part of the combustion is lost while the fuel-air mixture is being ignited which could otherwise be used to force the piston downwardly towards BTC to provide useful power and torque to the crankshaft. These losses undesirably further contribute to engine inefficiencies.

Such engines also comprise a conventional crankshaft and connecting rod arrangement wherein the length of each stroke is limited by the length of the connecting rod and conventional crankshaft design. Friction losses are also undesirably high with a conventional arrangement and the lateral forces on the piston resulting from the motion of the crankshaft/connecting rod undesirably require a large piston skirt to compensate for these relatively high later forces and displacements of the piston in the cylinder during use. Furthermore, such an arrangement requires a relatively large space for at least the crankshaft to rotate and end bearings to mount. A first aspect of the present invention provides a rotary power device comprising:

- a stationary block;

- at least one cylinder defining a cylinder axis formed in the block;

- a piston slideably supported in the cylinder;

- a cylindrical crankshaft arranged to rotate about a crankshaft axis which is parallel to the cylinder axis; and

- a connecting rod attached at a first end to the piston and coupled at a second end to the crankshaft by at least one piston bearing;

wherein the crankshaft comprises a curved annular track defining first and second axially spaced bearing surfaces for engagement with the piston bearing.

The device is adapted for use as an internal combustion engine but may conveniently and easily be adapted for use as a compressor, pump or generator, for example. For an internal combustion engine, fuel flow and ignition means are provided to charge the cylinder and power is taken from the crankshaft which is driven in a rotary manner by the piston(s) which is oscillating in a linear manner. For a pump, an inlet and an outlet are provided for liquid to flow into and out of the cylinder and an external power source is provided to the crankshaft to drive the same and the piston(s). Alternatively, the crankshaft may be configured to be a rotor which corresponds with a stator to provide an electrical generator. Further alternatively, the device may be a hybrid of differing applications, e.g. some of the cylinders of a multiple-cylinder device may be adapted to power the crankshaft whilst a number of other cylinders may be adapted to pump liquid, for example.

Where the device is an internal combustion engine, ignition of fuel in the cylinder forces the piston and stem towards the crankshaft. The piston bearing is thereby urged to follow the curved track but is prevented from doing so because of the constraint of the piston/cylinder arrangement. The crankshaft is therefore caused to rotate about its axis and the power or torque is transferred as desired by known means, e.g. to a wheel of a vehicle via a differential. The piston bearing allows the linear motion of the piston to be transformed into rotary motion of the crankshaft, and vice versa, whilst allowing for power transmission from the piston to the crankshaft. Suitably the curved annular track of the crankshaft may be selectively adapted to define a desired piston path.

Preferably the track is adapted to provide a five-stroke rotary internal combustion engine for optimum engine efficiency. Suitably the track defines five separate strokes for a single revolution of the cylindrical crankshaft, namely intake, compression, combustion, expansion and exhaust strokes. Defining a separate combustion stroke desirably eliminates the losses caused by the combustion stage otherwise overlapping the compression and expansion strokes as in the case of a conventional four-stroke engine, as described above.

Preferably a minor portion of the track corresponding to the combustion stroke defines substantially flat first and second bearing surfaces having zero slope angle thereby to ensure the cylinder volume is kept constant during the combustion stroke. This has the effect of increased cylinder pressure as the cylinder temperature produced during combustion increases resulting in increased power transmission from the piston to the crankshaft during the expansion stroke and thereby improving engine efficiency.

Suitably the track may be adapted to define a relatively long and gradual intake stroke. This is most suitable where the device is a naturally aspirated internal combustion engine. Suitably the portion of track corresponding to the intake stroke is from 30 to 60% of a crankshaft revolution. Preferably the portion of track corresponding to the intake stroke is approximately 50% of a crankshaft revolution. This has the effect of an increased amount of air drawn into the cylinder during the intake stroke thereby allowing for a more efficient combustion. Suitably the track may be adapted to define a two-stage compression stroke which follows the intake stroke.

Suitably a first portion of the track relative to the direction of crankshaft rotation and corresponding to a first stage of the compression stroke defines a relatively shallow slope angle to create a relatively slow and gradual piston movement. This allows for maximum heat transfer from the relatively hot cylinder wall to the relatively cold air inside the cylinder and has the effect of cooling the cylinder wall whilst increasing the temperature of the air prior to combustion of the air-fuel mixture and thereby the cylinder pressure. Suitably the portion of track corresponding to the first stage of the compression stroke is from 10 to 15% of a crankshaft revolution. Preferably the portion of track corresponding to the first stage of the compression stroke is 12.5% of a crankshaft revolution. Suitably a second portion of the track relative to the direction of crankshaft rotation and corresponding to a second stage of the compression stroke defines a relatively steep slope angle to create a relatively quick piston movement and thereby fast compression. Preferably the track is adapted so that the second stage of compression begins when the air in the cylinder has approximately reached the temperature of the cylinder wall. Suitably the portion of track corresponding to the second stage of compression is from 7.5 to 15% of a crankshaft revolution. Preferably the portion of track corresponding to the second stage of the compression stroke is 9.72% of a crankshaft revolution. As described above, preferably the track is adapted so that during the combustion stoke, following the compression stroke, the cylinder volume is kept constant to effect an increase in cylinder temperature and thereby cylinder pressure prior to the expansion stroke. Suitably the portion of track corresponding to the combustion stroke is from 1 to 5% of a crankshaft revolution. Preferably the portion of track corresponding to the combustion stroke is 2.8% of a crankshaft revolution. Preferably the track is adapted to define relatively short expansion and exhaust strokes so that a relatively large portion of the annular track may suitably correspond to the longer intake stroke as described above. Preferably the portion of track corresponding to the expansion stroke is from 7.5 to 15%. Suitably the portion of track corresponding to the expansion stroke is 11.1% of a crankshaft revolution.

Suitably the portion of track corresponding to the exhaust stroke is from 10 to 15% of a crankshaft revolution. Preferably the portion of track corresponding to the exhaust stroke is 13.9% of a crankshaft revolution.

Suitably the annular track may be selectively adapted to affect a desired stroke length and limits thereof. The track may be adapted so that the cylinder volume swept by the piston during the compression stroke is greater than the volume swept during the preceding intake stroke. Preferably the volume swept by the piston during the compression stroke is around 20% greater than the volume swept during the intake stroke. This has the effect of increasing the pressure in the cylinder prior to combustion and thereby increasing the efficiency of the engine. Suitably the track is adapted so the piston finishes the compression stroke at an effective TDC which is further along the cylinder or 'higher' than the effective TDC when the piston began the intake stroke.

Suitably the track may be further adapted so that the cylinder volume swept by the piston during the expansion stroke is greater than the volume swept during the compression stroke. Preferably the volume swept during the expansion stroke is around 50% greater than that during the intake stroke. Preferably the volume swept during the expansion stroke is around 30% greater than that during the compression stroke. Suitably the effective BTC of the expansion stroke is further along the cylinder or 'lower' than the effective BTC of the intake stroke. The effect of this is to gain a degree of efficiency from the exhaust gas pressure which would otherwise be lost in the exhaust of a typical four-stroke engine.

The track may be further adapted so that the cylinder volume swept by the piston during the exhaust stroke is less than the volume swept during the expansion stroke. Suitably the difference in swept volume is around 20%. Preferably the effective TDC of the exhaust stroke is 'lower' than the effective TDC of the expansion stroke. This has the effect of harvesting an amount of exhaust gas and not exhausting all the products of combustion via the exhaust valve. This is an alternative means of exhaust gas recirculation (EGR) to increase the efficiency of the engine.

Preferably the track is adapted to provide three TDC's and two BDC's. Of course, the number of TDC's and BDC's can be selected depending on the application.

Such an engine configuration desirably provides improved efficiency levels whilst also providing improved power density.

The crankshaft may comprise axially spaced first and second crankshaft portions wherein the curved annular track is provided therebetween. In this case, each crankshaft portion would define a bearing surface for the piston bearing to engage. Alternatively or additionally, a curved annular track may extend laterally from the cylindrical crankshaft to define an annular flange having first and second bearing surfaces for the piston bearing to engage. Further alternatively, the piston bearing may engage with a single bearing surface provided by the cylindrical crankshaft or the crankshaft may be arranged between two piston bearings, for example.

Preferably the piston bearing comprises at least one first bearing adapted to engage with the first bearing surface and at least one second bearing adapted to engage with the second bearing surface. Preferably the piston bearing comprises a first bearing set and a second bearing set. Suitably the bearings may be roller bearings. Preferably the first and second bearing sets each comprise inner and outer roller bearings arranged relative to the crankshaft axis. Suitably the inner roller bearing of each bearing set is smaller in diameter to the outer roller bearing of each bearing set. This is to accommodate for the difference in circumference of crankshaft bearing surface passing under or over the inner and outer bearings in a single revolution of the crankshaft due to their different radial positions relative to the crankshaft axis. The inner bearing of each bearing set engages a smaller distance of crankshaft surface during a single crankshaft revolution than the outer bearing of each bearing set. Therefore, the inner bearings must be smaller in diameter to the outer bearings to ensure their rotational speeds correspond with their different radial positions relative to the crankshaft axis.

Preferably the roller bearings are tapered roller bearings having a narrow end directed towards the crankshaft axis. Suitably contact sides of each roller bearing are parallel with each other to engage with substantially flat and parallel bearing surfaces of the first and second crankshaft portions.

Suitably an axis of the first bearing set is parallel with an axis of the second bearing set. These axes may suitably be perpendicularly arranged relative to the crankshaft axis. In this case, the bearing surfaces of the crankshaft portions will be angled relative to each other. Alternatively, the axis of the first bearing set may be angled relative to the axis of the second bearing set and the first and second bearing surfaces of the crankshaft portions are parallel to each other. Further alternatively, a combination of the above bearing axis arrangements may be provided.

Use of tapered roller bearings or conical shaped roller bearings prevents slippage between the bearings and the crankshaft bearing surfaces and ensures positive engagement therebetween in use. Suitably the device may further comprise biasing means to urge the bearings towards the crankshaft axis. This is to provide a minimum surface force (preload) between the bearings and the crankshaft bearing surfaces to reduce slip when no load exists. Such a biasing means may also provide a constant contact pressure on the roller so that it is more likely to roll instead of slipping on the crankshaft surfaces. In addition, in case the roller or crankshaft surface becomes worn, the biasing means will urge the roller towards the crankshaft axis to accommodate the worn material, thereby increasing the operating life of the device.

Suitably the biasing means may comprise a spring disposed between a bearing roller and the connecting rod. A bearing set may comprise first and second tapered roller connected by an axle portion coupled to the connecting rod. The axle portion may be mounted in a bearing sleeve or bush of the connecting rod. At least one compression spring may be arranged around the axle portion and between at least one of the tapered rollers and the connecting rod. Other biasing means may be suitable for biasing the rollers of a bearing set towards the crankshaft axis, such as one or more tapered or spring washers or an hydraulic feed, such as a lubrication oil pressure feed, provided to the roller via internal and/or external conduits connected to an hydraulic pressure source.

Preferably the connecting rod is disposed within a peripheral boundary of the cylindrical crankshaft when viewed from an end thereof to provide a compact rotary power device. Preferably the first crankshaft portion comprises a continuous annular opening to support and guide the connecting rod as the crankshaft rotates about its axis. Suitably the annular opening is adapted to support the connecting rod in a radial direction during rotation of the crankshaft and linear motion of the piston. The piston and connecting rod assembly is also vertically supported by the annular opening in light of its curved profile. This allows the reciprocating masses of the device to be desirably as light as possible.

Suitably the annular opening defines first bearing surfaces to both sides thereof on the first crankshaft portion for the piston bearing to engage in use. Suitably the connecting rod may be generally cylindrical or oval in cross section. Suitably the connecting rod is constrained in rotation about its axis by a rotation constraint at least when following a horizontal path of the curved annular track of the crankshaft. Such a constraint may comprise a flat portion provided on at least a portion of the connecting rod adapted to engage with the first crankshaft portion during rotation of the same to prevent rotation of the connecting rod and piston. Such an arrangement provides a compact and integral means for preventing the connecting rod and piston from rotating relative to the block. A clearance fit may be provided between the connecting rod and crankshaft portion and/or one or more bearings may be provided therebetween.

Suitably the connecting rod may comprise a guide portion fixed thereto or integral therewith which is adapted to engage with at least the crankshaft thereby to support the connecting rod and prevent the same rotating. The guide member preferably extends outwardly from the connecting rod and further preferably comprises two opposing portions each outwardly extending from the connecting rod in leading and trailing directions relative to the direction of crankshaft rotation. Preferably the guide member comprises curved surfaces adapted to correspondingly engage with the curved annular slot. Alternatively the guide member may be adapted to engage with the crankshaft and a portion of the stationary block.

Suitably the device may further comprise at least one linear bearing arranged between the connecting rod and the stationary block to support and guide the connecting rod during use. Suitably the at least one linear bearing may comprise a plurality of linear roller bearings disposed on opposite sides of the connecting rod. Suitably the connecting rod comprises opposing bearing surfaces for the linear roller bearings to engage. Suitably the connecting rod may comprise opposing flat surfaces along its length to provide the rotation constraint and the opposing bearing surfaces. Advantageously the piston does not require a piston skirt as is the requirement for a conventional piston. This is due to the reduction in lateral forces acting on the piston and the cylinder wall which are otherwise relatively high for a conventional engine using a crankshaft and connecting rod arrangement. Also, any lateral forces will be transferred to the block by the linear bearing disposed between the connecting rod and the block. Therefore, the piston of the present invention may desirably be smaller in height to a conventional piston thereby saving on weight and associated manufacturing and material costs. A vehicle comprising a rotary power device as described above is also provided.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows the working principle of a known four-stroke engine;

- Figure 2 is a simplified representation of a device in accordance with the invention not showing the curved track;

Figure 3 shows a sectional view of the device of Figure 2;

Figure 4 shows a simplified representation of an alternative embodiment of the device;

- Figure 5 shows a section view of the device of Figure 4;

Figure 6 shows a further embodiment of the present invention;

Figure 7a is a schematic showing the start of the intake stroke;

Figure 7b is a schematic showing the start of the compression stroke;

Figure 7c is a schematic showing the start of the static combustion stroke; - Figure 7d is a schematic showing the start of the expansion stroke;

Figure 7e is a schematic showing the start of the exhaust stroke;

Figure 8 shows a first piston bearing arrangement;

Figure 9 shows a second piston bearing arrangement; and

Figure 10 shows a further bearing arrangement. As shown in Figure 1, a known four stroke engine comprises a piston 2, a connecting rod 4 and a crank pin 6 connecting the connecting rod to a crankshaft. The four strokes are intake, compression, expansion and exhaust which occur during two revolutions of the crankshaft. As described above, a single combustion stroke occurs for two revolutions of the crankshaft. Therefore, improved efficiency is desired.

As shown in Figures 2 and 3, the rotary device according to one embodiment of the present invention includes a piston 8, a connecting rod 10 and a cylindrical crankshaft 26 rotatable about a crankshaft axis 40. The crankshaft is mounted or coupled to a shaft 28 supported in bearings 34, 36 which may be a driveshaft or power takeoff or may be a driven shaft depending on the application of the rotary device, e.g. an engine or a pump/compressor. Bearings 34, 36 may be tapered roller bearings or ball bearings and hold the cylindrical crankshaft in the engine block. The connecting rod 10 is supported and guided in at least one linear bearing 38 mounted in the engine block. As shown in Figure 6, a number of linear bearings 38 may be provided along the length of the connecting rod 10 to support the same.

A bearing carrier 12 mounted at an end of the connecting rod 10 distil to the piston 8 supports a set of inner roller bearings 15 and a set of outer roller bearings 14, relative to a crankshaft axis 40, which engage with first 16 and second 18 portions of the crankshaft 26. The first and second portions of the crankshaft are connected together and axially spaced by connecting members 24. The first crankshaft portion 16 defines a first bearing surface 20 for the upper roller bearings (as shown in the figures) to engage. Likewise, the second crankshaft portion 18 defines a second bearing surface 22 for the lower roller bearings (as shown in the figures) to engage. The first and second bearing surfaces are shown as flat surfaces in figures 2 and 3 for ease of description only, as will be described later. The first crankshaft portion 16 includes an annular slot 32 which defines inner 30 and outer 16 first crankshaft portions relative to the crankshaft axis 40. The bearing carrier 12 may engage with and be guided by the annular slot 32. Alternatively or additionally, a guide member 25 is fixed to or integral with the connecting rod 10 and adapted to move therewith to engage with and be supported and guided by the annular slot 32 of the crankshaft portions 30,16. The inner and outer surfaces of the guide member 25 are correspondingly curved with the crankshaft portions 30 and 16. Such engagement and support prevents the piston 8 and connecting rod 10 rotating and moving radially relative to the crankshaft when in use.

The bearings 14, 15 are shown as tapered roller bearings but may be ball bearings. The inner and outer bearing of each set may be individually coupled to the connecting rod 10 or a single shaft may couple both bearings of each set to the connecting rod 10.

As shown in Figure 3, the bearing axes are arranged at a bearing axis angle to each other so that their contact faces and the bearing surfaces 20, 22 of the corresponding crankshaft portions 16, 18 to which they engage are parallel. However, the bearing axes may be arranged parallel to each other and the bearing surfaces 20, 22 of corresponding crankshaft portions 16, 18 machined at a bearing surface angle to each other. Such arrangements are shown in Figures 8 and 9. A combination of the above arrangements may be used.

A spring 42 or spring washer (as shown in Figure 10) is provided between the connecting rod 10 (or bearing carrier 12) and the roller bearings 14, 15 to urge the same towards the crankshaft axis 40. Suitably the spring 42 is a compression spring. The rollers 14,15 may coupled together by an intermediate axle member 44 or may be integral with each other. The axle member 44 is suitably mounted in a bearing sleeve 46. This provides a minimum contact force between the bearings and the bearings surfaces 20, 22 of the crankshaft portions 16, 18 to prevent/reduce slippage. The spring also provides a constant contact pressure on the rollers to ensure rolling instead of slipping on the crankshaft surfaces. In addition, in case the roller or crankshaft surface becomes worn, the spring 42, or similar, tends the roller towards the crankshaft axis to accommodate the worn material, thereby increasing the operating life of the device.

The piston rings are not shown for simplicity. However, although the piston(s) requires a piston ring, a piston skirt is not required due to the reduced lateral force acting on the piston as a result of the linear bearing 38 and the working arrangement of the present invention. Furthermore, the piston can be a single component and in particular the connecting rod may be integral with the piston, i.e. no gudgeon pin is required coupling the piston with the connecting rod.

A further embodiment of the invention is shown in Figures 4 and 5 where the cylindrical crankshaft 26 includes an annular flange or shoulder 50 outwardly extending therefrom to provide the first and second bearing surfaces 20,22. The annular shoulder 50 is shown flat for simplicity but would of course be curved to define the curved track and define the desired path for the piston to follow as the crankshaft rotates about its axis 40. Upper and lower roller bearings 52,54 are mounted in a bearing carrier 12 provided a distal end of the connecting rod 10 relative to the piston 8. As shown in Figure 4, the connecting rod 10 comprises a guide member 56 which moves with the connecting rod relative to the crankshaft 26 and engine block. The guide member 56 is correspondingly curved to engage with the crankshaft 26 and the engine block (not shown) to be supported thereby in use. This arrangement prevents the piston 8 and connecting rod 10 rotating and moving radially relative to the crankshaft. In either embodiment shown in Figures 2 or 4, a linear bearing may also be provided between the connecting rod 10 and the engine block.

The bearing axes are arranged at a bearing axis angle to each other so that their contact faces and the bearing surfaces 20, 22 of the corresponding crankshaft shoulder 50 to which they engage are parallel. However, the bearing axes may be arranged parallel to each other and the bearing surfaces 20, 22 of the crankshaft shoulder 50 machined at a bearing surface angle to each other.

The curved track defined by the first and second bearing surfaces 20, 22 of the first and second 16, 18 crankshaft portions actuates the piston in a linear motion upon rotation of the cylindrical crankshaft. Selective configuration of the curved track provides for desired stoke length and characteristics for improved engine efficiency. As shown in Figure 7a, a gradual intake stroke (Int) is effected by the track design of this embodiment. This has the effect of an increased amount of air drawn into the cylinder during the intake stroke thereby allowing for a more efficient combustion. The compression stoke (Cmp) is in two stages as shown in Figure 7b. The first portion of the track relating to the compression stroke defines a relatively shallow slope angle to create a relatively slow and gradual piston movement. This allows for maximum heat transfer from the relatively hot cylinder wall to the relatively cold air inside the cylinder and has the effect of cooling the cylinder wall whilst increasing the temperature of the air prior to combustion of the air-fuel mixture and thereby the cylinder pressure. The second portion of the track relating to the compression stroke defines a relatively steep slope angle to create a relatively quick piston movement and thereby fast compression.

As described above and as shown in Figure 7c, the present invention introduces a stationary combustion stroke (Cmb) as a fifth stroke to the conventional four-stroke Otto cycle. The cylinder volume is advantageously kept constant to effect an increase in cylinder temperature and thereby cylinder pressure prior to the expansion stroke. The combustion stroke which is shown as stationary in this embodiment may of course be optimised along with the other strokes to produce the best overall engine cycle efficiency. This may require a non-stationary combustion stroke which is distinguishable from the other four strokes, for example. As shown in Figures 7d and 7e, the tracks defines relatively short expansion (Exp) and exhaust (Exh) strokes to minimise the heat losses from the cylinder and so that a relatively large portion of the annular track may suitably correspond to the longer intake stroke, as described above.

In addition, the present invention allows for up to two different bottom dead centres and three top dead centres. This is accomplished by the variable height of the curved annular track defined by the crankshaft portions or variable end of stroke heights. Furthermore, the present invention provides for variable duration of the strokes (in degrees) to suit a particular application/efficiency criterion.

All the above described parameters must be carefully selected during the design stage depending on the engine specifications, requirements and fuel to burn. These design variables will determine whether the engine is going to be a high torque/low speed device or a low torque/high speed device, as well as its thermal efficiency.

An engine in accordance with the present invention may be geometrically optimised to burn any fuel following a constant volume or a constant pressure cycle (Otto or Diesel cycles respectively). The Atkinson's cycle over-expansion can be used with this crankshaft design as two different bottom dead centres can be designed as described above.

Claims

A rotary power device comprising:

- a stationary block;

- at least one cylinder defining a cylinder axis formed in the block;

- a piston slideably supported in the cylinder;

A rotary power device according to claim 1 wherein the track defines five separate strokes for a single revolution of the cylindrical crankshaft, namely intake, compression, combustion, expansion and exhaust strokes to provide a five-stroke rotary internal combustion engine.

A rotary power device according to claim 2 wherein a minor portion of the track corresponding to the combustion stroke defines substantially flat first and second bearing surfaces having zero slope angle to ensure the cylinder volume is kept constant during the combustion stroke.

A rotary power device according to claim 2 or 3 wherein the track is adapted to define a relatively long and gradual intake stroke.

A rotary power device according to claim 4 wherein the portion of track corresponding to the intake stroke is from 30 to 60% of a crankshaft revolution. 6. A rotary power device according to claim 5 wherein the portion of track corresponding to the intake stroke is 50% of a crankshaft revolution.

7. A rotary power device according to any one or more of claims 2 to 6 wherein the track is adapted to define a two-stage compression stroke which follows the intake stroke.

8. A rotary power device according to claim 7 wherein a first portion of the track relative to the direction of crankshaft rotation and corresponding to a first stage of the compression stroke defines a relatively shallow slope angle to create a relatively slow and gradual piston movement.

9. A rotary power device according to claim 7 or 8 wherein the portion of track corresponding to the first stage of the compression stroke is from 10 to 15% of a crankshaft revolution.

10. A rotary power device according to claim 9 wherein the portion of track corresponding to the first stage of the compression stroke is 12.5% of a crankshaft revolution.

11. A rotary power device according to any one or more of claims 7 to 10 wherein a second portion of the track relative to the direction of crankshaft rotation and corresponding to a second stage of the compression stroke defines a relatively steep slope angle to create a relatively quick piston movement and thereby relatively fast compression.

12. A rotary power device according to claim 11 wherein the track is adapted so that the second stage of compression begins when the air in the cylinder has approximately reached the temperature of the cylinder wall. 13. A rotary power device according to claim 11 or 12 wherein the portion of track corresponding to the second stage of compression is from 7.5 to 15% of a crankshaft revolution.

14. A rotary power device according to claim 13 wherein the portion of track corresponding to the second stage of the compression stroke is 9.72% of a crankshaft revolution.

15. A rotary power device according to any one or more of claims 2 to 14 wherein the portion of track corresponding to the combustion stroke is from 1 to 5% of a crankshaft revolution.

16. A rotary power device according to claim 15 wherein the portion of track corresponding to the combustion stroke is 2.8% of a crankshaft revolution.

17. A rotary power device according to any one or more of claims 2 to 16 wherein the track is adapted to define relatively short expansion and/or exhaust strokes so that a relatively large portion of the annular track corresponds to a relatively longer intake stroke.

18. A rotary power device according to claim 17 wherein the portion of track corresponding to the expansion stroke is from 7.5 to 15%.

19. A rotary power device according to claim 18 wherein the portion of track corresponding to the expansion stroke is 11.1% of a crankshaft revolution.

20. A rotary power device according to any one or more of claims 17 to 19 wherein the portion of track corresponding to the exhaust stroke is from 10 to 15% of a crankshaft revolution. 21. A rotary power device according to claim 20 wherein the portion of track corresponding to the exhaust stroke is 13.9% of a crankshaft revolution.

22. A rotary power device according to any preceding claim wherein the annular track is selectively adapted to affect a desired stroke length and limits thereof.

23. A rotary power device according to claim 22 wherein the track is adapted so that the cylinder volume swept by the piston during the compression stroke is greater than the volume swept during the preceding intake stroke.

24. A rotary power device according to claim 23 wherein the volume swept by the piston during the compression stroke is around 20% greater than the volume swept during the intake stroke.

25. A rotary power device according to claim 23 or claim 24 wherein the track is adapted so the piston finishes the compression stroke at an effective TDC which is further along the cylinder than the effective TDC when the piston began the intake stroke.

26. A rotary power device according to any one or more of claims 22 to 25 wherein the track is further adapted so that the cylinder volume swept by the piston during the expansion stroke is greater than the volume swept during the compression stroke.

27. A rotary power device according to claim 27 wherein the volume swept during the expansion stroke is around 30% greater than that during the compression stroke.

28. A rotary power device according to any one or more of claims 22 to 27 wherein the volume swept during the expansion stroke is around 50% greater than that during the intake stroke. 29. A rotary power device according to claim 28 wherein the effective BTC of the expansion stroke is further along the cylinder than the effective BTC of the intake stroke.

30. A rotary power device according to any one or more of claims 22 to 29 wherein the track is further adapted so that the cylinder volume swept by the piston during the exhaust stroke is less than the volume swept during the expansion stroke.

31. A rotary power device according to claim 30 wherein the effective TDC of the exhaust stroke is 'lower' than the effective TDC of the expansion stroke.

32. A rotary power device according to any one or more of claims 22 to 31 wherein the track is adapted to provide three TDC's and two BDC's.

33. A rotary power device according to any preceding claim wherein the crankshaft comprises axially spaced first and second crankshaft portions wherein the curved annular track is provided therebetween.

34. A rotary power device according to any preceding claim wherein the curved annular track extends laterally from the cylindrical crankshaft to define an annular flange having first and second bearing surfaces for the piston bearing to engage.

35. A rotary power device according to any preceding claim wherein the connecting rod is disposed within a peripheral boundary of the cylindrical crankshaft.

36. A rotary power device according to claim 35 wherein a first crankshaft portion comprises an annular opening to support and guide the connecting rod. 37. A rotary power device according to claim 36 wherein the annular opening defines first bearing surfaces to both sides thereof on the first crankshaft portion for the piston bearing to engage in use.

38. A rotary power device according to any preceding claim wherein the piston bearing comprises at least one first bearing adapted to engage with the first bearing surface and at least one second bearing adapted to engage with the second bearing surface.

39. A rotary power device according to claim 38 wherein the piston bearing comprises a first bearing set and a second bearing set.

40. A rotary power device according to claim 39 wherein the first and second bearing sets each comprise inner and outer roller bearings arranged relative to the crankshaft axis.

41. A rotary power device according to claim 40 wherein the inner roller bearing of each bearing set is smaller in diameter to the outer roller bearing of each bearing set.

42. A rotary power device according to claim 41 wherein the roller bearings are tapered roller bearings having a narrow end directed towards the crankshaft axis.

43. A rotary power device according to claim 42 wherein an axis of the first bearing set is parallel with an axis of the second bearing set and wherein the first and second bearing surfaces defined by the track are angled relative to each other. 44. A rotary power device according to claim 42 wherein the axis of the first bearing set is angled relative to the axis of the second bearing set and the first and second bearing surfaces defined by the track are parallel to each other.

45. A rotary power device according to any preceding claim further comprising biasing means to urge the at least one piston bearing towards the crankshaft axis.

46. A rotary power device according to claim 45 wherein the biasing means comprises a spring disposed between the bearing and the connecting rod.

47. A rotary power device according to any preceding claim wherein the device further comprises at least one linear bearing arranged between the connecting rod and the block to support and guide the connecting rod during use.

48. A vehicle comprising a rotary power device according to any preceding claim.