WO2007030021A1

WO2007030021A1 - Stirling machine

Info

Publication number: WO2007030021A1
Application number: PCT/NZ2006/000231
Authority: WO
Inventors: Donald Murray Clucas; Bruce Robertson
Original assignee: Whisper Tech Limited
Priority date: 2005-09-06
Filing date: 2006-09-06
Publication date: 2007-03-15
Also published as: WO2007030021A8

Abstract

A Stirling machine has a pressure vessel configured for demountable attachment to the block to contain the working fluid. The pressure vessel and engine block may comprise a latch flange provided on one of the pressure vessel and the engine block and cooperating latch tabs on the other of pressure vessel and the engine block for fastening the pressure vessel to the engine block, the flange and a mating one of the tabs defining inter-engaging locking surfaces, the locking surfaces being urged toward one another when the pressure vessel is pressurised by the working fluid. The pressure vessel may be configured to enclose the drive mechanism and the generator but is demountable independently of the drive mechanism and generator. A fan may be operatively connected to circulate the working fluid inside the pressure vessel for cooling the drive mechanism. The fan may comprise a balance weight fixed to, or integral with the fan, to counter imbalance in the drive mechanism.

Description

"STIRLING MACHINE"

TECHNICAL FIELD

The invention relates generally to the construction of Stirling machines, and particularly to machines with pressurised drive casings.

BACKGROUND ART

A feature that has a significant impact on Stirling engine design is the containment of the high pressure working fluid. To avoid providing a sliding seal around the connecting rods, a large part of the crankcase or housing may be exposed to the high pressures of the working fluid. A drive mechanism (such as wobble-type drive or crank) provides an output shaft which can pass through the pressure shell, but doing this requires a costly rotating seal which may be prone to leakage. The rotating seal problem is overcome by placing the driven device, such as a generator, inside of the Stirling engine housing. The housings of such machines are typically assembled in several axial housing sections which are secured to one another e.g. by means of radial flanges on each housing section. The flanges are bolted, screwed or clamped together to hold the various sections against the internal fluid pressures and in combination with sealing rings or gaskets to make high pressure gas tight seals. Particularly for machines intended for high volume production, it is important that they may be manufactured efficiently with regard to component costs, processing, and parts assembly.

Disadvantageous^ with this design, a large number of accurately tightened fasteners are necessary. A related problem with this arrangement may arise when the engine is serviced by a workman not sufficiently skilled for this work to understand that the pressure of the working fluid must be released before any attempt is made to remove the bolts. As is the case with any pressure vessel such actions pose a safety risk.

In the so called "modular" construction employed in typical Stirling engines, the major components of the engine are sub-assemblies, each with respective housing sections which are assembled together. In machines of this type, where the housing is pressurised and encloses both the drive mechanism and a driven device, servicing is made more difficult since the housing sections cannot be removed without removal of the respective component to which it is fastened. Also, during assembly of engines an inspection and other quality checks on the components must be made before each is assembled onto the engine, since the housing sections are fixed to each component respectively.

Various types of engine drive mechanisms are used for converting reciprocating piston movement to a rotating output and they may use lubricated-for-life rolling element bearings to reduce friction. These beatings may include ball, needle, cylindrical, tapered and spherical rolling elements. Seals serve to retain the grease inside the bearing and between the rolling elements and the races, to ensure satisfactory bearing life. Because of this design, however, bearing life is reduced at elevated temperatures. In Stirling engines used in cogeneration systems, engine coolant is supplied for providing space heating, process heat and the like and is thus necessarily at a relatively high temperature (e.g. 70-80°C). Therefore, heat built up in the bearings cannot be readily dissipated to the surroundings, due to high coolant temperatures and the drive mechanism being enclosed.

It is an object of the present invention to address at least one of the foregoing problems or at least to provide the public with a useful choice.

DISCLOSURE OF INVENTION

According to one aspect of the invention there is provided a Stirling machine including an engine block having at least one cylinder in which a working fluid is containable, and a pressure vessel configured for demountable attachment to the block to contain the working fluid, the pressure vessel and engine block containing a latch flange provided on one of the pressure vessel and the engine block and cooperating latch tabs on the other of pressure vessel and the engine block for fastening the pressure vessel to the engine block, the flange and a mating one of the tabs defining inter-engaging locking surfaces, the locking surfaces being urged toward one another when the pressure vessel is pressurised by the working fluid.

The latch flange preferably defines an L-shaped recess of a bayonet joint for receiving each latch tab to allow the pressure vessel to be connected to the engine block by a push-twist action. At least the portions of the pressure vessel and the engine block on which the latch flange and latch tabs are provided are axisymmetrical, with each L-shaped recess having an axial and a circumferential portion. Preferably, the pressure vessel may be demounted from the engine block by at least partially rotating the pressure vessel less than one half turn, preferably by less than one eighth of a turn.

The Stirling machine preferably includes a generator for producing electrical power and means for supplying heat from the machine to a thermal load. Preferably apertures are provided in the engine block and pressure vessel which, when aligned, vent the space containing the working fluid and which are closable by a plug. This feature provides a safety interlock, ensuring the pressure vessel is depressurised by removing the plug, before the pressure vessel and engine block are separated.

By employing this arrangement of a latch flange and cooperating latch the pressure vessel can be readily mounted avoiding, for example, the requirement to accurately torque a large number of fasteners. Due the high factional forces between the inter-engaging locking surfaces when the pressure vessel is under pressure, it is necessary that the pressure vessel is depressurised before the pressure vessel can be demounted, avoiding possible safety issues arising from uncontrolled release of the pressure vessel. The pressure vessel preferably encloses a drive mechanism e.g. a wobble-type drive, crank, or swash plate operatively connected to one or more piston(s) received in cylinders), for converting reciprocating movement of the piston(s) to a rotary output. For electrical power generating applications, the pressure vessel also preferably encloses a generator connected to the rotary output. In another aspect the invention provides a Stirling machine including: an engine block having at least one cylinder in which a working fluid is containable; a drive mechanism having a drive mount fixed to the engine block, the drive mechanism being operatively connected to a piston received in the cylinder, for converting reciprocating movement of the piston to a rotary output; a generator having a generator mount fixed to the engine block, the generator being connected to the rotary output for generating electrical power and; a pressure vessel configured for demountable attachment to the block independently the drive mechanism and generator, to contain the -working fluid and enclose the drive mechanism and the generator. It will be appreciated that by having both the drive mechanism and generator fixed independently of the pressure vessel, or of respective pressure vessel portions, then the pressure vessel can be readily removed to access these components for servicing. Also, during assembly of the engine ready access is provided to both the drive mechanism and generator, before the pressure vessel is attached to the block. Preferably a latch flange is provided on one of the pressure vessel and the engine block, and cooperating latch tabs on the other of pressure vessel and the engine block for fastening the pressure vessel to the engine block, the flange and a mating one of the tabs defining inter-engaging locking surfaces, the locking surfaces being urged toward one another when the pressure vessel is pressurised by the working fluid. In another aspect the invention provides a Stirling machine including: an engine block having at least one cylinder in which a working fluid is containable; a drive mechanism fixed to the engine block, the drive mechanism being operatively connected to a piston received in the cylinder, for converting reciprocating movement of the piston to a rotary output; a pressure vessel attached to the block to enclose the drive mechanism and contain the working - A- fluid, and a fan is operatively connected to the rotary output to circulate the working fluid inside the pressure vessel for cooling the drive mechanism.

Due to the working fluid being highly pressurised (e.g. 10-40 Bar in a typical engine) a relatively smaE flow can provide sufficient cooling. This cooling is particularly advantageous to extend the life of lubricated-for-Hfe bearings.

The engine preferably includes a generator connected to the rotary output for generating electrical power, the fan circulating the working fluid through and/or about the generator. The fan is preferably a centrifugal type with radial blades. Preferably a balance weight is fixed to, or formed integrally with the fan, to counter imbalance in the drive mechanism.

By incorporating all of the three above-recited independent aspects of the invention in combination in a Stirling machine its "total life" costs are reduced by providing for more efficient manufacture and maintenance.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning — i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non- specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a partially cut away pictorial view of a Stirling machine of the present invention, shown partly demounted, and

Figure 2 is a longitudinal sectional view through the machine of Fig 1;

Figure 3 is a pictorial view of a fan of the engine of Fig. 1;

Figure 4 is a transverse sectional view showing the connection between the engine block and the pressure vessel of the of the machine of Fig. 1

Figure 5 is a detail showing the latch tabs and mating latch flange, and

Figureόis a plan view of the non-cast component of the engine referred to previously,

Figure 7 is a side view of the component of Figure 6, Figure 8 is a transverse sectional view of the non-cast component of Figures 6 and 7 along liαe D-D of Figure 7,

Figute 9 is a longitudinal sectional view of the component along line C-C of Figure 6, and

Figure 10 is a longitudinal sectional view through a single cylinder and piston and connecting rod of the preferred form engine.

BEST MODES FOR CARRYING OUT THE INVENTION

The drawings illustrate a preferred form Stirling machine assembly 100 embodying features of the invention. In general, the assembly 100 includes an engine block 1 to which is mounted an engine drive mechanism 2, a generator 3 and a pressure vessel 4. The engine block 1 has four coaxial cylinders 5 in which a working fluid is contained. A single cylinder and piston is shown in Figure 10 in cross-section. Heater heads 6 extend from an upper side the block 1 into the engine's combustion chamber 7, each closing an upper end of each cylinder 5. The drive mechanism 2 includes four connecting rods 8, each connected to a piston 71 received in each cylinder 5. The connecting rods 8 project from apertures 9 in a biscuit 33 fixed to the lower side of the block 1. The biscuit 33 has a downwardly-projecting transverse face 10. the biscuit may be considered part of the engine block.

The engine drive mechanism 2 although a separate component, converts the reciprocating movement of the pistons 7 to a rotation of the output shaft 11 and is of a wobble-type described in international patent application WO 00/37778. The drive mechanism 2 is fixed to a drive mount in the form of a pedestal 12 which mates with the face 10 of the biscuit 33. Like the arrangement of the cylinders 5, the drive mechanism 2 is generally symmetrical about a central longitudinal axis of the machine.

The generator 3 is operatively connected to the rotating output shaft 11 of the drive mechanism 2 and is fixed by generator mount 13 to the block 1. An upper end of the generator mount 13 abuts the transverse face 10 and is held by fasteners 14a. The lower end of the generator mount 13 is joined by fasteners 14b to the generator's stator 15.

Mounted at the end of the generator 3 on the output shaft 11 is a fan 16 which circulates the working fluid within the pressure vessel 4 generally along path 40 for cooling the drive mechanism 2. Air flow from the fan is deflected axially upward around the generator 3 by the concave inner surface at the lower end of the pressure vessel 4. The axial flow is stopped by the transverse face 10 and the flow then extends radially inward and downward on path 40, through and about the components of the drive mechanism 2, before being drawn back through the generator 3 to the fan 16. As seen in Fig. 3, the fan 16 is a centrifugal type with a hub 17 having an aperture 18 for receiving the shaft 11. Radial blades 20 are fixed to a disc 19. A balance weight 22 is fixed to the fan 16 and is offset from its axis of rotation to counter imbalance in the drive mechanism 2.

The pressure vessel 4, as best seen in Fig. 1, is fixed to the block 1 and encloses both the drive mechanism 2 and the generator 3, to which it is not directly connected. As seen in Fig 5, sixteen latch tabs 23a, 23b are arranged in eight regularly spaced pairs 24 and project radially outward from the adjacent cylindrical section 25 of the pressure vessel 4. The latch tabs 23a, 23b are elongated circumferentially and the latch tabs 23a, 23b of each pair are aligned axially.

The block 1 has a latch flange 26 projecting from its lower edge for cooperating with the latch tabs 23a, 23b to demountably fix the pressure vessel 4 and block 1 together. The latch flange 26 includes sixteen L-shaped recesses 26a, 26b (shown as dashed lines in Fig. 5) arranged in eight regularly spaced pairs, one receiving each of the latch tabs 23a, 23b. Each of the recesses 26a, 26b has an axially extending portion 27 into which the latch tabs 23a, 23b are pushed, before a turning movement rotates each tab 23a, 23b along circumferentially extending portion 28. The pressure vessel 4 is pushed into the block 1 and rotated to align the threaded opening 29 in the pressure vessel 4 with a corresponding opening (not shown) in the block 1 and when aligned, these apertures vent the space containing the working fluid. In the preferred form a plug (not shown) is then secured to close the opening 29 and also to prevent further rotation. When the pressure vessel 4 is fixed by this bayonet joint the locking surface 30 of each latching tab 23a, 23b inter- engages with a corresponding locking surface 31a, 31b of the latch flange, the locking faces 30, 31 extend generally radially and resist the axial force applied when the vessel 4 is pressurised. The apertures and cooperating plug act as a safety interlock, requiring that the pressure vessel is depressurised (by removing the plug) before the pressure vessel 4 and engine block 1 are separated. The biscuit 33 fixed at the lower end of the block 1 also provides the interface with the pressure vessel 4. The interface is cylindrical and the O-ring 32 produces a gas tight seal to contain the working fluid.

As referred to previously, in the preferred form shown the biscuit 33 and engine block 1 are separate components. The biscuit 33 is formed by machining from solid metal. In operation of the Stirling engine the working fluid passes between the cylinders via transfer ports 50 and in accordance with the invention the ports 50 are formed (by drilling and machining) in the biscuit 33 which is a non-cast component formed separately from the balance of the engine block 1, which is in turn manufactured by casting. The transfer ports 50 are shown in Figures 6-9, which show the biscuit 33 separate from the engine block 1. As shown in Figures 1 and 2 the cylinders 5 are mounted to the biscuit 33. The circular cross-hatched area in Figure 6 indicates a contact area of the lower face of one cylinder on the upper face of the biscuit 33. Ports 51 in the cylinder side walls transfer the working fluid to and from the cylinders during operation of the heat engine, as is known in the alt. When the cylinders are assembled to the biscuit 33 the transfer ports 50 in the upper face of the biscuit 33 (see Figure 6) align with the lower ends 51a (see Figure 10) of the ports 51 in the side walls of the cylinders 5 .

This construction comprising a non-cast biscuit component 33 manufactured separately from a cast engine block component, provides significant advantages in cost and ease of manufacture by facilitating casting of the engine block 1. Cast blocks have not previously been used in the applicant's Stirling engines because leakage would result from exposing a cast and porous block 1 to the highly pressurised working fluid. The provision of the biscuit 33 for connecting the block 1 and pressure vessel 4 in this manner advantageously allows the block 1 to be manufactured as a casting since, by closing the spaces receiving the working fluid and sealing these spaces against the biscuit 33, this design prevents the working fluid being exposed to the block 1.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as described in the accompanying claims.

Claims

CLAIMS:

1. A Sliding machine including an engine block having at least one cylinder in which a working fluid is containable, and a pressure vessel configured for demountable attachment to the block to contain the working fluid, the pressure vessel and engine block comprising a latch flange provided on one of the pressure vessel and the engine block and cooperating latch tabs on the other of pressure vessel and the engine block for fastening the pressure vessel to the engine block, the flange and a mating one of the tabs defining inter-engaging locking surfaces, the locking surfaces being urged toward one another when the pressure vessel is pressurised by the working fluid.

2. A Stirling machine according to claim 1 wherein the latch flange defines an L-shaped recess of a bayonet joint for receiving each latch tab to allow the pressure vessel to be connected to the engine block by a push-twist action.

3. A Stirling machine according to claim 2 wherein at least the portions of the pressure vessel and the engine block on which the latch flange and latch tabs are provided are axisymmetrical, with each L-shaped recess having an axial and a circumferential portion.

4. A Stirling machine according to any one of claims 1 to 3 wherein the latch tabs are elongated circumferentially.

5. A Stirling machine according to any one of claims 1 to 4 comprising multiple latch tabs are arranged in regularly spaced pairs projecting radially outwardly from the pressure vessel.

6. A Stirling machine according to claim 5 wherein the latch tabs of each pair are aligned axially.

7. A Stirling machine according to any one of claims 1 to 6 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one half turn.

8. A Stirling machine according to any one of claims 1 to 6 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one eighth of a turn.

9. A Sliding machine according to any one of claims 1 to 8 including a generator fixed to the engine block and connected to the rotary output for generating electrical power, and wherein the pressure vessel when attached to the engine block to contain the working fluid encloses a drive mechanism of the Stirling engine and the generator.

10. A Stirling machine according to any one of claims 1 to 9 also including means for supplying heat from the machine to a thermal load.

11. A Stirling machine according to any one of claims 1 to 10 wherein apertures are provided in the engine block and pressure vessel which align when the pressure vessel is mounted fully home to the engine block and vent the space for containing the working fluid and are closable by a common plug so as to require that the plug is removed before the pressure vessel and engine block can be separated.

12. A Stirling machine according to claims 5 to 11 including a fan configured to circulate the working fluid within the pressure vessel and through and/ or about the generator.

13. A Stirling machine according to claim 12 wherein the fan is a centrifugal type with radial blades.

14. A Stirling machine according to either one of claims 12 and 13 wherein a balance weight is fixed to, or formed integrally with the fan, to counter imbalance in the drive mechanism.

15. A Stirling machine including: an engine block having at least one cylinder in which a working fluid is contained; a drive mechanism having a drive mount fixed to the engine block, the drive mechanism being operatively connected to a piston received in the cylinder, for converting reciprocating movement of the piston to a rotary output; a generator having a generator mount fixed to the engine block, the generator being connected to the rotary output for generating electrical power; and a pressure vessel configured for demountable attachment to the block independently of the drive mechanism and generator, to contain the working fluid and enclose the drive mechanism and the generator.

16. A Stirling machine according to claim 15 wherein a latch flange is provided on one of the pressure vessel and the engine block and cooperating latch tabs on the other of pressure vessel and the engine block for fastening the pressure vessel to the engine block, the flange and a mating one of the tabs defining inter-engaging locking surfaces, the locking surfaces being urged toward one another when the pressure vessel is pressurised by the working fluid.

17. A Stirling machine according to claim 16 wherein the latch flange defines an L-shaped recess of a bayonet joint for receiving each latch tab to allow the pressure vessel to be connected to the engine block by a push-twist action.

18. A Stirling machine according to claim 17 wherein at least the portions of the pressure vessel and the engine block on which the latch flange and latch tabs are provided are axisymmetrical, with each L-shaped recess having an axial and a circumferential portion.

19. A Stirling machine according to any one of claims 1 to 3 wherein the latch tabs are elongated circumferentially.

20. A Stirling machine according to any one of claims 1 to 4 comprising multiple latch tabs are arranged in regularly spaced pairs projecting radially outwardly from the pressure vessel.

21. A Stirling machine according to claim 5 wherein the latch tabs of each pair are aligned axially.

22. A Stirling machine according to any one of claims 15 to 21 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one half turn.

23. A Stirling machine according to any one of claims 15 to 21 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one eighth of a turn.

24. A Stirling machine according to any one of claims 15 to 23 wherein apertures are provided in the engine block and pressure vessel which align when the pressure vessel is mounted fully home to the engine block and vent the space for containing the working fluid and are closable by a common plug so as to require that the plug is removed before the pressure vessel and engine block can be separated.

25. A Stirling machine according to claims 15 to 24 including a fan configured to circulate the working fluid within the pressure vessel and through and/or about the generator.

26. A Stirling machine according to claim 25 wherein the fan is a centrifugal type with radial blades.

27. A Stirling machine according to either one of claims 25 and 26 wherein a balance weight is fixed to, or formed integrally with the fan, to counter imbalance in the drive mechanism.

28. A Stirling machine including: an engine block having at least one cylinder in which a working fluid is contained; a drive mechanism fixed to the engine block, the drive mechanism being operatively connected to a piston received in the cylinder, for converting reciprocating movement of the piston to a rotary output. a pressure vessel attached to the block to enclose the drive mechanism and contain the working fluid, and a fan operatively connected to the rotary output to circulate the working fluid inside the pressure vessel for cooling the drive mechanism.

29. A Stirling machine according to claim 28 including a generator connected to the rotary output for generating electrical power, and wherein the fan is configured to circulate the working fluid through and/ or about the generator.

30. A Stirling machine according to claim 29 wherein the fan is a centrifugal type with radial blades.

31. A Stirling machine according to any one of claims 28 and 30 wherein a balance weight is fixed to, or from integrally with the fan, to counter imbalance in the drive mechanism.

32. A Stirling machine according to any one of claims 1 to 25 wherein the engine block is formed by casting, and comprising a non-cast component coupled to the engine block and to which cylinders of the Stirling engine are mounted and which comprises transfer ports through the non-cast component for transferring working fluid between the cylinders of the engine.

33. A Stirling machine including a pressure vessel configured for demountable attachment to an engine block to contain the working fluid, the pressure vessel being demountable from the engine block by rotational movement of the pressure vessel relative to the engine block, and wherein apertures are provided in the engine block and pressure vessel which align when the pressure vessel is mounted fully home to the engine block and vent the space for containing the working fluid and are closable by a common plug so as to require that the plug is removed before the pressure vessel and engine block can be separated.

34. A Stirling machine according to claim 33 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one half turn.

35. A Stirling machine according to claim 33 wherein the pressure vessel is demountable from the engine block by at least partially rotating the pressure vessel less than one eighth of a turn.