GB2296047A

GB2296047A - Stirling cycle engine

Info

Publication number: GB2296047A
Application number: GB9521170A
Authority: GB
Inventors: Jonathan Maxwell Boardman
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-15
Filing date: 1995-10-17
Publication date: 1996-06-19
Anticipated expiration: 2015-10-17
Also published as: GB9521170D0; GB2296047B; GB2296047A8

Abstract

A Stirling cycle engine comprises a central "Z" crank, with a spider structure mounted upon it, the arms of which radiate outwards, so that when the "Z" crank rotates, the whole of the spider structure has the motion of a wobble plate. Attached to the spider arms are flexible diaphragms, defining hot working chambers 7 and cold working chambers 8, in such a way that they pump the working gas between the hot and cold chambers when the "Z" crank rotates. The spider structure may also contain regenerators 9. The engine need only have two rigid moving parts, the "Z" crank and the spider structure. The engine could be used in solar power applications. <IMAGE>

Description

DIAPHRAGM STIRLING ENGINE 2296047 This invention relates to a diaphragm

Stirling engine of the Siemens type.

Stirling cycle engines, formally known as hot-air engines, have a well known variant consisting of four double-acting pistons in four cylinders arranged in square formation, known as a Siemens or Rinia type engine, (British Patent number 2074, dated 1860) of which the diaphragm Stirling engine here referred to has the same thermodynamic principles. The theoretical Stirling cycle engine produces power in relation to the temperature differential between hot heat source and cold heat sink. However, the internal friction between piston, cylinder and associated mechanism in existing types has first to be overcome before any net useful power can be produced. This has prohibited their utilisation for the extraction of mechanical power from such energy sources that have low temperature differentials between heat source and heat sink. This deficiency promoted the search to replace pistons in cylinders with flexible diaphragms. Diaphragms also provide a simple and cheep solution to the otherwise complicated kinematics of a wobble plate drive.

According to the present invention there is provided a diaphragm Stirling engine comprising a central " Z " crank, with a spider structure mounted upon it, having a plurality of arms radiating outwards, so that when the Z crank rotates, the end of each of the arms traverses an arc, the whole of the spider structure having the motion of a wobble plate. Attached to the spider arms are flexible diaphragms, resilient enough to accommodate the motion at the ends of the arms, in such a way that they press upon the diaphragms and pump the working gas when the Z crank rotates. The diaphragms each close-in either a hot or a cold chamber and displace the working gas therein. Diaphragms at different angular positions around the central Z crank, have hot and cold chambers paired together via ducting containing their regenerator. The consequent phase difference is in such a manner that the Stirling cycle can operate.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings;- Figure 1. shows a plan view of the insides of the engine with the top diaphragms removed for clarity.

Figure 2. shows engine.

a cross-section "AA" of the insides of the Figure 3. shows an alternative crosssection "AA" of the insides of an engine suitable for use with stiffer or metallic diaphragms, where the plane of each of the diaphragms is angled, so as to intercept the centre of wobble, ie. the position where the "Z" crank axis cross.

1 0 Referring to the drawing, the engine comprising a central 91 Z " crank 1, mounted on ball bearings 4 in the housing 5.

A spider structure 2 is mounted on another set of ball bearings 6 upon the Z crank 1, the eight arms of the spider structure 2 radiating outwards in four pairs, so that when the Z crank 1 rotates the end of each of the arms traverses an arc, the whole of the spider structure 2 having the motion of a wobble plate. Any number of arm pairs may be provided but for the purpose of this example, four pairs will be used.

Attached to either side of the spider structure 2 arms are the centres of eight flexible diaphragms 3, so that the arms press upon the diaphragms 3 and displace the working gas when the Z crank 1 rotates. The diaphragms 3 are attached at their periphery to the housing 5, and are resilient enough to accommodate the motion at the ends of the arms.

The diaphragms 3 attached to housing 5 form either four hot chambers 7 on the top side of the spider structure 2, or four cold chambers 8 on the under side of the spider structure 2.

The four separate Stirling engine regenerators 9 are contained within the spider structure 2 and consequently are a moving part. Each hot chamber 7 has a duct through the diaphragm 3 connecting it to a similar duct through the diaphragm 3 of the cold chamber 8 via their respective regenerator 9. This connection has a 90 degree angular displacement, each regenerator 9 being of " L " shape, occupying two arms of the spider structure, and independent of the others. Consequently the diaphragm 3 pairs have a kinematic phase difference of 90 degrees in such a manner that the Stirling cycle can operate.

The four, hot chamber 7 / regenerator 9 / cold chamber 8 systems, each contain their own independent working gas, which is so balanced that no net negative work for the engine as a whole, at any angular position of the crank, has to be done compressing the working gases.

A diaphragm Stirling engine of this type could be adapted for Solar Power, by fitting suitable transparent covers over the large surface areas of the top hot chamber 7, which could then be heated by solar radiation.

A diaphragm Stirling engine of this type could be arranged so that the plane of some or all of the diaphragms be angled, so as to intercept the centre of wobble, ie. the position where the "Z" crank axis cross. This reduces the lateral deflection required of the diaphragms, facilitating the use of stiffer or metallic diaphragms. The diaphragm plane of either all the hot chamber diaphragms or alternatively, of all the cold chamber diaphragms could still be arranged to all lie on one flat plane by placing the centre of wobble on that plane.

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Claims

1. A diaphragm Stirling engine comprising a central " Z " crank, with a spider structure mounted upon it, having a plurality of arms radiating outwards, so that when the Z crank rotates, the end of each of the arms traverses an arc, the whole of the spider structure having the motion of a wobble plate. Attached to the spider arms are flexible diaphragms, resilient enough to accommodate the motion at the ends of the arms, in such a way that they press upon the diaphragms and pump the working gas when the Z crank rotates. The diaphragms each close-in either a hot or a cold chamber and displace the working gas therein. Diaphragms at different angular positions around the central Z crank, have hot and cold chambers paired together via ducting containing their regenerator. The consequent phase difference is in such a manner that the Stirling cycle can operate.

2. A diaphragm Stirling engine as claimed in claim 1 wherein the number and position of the hot and cold chamber pairs is such that when each is filled with the correct quantity of working gas, the engine is such that being balanced, no net negative work for the engine as a whole, at any angular position of the crank, has to be done compressing the working gases.

3. A diaphragm Stirling engine as claimed in claim 1 or claim 2 wherein the Stirling engine regenerators are independently contained within the spider structure.

4. A diaphragm Stirling engine as claimed in claim 1 wherein the diaphragms may be attached to one or both sides of the spider structure.

5. A diaphragm Stirling engine as claimed in claim 1 wherein the Z crank may be extended on one or both sides outside the plane of the diaphragms to reduce the force couple experienced by its bearings.

6. A diaphragm Stirling engine as claimed in claim 1 or claim 3 wherein the engine may be so manufactured, to be made out of two rigid moving parts, namely the Z crank and the spider structure.

7. A diaphragm Stirling engine as claimed in claim 1 wherein the working gas is hermetically sealed in.

8. A diaphragm Stirling engine as claimed in claim 1 and claim wherein the engine may be self-starting when the hot chamber is heated.

9. A diaphragm Stirling engine as claimed in claim 1 could be adapted for use in solar power applications.

10. A diaphragm Stirling engine as claimed in claim 1 suitable for use with stiffer or metallic diaphragms, where the plane of some or all of the diaphragms may be angled, so as to intercept 3 the centre of wobble, ie. the position where the "Z" crank axis cross.

11. A diaphragm Stirling engine substantially as described herein with reference to the accompanying drawings, figures 1 - 3.

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