EP2446158A1

EP2446158A1 - Flexible connecting rod

Info

Publication number: EP2446158A1
Application number: EP09770449A
Authority: EP
Inventors: Damian Blogg
Original assignee: Whisper Tech Ltd
Current assignee: Suma Algebraica SL
Priority date: 2008-06-26
Filing date: 2009-06-26
Publication date: 2012-05-02
Also published as: EP2446158A4; WO2009157787A1

Abstract

A connecting rod comprising a body with two ends extending along a longitudinal axis of the connecting rod, a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod, a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod, and a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

Description

FLEXIBLE CONNECTING ROD

FIELD OF THE INVENTION

The invention relates generally to a connecting rod, and particularly, although not exclusively, to a flexible connecting rod. The connecting rod may be used in an engine, pump, refrigerator, compressor, or micro combined heat and power unit for example.

BACKGROUND TO THE INVENTION

In a reciprocating piston engine, linear reciprocating motion from one or more pistons is converted to rotary motion of for example a crankshaft, to which each piston is coupled by a connecting rod. Alternatively in a pump or compressor input rotary motion is converted to linear reciprocating motion of one or more pistons. Swash plate mechanisms and wobble or z-crank mechanisms are also known for converting between linear reciprocating piston motion, and rotary motion about an axis parallel to the axis or axes of the linear reciprocating piston motion(s). In some configurations multiple pistons are arranged around the axis of the output shaft of the engine. In each case connecting rod(s) connect the piston(s) and mechanism.

Connecting rods are generally rigid but, in some configurations particularly of some wobble yoke, or z-crank mechanisms for example, during operation of the mechanism the lower ends of the connecting rods tend to undergo, as well as reciprocating motion _'4n axis, some motion transverse to the connecting rod axis, such as transverse motion in a^60° orbit in one case, when viewed down the axis of the piston cylinder. At least this can accelerate wear of piston rings, guides, or cylinders, and in the extreme can cause the connecting rod(s) to fail by buckling for example.

It is an object of the present invention to provide an improved connecting rod or at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect, the invention broadly consists in a connecting rod comprising a body with two ends; a first flexible part provided on the body and capable of flexing in a first direction perpendicular to a longitudinal axis of the connecting rod; and a second flexible part provided on the body and capable of flexing in a second direction perpendicular to the longitudinal axis. Preferably, the body comprises a third flexible part capable of flexing in the second direction.

Preferably, the first direction is perpendicular to the second direction.

Preferably in a first form, one or more of the first, second, and third flexible parts are a necked section of the body. Preferably in a second form, one or more of the first, second, and third flexible parts are recessed sections. Typically in this second form, the flexible parts comprise a thinned section of the body comprising two indented sections diametrically opposed to one another. More preferably, the indented sections are concave shaped or scalloped.

Preferably, the first flexible part is provided between the second and third flexible parts.

In a second aspect the invention consists in an engine including a connecting rod as defined above.

In a third aspect the invention consists in a connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod; and a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

Preferably, the second flexible part is oriented 90 degrees relative to the first flexible part.

Preferably, the third flexible part is oriented in the same direction as the second flexible part. Preferably, the first flexible part is provided between the second flexible part and the third flexible part.

Preferably, the second flexible part is provided in close proximity to one end of the connecting rod.

Preferably, the third flexible part is provided in close proximity to one end of the connecting rod.

Preferably, the second flexible part is provided in close proximity to one end of the connecting rod and the third flexible part is provided in close proximity to the other end of the connecting rod.

Preferably, the first flexible part is provided in close proximity to the second flexible part.

Preferably, one or more of the first, second, and third flexible parts are a necked section of the body.

Preferably, one or more of the first, second, and third flexible parts are recessed sections.

Preferably, the flexible parts comprise a thinned section of the body comprising two indented sections diametrically opposed to one another.

Preferably, the indented sections are concave shaped or scalloped.

Preferably, the connecting rod is made from steel.

In a fourth aspect the invention broadly consists in a connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod. Preferably, the connecting rod comprises a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

Preferably, the third flexible part is oriented in the same direction as the second flexible part.

Preferably, the first flexible part is provided between the second flexible part and the third flexible part.

Preferably, the flexible parts are a necked section of the body.

Preferably, the flexible parts are recessed sections.

Preferably, the indented sections are concave shaped or scalloped.

Preferably, the connecting rod is made from steel. In a fifth aspect the invention broadly consists in an engine including at least one piston operating in a cylinder of the engine and a linear to rotational motion converter, the piston coupled to the linear to rotational motion converter by a connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod.

Preferably, the connecting rod comprises a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

Preferably, the linear to rotary motion conversion mechanism is a wobble yoke.

Preferably, the linear to rotary motion conversion mechanism is a z-crank shaft.

Preferably ,the engine is a Stirling engine.

In a sixth aspect the invention broadly consists in a micro combined heat and power system comprising: an engine arranged to drive an electrical alternator or generator and including at least one piston operating in a cylinder of the engine and a linear to rotational motion converter, the piston coupled to the linear to rotational motion converter by a connecting rod, the connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod.

The term "comprising" as used in this specification and claims means "consisting at least in part of. When interpreting each statement in this specification and claims that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. The invention consists in the foregoing and also envisages constructions of which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described by way of example only and with reference to the drawings, in which

Figure 1 is a perspective view of a z-crank shaft engine motion conversion mechanism showing a wobble member, pistons, connecting rods, and torque restraint member of one form of Stirling engine removed from the engine casing,

Figure 2 is a peispective view of the z-crank shaft engine motion conversion mechanism of Figure 1 and separate from the pistons and connecting rods, showing however four knuckle joints carried by the wobble member for coupling to the connecting rods; Figure 3 is a side view of the z-crank shaft engine motion conversion mechanism showing the same parts as in Figure 2, and also the connecting rods;

Figure 4 is a top view of the z-crank shaft engine motion conversion mechanism of Figure 3,

Figure 5 is a cross-section view of the z-crank shaft engine motion conversion mechanism of Figures 3 and 4 along line A-A of Figure 4;

Figure 6 is a perspective view of a wobble yoke engine motion conversion mechanism showing a wobble yoke, pistons, and connecting rods of one form of Stirling engine removed from the engine casing;

Figure 7 is a perspective view of the wobble yoke engine motion conversion mechanism of Figure 6, and separate from the pistons and connecting rods;

Figure 8 is a side view of the wobble yoke engine motion conversion mechanism showing the same parts as in Figure 7, and also the connecting rods and pistons, from one side;

Figure 9 is a cross section view of the wobble yoke engine motion conversion mechanism of Figure 6, and separate from the pistons; Figure 10 is a first side elevation view of a first preferred embodiment connecting rod showing the connecting iod flexing in one flexed condition;

Figure 11 is a second side elevation view of the connecting rod of Figure 10 showing the connecting rod flexing in another flexed condition, Figure 12 is a perspective view of a second preferred embodiment connecting rod of the invention;

Figure 13 is a first side view of the connecting rod of Figure 12;

Figure 14 is a second side view of the connecting rod of Figure 12 where the view of Figure 13 has been rotated 90 degrees;

Figure 15 is the first side view of the connecting rod of Figure 13 where the ends of the connecting rod are misaligned in a first plane; and

Figure 16 is the second side view of the connecting rod of Figure 14 where the ends of the connecting rod are misaligned in a second plane.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A first particular engine motion conversion mechanism shown by way of example in Figures 1 to 5 comprises a z-crank shaft and is used for converting linear reciprocating piston motion to rotary motion of an output shaft of the engine about an axis parallel to the axis of the piston motion, and is described as part of a Stirling engine which drives an electrical generator or alternator (herein referred to as a generator for convenience). A second particular engine motion conversion mechanism shown by way of example in figures 6 to 9 comprises a wobble yoke mechanism. In this description the terms "upper" or "top" and "lower" or "bottom" or similar are used to describe the mechanism in an orientation in which the output drive end of the mechanism is lowermost, and the crank pin of the z-crank shaft or the eccentric bearing of the wobble yoke shaft is uppermost, but it will be appreciated that the mechanism may be used in an engine (or pump or compressor) in which the output end of the crank shaft is uppermost, or to either side, or in any orientation, and the use of the relative terms upper or top and lower or bottom or similar should not be read as limiting the following description.

Referring to Figures 1 to 5, the first particular engine motion conversion mechanism comprises a z-crank shaft which is indicated at 1. It comprises an output drive end 2 and an angled crank pin 3 (see particularly Figure 5). The z-crank shaft 1 is mounted, for rotation about the longitudinal axis of the output drive end 2, in bearings in an engine casing (not shown). The rotor assembly of a generator (not shown) is carried on the output drive end 2 of the z-crank shaft.

A wobble member 6 is rotationally mounted on the angled crank pin 3. In the preferred form the wobble member 6 is of a generally tubular or cylindrical form as shown and is carried on the z-crank shaft 1 by upper and lower bearings 7a and 7b (see Figure 5), provided at or near either end of the wobble member 6, and in particular on either side of a boss portion 6a of the wobble member, at which four knuckle joints for coupling to the lower ends of connecting rods 14 from four pistons 19 (see Figure 1) are mounted to the wobble member 6. At the same boss portion 6a a torque restraint member is coupled to the wobble member 6. Bolt 30 passes through the top of the wobble member 6 and threads into an axial bore in the top of the crank pin 3 (see Figure 5). For convenience in this description the wobble member 6 will hereafter be referred to as the boss 6.

Four knuckle joints for coupling to the connecting rods of pistons of the engine are equidistantly spaced around the boss 6 as shown, and are fixed to the boss 6. A clevis 11 is pivotally mounted to the outer end of each hub pin 9 about a transverse axis via a hub pin bearing or bush 12. A con rod pin 18 has an enlarged yoke 14 with a bore transverse to the longitudinal axis of the con rod pin 18, whereby the con rod pin fits over the outer end of the hub pin 9, and is mounted to the hub pin 9 via hub pin bearing or bush 12. The lower end of a connecting rod 14 couples to each clevis 11 , for example by a threaded connection into the upper bridge part of each clevis (see in particular Figure 5).

In operation, linear reciprocating motion of the connecting rods 14, driven by the pistons of the engine, in the direction of arrows LM in Figure 3, is converted to rotary motion of the output shaft end 2 of the z-crank member 1 , as indicated by arrow RM (or vice versa is a pump or compressor application for example). Also, as the boss 6 oscillates as indicated by the arrows OM the lower end of the connecting rods 14 the knuckle joint 11 undergoes, as well as reciprocating motion in axis, some motion transverse to the axis of the connecting rods, and in particular with the mechanism described the lower end of the connecting rod executes a figure of eight motion in a plane transverse to the connecting rod plane.

Referring to Figures 6 to 9, the second particular engine motion conversion mechanism comprises a wobble yoke 50 and an output shaft 2. The output shaft 2 is mounted for rotation about its longitudinal axis. The output shaft 2 is mounted in an eccentric bearing 52. The rotary assembly of a generator (not shown) is carried on the output shaft 2.

The wobble yoke 50 comprises a first beam 54 which is able to pivot around its centre point and which is connected to pistons 56 through connecting rods 14 and pivotable con rod pins 55. The wobble yoke 50 also comprises a second beam58 which is able to pivot around its centre point and is connected to pistons 60 through connecting rods 14 and pivotable con rod pins 55. The beams 54, 58 are pivotally coupled to a nutating pin 62 (shown in Figure 9) which is coupled to the eccentric bearing 52.

The second beam 58 may be positioned at a right angle to the first beam 54. The first beam54 controls the motion of the pistons 56, and the second beam 58 controls the motion of the pistons 60.

As the pistons 56 reciprocate inside respective cylinders (not shown), for example due to heat applied to a hot head of a Stirling engine, the first beam 54 pivots about its centre point. Similarly, as the pistons 60 reciprocate inside respective cylinders (not shown), the second beam 58 pivots about its centre point. The reciprocating motion of the beam 54, 58 causes the nutating pin 62 to rotate the output shaft 2.

As the beams 54, 58 pivot around their centres and the pistons 56, 60 move reciprocally, each con rod pin 55 moves in an arc A (shown in Figure 9). During this movement the lower end of the connecting rod 14 becomes misaligned with the axis of its cylinder. Flexible parts are provided in the connecting rods 14 of the invention, which allow the connecting rods 14 to flex to accommodate this motion..

Referring to Figures 10 to 16, an individual connecting rod 14 of the invention is shown.

The connecting rod 14 has a body 15 which extends along a longitudinal axis L (shown in Figures 12 to 14) of the connecting rod. The connecting rod 14 has a first end 20 at which the connecting rod attaches to a piston, and a second end 22 at which the connecting rod attaches to the engine motion conversion mechanism such as at a clevis 11 in the z-crank mechanism of Figures 1 to 5, or at the con rod pins 55 in the wobble yoke mechanism of Figures 6 to 9. The first end 20 and second end 22 may be formed to enable the connecting rod to connect to a piston and engine mechanism (linear-rotary motion converter) by any suitable coupling. The connecting rod 14 may have a circular or other symmetrical cross-section other than at the sections 24, 26, and 28 referred to below, and may for example be formed of steel. The connecting rod 14 may be made from a single bar and preferably the bar is a steel bar. However, the connecting rod 14 may be made from two or more pieces, and each different part may be treated to alter physical characteristics such as rigidity or strength, for example by heat treatment. The connecting rod 14 may have a diameter which is more than ten times less than its length. The connecting rod 14 may have a diameter less than one tenth of its length. Referring to Figures 10 and 11, in a first preferred embodiment, the body 15 of the connecting rod 14 includes two parts 24, 26 which are shaped so as to be capable of flexing. The first embodiment connecting rod 14 may be used in an engine comprising a z-crank shaft motion converter for example, however it may be used in any other suitable application. Referring to Figures 12 to 16, in a second preferred embodiment, the body 15 of the connecting rod 14 includes three parts 24, 26, 28 which are each shaped so as to be capable of flexing. The second embodiment connecting rod 14 may be used in an engine comprising a wobble yoke motion converter for example, however it may be used in any other suitable application. The parts 24, 26, 28 (herein flexible parts) are relatively more flexible than the rest of the body 15 of the connecting rod 14. Referring to Figures 10 to 16, the flexible parts 24, 26, 28 may be machined or milled into the body 15 of the connecting rod 14. Alternatively, the flexible parts 24, 26, 28 may be formed in die bar by casting, forging, or cutting the bar or in any other suitable manner.

Referring again to Figures 10 and 11, the flexible parts 24, 26 may be necked sections of the body 15 of the connecting rod 14. Necked means having a section of reduced diameter. The necked section may gradually, quickly, or instantaneously reduce in diameter. The flexible parts 24, 26, 28 may be any combination of recesses or necked sections or any other suitable flexible element.

Referring again to Figures 12 to 16, the flexible parts 24, 26, 28 may be recesses that are concave or scalloped indented sections in the connecting rod 14. Alternatively, the indented sections may have flat faces or be of any other suitable shape. Preferably, each flexible part 24, 26, 28 comprises a thin section comprising two indented sections diametrically opposed to one another. The connecting rod 14 may flex at each part 24, 26, 28 in a direction perpendicular to the thinned section.

The first flexible part 24 is orientated so that it is capable of flexing in a first direction perpendicular to the longitudinal axis L of the connecting rod 14. The second flexible part 26 is oriented so as to be capable of flexing in a second direction perpendicular to the longitudinal axis L of the connecting rod 14. In embodiments with a third flexible part 28, the third flexible part 28 is oriented so as to be capable of flexing in a direction perpendicular to the longitudinal axis L of the connecting rod 14. The third flexible part 28 preferably has the same orientation as the second flexible part 26, however any suitable orientation may be used. Preferably, the first direction is also perpendicular to the second direction (as illustrated in the second preferred embodiment in Figures 12 to 16 where the first flexible part 24 is orientated at 90 degrees relative to the second 26 and third 28 flexible parts). In embodiments provided with three flexible parts, preferably, the first flexible part 24 is provided between the second 26 and third 28 flexible parts. Preferably, the second 26 and third 28 flexible parts are spaced as far apart from each other as possible. Typically the second flexible part 26 will be provided in close proximity to the first end 20 and the third flexible part 28 will be provided in close proximity to the second end 22 Preferably, the first flexible part 24 is provided in close proximity to the second flexible part 26 while still being provided between the second 26 and third 28 flexible parts. Alternatively, the flexible parts 24, 26, 28 may be provided in any order along the length of the connecting rod 14 and at any suitable distance from either end 20, 22, and from each other

In other embodiments, the connecting rod 14 may be provided with any suitable number of flexible parts The flexible parts may be oriented to allow the connecting rod 14 to flex in any suitable direction transverse to the longitudinal axis L. One or more of the length, width, number, axial position along the connecting rod 14, and rotational position around the connecting rod 14 may be changed as required. Further, the length, or diameter, or both of the connecting rod 14 may be changed as required Preferably, the flexible parts 24, 26, 28 allow the connecting rod 14 to flex in two perpendicular axes transverse to the longitudinal axis L The flexible parts 24, 26, 28 may allow the connecting rod 14 to flex in the plane perpendicular to its longitudinal axis L. This may allow the connecting rod 14 to flex to remove adverse forces on the piston rings, piston seals, cylinders, or other parts of the engine while still allowing it to be rigid enough to transfer an axial load from the pistons 19 to the motion conversion mechanism without buckling or breaking

During operation of the engine motion conversion mechanism, such as the z-crank mechanism or the wobble yoke mechanism, the upper end 20 of the connecting rod 14 (connected to the piston) may move in a reciprocating linear motion which may be defined by a longitudinal axis of a piston cylinder Simultaneously, the lower end 22 of the connecting rod 14 may move in a combination of rotational motion and reciprocating linear motion, such as a 360 degree orbit or a figure of eight, when viewed down the longitudinal axis of the piston cylinder With the z-crank shaft motion converter, the motion of the lower end 22 is determined by the knuckle _joint 11. With the wobble yoke motion converter, the motion of the lower end 22 is determined by the arc of the beams 54, 58 and the pivotal position of the con rod pin 55 A connecting rod 14 of the invention is able to flex in the plane perpendicular to its longitudinal axis L in order to accommodate any axial misalignment between the upper end 20 and the lower end 22 due to the differing motions of the upper end 20 and the lower end 22 The connecting rods 14 may still have sufficient rigidity to effectively transfer the downward piston force to the z-crank mechanism or wobble yoke mechanism without buckling or breaking. The connecting rods 14 may be described as multiple flexure connecting rods as they can flex independendy in two or more planes The connection of the connecting rods 14 to the pistons at the upper ends 20 of the connecting rods 14 may be rigid, thereby avoiding the need for a universal joint at this connection. There is then also no need to provide lubrication at any such joint between the upper end of the connecting rod and piston. The connection of the connecting rods 14 to the knuckle joints 11 or con rod pins 55 may be rigid, however the knuckle joints 11 and con rod pins 55 may themselves pivot.

Figure 15 shows a connecting rod 14 from a first side when die lower end 22 is misaligned from the upper end 20 due to the motion of the motion conversion mechanism. From this first side view, it is apparent that when the ends become misaligned, the axis of the upper end U may no longer be parallel with the axis of the lower end L in this plane, so that the connecting rod 14 approximates a "C" shape. This may be due to the arc A of the beams and the pivoting of the con rod pin 55. Figure 16 shows the same connecting rod 14 from a second side view rotated 90 degrees relative to the first side view.. From this second side view, it is apparent that when the ends become misaligned, the axis of die upper end U may be parallel with the axis of the lower end L in this plane, so that the connecting rod 14 approximates a "S" or "Z" shape. The axes U, L are able to remain parallel in this plane due to the two flexible parts 26, 28. The con rod pins 55 are not able to pivot in this plane and so the axes U, L may always be parallel, including when they are misaligned. Providing two flexible parts 26, 28 which can flex this plane means that the bearings do not need to accommodate for any relative motion or misalignment between the ends 20, 22. Cheaper, less complex, and/or easier to manufacture bearings may therefore be used which may decrease the manufacturing cost, material cost, and manufacturing complexity of the engine. Using die connecting rods 14 of the invention may increase required manufacturing tolerances of other parts of the engine, such as pistons, piston rings, piston seals, and cylinders, which may make it cheaper and/or easier to manufacture such parts. This may also decrease the care required when manufacturing an engine which may make it faster, easier, and/or cheaper to assemble.

The orientation of a connecting rod 14 is important when it is being used with a wobble yoke motion converter. Referring to Figure 9, the connecting rod 14 is oriented so that the first flexible part 24 is able to flex about an axis aligned with the pivot axis of its associated con rod pin 55. Conversely, the connecting rod 14 is oriented so that the second 26 and third 28 flexible parts are able to flex about an axis perpendicular to the pivot axis of its associated con rod pin 55.

The connecting rod 14 may flex in one manner in the first direction while flexing in a different manner in the second direction to provide the required rigidity to transfer the axial load from the piston 19 to the linear rotary motion converter, while reducing adverse forces on the piston, piston rings, piston seals, cylinders, or other parts of the engine. Other embodiments of the connecting rod 14 may work in a similar manner.

Connecting rods of the invention may be used in any suitable engine for example in an engine comprising a linear to rotary motion converter, such as a z-crank shaft motion converter or a wobble yoke motion converter. The connecting rods may be used in a heat engine such as a

Stirling engine, a Rankine cycle engine, or any other type of suitable engine. The connecting rods

14 may be used in a pump, gas compressor, heater, refrigerator, or the engine of any other suitable application. The connecting rods of the invention may be used in a cogeneration system such as a micro combined heat and power unit. Typically a micro combined heat and power unit comprises a Stirling engine which drives an electrical alternator or generator to supply electrical energy.

The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod; and a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

2. A connecting rod according to claim 1 where the second flexible part is oriented 90 degrees relative to the first flexible part.

3. A connecting rod according to either of claims 1 or 2 where the third flexible part is oriented in the same direction as the second flexible part.

4. A connecting rod according to any one of claims 1 to 3 where the first flexible part is provided between the second flexible part and the third flexible part.

5. A connecting rod according to any one of claims 1 to 4 where the second flexible part is provided in close proximity to one end of the connecting rod.

6. A connecting rod according to any one of claims 1 to 5 where the third flexible part is provided in close proximity to one end of the connecting rod.

7. A connecting rod according to any one of claims 1 to 4 where the second flexible part is provided in close proximity to one end of the connecting rod and the third flexible part is provided in close proximity to the other end of the connecting rod.

8. A connecting rod according to any one of claims 1 to 7 where the first flexible part is provided in close proximity to the second flexible part.

9. A connecting rod according to any one of claims 1 to 8 where one or more of the first, second, and third flexible parts are a necked section of the body.

10. A connecting rod according to any one of claims 1 to 8 where one or more of the first, second, and third flexible parts are recessed sections.

11. A connecting rod according to claim 10 where the flexible parts comprise a thinned section of the body comprising two indented sections diametrically opposed to one another.

12. A connecting rod according to claim 11 where the indented sections are concave shaped or scalloped.

13. A connecting rod according to any one of claims 1 to 12 made from steel.

14. A connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod.

15. A connecting rod according to claim 14 comprising a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod.

16. A connecting rod according to either of claims 14 or 15 where the second flexible part is oriented 90 degrees relative to the first flexible part.

17. A connecting rod according to claim 15 where the third flexible part is oriented in the same direction as the second flexible part.

18. A connecting rod according to any one of claims 15 to 17 where the first flexible part is provided between the second flexible part and the third flexible part.

19. A connecting rod according to any one of claims 14 to 18 where the second flexible part is provided in close proximity to one end of the connecting rod.

20. A connecting rod according to claim 15 where the third flexible part is provided in close proximity to one end of the connecting rod

21. A connecting rod according to any one of claims 15 to 18 where the second flexible part is provided in close proximity to one end of the connecting rod and the third flexible part is provided in close proximity to the other end of the connecting rod.

22. A connecting rod according to any one of claims 14 to 21 where the first flexible part is provided in close proximity to the second flexible part.

23. A connecting rod according to any one of claims 14 to 22 where the flexible parts are a necked section of the body.

24. A connecting rod according to any one of claims 14 to 23 where both the flexible parts are recessed sections.

25. A connecting rod according to claim 24 where the flexible parts comprise a thinned section of the body comprising two indented sections diametrically opposed to one another.

26. A connecting rod according to claim 25 where the indented sections are concave shaped or scalloped.

27. A connecting rod according to any one of claims 14 to 27 made from steel.

28. An engine including at least one piston operating in a cylinder of the engine and a linear to rotational motion converter, the piston coupled to the linear to rotational motion converter by a connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod; a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod.

29 An engine according to claim 28 where the connecting rod comprises a third flexible part provided on the body and oriented so that the connecting rod may flex in a third direction perpendicular to the longitudinal axis of the connecting rod

30 An engine according to either of claims 28 or 29 where the linear to rotary motion conversion mechanism is a wobble yoke.

31. An engine according to any one of claims 28 to 29 where the linear to rotary motion conversion mechanism is a z-crank shaft.

32. An engine according to any one of claims 28 to 31 where the engine is a Stirling engine.

33. A micro combined heat and power system comprising- an engine arranged to drive an electrical alternator or generator and including at least one piston operating in a cylinder of the engine and a linear to rotational motion converter, the piston coupled to the linear to rotational motion converter by a connecting rod, the connecting rod comprising: a body with two ends extending along a longitudinal axis of the connecting rod, a first flexible part provided on the body and oriented so that the connecting rod may flex in a first direction perpendicular to the longitudinal axis of the connecting rod; and a second flexible part provided on the body and oriented so that the connecting rod may flex in a second direction perpendicular to the longitudinal axis of the connecting rod