AXIAL PISTON MACHINE CONNECTION ROD ASSEMBLIES

FIELD OF INVENTION This invention, relates to piston connection rod assemblies for 2-Crank axial piston machines, including but not limited to engines, fluid pumps and motors. BACKGROUND

In particular, although not solely, this invention relates to piston connection rød assemblies for Z-Crank axial piston machines such as two or four-stroke axial piston internal ^' ' combustion engines and pumps in general. More specifically but not solely, it relates to elements of piston connection, rod assemblies used to drive the reciprocating motion of pistons in axial piston machines suitable for operation at relatively high speeds and loads.

An axial piston machine is a machine in which a plurality of axially extending cylinders, together comprising the cylinder cluster, are arranged in a generally rotationally symmetrical layout around a central axis coincident with the rotational axis of a crankshaft. Each cylinder contains a reciprocating piston that may reciprocate along an axis parallel or slightly inclined to that of the other cylinders. Axial piston machines may offer a number of potential advantages over other multi-cylinder piston machine configurations including: reductions in size and weight, simplified fluid porting, and the ability to achieve close to perfect balancing of the dynamic inertial forces.

There are a number of different mechanisms that can be used to drive the reciprocating motion of the pistons in their cylinders, two of the most common types being Swashplate drives and Wobbleplate or Z-Crank drives. While terminology can vary, a swashplate is in effect a cam surface attached to and rotating with the crankshaft that drives or is driven by the reciprocating linear motion of the pistons. Each piston has a bearing or bearings attached to it that slides or rolls over the surface of the swashplate cam surface. Each piston also has some form of linear bearing such as the side of the piston within its cylinder that reacts the lateral forces created by the action of the piston-driving bearings when on the inclined surface of the swashplate. The piston-swashplate bearings will generally have a sliding or rolling speed over the swashplate in the order of two times the peak piston reciprocating speed. While this arrangement is adequate for axial piston machines having relatively low piston speeds such as compressors and hydraulic pumps or

motors, modern internal combustion engines commonly have much higher piston reciprocity speeds, and the high inertial loads and bearing sliding or rolling speeds in a swashplate drive operating with high piston speeds can lead to high frictional losses that make piston roller bearings less attractive for internal combustion engines. Z-Crank drives employ an intermediate body known variously as a Wobbleplate,

Wabbler, Reciprocator or Spider that rotates on bearings mounted on a crank section of the Z-Qank crankshaft inclined to and intersecting with the crankshaft's rotational axis at an acute angle hereinafter referred to as the "swash angle" at a point hereinafter referred tb as "point X". The reciprocator is restrained against rotation with respect to the cylinder cluster by a torque restraint mechanism that may be implemented using a variety of mechanisms so that the rotation of the inclined section of the crankshaft causes the reciprocator to nutate. US4235116 described such a mechanism. So does WO9859160. As a result points on the body of the reciprocator in a plane perpendicular to the axis of the inclined crank section of the crankshaft (hereinafter referred to as the "reciprocator axis" or "inclined crank axis" as they are both coincident) at point X move in a predominantly axial oscillatory motion, with motion in the plane perpendicular to the crankshaft axis being of relatively small magnitude. The connection between the reciprocator and pistons can take many forms but generally connection rods having joints with two ot more rotational degrees of freedom are utilised at both ends to connect to the piston and the reciprocator respectively. WO9859160 shows an example. The reciprocator bearings typically operate at much lower sliding speeds than would the piston bearings of an equivalent Swashplate drive. As a consequence frictional losses will generally be reduced.

Known joints between the piston and the connection rod (hereinafter referred to as the "little end joint") and the reciprocator and the connection rod (hereinafter referred to as the "big end joint") may have a number of disadvantages. The piston, little end joint, connection rod and big end joint together comprise the piston connection rod assembly. Unlike conventional crank driven piston machines each of these connections require two ox more rotational degrees of freedom, and this can significantly increase the weight and complexity of these joints. The little end and big end joints both oscillate through a range of angular motion as the pistons reciprocate in their cylinders, with the little end joint typically being subjected to a far smaller range of angular oscillatory motion than is the big end joint.

The axial piston machine of US Patent 4,207,779 utilises concentric internal and external spherical bearing surfaces for both the little end and the big end joints so that these joints posses three rotational degrees of freedom. However, in an axial piston machine having just three or five pistons packed closely together in the cylinder cluster and having a piston stroke that is of similar dimension to the diameter of the piston as is generally desirable for efficient operation of an internal combustion engine, it may become necessary to use a large swash angle, perhaps as great as 40 degrees or more in the case of a three cylinder engine. Large swash angles in combination with the relatively large radius of the sliding surface in a spherical big end joint necessitated by the need for sufficient bearing area to transfer the connection rod loads to the reciprocator may lead to unacceptably high surface sliding speeds in big end joint spherical bearings with high frictional losses and limited life due to the high sliding speeds. Also the bearing contact area when the connection rod is in tension may be severely restricted with large swash angles. Spherical bearings are also generally more difficult to manufacture accurately when compared to cylindrical bearings.

The axial piston engine of NZ Patent 328,190 as shown in Figure 1 uses joints with two orthogonal rotational degrees of freedom at both the little end and the big end. In the case of the little end the two axes of rotation intersect and are formed from a truncated cylindrical bearing bush that is free to rotate within a lateral cylindrical cavity in the piston end of the connection rod. This cylindrical bearing bush has a conventional wrist pin penetrating through its centre perpendicular to its axis, and this wrist pin itself runs in bearing contact with the piston in conventional piston wrist pin bosses. The big end is comprised of two fork and clevis type joints displaced from each other such that their axes of rotation do not intersect and each incorporating thrust bearing surfaces in addition to their radial bearing surfaces.

There are a number of potential problems associated with the connection rod mechanism of Figure 1: The reciprocating motion of the piston and associated rotation of the big end joint gives rise to rotational oscillations in the connection rod about its long axis, these oscillations similar to the "gknbal error" encountered in Hookes or Cardan joints occur at twice the frequency of the piston oscillation and result in relatively large torsional torques being induced in the connection rod about its longitudinal axis as it in turn oscillates the piston angularly about its axis. A typical I-beam cross section of a connection rod is not

well suited to transmitting these torsional loads; Another issue is that in high specific output axial piston engines having relatively large swash angles the loads on the big end bearings may exceed the limits of what can be born while still achieving acceptable longevity. The loads at the big end are typically higher owing to the added inertial forces from the connection rod assembly in addition to that of the piston, and increasing the diameter of the big end bearing will increase the sliding speeds and frictional losses of the bearings, while increasing the bearing lengths is ultimately limited by the deflection of the bearing pins 24,25 cantilevered out the sides of the big end block 34.

It is accordingly an object of this invention to provide a piston to reciprocator connection rod arrangement that is suitable for operation in high specific output internal combustion engines and that offer a number of improvements to the general principles outlined by prior art above, or at least to offer the public a useful choice. BRIEF DESCRIPTION OF THE INVENTION

Accordingly in a first aspect the present invention consists in an axial piston machine acting as a thermodynamic engine, compressor, motor or pump comprising; a crankshaft having a crankshaft axis and carrying an inclined crank journal having an inclined crank axis that is oblique to the crankshaft axis but aligned to intersect therewith at an acute angle A at point X, a cylinder cluster defining or comprising of at least two cylinders rigidly located with respect to each other, each cylinder containing a complementary piston to each reciprocate along a reciprocating axis defined by its respective cylinder and each having a cross section matched to the cross section of the cylinder, each said cylinder including at least one fluid inlet/outlet port, a reciprocator mounted to rotate relative to said inclined crank journal about said inclined crank axis/reciprocator axis, rotational restrainer to restrict the relative rotation between said cylinder cluster body and said reciprocator so that relative rotation between said cylinder cluster and said reciprocator is restrained relative to the crankshaft axis, connection rods, one for each piston and (a) linked to each piston by a little end joint possessing two or more rotational degrees of freedom and (b) linked to said reciprocator by a big end joint possessing two rotational degrees of freedom to allow the requisite

reciprocating displacement of each piston within its respective cylinder between top dead centre (TDC) and bottom dead centre (BDC) upon the crankshaft rotating relative to said cylinder cluster about the said crankshaft axis, each connection rod having a connection rod axis defined with respect to the body of each said connection rod as the axis that intersects at least one of the connection rod's big end rotational degrees of freedom as well as at least one of connection rod's little end rotational degrees of freedom.

Preferably there is an indexing drive to transmit rotation between said cylinder cluster and said crankshaft to, in use, rotate said cylinder cluster relative a ported member about said crankshaft axis at a rotational rate indexed to the rate of rotation of the crankshaft, said ' ported member including fluid transfer facilities at spaced apart locations and about the crankshaft axis, thereby said cylinder openings are sequentially presented to the facilities of the ported member to allow cyclic communication of each cylinder opening with each port, corresponding to the desired phase of motion of a said piston in its respective cylinder between its TDC and BDC positioning. Preferably said cylinder cluster is mounted to rotate about said crankshaft axis and relative to said ported member.

Preferably said reciprocating axis of each said cylinder is parallel to the crankshaft axis. Preferably said crankshaft axis is coaxial with the axis of rotation of cylinder cluster about which the cylinder cluster rotates to move relative to said ported member. Preferably oxygen/fuel mixture is introduced into a said cylinder via at least one appropriate port opening to be compresses by said piston and to combusts in the cylinders when their respective piston of said cylinder is approaching TDC.

Preferably the machine is a engine that is a four stroke engine and each cylinder has a working cycle of four cycle stages.. Preferably said pistons complete one cycle of reciprocal motion per rotation of the crankshaft with respect to the cylinder cluster..

Preferably the engine is a four stroke internal combustion engine and said cylinder cluster body includes an odd number of three or more cylinders..

Preferably the engine is a four-stroke internal combustion engine and said port openings of said ported member comprises of at least two of a set of ports comprising (i) at least one inlet port to allow inlet of at least one of the fluid components for combustion into

the cylinder and (ϋ) at least one exhaust port to allow exhaust of combustion fluids from said cylinder..

Preferably said sets of ports are equally spaced around the axis of said cylinder cluster.. Preferably said big end joint has two rotational degrees of freedom defined by two pivot axes, a first (the big end joint to connection rod pivot axis) intersects the inclined crank axis and a second (the big end joint to reciprocator pivot axis) is tangential to inclined crank axis. Preferably the big end joint to connection rod pivot axis intersects the big end joint to reciprocator pivot axis.

Preferably said big end joint comprises a big end intermediate body linked to said connection rod by a pivot having a connection rod to big end pivot, axis, said big end intermediate body also being linked to said reciprocator by a pivot with a reciprocator to big end pivot axis that is perpendicular to the connection rod to big end pivot axis.

Preferably said connection rod to big end pivot axis intersects with the inclined crank axis at all times.

Preferably said big end reciprocator to big end pivot axis is tangential to a circle around the inclined crank axis.

Preferably said reciprocator to big end pivot axis is proximal more the reciprocating axis of the piston when the piston is at top dead centre than when the piston is half way between its top dead centre and bottom dead centre positions.

Preferably said connection rod to big end pivot axis and said reciprocator to big end pivot axis do not intersect; the connection rod to big end pivot axis is more proximal to the piston than is the reciprocator to big end pivot axis when the piston is at top dead centre.

Preferably said big end intermediate body to connection rod pivot and/ or said big end intermediate body to reciprocator pivot is/are of a plain journal bearing.

Preferably said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot comprise a plain journal bearing and plain thrust bearings.

Preferably said plain thrust bearings of said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot include floating thrust washers that fit between the big end intermediate body and the connection rod and/or

teciprocator respectively to reduce the sliding speed of the thrust bearing contacts at these pivots.

Preferably said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot includes a pivot shaft (acting as part of the plain journal bearing) that pivotally connects the big end intermediate body to the connection rod.

Preferably said pivot shaft has at least two or mote axially spaced and discrete spans at where it is located in bearings defined or supported by the intermediate body.

Preferably said pivot shaft has at least two or mote axially spaced and discrete spans at where it is located in bearings defined or supported by the connection rod. Preferably there are three axially spaced and discrete spans located in bearings of said intermediate body and two axially spaced apart and discrete spans located in bearings of said connection rod.

Preferably the pivot shaft is hollow and open at at least one of its ends.

Preferably said big end plain bearings incorporate grooves and/or galleries and/or other lubricant oil distribution features to facilitate supply of lubricating oil to said plain bearings.

Preferably, in use, lubricating oil is supplied to the bearings of said big end joint under pressure from coolant galleries in the reciprocator that are in turn supplied from oil galleries in the crankshaft

Preferably said big end plain journal bearings incorporate bush inserts of appropriate plain bearing materials.

Preferably said little end joint possesses two rotational degrees of freedom.

Preferably the little end joint has only two rotational degrees of freedom oriented such that in use the little end joint can transfer torsional forces between said connection rod and piston. Preferably two little end pivots are provided to define the two rotational degrees of freedom their axes preferably being perpendicular to each other, one of them perpendicular to the axis of the cylinder and the other perpendicular to the axis of the connection tod, and both mutually perpendicular.

Preferably said connection rod between the little end joint and big end joint is of circular (constant ot not) cross section between said little end and big end joints.

Preferably the gudgeon pin of the piston to be aligned tangentially to the rotation of the cylinder cluster so that centrifugal forces don't try to force the gudgeon pin out of the piston.

Preferably said little end joint comprises of a little end intermediate body linked to said piston by a pivot and a piston to little end pivot axis that is perpendicular to said piston reciprocating axis, said little end intermediate body also being linked to said connection rod by a pivot having a connection rod to little end pivot axis that is perpendicular to die piston to little end pivot axis.

Preferably said connection rod to little end pivot axis and the connection rod to big end ' pivot axis do not intersect.

Preferably said connection rod to little end pivot axis and the connection rod to big end pivot axis intersect.

Preferably when the cylinder cluster rotates about said crankshaft axis during operation of the axial piston machine, the piston to little end pivot axis is oriented so as to maintain a large average distance between said piston to little end pivot axis and said crankshaft axis.

Preferably in use said cylinder cluster and said crankshaft rotate relative each other and about said crankshaft axis..

Preferably said little end joint possesses three rotational degrees of freedom. Preferably said little end joint comprises of a part spherical bearing at said piston to connection rod interface.

Preferably said spherical bearing includes a concave partially spherical contact area defined by or connected to one of said piston and connection rod and a convex partially spherical contact area defined by or connected to the other of the piston and connection rod. Preferably said bearing includes secondary partially spherical bearing surfaces to provide bearing interface between the connection rod and piston for forces acting in a direction opposite to the first mentioned partially spherical bearing surfaces (herein after "primary partially spherical bearing surfaces").

Preferably the surface area of the secondary partially spherical bearing surfaces is smaller than the surface ^" area of the primary partially spherical bearing surfaces.

Preferably the primary partially spherical bearing surfaces are operative when compressive forces applied to the connection rod.

Preferably said connection rod is generally substantially I-beam in cross section between said little end joint and said big end joint as high torsional strength due to the piston not being torsionally oscillated by the little end joint is not required..

In a second aspect the present invention consists in a Z-crank axial piston internal combustion engine comprising a cylinder cluster of at least two piston containing cylinders rigidly located with respect to each other, each said cylinder including at least one working fluid transfer port, a crankshaft rotatable ϊelaύve to said cylinder cluster and carrying an angled crank about which a reciprocator can rotate that is in mechanical connection with the pistons, and a ported member relative to which the cylinder cluster can rotate and that can seal the at least one fluid transfer port of each cylinder yet offers, at intervals, their exposure to spark plug(s) and/or working fluid delivery and removal facilities, an indexing drive to transmit rotation between said cylinder cluster and said crank shaft to, in use, rotate said cylinder cluster relative said ported member about said crankshaft axis at a rotational rate timed to coincide with the desired range of movement of the piston in each cylinder between TDC and BDC, and wherein for each piston, said mechanical connection between said pistons and the reciprocator is provided by a connection rod.

Preferably the mechanical connection is a herein described with reference to the first aspect of the invention as described above. In a further aspect the present invention consists in a connection mechanism between a reciprocator and a piston of a Z-crank engine or pump that includes a crankshaft having a crankshaft axis and carrying an angled crank about which said reciprocator can rotate, said connection mechanism comprising; a connection rod extending between the piston and the reciprocator and that is connected to the reciprocator by a big end joint has two rotational degrees of freedom defined by two pivot axes, a first (the big end joint to connection rod pivot

axis) intersects the angled crank axis and a second (the big end joint to reciprocator pivot axis) is tangential to the axis of the angled crank.

Preferably the big end joint to connection rod pivot axis intersects the big end joint to reciprocator pivot axis. Preferably said big end joint comprises a big end intermediate body linked to said connection rod by a pivot having a connection rod to big end pivot axis, said big end intermediate body also being linked to said reciprocator by a pivot with a reciprocator to big end pivot axis that is perpendicular to the connection rod to big end pivot axis. Preferably said connection rod to big end pivot axis intersects with the inclined crank axis at all times.

Preferably said big end reciprocator to big end pivot axis is tangential to a circle around the angled crank axis.

Preferably said reciprocator to big end pivot axis is proximal more the reciprocating axis of the piston when the piston is at top dead centre than when the piston is half way between its top dead centre and bottom dead centre positions.

Preferably said connection rod to big end pivot axis and said reciprocator to big end pivot axis do not intersect; the connection rod to big end pivot axis is more proximal to the ^■ piston than is the reciprocator to big end pivot axis when the piston is at top dead centre. Preferably said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot is/are of a plain journal bearing.

Preferably said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot comprise a plain journal bearing and plain thrust bearings. Preferably said plain thrust bearings of said big end intermediate body to connection rod pivot and/ or said big end intermediate body to reciprocator pivot include floating thrust washers that fit between the big end intermediate body and the connection rod and/ or reciprocator respectively to reduce the sliding speed of the thrust bearing contacts at these pivots. Preferably said big end intermediate body to connection rod pivot and/or said big end intermediate body to reciprocator pivot includes a pivot shaft (acting as part of the plain journal bearing) that pivotally connects the big end intermediate body to the connection rod.

Preferably said pivot shaft has at least two or more axially spaced and discrete spans at where it is located in beatings defined or supported by the intermediate body.

Preferably said pivot shaft has at least two or more axially spaced and discrete spans at where it is located in bearings defined or supported by the connection rod. Preferably there are three axially spaced and discrete spans located in bearings of said intermediate body and two axially spaced apart and discrete spans located in bearings of said connection rod.

Preferably the pivot shaft is hollow and open at at least one of its ends.

Preferably said big end plain bearings incorporate grooves and/or galleries and/or other lubricant oil distribution features to facilitate supply of lubricating oil to said plain bearings..

Preferably , in use, lubricating oil is supplied to the bearings of said big end joint under pressure from coolant galleries in the reciprocator that are in turn supplied from oil galleries in the crankshaft.

Preferably said big end plain journal bearings incorporate bush inserts of appropriate plain bearing materials.

Preferably said little end joint possesses two rotational degrees of freedom.

Preferably the little end joint has only two rotational degrees of freedom oriented such that in use the little end joint can transfer torsional forces between said connection rod and piston. ' Preferably two little end pivots are provided to define the two rotational degrees of freedom their axes preferably being perpendicular to each other, one of them perpendicular to the axis of travel of the piston with its cylinder and the other perpendicular to the axis of the connection rod, and both mutually perpendicular.

Preferably said connection rod between the little end joint and big end joint is of circular (constant ot not) cross section between said little end and big end joints.

Preferably the gudgeon pin of the piston to be aligned tangentially to the rotation of the cylinder cluster so that centrifugal forces don't try to force the gudgeon pin out o£ the piston..

Preferably said little end joint comprises of a little end intermediate body linlced to said piston by a pivot and a piston to little end pivot axis that is perpendicular to said piston reciprocating axis, said little end intermediate body also being linked to said connection rod

by a pivot having a connection ϊod to little end pivot axis that is perpendicular to the piston to little end pivot axis.

Preferably said connection rod to little end pivot axis and the connection rod to big end pivot axis do not intersect. Preferably said connection rod to little end pivot axis and the connection rod to big end pivot axis intersect.

Preferably in use said cylinder cluster and said crankshaft rotate relative each other ^" and about said crankshaft axis..

Preferably said little end joint possesses three rotational degrees of freedom. ' Preferably said little end joint comprises of a part spherical bearing at said piston to connection rod interface.

Preferably said spherical bearing includes a concave partially spherical contact area defined by or connected to one of said piston and connection rod and a convex partially spherical contact area defined by or connected to the other of the piston and connection rod.

Preferably said bearing includes secondary partially spherical bearing surfaces to provide bearing interface between the connection rod and piston for forces acting in a direction opposite to the first mentioned partially spherical bearing surfaces (herein after "primary partially. spherical bearing surfaces"). • - Preferably the surface area of the secondary partially spherical bearing surfaces is smaller than the surface area of the primary partially spherical bearing surfaces.

Preferably the primary partially spherical bearing surfaces are operative when compressive forces applied to the connection rod.

Preferably said connection rod is generally substantially I-beam in cross section between said little end joint and said big end joint as high torsional strength due to the piston not being torsionally oscillated by the little end joint is not required..

In a further aspect the present invention consists in an axial piston machine comprising;

(i) a cylinder cluster comprising at least two cylinders rigidly located with respect to each other, each said cylinder including at least one cylinder opening for fluid inlet and/or outlet to and/or from said cylinder,

(ii) in each cylinder, a complementary piston to reciprocate along a reciprocating axis defined by its respective cylinder,

(iϋ) a crankshaft rotatable relative to said cylinder cluster about a crankshaft axis said crankshaft carrying a crank that has a crank axis passing through said crankshaft axis at an angle,

(iv) a reciprocator rotatably mounted by and about said crank journal to rotate about said inclined crank axis, said reciprocator operatively connecting said crank journal with each said piston via a connection rod, such that the rotational motion of the crankshaft with respect to the cylinder cluster drives the reciprocal motion of the pistons within their respective cylinders or visa versa, between top dead centre ^" (TDC) and bottom dead centre (BDC)

(v) a ported member to facilitate a sealing of and opening of at least one cylinder opening of each cylinder timed to coincide with the desired range of movement of a piston in a cylinder between TDC and BDC, wherein each said connection rod is linked to (a) a respective piston by a little end joint possessing two or more rotational degrees of freedom and (b) to said reciprocator a big end joint possessing two rotational degrees of freedom to allow the requisite reciprocating displacement of each piston within its respective cylinder between top dead centre (TDC) and bottom dead centre (BDC) upon the crankshaft rotating relative to said cylinder cluster about the said crankshaft axis, each connection rod having a connection rod axis defined with respect to the body of each said connection rod as the axis that intersects both of the connection rod's big end rotational degrees of freedom as well as one or more of connection rod's little end rotational degrees of freedom.

Preferably the connection rod and/or its connection mechanism is as per that described with reference to the first and/ or second aspects of the invention as described above.

In a yet a further aspect the present invention consists of an axial piston machine acting as a thermodynamic engine, compressor, motor or pump comprising; a crankshaft rotatable about a crankshaft axis and carrying a crank journal having an inclined crank axis that is oblique to the crankshaft axis but aligned to intersect therewith at an acute angle A at point X,

a cylinder cluster comprising at least two cylinders rigidly located with respect to each other, each cylinder spaced relative to the other(s) and about a cylinder cluster axis, each said cylinder including at least one cylinder opening to allow fluid inlet and/or outlet to/from said cylinder, in each cylinder, a complementary piston to reciprocate along a reciprocating axis defined by its respective cylinder, a reciprocator mounted to rotate about said crank journal about said inclined crank axis, said reciprocator operatively connecting said pistons with said crank journal by a connection rod, such that the rotational motion of the crankshaft with respect to the cylinder cluster drives the reciprocal motion of the pistons within their respective cylinders or visa versa, and allows consistent and controlled reciprocating displacement of each piston within its respective cylinder between top dead centre (TDC) and bottom dead centre (BDC) each said connection rods, linked to (a) a respective piston by a little end joint possessing two or more rotational degrees of freedom and (b) to said reciprocator by a big end joint possessing two rotational degrees of freedom to allow the requisite reciprocating displacement of each piston within its respective cylinder between top dead centre (TDC) and bottom dead centre (BDC) upon the crankshaft rotating relative to said cylinder cluster about the said crankshaft axis, each connection rod having a connection rod axis defined with respect to the body of each said connection rod as the axis that intersects both of the connection rod's big end rotational degrees of freedom as well as one or more of connection rod's little end rotational degrees of freedom.

Preferably the connection rod and/or its connection mechanism is as per that described with reference to the first and/or second aspects of the invention as described above. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements ot features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

If and as used herein the term "and/or" means "and" or "or", ot both.

If and as used herein "(s)" following a noun means the plural and/or singular forms of the noun.

The term "comprising" as used in this specification means "consisting at least in part- of '. When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of ' providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, ot such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the present invention will now be described with reference to the accompanying drawings in which;

Figure 2 is a partial cross sectional view of a three cylinder axial piston machine showing the layout of the major components while omitting the cylinder heads and porting arrangements (and wherein components shown are representative only with simplified bearings and lacking assembly details and other features that may be required in a practical machine),

Figure 3 is an isometric view of die cross sectioned axial piston machine of Figure 2 and for clarity with many components hidden and several components unsectioned,

Figure 4 is an isometric view of a three cylinder axial piston machine with many components hidden and several components unsectioned, showing another preferred embodiment of connection rod and little and big end joints,

Figure 5 is an isometric view of a three cylinder axial piston machine with many components hidden and several components unsectioned, showing another preferred embodiment of connection rod, little end and big end joints, Figure 6 is a detail view of the big end intermediate body of the preferred embodiment of Figure 5,

Figure 7 is a partial cross sectioned view of an engine showing other components,

Figure 8 shows a rotation restraint mechanism that may be used to restrain relative rotation of the reciprocator and the cylinder cluster about the crankshaft axis,

Figure 9 is a cross sectional view through another engine of the present invention wherein a different rotation restraint mechanism is shown, Figure 10 is a view of multiple rotation restraint mechanisms that may be used,

Figure lla-c shows the path travelled by the big end of the connection rod where die big end is positioned at one location relative the reciprocator,

Figure 12a-c shows the path travelled by the big end of the connection rod where 'the big end is positioned at a different location relative the reciprocator to that of figure lla-c, Figure 13 is a view from 90 degrees around to that of figure 12 and wherein other geometric aspects are shown,

Figure 14 is a view from 90 degrees around to that of figure 11 and wherein other geometric aspects are shown, and

Figure 15 is a representative view of the figure of eight path as described with reference to figures 11-14.

Where reference is made herein to acute angle S, it is also referred to as the "swash angle". Where reference is made to "rotation constraint" ot "restraint" it is also known as "torque restraint", "rotational constraint" or "rotational restraint".

With reference to Figure 2 there is shown in a simplified cross sectional drawing of a preferred form of an axial piston machine omitting any cylinder head or fluid porting detail.

By way of example, US 6,494,171 describes the relationship between the cylinder cluster and the cylinder and the ports that provide the utilities for the operation of an axial piston combustion machine. US 6,494,171 is accordingly hereby incorporated by way of reference.

While in Figure 2 there is shown the geometry for a z-crank axial piston machine with three cylinders 4, any number of cylinders could be utilised. However, the current invention has greatest utility in a compact three cylinder engine such as is depicted in Figure 2 and three or more cylinders are preferred for the purposes of dynamic balancing.

The axial piston machine of the present invention and with reference to Figure 2 consists of a crankshaft 6 having a crankshaft axis 8. The crankshaft may be supported along its length by multiple coaxial journal bearings 10, 12 (alternatively rolling element bearings could be used) that allow the crankshaft to rotate with respect to the cylinder cluster 8. Preferably one of the crankshaft support bearings 10 is mounted off of the

cylinder cluster 16, while another of the crankshaft support bearings 12 is mounted within a cylinder cradle 18 that is mounted off of the cylinder cluster 16 and provides a wide bearing support base for the crankshaft 6. The crankshaft support bearing 12 may also incorporate a thrust bearing 14 that accommodates the thrust force on the crankshaft 6 created by fluid pressure on each of the pistons 20. In the preferred form the crankshaft 6 operates as a power output or input shaft to the axial piston machine.

Formed as either an integral part of, or securable to the crankshaft 6, is an inclined crank journal 22 having an inclined crank axis 24. The crankshaft axis 8 and inclined crknk axis 24 intersect at a point X at an acute angle S. A reciprocator 32 rotates with respect to ^' the crankshaft 6 on journal bearings 26, 28 and thrust bearing 30 about the inclined crank journal 22. These plain journal bearings 26, 28 may be substituted for by rolling element bearings in the same location or in the case of the thrust bearing 30 at a different location along the inclined crank 22. The reciprocator bearings 26, 28 are preferably separated by as large an axial distance on said inclined crank journal 22 as can be easily accommodated within other constraints so as to reduce the loads and frictional losses in the reciprocator bearings 26, 28.

For a three cylinder version of the machine, three identical connection rod piston assemblies are provided, one for each of the three cylinders 4 in the cylinder cluster. Each comprise a piston 20 connected through a little end joint 40 to a connection rod 34 that is in turn linked to the reciprocator 32 by a big end joint 38. Each is connected to the reciprocator 32 at locations that are rotationally symmetric about the inclined crank axis 24. The body of the reciprocator 32 bridges between said reciprocator bearings and the joints with the connection rod big end intermediate bodies 36 with a structure that is robust enough to withstand the.inertial and fluid forces transmitted to or from the pistons 20 and connection rod piston assemblies while endeavouring to minimise the moment of inertia of the reciprocator 32 about point X so as to reduce the inertial forces on the reciprocator bearings 26, 28, 30.

The reciprocator 32 controls the reciprocating motion of the pistons 20 within the cylinders 4 of the cylinder cluster 16 by means of connection rods 34. Each connection rod links together the reciprocator 32 and one of the pistons 20 through a big end joint 38 having two rotational degrees of freedom with respect to the

reciprocator, and a little end joints 40 having three rotational degrees of freedom with respect to the piston 20.

A rotational constraint mechanism constrains the relative rotation of the reciprocator

32 and cylinder cluster 16. It does so such that the reciprocator 32 rotates at the same angular rate about the inclined crank journal 22 as does the cylinder cluster 16 about the crankshaft 6 in order to minimise die average angle between the connection rod axis 46 and the cylinder axis 48. The restraint mechanism can take many forms. This is herein after described.

Dynamic balance masses 42, 44 forming either an integral part of, or securable to the ' crankshaft 6 contribute to the dynamic balancing of the inertial forces and moments created by the pistons 20, connection rods 32, reciprocator 16, and big end intermediate bodies 36 of the axial piston machine.

The big end joint of the- axial piston machine of Figure 2 is comprised of one big end intermediate body 36 possessing two orthogonal pivot joints having pivot axes 50, 52 that connect to the reciprocator 32 and connection rod 34 respectively. The big end intermediate body to reciprocator joint axis 50 is orthogonal to the inclined crank axis 24 while the big end intermediate body to connection rod joint axis 52 intersects the inclined crank axis 24.

This orientation of axes in the big end joint has the advantage of reducing the axial loadings on the big end pivot joint bearings to a degree where thrust washers can in general be used to react the axial loadings on the big end pivot joints. Thrust washers between the components of the big end pivots effectively halve the sliding speeds.

For an internal combustion engine the big end intermediate body to reciprocator joint axis 50 is preferably displaced outwards from the inclined crank axis 24 to decrease the angle of the connection rod when the piston is subjected to the greatest gas pressure and inertial forces at TDC and BDC so that lateral forces on the pistons 20 and consequently friction are reduced. This also provides greater radial space between the connection rods 34 and reduces the necessary swash angle for a given piston stroke as well as reducing the range of oscillatory motion of the big end joints.

The range of oscillatory angular motion of the pivots in the big end joint of a z-crank axial piston machine is relatively large, particularly for compact three or five cylinder axial piston machines such as that shown in Figure 2. To reduce the adverse impact of high sliding speeds for the bearings in the big end joints in conjunction with high loads, oil

lubrication and cooling may help to prevent big end bearing failures so may increasing the area of the bearings. Increasing the diameter of the big end joint plain bearings increases bearing area but may increase the mass of the big end joint and increase the sliding speeds of the bearings as their angular velocities remain the same. Increasing the length in the direction of their rotational axis of the big end pivot bearings is of potentially greater advantage as it increases the bearing area without increasing the sliding speeds. It also allows for more locations at which the radial to the rotational axis forces can be taken up thereby allowing moϊe radial load sharing that can also help tend the load to be more of a uniformly distributed load. At the connection rod to big end joint of Figure 2, a hollow doubly supported plain bearing pin 54 may be supported at two or more positions along its length by the connection rod 34 such that the deflection in a direction radial to the pin of the pin 54 is far reduced as compared to what it would be if a pin of the same length and diameter supported by the connection rod in a single central axial position were subjected to the same total radial bearing load.

The positions of the connection rod 34 to pin 54 connections are preferably selected such that the bearing loads produce similar amounts of deflection in the pin 54 at both the centre and the ends. The bearing surfaces of this joint in the big end intermediate body 36 is split into three or more co-axial and preferably co-radial (same diameter) bearing surfaces 56. These are preferably lined with a suitable plain bearing material such as bronze for improved bearing durability, and the axial or thrust loadings on this joint are accommodated by thrust washers 58 that are preferably free to rotate with respect to the pin 54 and connection rod 34 and intermediate body 36.

The big end joint- 38 induces oscillatory rotations in the connection rods 34 about its axis 46 in a similar manner to that encountered in vehicle universal joints (also known as Cardan or Hookes joints) at double the frequency of the piston reciprocation. If this oscillation were to be transferred to the piston then large torsional loadings may be induced in the connection rod when operating at high speeds. As a means of reducing this loading the little end pivot joint 40 may be comprised a spherical bearing with three rotational degrees of freedom. This may be defined by a spherically domed convex head 60 to the connection rod 34 that slides in contact with a spherical cavity 62 in the piston 20. The spherically domed convex head 60 has a second spherical surface 64 that is concave,

concentric, of smaller radius and lesser area to the convex spherical surface of the spherically domed convex head 60. This concave surface is in contact with a second spherical bearing surface in the piston. Contact is preferably lubricated and preferably oil cooled.

This little end joint 40 arrangement is particularly suitable for use in internal combustion engines in which the gas forces are much greater than the inertial acceleration forces created by the reciprocating motion of the piston. The spherically domed convex head 60 is formed as a body of revolution about the connection rod spherical bearing axis 66, that intersects the connection rod axis at an angle E. This may be chosen such that the spherically domed head 60 has as much contact area as possible with spherical bearing cavity ^' 62 of set dimensions without coming into interference with said piston 20 as it rotates about and reciprocates along cylinder axis 48.

The offset between the pivot axes 50,52 of the big end intermediate body 36 is convenient for reducing weight and creating a mote compact design, but it creates higher order harmonics in the otherwise generally sinusoidal reciprocating motion of the pistons 20 in a similar manner to the connection rods in conventional crank-piston machines. These higher order harmonic inertial forces are generally more difficult to balance than is the primary harmonic that can typically be balanced using suitable mass distributions on the crankshaft. However, and with reference to figures 12 and 13, it can be seen that the path travelled- at point 52 provided the benefit that side loadings of the piston onto the cylinder wall due to the connection rod not being parallel to the cy]indeϊ axis at and near Top Dead Centre is reduced due to the skewed figure of eight locus that is traced by point 52. Angle α tends towards zero the greater the distance P becomes as can be seen between figure 13 and 14.

The figure-of-eight .movement 799 shown in figure 15 describes any fixed point 50 on a truly 'homokinetic' reciprocator (relative to the cylinder cluster) that is not on the reciprocator axis 24. When that fixed point (on an imaginary 'sphere') is on a plane to which the reciprocator axis 24 is normal and intersecting point X, then the. figure-of-eight is perfectly symmetrical about two axes of symmetry. The deviation from the vertical centreline of the figure of eight at or near top dead centre is less in the skewed figure of eight than in the symmetrical figure of eight. Both the width of the top part of the figure of 8 (also known as a lemniscate) is smaller than the bottom part as well as the net deviation from the vertical centre line being less at the top half of the figure of 8 compared to the

bottom. At and near top dead centre the working fluid gas pressures ^' acting on the piston and hence the connection rod are greatest.

Figure 3 shows the same cross sectioned axial piston machine of Figure 2 in isometric cross section with the cylinder cluster 16, crankshaft 6 and cylinder cradle 18 hidden and one of the connection rods piston assemblies shown unsectioned. The joint between the big end intermediate body 36 and the reciprocator 32 is formed by a hollow pin 68 that passes through the big end intermediate body such that it extends to either side of the big end intermediate body and fits into lubricated sliding contact with the plain bearing bushings 70 in the reciprocator on either side of the big end intermediate body. Floating thrust washers ' 72 on either side of the big end intermediate body 36 and concentric with the hollow pin 68 accommodate the axial loadings on the big end intermediate body to reciprocator joints that may be higher than the axial loadings on the connection rod 34 to big end intermediate body joint. The big end intermediate body to reciprocator pivot hollow pin 68 is preferably of larger diameter than the big end intermediate body to connection rod hollow pin 54 owing to its singly supported cantilevered nature. However in internal combustion engines the highest loadings typically occur when the piston is close to TDC or BDC and at these instants the sliding velocities of the big end intermediate body to reciprocator pivots is much less than maximum and this may make a singly supported large diameter plain bearing 68 as is depicted in Figures 2 and 3 more acceptable. Figure 4 shows an isometric partial cross section of part of a three cylinder axial piston machine similar to that of Figures 2, 3 having an alternative preferred embodiment of connection rod piston assembly and in which the cylinder cluster 16, crankshaft 6, cylinder cradle 18 and two of the pistons 104 are hidden and one of the connection rod piston assemblies comprising a connection rod 100 and its little end joint 114 and big end joint 112 are shown unsectioned. Each little end joint 114 includes a little end intermediate body 116 that rotates with respect to and within a cylindrical cavity in the connection rod 100 about little end intermediate body to connection rod pivot axis 118 on cylindrical bearing surface 120 with axial thrust bearing faces 124, 126. This prevents relative motion of the little end intermediate body 116 with respect to the connection rod 100 along the pivot axis 118. The . little end intermediate body 116 also rotates with respect to the piston (not shown but exemplified by piston 104) about little end intermediate body to connection rod pivot axis 122 on the cylindrical outer bearing surface of hollow pin 128 inserted through the middle of

the little end intermediate body 116. Axial thrust bearings restrict the motion of the little end intermediate body 116 along the pivot axis 122 with respect to the piston. The two pivot axes 118, 122 intersect each other at right angles and the pivot axis 118 also intersects the connection rod axis 130 at a right angle. Each little end joint 114 has just two rotational degrees of freedom and this means that angular oscillations in each connection rod 100 about its axis 130 created by the big end joint 112 produce significant torsional loadings in the connection rods at twice the frequency of piston 104 reciprocation along their respective axes 132. This is mainly due to the relatively large rotational inertia of the pistons 104 that are being subjected to these oscillating angular accelerations through the little end joints 114. In this preferred embodiment a connection rod 100 that is tubular, partially tubular on circular (constant diameter or not) in cross section between the little end 114 and big end 112 joints along the connection rod axis 130 is used as it has greater strength and- rigidity in torsion than I-beam or H-beam cross sections that are commonly employed in conventional engine connection rods. The big end joint 112 has two orthogonal non-intersecting pivot axes offset from each other by a distance P and preferably oriented such that the connection rod to big end intermediate body pivot axis 134 at all times intersects the inclined crank axis 24 and is more proximal the little end joint 114 than the reciprocator to big end intermediate body pivot axis 136. In this embodiment both of the orthogonal big end pivot joints incorporate hollow doubly supported plain bearing pins 108, 110 that are each supported at two or more positions along their length by the connection rod 100 and the reciprocator 102 respectively such that when the connection rod 100 is subjected to its peak tensile or compressive loadings the maximum bending deflections of the pins 108, 110 are approximately reduced, thereby increasing the load bearing capacity of the big end joint bearings. Two or more floating thrust washers, for example; 138, 140 free to rotate upon their respective pins 108, 110 are incorporated into each of the pivots in the big end joint 112 to accommodate the oscillating bi-directional axial loadings on the pivots. The hollow pins 108, 110 are preferably fitted into the connection rod 100 and reciprocator 102 using interference fits or other retaining methods. Hollow pins allow lubrication and cooling to be effectively distributed to areas that require such.

This preferred embodiment of big end joint has the advantage of not requiring honed bearing surfaces or bushings in either the reciprocator 102 or the end of the connection rod

100 proximal to the big end joint as all of the honed bearing surfaces or bearing bushes for the big end joint are within the big end intermediate body 106. The smaller diameter of the reciprocator 102 to big end intermediate body pivot pin 110 may also make it possible to reduce the distance P between the pivot axes 134, 136 as compared to the big end joint 38 of Figures 2 and 3, which may help to reduce the size of engine vibrations.

Figure 5 is an isometric partial cross section of part of a three cylinder axial piston machine similar to that of Figures 2, 3 and 4 in which the cylinder cluster 16, crankshaft 6 and cylinder cradle 18 are hidden and one of the three identical connection rods 200 and its big end joint 204 are shown unsectioned. The piston connection rod assembly of Figure 5 is ' an alternative preferred embodiment with a little end joint 206 similar to the little end joint 38 shown in the preferred embodiment of Figures 2, 3. The primary difference is that it instead utilises an oil cooled and lubricated concave ot cupped spherical bearing surface 208 on the terminal face of the connection rod that slides in lubricated contact with a convex spherical surface in the piston 202, The connection rods 200 have a second spherical surface 214 concentric and of greater radius to the concave surface 208 that is in lubricated contact with a second generally annular spherical bearing surface in the piston. The spherical bearing surfaces of the piston are cavities of revolution about the cylinder axis 48 and the perimeter boundaries of the spherical bearing surfaces 208, 214 are made such that the spherical bearing contact area with the piston is approximately increased without causing interference even as the piston reciprocates and rotates within its cyiinder 4. The greater bearing contact area of spherical surface 208 as compared to the bearing contact area of spherical surface 214 means that the little end joint 206 is suited to internal combustion engines in which the gas forces are greater than the inertial acceleration forces created by the acceleration of the piston 202 on the connection rod 200. The big end joint 204 is similar to the preferred embodiments of Figures 2-4 in that it has two orthogonal rotational degrees of freedom and the big end intermediate body 216 to connection rod 200 pivot axis intersects the inclined crank axis 24 at all times. However the big end joint pivot axes 210, 212 of the preferred embodiment of Figure 5 intersect each other. This helps to reduce the size of harmonic imbalances otherwise caused by an offset between the two pivot axes 210, 212 such as is present in the embodiments of Figures 2-4. The big end intermediate body 216 to connection rod 200 pivot is made up of a pin 218 that is rigidly fixed at two locations along its length to the connection rod 200 and which rotates

in lubricated sliding contact within three or more axially separated plain bearing journals formed as part of the big end intermediate body 216, such that when bearing loads are applied to the pin the maximum deflections of the pin are approximately minimised. Thrust washers 220 free to totate with respect to both the connection rod 200 and big end intermediate body 216 accommodate oscillating bi-directional loadings along the pivot axis 210. The big end intermediate body 216 to reciprocator 222 pivot is made up of two identical pins 224 sharing a coaxial pivot axis 212 and lying on either side of pin 218. These pins 224 are rigidly fixed to the big end intermediate body 216 at both ends and rotate in bearing bosses 226 formed as part of the reciprocator 222 to provide the bearings that are ' the big end intermediate body 216 to reciprocator 222 pivot. Floating thrust washers 228 accommodate the oscillating bi-directional axial loads transmitted between the reciprocator 222 and the big end intermediate bodies 216.

Figure 6 illustrates in greater detail the big end intermediate body 216 of the preferred embodiment of Figure 5. Accordingly the current invention may have the advantage of offering a connection rod to reciprocator big end joint that utilises plain bearings having good load capacity and longevity as well as reduced manufacturing costs as compared to big end joints employing rolling element bearings. Plain thrust and journal bearings may be lighter, have greater load capacity .and are more manufacturer friendly. Additionally the current invention may make it possible to reduce die mass of the reciprocating components of the engine with consequent reductions in engine mass, average bearing loads and frictional losses.

The current invention may also offer a more durable connection rod design that is capable of operating at higher speeds when a little end joint having just two rotational degrees of freedom is employed

The current invention may also offer the advantage of being able to operate at the relatively high speeds, loads and swash angles that may be encountered within compact three or five cylinder high specific output axial piston internal combustion engines without unacceptable friction or wear when compared to alternative designs of connection rod and their joints.

The current invention may additionally offer the advantage of a reduction in unbalanced harmonic vibrations.

The machine and features described above have application for many types of axial piston machines such as pumps and engines.

Reference will now be predominantly be made to a four stroke version of an axial piston engine. However it will be appreciated by a person skilled in the art how what is described can be applied to two stroke axial piston engines and axial piston engines or pumps utilising Swashplate drives or otherwise.

Figure 7 is a cross-sectional view of a simplified four-stroke five cylinder axial piston engine omitting some of the details necessary for construction for the sake of clarity. The ported member 302 has three sets of inlet ports 304, exhaust ports 306 and spark plug or ' fuel injection orifices 308 passing through it, though only some of all the ports are visible in tliis cross sectional view. The ports and orifices have a rotational symmetry of order three around the crankshaft axis 316.

The inlet ports 304 and exhaust ports 306 would generally have inlet and exhaust manifolds (not shown) respectively attached to them to guide the inlet and exhaust flow. The ported member 302 is mounted rigidly to an engine casing 310.

A cylinder cluster 312 defines ot holds five cylinders 314 equi-spaced around the crankshaft axis 316.

Each of the cylinders has a cylinder opening 348 (there may be more than one opening.per cylinder) that comes into cyclic communication with each of the ports 304, 306 and spark plug or fuel injection orifices 308. By way of a sliding face seal 350 a gas-tight seal between the cylinder head and face of the ported member 2 can be maintained.

The cylinder openings 348 of each cylinder may be provided directly at the main combustion zone and each cylinder or at an extension therefrom.

Each cylinder 314 contains a piston 318 (shown in figure 1 at TDC) linked to a connection rod 34 by means of a rotational little end joint 40 (that in this diagram is simplified for clarity). Each piston 318 is of a cross section matched to the cross section of its respective cylinder 314. The connection rod 34 is in turn linked to the reciprocator 32 through a rotational big end joint 38, (also simplified for clarity). The reciprocator is mounted on an inclined crank journal 22 that is formed as part of the crankshaft 6 and that has an inclined crank axis 24 that intersects with the crankshaft axis 316 at an acute angle at a point X.

The reciprocator 32 is restrained against rotation with respect to the cylinder cluster 312 by a rotation constraint mechanism. This may be comprised of two gimbal arms 352, 354 mounted on bearings off of the cylinder cluster 312 and the reciprocator 32 respectively and linked together by a spherical joint 356. TMs ensures operational syncronicity between the reciprocator and the cylinder cluster.

In Figure 8 there is shown part of the components of the rotational constraint mechanism that includes the two gimbal arms 352 and 354. The lower gimbal arm 354 is mounted to rotate with the reciprocator and can pivot about pivot axis 448 by for example journalled bearings 370. The upper gimbal 352 is mounted to the cylinder cluster 312 by the - journals 372. The journals 372 allow for relative rotation between the gimbal 352 and the cylinder cluster to occur about axis 446. The gimbal link joint 356 allows for appropriate rotational degrees of freedom between the reciprocator gimbal 354 and the cylinder gimbal 352, yet allows for a torque transfer to occur therebetween.

Figure 9 shows an alternative torque constraint mechanism wherein a plurality of gimbal arms pairs are provided. Towards the right hand side of the engine a sectional view through a pair of gimbal arms 502 and 504 is shown. The cylinder gimbal arm 502 is joined to the cylinder cluster 512 at rotational joint Cl. It is also joined to the reciprocator gimbal 504 at the rotational joint Tl. The reciprocator gimbal 504 is connected to the reciprocator at rotational joint Rl . pairs. In this multi-arm rotation restraint system a number of identical pairs of rotation arms equal to the number of cylinders is arrayed about the engine in a symmetrical manner. Each pair of rotation arms being comprised of: a cylinder rotation arm 502 pivotably mounted on a cylinder arm hinge axis Cl as part of or attached to the cylinder cluster 512. The pivot mount allows the cylinder rotation arm 502 to rotate with respect to the cylinder cluster 512 about an axis perpendicular to the crankshaft axis, while constraining any motion along the cylinder arm hinge axis Cl. A reciprocator rotation arm 504 is pivotably mounted on a reciprocator arm hinge axis Rl off of the reciprocator 32. The pivot mount allows the reciprocator rotation arm 504 to rotate about an axis perpendicular to the crank axis, relative to the reciprocator 32 while preventing any motion along the reciprocator arm hinge axis Rl. The cylinder arm 502 and the reciprocator arm 504 of each rotation arm pair in the multi arm rotation reaction system are linked together by a universal tip joint possessing three rotational degrees of freedom that intersect at a point Tl. In the case of Fig 9 a

spherical bearing is used for simplicity, though other tip joint configurations having three intersecting rotational degrees of freedom may be more advantageous. The point Tl of the tip joint is at an identical distance from the respective pivoting hinge axes Rl and Cl of the rotation arm pairs and in operation the locus of the tip joints Tl for all of the pairs of rotation arms will always lie on the medial plane M which in figure 9 is in an instantaneous orientation perpendicular to the plane of the drawing. This implies and requires that the pivoting hinge axes Rl and Cl of each pair of rotation arms be exact mirrors of each other in the medial plane M, or in other words the cylinder arm hinge axis Cl must be exactly - ^' the same distance from the crankshaft axis 516 and point X as the reciprocatσr arm hinge axis Rl is from the crank axis 24 and point X respectively, to ensure homo-kinetic operation of the multiple rotation arm rotation restraint system.

All the cylinder arm hinge axes and all the reciprocator arm hinge axes are positioned to be rotationally symmetric about the crankshaft axis 516 and crank axis 24 respectively, and are preferably located between the connection rod 34 to reciprocator 32 rotational joints (shown in simplified form) to allow for a more compact implementation of the multiple rotation arm rotation restraint system. The bearings of the cylinder arm hinge axes and the bearings of the reciprocator hinge axes must be able to withstand operation with substantial loads applied to them both parallel and perpendicular to their hinge axes as each arm applies a significant moment and inertial load to its hinge mount, the moments in particular necessitate relatively large axial spacings between the bearings that form the hinge axes as is illustrated by the example of reciprocator hinge bearings 506 that form one of the reciprocator arm hinge axes.

The total rotation restraint required is shared between the multiple pairs of rotation arms, so that the individual arms and their bearings need only take a proportion of the total load and may thus be made individually smaller than for a single pair of rotational constraint gimbals. In order to ensure that sharing of the total restraining rotation occurs between the multiple pairs of rotation arms 502, 504 etc a small degree of compliance may be useful either in the form of slight bending of the rotation arms 502, 504 themselves in response to applied loads at Tl parallel to their respective hinge axes Rl or Cl, ot alternatively from a small amount of sprung axial compliance in the thrust bearings of the rotation arms' respective hinge axes Rl, Cl. ■

The rotationally symmetric positioning of the rotation arm pairs means that for engines with three or more rotation arm pairs the inertial forces and moments produced by the motion of the wtaύon arms can be almost completely balanced out by suitable balance masses attached to the crankshaft, thereby resulting in an engine with less noticeable vibrations. By offsetting the hinge axes Cl, Rl radially outwards from the crankshaft axis 516 and crank axis 24 respectively there is more space made available for the structure of the reciprocator 32.

Figure 10 shows detail of the arms of Figure 9 with an alternative design of universal tip joint for the multiple rotation arm pairs that instead employs a compound joint ' possessing three independent and intersecting rotational degrees of freedom. All components excepting the crankshaft and five rotation arm pairs (two of which are directly behind other rotation arm pairs and so are completely obscured) are hidden for clarity. Describing the components for one of the rotation arm pairs: The cylinder arm 602 pivots about the cylinder arm hinge axis Cl on two coaxial radial bearing for example 614 and for thrust. The cylinder arm 602 incorporates a complementary cylinder arm forked knuckle that rotates about axis Vl with respect to the cylinder arm 602 on two axially separated bearings at location 614 that also prevent axial movement of the cylinder arm forked knuckle along the axis Vl with respect to the cylinder arm 602. The reciprocator arm 604 pivots about the reciprocator arm hinge axis Rl on two coaxial radial bearings and thrust bearings. The reciprocator arm 604 incorporates a complementary reciprocator arm clevis knuckle 630 that rotates about axis Ul with respect to the reciprocator arm 604 on two axially separated bearings that also prevent axial movement of the reciprocator arm clevis knuckle 630 along the axis Ul with respect to the reciprocator arm 604. The cylinder arm forked knuckle 618 and the reciprocator arm clevis knuckle 630 are linked together in the fork-and-clevis type knuckle pivot by radial and thrust bearings that allow them to rotate with respect to each other about the tip hinge axis Wl which is perpendicular to the axes Ul and Vl. All three axes Ul, Vl, Wl intersect at tip joint point Tl which lies on the medial plane M (not shown).

The rotation arm bearings may be rolling element or plain bearings, but if plain bearings are utilised then in some cases it may be necessary to utilised floating bushes and/ or thrust washers in order to reduce the friction and wear of the bearings. For example in the implementation depicted in Figure 10 the knuckle pivot is subjected to a greater range of

angular motion than are the other rotation arm bearings and may benefit significantly from the utilisation of floating bearings.

With reference to figure 7, in use, as the crankshaft 6 rotates with respect to the cylinder cluster 312 the reciprocate* 32 moves the pistons 318 to reciprocate in their respective cylinders 314. Whilst reference herein may be made axial piston machines where the pistons may travel parallel to each other and parallel to the crank shaft, it is also to be understood to cover a configuration where the pistons move at an incline to each other and to the crank shaft.

In the configuration shown the cylinder cluster 312 rotates in the opposite direction ' to the crankshaft with respect to the ported member 302 at a rate equal to one fifth that of the crankshaft for the four-stroke five cylinder engine depicted in order to create the required synchronisation of port timing with piston motion. Different rates of co or counter rotation may be required where different cylinder numbers are provided. This described in greater detail in US Patent 6,494,171 which is hereby incorporated. . The relative rate of rotation of the crankshaft 6 and cylinder cluster 312 with respect to the ported member 302 is controlled by an indexing drive. Referring to Figure7 this may be provided by an epicyclic gear set in this preferred embodiment and is comprised of an annular gear 858, a sun gear 860 and three planet gears 862 mounted from the engine casing 310 and having an axis of rotation 864 that preferably remains stationary relative thereto. The machine or engine as herein described may include, other features that may provide some benefits. Such are described in co existing complete specifications of NZ 560586 and NZ 560589.

Where reference here in is made to "rotation about" or similar, such as "rotation about the crankshaft axis" it is to be understood that is could mean to refer to a complete revolution or revolutions or partial revolution about for example the crankshaft axis.

The engine or machine of the present invention may be configured of any number of cylinders though 3 or more is preferred. Where the machine is operating as an internal combustion engine, fluid that passes through the ports may be a fuel and/or fuel/ air mixture. The cylinder cluster as herein referred to can be a cylinder block that has cylindrical bores provided therein. Alternatively it ^" may be comprised of discrete cyclinders that are affixed to each other by way of a frame or the like. Each cylinder defines a combustion

chamber where the present invention is provided to operate as an internal combustion engine.