Patent Application
20140216244
The invention relates to a rocking cylinder assembly, a method of operating a rocking cylinder assembly, a machine comprising a rocking cylinder assembly, a bearing component for a rocking cylinder assembly and a cylinder for a rocking cylinder assembly.
The term “rocking cylinder assembly” is used throughout the specification to refer to a cylinder assembly comprising a cylinder which is rotatable (e.g. rotatably mounted so that it can rotate) about a rocking axis.
Rocking cylinder assemblies typically comprise a piston (typically driven by a crankshaft) reciprocating within a cylinder such that, when the piston reciprocates within the cylinder, the cylinder rotates about a rocking axis periodically between first and second end positions. The cylinder typically comprises a bore terminating at a cylinder bearing surface, the line of intersection between the bore and the bearing surface defining a circular cylinder aperture through which fluid can flow into/out of the cylinder. The cylinder bearing surface typically bears against a bearing surface of a bearing component comprising a bearing component bore terminating at the bearing surface of the bearing component. A line of intersection between the bore and bearing surface of the bearing component defines a circular aperture through which fluid can flow through the bearing component. As the cylinder rotates between the first and second end positions, the cylinder bearing surface bears against the bearing surface of the bearing component, while the cylinder and bearing component apertures remain in fluid communication.
In order to improve the performance of a machine comprising such a rocking cylinder assembly, it is typically desirable to increase the fluid flow area through the bearing component and/or cylinder apertures. However, the minimum diameter of the cylinder aperture is typically set such that there is no overlap between the cylinder bearing surface and the bearing component aperture throughout the entire sweep of the cylinder between the first and second end positions. Overlap is undesirable because the size of the swept area of the bearing surface of the bearing component is reduced (since part of the cylinder bearing surface no longer bears against the component bearing surface during the overlap) leading to reduced load capacity and rapid wear at the interface between the part of the cylinder surface that bears against the component bearing surface and the component bearing surface. In addition, the overlapping portion of the cylinder aperture may offer a sharp lip to the fluid flow, causing flow separation and creating non-laminar flow, vortices and/or stagnant regions. The flow is also constricted periodically by the overlap, while there may also be a reduction in hydrostatic clamping force. All of these factors lead to instability and unpredictable effects. Accordingly, increasing the size of the component aperture typically requires a corresponding increase in the size of the cylinder aperture, and thus of the diameter of the cylinder as a whole, and of the size of the machine.
One way of improving the flow rate through the cylinder and component apertures is to change the bore to stroke ratio (e.g. to increase the ratio of the width of the cylinder bore to the length of the stroke of the piston). However, this would significantly increase the bearing load on the bearing surfaces of the crankshaft and hence the bending stress on the crankshaft. Also, this would lead to longer sealing lines which may lead to increased fluid leakage. In any event, the bore to stroke ratio is typically chosen to optimise various factors such as weight, efficiency, cost and fixed operating speeds (e.g. fixed operating speeds of the crankshaft). Accordingly, it may not be possible to alter the bore to stroke ratio without significantly affecting other features of the design.
The invention relates to a rocking cylinder assembly which allows an increased fluid flow rate through the combination of the bearing component and the cylinder for a given size of cylinder.
A first aspect of the invention provides a rocking cylinder assembly comprising: a cylinder having a cylinder bore terminating at a cylinder bearing surface and a cylinder aperture defined by a line of intersection between the cylinder bore and the cylinder bearing surface, the cylinder being rotatable about a rocking axis between first and second end positions; and a bearing component having a component bore terminating at a component bearing surface and a component aperture defined by a line of intersection between the component bore and the component bearing surface, the cylinder bearing surface bearing against the component bearing surface and the cylinder and component apertures being in fluid communication as the cylinder rotates between the first and second end positions, a first one of the cylinder and component apertures having a greater area than the second one of the cylinder and component apertures, the first one of the cylinder and component apertures defining a first fluid flow path having a first principal fluid (e.g. hydraulic liquid) flow axis along which fluid (e.g. hydraulic liquid) flows through the said first one of the apertures and a second one of the cylinder and component apertures defining a second fluid (e.g. hydraulic liquid) flow path having a second principal fluid flow axis along which fluid (e.g. hydraulic liquid) flows through the second one of the apertures, characterised in that the ratio of the area of the said second one of the apertures to the square of the maximum extent of the said second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second principal fluid flow axis is greater than the ratio of the area of the said first one of the apertures to the square of the maximum extent of the said first one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the first principal fluid flow axis.
The ratio of the area to the square of the maximum extent of an aperture in a direction perpendicular to the rocking axis and perpendicular to the its principal fluid flow axis is a unitless ratio which is independent of the actual size of the aperture. Accordingly, defining this ratio with respect to both apertures enables their shapes to be compared independently of size.
In the event that the first one of the apertures has a perfectly circular area, the said ratio of the area of the said first one of the apertures to the square of the maximum extent of the said first one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the first principal fluid flow axis is equal to π/4 (πr2/(2r)2=π/4, where r is the radius of the circle), in this case, the said ratio of the area of the said second one of the apertures to the square of the maximum extent of the said second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second principal fluid flow axis is typically greater than π/4. Put another way, in this case the said second one of the apertures typically has a greater area than a notional circular area having a diameter equal to the maximum extent of the said second one of the apertures in the said direction perpendicular to the rocking axis and perpendicular to the second principal fluid flow axis.
It will be understood that the cylinder aperture rotates about the rocking axis with the cylinder, but that the said maximum extent of the cylinder aperture in a direction perpendicular to the rocking axis typically remains perpendicular to the rocking axis as the cylinder rotates between the first and second end positions.
The principal fluid flow axis of the component aperture is typically perpendicular (and fixed relative) to the rocking axis. The principal fluid flow axis of the cylinder aperture typically rotates with the cylinder about the rocking axis.
It will be understood that the area of the cylinder aperture is the area of the cylinder aperture through which fluid can flow.
The cylinder aperture may lie on a single plane (the cylinder aperture may have a two dimensional shape). For a cylinder aperture which lies on a single plane, the area of the cylinder aperture may be a planar area of the cylinder aperture in a plane perpendicular to the principal fluid flow axis of the fluid flow path of the cylinder aperture.
It may be that the cylinder aperture does not lie on a single plane (the cylinder aperture may have a three dimensional shape). For example, the cylinder aperture may follow a curved path, such as a (e.g. concave or convex—see below) contour of the cylinder bearing surface. For a cylinder aperture which does not lie on a single plane (or even for a cylinder aperture which does lie on a single plane), the area of the cylinder aperture may be the area of a projection of the cylinder aperture along the principal fluid flow axis of the fluid flow path defined by the cylinder aperture onto a plane perpendicular to the said principal fluid flow axis.
It will also be understood that the area of the component aperture is the area of the component aperture through which fluid can flow.
The component aperture may lie on a single plane (the component aperture may have a two dimensional shape). For a component aperture which lies on a single plane, the area of the component aperture may be a planar area of the component aperture in a plane perpendicular to the principal fluid flow axis of the fluid flow path of the component aperture.
It may be that the component aperture does not lie on a single plane (the component aperture may have a three dimensional shape). For example, the component aperture may follow a curved path, such as a contour (e.g. concave or convex—see below) of the component bearing surface. For a component aperture which does not lie on a single plane (or even for a component aperture which does lie on a single plane), the area of the component aperture may be the area of a projection of the component aperture along the principal fluid flow axis of the fluid flow path defined by the component aperture onto a plane perpendicular to the said principal fluid flow axis.
It will be understood that, if the cylinder and/or component apertures lie on a single plane (the said aperture has a two dimensional shape), the maximum extents of the said aperture in the direction parallel and perpendicular to the rocking axis (and perpendicular to the principal fluid flow axis of the aperture) are each typically the lengths of respective straight lines extending in those directions between opposing edges of the respective aperture. It will also be understood that, if the cylinder and/or component apertures do not lie on a single plane (the aperture has a three dimensional shape), the maximum extents of the said aperture in the directions parallel and perpendicular to the rocking axis (and perpendicular to the principal fluid flow axis of the aperture) are each typically the lengths of respective straight lines extending in those directions between opposing edges of the area of the projection of the aperture along the principal fluid flow axis of the aperture onto a plane perpendicular to the said principal fluid flow axis.
It will also be understood that, if the cylinder and/or component apertures do not lie on a single plane (the said aperture has a three dimensional shape), references to the shape of the aperture are typically references to the shape of the projection of the aperture along the principal fluid flow axis of the aperture onto a plane perpendicular to the said principal fluid flow axis. This also typically applies to cylinder and/or component apertures which do lie on a single plane (apertures having a two dimensional shape).
Accordingly, that the first one of the cylinder and component apertures has a greater area than the second one of the cylinder and component apertures can typically be taken to mean that a projection of the first one of the apertures along the first principal fluid flow axis onto a plane perpendicular to the first principal fluid flow axis has an area which is greater than an area of a projection of the second one of the apertures along the second principal fluid flow axis onto a plane perpendicular to the second principal fluid flow axis. In this case, the ratio of the area of the said projection of the second one of the apertures to the square of the maximum extent of the said projection of the second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second principal fluid flow axis is typically greater than the ratio of the area of the said projection of the first one of the apertures to the square of the maximum extent of the said projection of the first one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the first principal fluid flow axis.
The area of the cylinder aperture may be greater than the area of the component aperture (in which case the cylinder aperture is the said first one of the apertures and the component aperture is the said second one of the apertures). In another embodiment, the area of the component aperture may be greater than the area of the cylinder aperture (in which case the component aperture is the said first one of the apertures and the cylinder aperture is the said second one of the apertures). The first one of the apertures may have a substantially circular shape. The second one of the apertures may have a (quasi-oval) substantially elliptical shape. The (shape of the) second one of the apertures is typically elongate (or at least more elongate than the first one of the apertures) in a direction parallel to the rocking axis. Preferably (at least part of, preferably the majority of, even more preferably all of) the second one of the apertures has a shape which conforms to (or at least approximates or is identical to) a shape defined by the overlapping portion of two notional intersecting ellipses, preferably forming a symmetric lens shape. The notional ellipses may be the respective top-down projections (as viewed along the second principal fluid flow axis) of the (tilted) first one of the apertures when the cylinder is at the first and second end positions respectively.
One of the component bearing surface and the cylinder bearing surface may be substantially convex and the other of the component bearing surface and the cylinder bearing surface may be substantially concave.
Typically the concave bearing surface terminates at the said second one of the said apertures and the convex bearing surface terminates at the said first one of the said apertures. That is, an edge of the concave bearing surface typically at least partially defines the said second one of the said apertures and an edge of the convex bearing surface typically at least partially defines the said first one of the apertures.
When the area of the cylinder aperture is greater than the area of the component aperture, the required size of the cylinder (and a machine comprising the rocking cylinder assembly) may be dependent on the maximum extent of the component aperture in the said direction perpendicular to the rocking axis and perpendicular to the principal fluid flow axis of the component aperture. By providing the component aperture with a ratio of its area to the square of its maximum extent in a direction perpendicular to the rocking axis and perpendicular to the principal fluid flow axis of the component aperture which is greater than the ratio of area of the cylinder aperture to the square of its maximum extent in a direction perpendicular to the rocking axis and perpendicular to the principal fluid flow axis of the cylinder aperture, the flow capacity through the component aperture is increased for a given size of cylinder without introducing overlap/overrun between the cylinder and the component aperture as the cylinder rotates between the first and second positions. In this embodiment, the component bearing surface is typically substantially concave, while the cylinder bearing surface is typically substantially convex.
Alternatively, when the area of the component aperture is greater than the area of the cylinder aperture, the required size of the component (and a machine comprising the rocking cylinder assembly) may be dependent on the maximum extent of the cylinder aperture in a direction perpendicular to the rocking axis and perpendicular to the principal fluid flow axis of the cylinder aperture. Accordingly, by providing the cylinder aperture with a ratio of its area to the square of its maximum extent in a direction perpendicular to the rocking axis and perpendicular to the principal fluid flow axis of the cylinder aperture greater than the ratio of the area of the component aperture to the square of its maximum extent in a direction perpendicular to rocking axis and perpendicular to the principal fluid flow axis of the component aperture, the flow capacity through the cylinder aperture is increased for a given size of component without introducing overlap/overrun between the component and the cylinder aperture as the cylinder rotates between the first and second positions. In this embodiment, the cylinder bearing surface is typically substantially concave, while the component bearing surface is typically substantially convex.
Preferably, where the first one of the apertures is the cylinder aperture, there is no overrun/overlap between the cylinder and the component aperture in either the first or the second positions or therebetween. Preferably, where the first one of the apertures is the component aperture, there is no overrun/overlap between the component and the cylinder aperture in either the first or the second positions or therebetween.
Because the invention provides an increased flow area through the combination of the cylinder and component apertures, it is particularly suited to machines required to maintain high efficiency at high speeds while idling, pumping or motoring. Preferably the peak fluid flow speed through the cylinder and component apertures is below 10 m/s, more preferably below 5 m/s (but typically greater than 0.1 m/s). The rocking cylinder assembly of the invention may therefore be particularly suitable for use in larger applications, and helps to improve fill speed and volumetric efficiency at high speeds.
Typically, the rocking cylinder assembly is suitable for use with hydraulic liquid (the fluid communication between the cylinder and component apertures being hydraulic liquid communication).
In some embodiments, at least a portion of the shape of the said second one of the apertures extends beyond a notional circular area in a direction parallel to the rocking axis (and perpendicular to the second principal fluid flow axis), the notional circular area being concentric and co-planar with the shape of the said aperture and having a diameter equal to the maximum extent of the said aperture in a direction perpendicular to the rocking axis and perpendicular to the said second principal fluid flow axis. Typically, the area of the said second one of the apertures covers the entire notional circular area.
The cylinder typically rotates periodically between the first and second end positions. At the first end position, the cylinder is typically rotated in a first rotational sense about the rocking axis by a first extent from an intermediate third position (typically mid-way) between the first and second end positions. At the second end position, the cylinder is typically rotated in a second rotational sense opposite the first rotational sense about the rocking axis by a second extent from the intermediate third position. Typically the total sweep between the first and second positions is approximately 18°.
The cylinder bore may have a first inner diameter and a second inner diameter less than the first inner diameter, the said cylinder aperture having a diameter equal to the second inner diameter. Typically a transition region (e.g. a step or tapered region) is provided between the first and second inner diameters.
Typically, the fluid communication between the component bore and the cylinder bore is direct fluid communication. That is, fluid can flow between the component and cylinder bores without any further components or apertures being provided between the component and cylinder bores.
Typically the bearing component does not rotate about the rocking axis. That is, when the cylinder rotates about the rocking axis, the position of the component typically stays fixed with respect to the rocking axis.
Typically, the cylinder can rotate about the rocking axis but not along rocking axis.
Typically the cylinder and/or component apertures have at least partly (preferably substantially) curved perimeters.
The bearing component may be a separate component from a or the machine (e.g. internal combustion engine) in which the rocking cylinder assembly is provided. Alternatively the bearing component may be integrally formed with a machine in which the rocking cylinder assembly is provided. In some embodiments, the bearing component is integrally formed with a valve body of a valve of the machine in which the rocking cylinder assembly is provided.
Typically, the cylinder is rotatably mounted such that it can be rotated about the rocking axis by, for example, an eccentric of a crankshaft. The crankshaft may be provided as part of the rocking cylinder assembly, the eccentric of the crankshaft being configured to periodically rotate the cylinder about the rocking axis between the first and second positions as it rotates. The axis of rotation of the crankshaft is typically parallel to the rocking axis.
Typically, the ratio of the maximum extent of the said second one of the apertures in a direction parallel to the rocking axis to the maximum extent of the said second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second fluid flow axis is greater than the ratio of the maximum extent of the said first one of the apertures in a direction parallel to the rocking axis to the maximum extent of the said first one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the first fluid flow axis.
The cylinder bearing surface may be part-spherical, or part-spheroidal.
A piston may be provided which reciprocates within the cylinder. The inner volume of the cylinder between the piston and the cylinder aperture forms a working chamber of cyclically varying volume as the piston reciprocates therein. The piston may have a circular axial cross section (i.e. taken through a longitudinal axis of the piston).
The piston may further comprise a piston foot in communication with a or the crankshaft. The piston foot may have a part-cylinder shape which constrains the degree of freedom of the cylinder to rotation about the rocking axis.
The cylinder bearing surface may be a part-cylinder, in which case the degree of freedom of the cylinder may additionally or alternatively be constrained to rotation about the rocking axis by the interaction between the cylindrical bearing surface and the bearing surface of the bearing component.
The cylinder bearing surface may have an axial cross section (i.e. taken through the longitudinal axis of the cylinder) having a substantially circular shape. Alternatively, the cylinder bearing surface may have a substantially elliptical cross section (again taken through the longitudinal axis of the cylinder), the elliptical cross section having an elongate dimension parallel to the rocking axis.
If the area of the cylinder aperture is greater than the area of the component aperture, (at least part of, preferably the majority of, even more preferably all of) the component aperture typically conforms to (or at least approximates or is identical to) a boundary between an area of the component bearing surface swept by the cylinder bearing surface as the cylinder rotates between the first and second end positions and an area of the component bearing surface unswept by the cylinder bearing surface as the cylinder rotates between the first and second end positions. If the area of the component aperture is greater than the area of the cylinder aperture, (at least part of, preferably the majority of, even more preferably all of) the cylinder aperture typically conforms to (or at least approximates or is identical to) a boundary between an area of the cylinder bearing surface swept by the component bearing surface as the cylinder rotates between the first and second end positions and an area of the cylinder bearing surface unswept by the component bearing surface as the cylinder rotates between the first and second end positions.
Thus, (at least part of, preferably the majority of, even more preferably all of) the said second one of the apertures may have a shape which conforms to or at least approximates, or is substantially identical to, the boundary between swept and unswept areas.
Typically the boundary is an inner boundary (e.g. if there are two boundaries between swept and unswept areas of the said bearing surface, the boundary covered by the first one of the said apertures as the cylinder rotates between the first and second end positions, which is typically closer to a notional apex of a concave or convex portion of the bearing surface of the bearing component or cylinder respectively).
Typically, the said first one of the apertures is circular.
At least part of, preferably the majority of, even more preferably all of the shape of the second one of the apertures may conform to (or at least approximate or be) an elliptical, quasi-oval or vesica piscis shape.
The vesica piscis shape is more easily manufactured than the (in some embodiments more optimal) shape formed by two intersecting ellipses described above.
The shape of the second one of the apertures may be symmetrical about a line parallel to the rocking axis.
A shape retaining cross-brace may extend across the said second one of the apertures (typically between opposing portions of the said second one of the apertures). Typically the cross-brace extends between two opposite portions of the perimeter of the second one of the apertures. Typically, the cross-brace extends in a direction perpendicular to the rocking axis and perpendicular to the second fluid flow axis. Preferably the cross-brace extends across the maximum extent of the second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second fluid flow axis.
The cross-brace is typically configured to retain the shape of the said second one of the apertures to counteract expansion forces exerted on the second one of the apertures by pressurised fluid flowing through it.
The cross-brace may comprise one or more support arms. In one embodiment, the cross-brace may comprise a plurality of support arms extending radially inwards from a perimeter of the said second one of the apertures to a mount provided in the said second one of the apertures (e.g. at the centre of the said second one of the apertures).
Where a cross-brace is provided, the area of the second one of the apertures may be the sum of the areas of the aperture not occupied by the cross brace. That is, the area of the second one of the apertures is (as above) the area of the second one of the apertures through which fluid can flow. Where the second one of the apertures does not lie on a single plane (the second one of the apertures has a three dimensional shape) the area of the second one of the apertures is typically the sum of the projection of the areas of the aperture not occupied by the cross brace (through which fluid can flow) along the principal fluid flow axis of the aperture onto a plane perpendicular to the said principal fluid flow axis.
The bearing component may incorporate or support a flow hat arranged with respect to a valve member of a valve so that fluid flowing towards the flow hat is diverted around the flow hat to thereby reduce one or more forces which would otherwise act on the valve member as a result of the flow of fluid to urge the valve member towards a valve seat of the valve (see published European patent publication no. EP2370717). The flow hat may be integrated with the mount and/or the support arms of the cross brace. In one embodiment, a poppet rod of a (or the) poppet valve may extend axially (i.e. parallel to or along the principal fluid flow axis through the component aperture) from the mount into the cylinder through the cylinder aperture.
Particularly when the component aperture is the said second one of the apertures, the component may comprise a non-axisymmetrical portion which is non-axisymmetrical about the second principal fluid flow axis, the non-axisymmetrical portion comprising the component aperture. The non-axisymmetrical portion may have parallel opposing inner walls. The component bore may further comprise an axisymmetrical portion which is axisymmetrical about the principal fluid flow axis along which fluid flows through the component bore. The axisymmetrical portion is typically integrally formed with the non-axisymmetrical portion.
Working fluid flowing through the rocking cylinder assembly may be highly pressurised, and this pressurised fluid causes loading of the components of the assembly, including the component bore. The axisymmetrical portion of the component bore will be deflected symmetrically about the principal fluid flow axis along which fluid flows through the component aperture (and loaded evenly). However, the non-axisymmetrical portion of the component bore will deflect non-axisymmetrically about the principal fluid flow axis along which fluid flows through the component aperture (and thus loaded unevenly). It is desirable to minimise this non-axisymmetrical deflection. Therefore, the maximum length of the non-axisymmetrical portion of the component in the direction parallel to the principal fluid flow axis through which fluid flows through the component aperture is preferably less than the maximum length of the axisymmetrical portion of the component in that direction (preferably less than half of the maximum length of the axisymmetrical portion of the component in that direction).
By minimising the length of the non-axisymmetrical region in the direction parallel to the principal fluid flow axis through which fluid flows through the component aperture, relative to that of the axisymmetric region, the non-axisymmetrical deflection acting on the component is correspondingly reduced and the axisymmetric deflection of the component core are correspondingly increased. Thus, expansion forces exerted by pressurised fluid on the inner walls of the component bore are more evenly distributed and lead to a more uniform deformation. Accordingly, in this case, there is typically no (or at least less) need for a shape retaining cross-brace to be provided in order to prevent deformation of the component aperture. When a shape-retaining cross-brace is provided, it is not typically possible to harden (or to fully harden) the bearing component without also hardening the cross-brace. Because the cross-brace is thin, hardening causes it to become brittle/weak. Accordingly, the component does not tend to be hardened (or fully hardened) to avoid weakening the cross-brace. By omitting a web brace, the component can be (fully) hardened thereby increasing its durability.
In some embodiments, at least a portion of the component bore has a cross sectional shape perpendicular to the principal fluid flow axis along which fluid flows through the component aperture and at least a portion of the cylinder bore has a cross sectional shape perpendicular to the principal fluid flow axis along which fluid flows through the cylinder aperture, wherein the said cross sectional shape of the component bore substantially matches the cross sectional shape of the cylinder bore.
Typically the size of the said cross sectional shape of the component bore also substantially matches the size of the cross sectional shape of the cylinder bore.
Typically the said at least a portion of the component bore is adjacent to the component aperture.
Typically the said at least a portion of the cylinder bore is adjacent to the cylinder aperture.
By matching the shape (and typically the size) of the component bore cross section with the shape (and typically size) of the cylinder bore cross section, the deformation caused by the forces on an inner surface of the component bore adjacent to the component aperture will (at least substantially) match the deformation caused by the forces on an inner surface of the cylinder bore adjacent to the component aperture (it will be understood that the component bore adjacent to the component aperture and the cylinder bore adjacent to the cylinder aperture are axially separated from each other along principal fluid flow axis of the component aperture). This means that any deformation of the said portion of the component bore will substantially match any deformation of the said portion of the cylinder bore, leading to improved conformity between the cylinder and component bearing surfaces throughout the lifetime of the rocking cylinder assembly (which lifetime will be increased accordingly).
The said portion of the cylinder bore may be non-axisymmetric about the principal fluid flow axis of the cylinder aperture. The said portion of the component bore may be non-axisymmetric about the principal fluid flow axis of the component aperture.
Typically, the cylinder and bearing component apertures remain in fluid communication between the first and second positions of the cylinder.
A second aspect of the invention provides a method of operating a rocking cylinder assembly comprising: a cylinder having a cylinder bore terminating at a cylinder bearing surface and a cylinder aperture defined by a line of intersection between the cylinder bore and the cylinder bearing surface, the cylinder being rotatable about a rocking axis between first and second end positions; a bearing component having a component bore terminating at a component bearing surface and a component aperture defined by a line of intersection between the component bore and the component bearing surface, a first one of the cylinder and component apertures having a greater area than the second one of the cylinder and component apertures, the first one of the cylinder and component apertures defining a first fluid flow path having a first principal fluid flow axis along which fluid flows through the said first one of the apertures and a second one of the cylinder and component apertures defining a second fluid flow path having a second principal fluid flow axis along which fluid flows through the second one of the apertures, the ratio of the area of the said second one of the apertures to the square of the maximum extent of the said second one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the second principal fluid flow axis being greater than the ratio of the area of the said first one of the apertures to the square of the maximum extent of the said first one of the apertures in a direction perpendicular to the rocking axis and perpendicular to the first principal fluid flow axis, the method comprising: rotating the cylinder between the first and second positions; bearing the cylinder bearing surface against the component bearing surface as the cylinder rotates between the first and second positions such that the cylinder and bearing component apertures are in fluid communication as the cylinder rotates between the first and second positions; and flowing fluid between the cylinder and bearing component apertures.
Typically, the fluid flowing between the cylinder and bearing component apertures is a hydraulic liquid.
Typically, the cylinder and bearing component apertures remain in fluid communication between the first and second positions.
A third aspect of the invention provides a bearing component for a rocking cylinder assembly, the bearing component comprising a bearing surface and a component bore terminating at the bearing surface such that a line of intersection between the bore and the bearing surface defines an aperture through which fluid can flow, characterised in that the area of a projection of the aperture along a longitudinal axis of the bore onto a plane perpendicular to the longitudinal axis extends beyond a notional circular area being concentric and co-planar with the said projected aperture area, and having a diameter equal to the length of, and being co-linear with, the straight line of shortest length extending between opposing sides of the said projected aperture area through the centre of the said area.
Typically, the ratio of the maximum extent of the said area in a first direction (typically co-linear with the straight line of shortest length extending between opposing sides of the said area through the centre of the said area) to the maximum extent of the aperture in a second direction perpendicular to the first direction is less than 1.00.
Typically, the said area of the projection of the aperture along the longitudinal axis of the bore onto the plane perpendicular to the longitudinal axis covers the entire notional circular area.
Typically the said area of the projection of the aperture along the longitudinal axis of the bore onto the plane perpendicular to the longitudinal axis is greater than the said circular area.
A fourth aspect of the invention provides a cylinder for a rocking cylinder assembly, the cylinder comprising a bearing surface and a cylinder bore terminating at the bearing surface such that a line of intersection between the bore and the bearing surface defines an aperture through which fluid can flow, characterised in that the area of a projection of the aperture along a longitudinal axis of the bore onto a plane perpendicular to the longitudinal axis extends beyond a notional circular area being concentric and co-planar with the said projected aperture area, and having a diameter equal to the length of, and being co-linear with, the straight line of shortest length extending between opposing sides of the said projected aperture area through the centre of the said area.
Typically, the ratio of the maximum extent of the aperture in a first direction (typically co-linear with the straight line of shortest length extending between opposing sides of the said area through the centre of the said area) to the maximum extent of the aperture in a second direction perpendicular to the first direction is less than 1.00.
Typically, the said area of the projection of the aperture along the longitudinal axis of the bore onto the plane perpendicular to the longitudinal axis covers the entire notional circular area.
Typically the said area of the projection of the aperture along the longitudinal axis of the bore onto the plane perpendicular to the longitudinal axis is greater than the said circular area.
The preferred and optional features discussed above are preferred and optional features of each aspect of the invention to which they are applicable. For the avoidance of doubt, the preferred and optional features of the first aspect of the invention may also be preferred and optional features in relation to the second, third and fourth aspects of the invention, where applicable.
An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:
It will be understood that the piston 10 (which has an outer diameter of just less than the first inner diameter 18a of the cylinder bore 12 but greater than the second inner diameter 18c of the cylinder bore 12) only reciprocates within the region of the internal bore 12 having the first inner diameter 18a. Typically, greater than 50% of the length of the bore 12, more typically greater than 70% of the length of the bore 12, and even more typically, greater than 80% of the length of the bore 12 is provided with the first inner diameter 18a.
The bearing component 8 has a body 19 comprising an internal bore 20 which extends from a first (typically circular) bearing component aperture 21 to the component bearing surface 6 where the bore 20 terminates. A line of intersection between the component bore 20 and the component bearing surface 6 forms a second aperture 22 opposite the first aperture 21 which defines a fluid flow area through which fluid flows through the bearing component 8 into or out from the cylinder 2.
The first cylinder aperture 16 defines a fluid flow path having a principal fluid flow axis (indicated by a dotted line in
As the piston 10 reciprocates within the cylinder bore 12, the cylinder 2 rotates periodically about a rocking axis (the rocking axis extends out of and into the page as viewed in
It will be understood that the principal fluid flow axis of the cylinder aperture 16 rotates about the rocking axis with the cylinder 2, but the principal fluid flow axis of the component aperture 22 remains fixed relative to the rocking axis. Both principal fluid flow axes extend perpendicularly to the rocking axis as the cylinder 2 rotates between the first and second end positions.
The first cylinder aperture 16 lies on a single plane and has a circular shape. The diameter of the first cylinder aperture 16 is greater than the maximum extent of the second component aperture 22 such that there is no overlap/overrun between the cylinder bearing surface 6 and the second component aperture 22 as the cylinder 2 rotates between the first and second end positions. As the cylinder 2 rotates between the first and second end positions, the first cylinder aperture 16 remains in direct fluid communication with the second component aperture 22 such that fluid can flow along a fluid flow path extending through the first cylinder aperture 16 and the second component aperture 22.
As shown most clearly in
It will be understood that references to the shape of the component aperture 22 are references to the shape of the said projection of the aperture 22 along its principal fluid flow axis onto a plane perpendicular to its principal fluid flow axis (i.e. the shape 22 shown in
As overlap/overrun between the cylinder bearing surface 4 and the second component aperture 22 of the bearing component 8 is undesirable, the area of the first cylinder aperture 16 is typically required to be (significantly) larger than the area of the second aperture 22 of the bearing component 8. It is desirable to maximise the fluid flow area through the component aperture 22 in order to reduce pressure drop and increase the efficiency of the cylinder assembly 1 (and thus the machine comprising the cylinder assembly 1), but it is also desirable for the cylinder 2 and machine to be made as small as possible. These are typically considered to be conflicting design constraints because if the second aperture 22 (which is traditionally circular) is extended in size to increase the fluid flow area through the component aperture, the first cylinder aperture 16, and thus the machine comprising the cylinder assembly, would also need to be increased in size. However, it has been realised that different design constraints apply to the component aperture in directions parallel and perpendicular to the rocking axis respectively. More specifically, it has been realised that if the second component aperture 22 is increased in size in a direction parallel to the rocking axis (e.g. direction 44 in
Referring back to
Working fluid flowing through the rocking cylinder assembly 1 may be highly pressurised, and this pressurised fluid causes symmetrical deflection of the axisymmetrical portion 24 about the principal fluid flow axis along which fluid flows through the component aperture 22 (and is also thus loaded evenly) and the non-axisymmetrical portion 23 of the component bore 20 is deflected non-axisymmetrically about the principal fluid flow axis along which fluid flows through the component aperture 22 (and is thus loaded unevenly). In order to minimise this non-axisymmetrical deflection, the maximum length of the non-axisymmetrical portion 23 in a direction parallel to the principal fluid flow axis through which fluid flows through the component aperture 22 is typically less than the maximum length of the axisymmetrical portion 24 of the component in that direction (e.g. less than half of the length of the axisymmetrical portion of the component in that direction). By minimising the length of the non-axisymmetrical portion 23 in this direction relative to that of the axisymmetric region 24, the non-axisymmetrical deflection acting on the component 8 is correspondingly reduced. In the axisymmetric section, the stress caused by the pressure forces is characterised more as hoop stress rather than bending stress due to its symmetric (cylindrical) nature, hence the deflection due to pressure is minimised. Accordingly, maximising axisymmetric length minimises the overall defection of the component. Accordingly, there is typically no (or at least less) need for a shape retaining cross-brace to be provided in order to prevent deformation of the component aperture 22. It is advantageous not to include a cross brace which both increases manufacturing cost, and itself obscures part of the flow passage.
Although it is stated as being advantageous to increase the length (and thus the influence) of the axisymmetric region 24, this may not always be the case. For example, if the second inner diameter 18c of the cylinder bore 12 is non-axisymmetric about the longitudinal axis of the cylinder 2 (or about the principal fluid flow axis of the cylinder aperture 16), it is typically advantageous for the shape and orientation of the internal bore 20 of the component to (at least substantially) match the shape of the second inner diameter 18c of the cylinder bore 12. This is because any deformation of the second inner diameter 18c of the cylinder bore 12 will at least approximately match the deformation of the component bore 20, which typically leads to improved conformity between the cylinder and component bearing surfaces 4, 6 throughout an increased lifetime of the rocking cylinder assembly.
The component aperture 58 is provided in a non-axisymmetrical portion 62 of the component bore 52 which is non-axisymmetrical about the principal fluid flow axis (indicated in dashed line in
As explained above, working fluid flowing through the rocking cylinder assembly 1 may be highly pressurised, and this pressurised fluid causes loading of the components of the assembly 1, including the component bore 52. The axisymmetrical portion 60 of the component bore 52 is deflected symmetrically about the principal fluid flow axis along which fluid flows through the component aperture (and is thus loaded evenly). However, the non-axisymmetrical portion 62 of the component bore is deflected non-axisymmetrically about the principal fluid flow axis along which fluid flows through the component aperture 22 (and is thus loaded unevenly). Accordingly, as shown in
In order to maximise the flow area through the apertures 22, 58 of components 8, 50, the shapes of the apertures 22, 58 may conform to (typically at least approximate and may be identical to) a symmetric lens shape formed by the overlapping portion 80 (see
It will be understood that, particularly when the cylinder aperture 16 is circular, any extension of the shape of the component apertures 22, 58 in a direction parallel to the rocking axis which increases the fluid flow area through the apertures 22, 58 beyond the notional circle 40 yields an increased fluid flow capacity through the component aperture compared to traditional circular apertures for the same size of cylinder 2.
In alternative embodiments, the bearing component 8, 50 may instead have a convex bearing surface, while the cylinder 2 may have a concave bearing surface. In this case, preferably (but not necessarily) the first cylinder aperture 16 may have the properties of the apertures 22, 58 of the components 8, 50 described above, while the component apertures 22, 58 may have the properties of the first cylinder aperture 16 of the cylinder 2 described above. In this case, the component aperture 22, 58 may have a larger area than the cylinder aperture 16.
Although the apertures 22, 58 are shown not to lie on a single plane, one or both of the apertures 22, 58 may alternatively lie on a single plane (i.e. the apertures 22, 58 may have two dimensional shapes).
Further modifications and variations may be made within the scope of the invention herein disclosed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13154494.2 | Feb 2013 | EP | regional |
