GB2610400A

GB2610400A - Intensive labyrinth sealing of pistons and cylinders in engines and compressors subject to gas leakage

Info

Publication number: GB2610400A
Application number: GB2112497.9A
Authority: GB
Inventors: Pirault Jean-Pierre; Veshagh Alireza
Original assignee: Applied Engine Tech Ltd
Current assignee: Applied Engine Tech Ltd
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2023-03-08
Anticipated expiration: 2041-09-02
Also published as: GB2610400B; GB202112497D0

Abstract

A labyrinth sealing arrangement for appositive displacement piston is provided. The labyrinth sealing arrangement forms a seal via a small clearance between a non-contacting surface of a piston skirt 2 and a non-contacting surface of a cylinder. The labyrinth pattern comprises a plurality of helical flow channels 70h, 80h, with multiple cavities separated by dams. The helical flow channels 70h, 80h have a major axis at a non-orthogonal angle, typically 20-70 degrees, to the main direction of the overall pressure gradient across the surfaces.

Description

Intensive Labyrinth Sealing of Pistons and Cylinders in E ngi nes and C ompressors subject to Gas Leakage

Background

This invention relates to the labyrinth sealing of positive displacement pistons in cylinders in which the piston is guided relative to the cylinder so that the sliding piston walls, also known as the piston 'skirts_ or surfaces, do not contact the cylinder walls, also known as cylinder surfaces. These non-contacting piston skirts are used in some compressors and internal combustion engines to reduce wear and friction and in some cases to avoid the need for oil lubrication between the piston and cyl i nder wal Is.

Labyrinth sealing is a contactless method to reduce gas leakage from a high pressure volume of gas to a lower pressure volume of gas in which the pressure gradient between the two volumes is gradually reduced by a contiguous sequence of shaped cavities and intennediate lands, also known as 'dams_ that are designed to impede the gas leakage. The geometry of the cavities and dams are arranged to create successive turbulent energy and momentum dissipation of the leakage fluid until the velocity of the leakage fluid is adequately small and the residual leakage is considered acceptable. The term ' I abyri nth_ indicates an i nterli nked series of cavities and dams so that the leakage flow into a first cavity loses energy and momentum by sudden expansion and turbulence generation before passing over a dam which locally increases the remaining fluid leakage velocity before entering the second cavity, where the same pattern of turbulence and momentum dissipation occurs, and so on to next dam and cavity until the last dam and cavity, at which point the leakage flow velocity will have reduced adequately to present only a small and tolerable leakage rate.

The object of this invention is to substantially reduce the fluid leakage rates of labyrinth sealed conduits between opposed non-contacting surfaces, flat or cylindrical, in particular concentrically arranged surfaces, such as a piston in cylinder bore assemblies, by arranging a more effective labyrinth geometry for the pistons and cylinder bores than prior art labyrinth patterns, so that the sealing effectiveness is closer to that achieved by piston ring surface contact sealing. The latter sealing method requires oil lubrication and imposes significant hydrodynamic friction losses on the compressor or internal combustion engine system and creates hydrocarbon emissions in the outlet gas flow.

Current state of art labyrinth sealing patterns between a moving surface and a parallel static surface can withstand approximately 10 bar maximum pressure differential between the upstream and downstream parts of the piston and cylinder bore with tolerable leak flowrates of about one percent of the gas compressor displacement, which is adequate for compressor applications in which 7-10 bar is the typical pressure rise for the first compression stage. However, for multi-stage compressors, the pressure rise at the 2nd and 3rd stages may be respectively 40 bar and 300 bar. For internal combustion engine applications, the maximum cylinder pressure differentials can be in excess of 200bar and therefore conventional labyrinth sealing is not viabl e. Additionally, i n internal combustion engine with conventional connecting rods and pistons, the latter contact the cylinder bore via an oil film, a condition which is unsuitable for labyrinth sealing.

Use of non-contacting piston arrangements for internal combustion engines, for instance with torque reacting crankshafts, enable labyrinth sealing to be considered and prompts the need for a labyrinth sealing capability of at least 30bar pressure differential for utility engine types, as used in garden and industrial equipment, at least 60bar pressure differential for engines used for hybrid electric applications, 90bar pressure differential for naturally aspirated diesel applications and at least 190bar pressure differential for turbocharged high output diesel engines. Similar pressure capabilities would also be suitable for compressors.

The invention addresses these higher pressure differentials across the piston which cannot be achieved by state of art labyrinth sealing and the invention applies to all sealing systems which have a pair of opposing and/or non-contacting surfaces forming a conduit between upstream and downstream of the leakage flow such as those in positive displacement compressors and engines with pistons in cylinders.

K eywords Labyrinth sealing, cavities, dams, turbulence, momentum, non-contacting piston, friction losses, lubrication, reciprocating engines, compressors, contactless sealing, helical labyrinths, helical path, helically arranged cavities, leakage flow, longitudinal channels, longitudinal cavities, side leakage, sealing effectiveness, turbulence degradation, turbulence generation, turbulence dissipation.

Some definitions are provided for terms used frequently in this text before describing the invention. These definitions are in context and not necessarily universally agreed definitions.

Definitions The following descriptions and definitions are provided to help the reader in the context of this document; they are not intended as universal definitions.

Annular groove: circumferential groove around piston diameter. Arcuate. curved shape.

Articulated piston, a piston in which the crown and pressure sealing function of the piston is performed by a first independent part, usually called the crown, and the piston guidance and connecting rod side thrust is taken by a second independent part, usually called the skirt, said two parts being joined, each with rotational clearance, to a common gudgeon pin, also known as a 'piston pin_ or 'wrist pin.

Channel: in this context, a two-dimensional sectional shape that extends for a limited distance, forming an empty volume closed on five sides, similar to a Wench. The channel may also be called a groove or a cavity.

Circumferential: following the locus of a radius rotated in a plane. Clearance: the space or gap between two non-contacting surfaces.

Connecting rod: a rigid link with rotatable end joints that connects the crankpin of a rotating crankshaft to a rotatable joint on the piston mechanism. The connecting rod link to the crankshaft is tamed the big-end; the connecting rod link to the piston or crosshead is termed the small-end.

Connecting rod angularity: this is the angle subtended between the major axis of the connecting rod and the axis of the cylinder, resulting from the motion of the connecting rod as the crankshaft is rotated. The angularity of the connecting rod generates side loads from the piston on the cylinder wall as the piston is loaded by axial forces.

Contact sealing: provides sealing of a fluid between two surfaces by introducing a relatively conformable member between the two surfaces, with appropriate support, so that the upstream fluid pressure exerts a force on the conformable member such that the conformable member blocks leakage flow between the two surfaces, but allows the two surfaces to slide over each other if necessary The contacting surfaces require lubrication to avoid wear.

Contiguous: one feature immediately following another feature.

Cross flows: flows that traverse or collide with each other because there is an angular difference in their direction of travel.

Crosshead: a mechanical joint that allows oscillation of a moving component as well as enabling linear motion of that component in a prescribed direction. The oscillation point has a bearing enabling low friction rotation. The linear movement portion of the mechanical joint has a bearing enabling low friction linear moti on. The mechanical joint in this context links the connecting rod to the piston so that the side loads arising from torque transmission of the piston, connecting rod and crankshaft assembly, can be transmitted directly to the static walls of the cylinder without imposing any side loads on the piston.

Dam: in this context, a partial flow barrier, to limit the volume of fluid flow between two non-contacting surfaces of a clearance, the barrier being formed by the piston diameter or radius being greater than that of the adjacent channels, also known as grooves or cavities.

Double diameter piston, also known as stepped piston: a piston with two diameters, each of which separately engages one of two female cylinder bores, the diameters of said cylinders bores lying on a common axis. The two piston diameters are usually rigidly connected, with the smaller diameter piston being the power piston and the larger diameter being the air transfer piston when used in an engine. For compressors, the larger area piston would provide a first stage of compression and the smaller diameter piston provides a second stage of compression.

Downstream: towards the direction of lower pressure in a flow system. F orvvard: in a particular direction.

F ully circumferential: following the locus of a radius rotated 360 degrees in a plane.

Gudgeon pin: a stiff prismatic member, usually cylindrical, that rotatably links a piston to the small-end of a connecting rod in a compressor or engine.

Helical: following a spiralling circular path.

Helix angle: angle relative to a reference line or plane on a cylindrical surface, in this case relative to the plane through the annular groove on the piston surface.

Labyrinth: in the context of this description, a combination of shapes or geometries that are repeated multiple times along a direction of fluid leakage flow to create turbulence dissipation and reduce fl ow velocities.

Labyrinth path: a contiguous sequence of cavities and darns that are arranged along a path on at least one of the surfaces which bound the fluid leakage.

Labyrinth sealing: is a contactless method to reduce fluid leakage from a high-pressure volume to a lower pressure volume in which the pressure gradient between the two volumes is gradually reduced by a contiguous sequence of shaped cavities, also known as 'grooves, and intermediate lands, also known as 'dams_. The geometry of the cavities and dams are arranged to create successive turbulent energy and momentum losses of the leakage fluid such that the velocity of the leakage fluid is adequately small and the leakage is considered tolerable.

Lead angle: angle relative to a reference line or plane, in this case relative to the plane through the annular groove of the piston. In this document, lead angle and helix angle have the same meaning.

Longitudinal: in a direction parallel to the major axis of the piston, and orthogonal to the circumference of the piston skirt.

Main direction of the overall pressure difference: this is in the direction of the shortest distance between the upstream and downstream pressures acting along the clearance between the two surfaces.

Major axis: the larger or largest dimension or direction of a mechanical component or feature. Multi-dimensional: along many directions.

One-di mensi ona I: along a single direction.

Non-contacting piston: a piston which is guided by some mechanism so that the piston does not contact the surfaces of the cylinder wall. Examples of these mechanisms are a crosshead system, a Stepped piston, torque reacting crankshafts in which the piston side thrust is taken within the crankshaft mechanism and a rectilinear drive mechanism which can support non-contacting pistons as described in UK Patent 2525213 (Opposed Piston Machine with Rectilinear D rive Mechanisms). These exemplary mechanisms are suitable for application of labyrinth sealing. In the case of a stepped piston, one of the piston diameters may be non-contacting while the other piston diameter will be contacting. It is usually the smaller diameter and higher pressure piston of a stepped piston that can be the non-contacting portion of the piston assembly and which can therefore adopt labyrinth sealing.

Non-orthogonal; at an angle which is greater or less than 90 degrees to an axis. Orthogonal; at 90 degrees angle to an axis.

Partial circumferential: a part or multiple parts of the locus of a radius rotated 360 degrees in a plane. There can be partial circumferential grooves or cavities and partial circumferential dams.

Piston: the moving part of a positive displacement volumetric machine that acts on the fluid to displace, compress or expand the fluid. The piston is usually of a male shape which engages in a cylinder of a female shape, the motion of the piston moving the fluid to and from the cylinder volume.

Piston crown: the portion of the piston that directly experiences and reacts the fluid pressure. It will also be the hottest part of the piston, both for compressors and internal combustion engines.

Piston rings: these contact seals are an annular section of robust but flexible material formed into a cylindrical shape with a small joint to enable fitment within an annular groove in the piston body below the crown. The small joint also known as a 'gap, allows for circumferential thermal expansion of the piston ring which slides on its outermost face against the cylinder wall. Piston rings have radial compliance so that they apply moderate pressure to the cylinder walls, when fitted into the annular groove in the piston which itself is fitted into the cylinder. The piston rings provide a sealing function for pressurized fluids either side of the piston by allowing some fluid to enter the annular groove in the piston and applying a force to the inner surface of the piston ring, forcing it radially outwards onto the cylinder bore and preventing the fluid from leaking between the outer surface of the piston ring and the cylinder bore. The fluid pressure also applies a force onto the upper surface of the piston rings at right angles to the aforementioned radial force, pushing the piston ring against one side of the annular groove, thus preventing fluid leaks between the under surface of the piston ring and the annular groove. The only fluid leak is via the small joint or gap, and this can be minimised by careful design so that the piston ring sealing is at least 99% effective, i.e. only 1% of the fluid volumetric flowrate displaced by the piston escapes as a leak from the piston and cylinder assembly.

Piston skirt: also referred to as piston surface, the portion of the piston below the piston crown, and below the piston ring grooves for the retention of the piston rings, that guides the piston in the cylinder bore and, in the case of slider crank systems, transfers the side load due to the piston angularity to the cylinder wall. The piston also transfers vertical loads on the piston from gas or inertia forces to the connecting rod. For cranktrains with crossheads, the piston only transfers vertical loads to the crosshead and connecting rod; it does not provide guidance and does not transfer side loads. The piston skirts of non-contacting pistons with labyrinth sealing can commence at the very top of the piston as these non-contacting pistons with labyrinth sealing do not require piston rings.

Piston surface: the peripheral or circumferential surface of the piston Positive displacement: a mechanism that moves a prescribed distance along a path in one direction and returns on the same path to the starting point usually cyclically.

Pressure gradient: pressure drop or reduction divided by the distance over which the pressure is reduced.

Random: without any obvious order.

Rectilinear drive mechanism: an assembly comprising a crankshaft fitted with paired discs, usually cylindrically shaped, which can rotate with clearance about the crankpin of the crankshaft each rotating disc of the pair being independently guided and constrained with clearance by at least one linear rail and the rail(s) guiding each disc being orthogonal to each other. Each of the paired discs, when fitted with a yoke and piston rod, can drive a positive displacement piston with no angularity of the piston rod, all the side forces being taken by the paired discs and their linear guiding rails. The rectilinear drive mechanism is a torque reacting crankshaft.

Reverse: in the opposite direction to forward.

Sealing capability: the maximum pressure difference between upstream and downstream of the seal.

Stepped cylinder: comprises a first cylinder bore which has a first diameter for a first length, and which is joined to a second cylinder bore which has a second diameter for a second length, the axes of first and second cylinder bores lying on the same is Stepped piston: see Double diameter piston Surfaces: these are the flow conduit non-contacting areas required to prevent or reduce the leakage flow from a higher-pressure side (upstream) of the areas to a lower pressure side (downstream) of the areas In many cases, the first of these areas may be static, such as a cylinder bore, and the second may be moving relative to the first with a controlled clearance between the two areas, such as a piston in the cylinder bore.

Torque reacting crankshafts: a crankshaft arrangement that reacts the piston side thrust hydrodynamically within the crankshaft mechanism, thus avoiding the need for the piston to contact the cylinder and enabling labyrinth sealing to be considered for sealing gases instead of contact piston ring sealing.

Upstream: towards the direction of higher pressure in a flow system. Zero side thrust no lateral force perpendicular to piston centreli ne Zig-zag: large and sudden changes of direction irregular twists and turns

Introduction

Contact piston ring sealing, which is widely used to seal the fluid volumes contained between the pistons and cylinders of positive displacement reciprocating compressors and internal combustion engines, relies on the use of lubricants between the piston ring and its contacting parts which are the piston groove and the cylinder walls. The lubricant provides partial hydrodynamic lubrication whi ch reduces wear and friction. However, the lubricants Iimit the piston ring and cylinder wall operational temperatures because the lubricant has its own temperature constraints for satisfactory performance. The performance of reciprocating compressors and internal combustion engines are therefore also limited by these piston ring and lubrication constraints. Lubricated piston ring sealing can withstand at least several orders of magnitude pressure differential compared to state of art conventional labyrinth sealing, dependent on the temperature of the lubricant.

Dry self-lubricated piston rings are an alternative to liquid lubricated piston rings, but these have restricted cylinder precsure and operational speed limits. The pressure differential capability of self-lubricated piston rings is similar or slightly better than labyrinth sealing, but the self-lubricating sealing rings have a finite life whereas the labyrinth sealing arrangement does not wear and has an infinite life.

Labyrinth sealing is a contactless method to reduce fluid leakage from a higher pressure volume to a lower pressure volume in which the pressure gradient between upstream and downstream is gradually reduced by a contiguous sequence of shaped cavities and intermediate lands, also known as 'darns_ that are designed to progressively reduce the momentum of the leakage to an acceptable level.

Pistons for labyrinth sealing must be guided by some means relative to the cylinder bore so that the sliding piston walls, also known as the piston 'skirt, do not contact the cylinder bore as this would result in damage to both the piston skirt and the cylinder bore in absence of a I ubri cant. Elimination of lubricants from the pistons ad cylinders of positive displacement compressors and engines is important as lubricants contaminate the working fluids in the cylinder and are discharged as particulate emissions in the compressor delivery or the engine exhaust.

This invention reduces the fluid leakage rates between any two non-contacting surfaces, subjected to a pressure difference, by arranging a more effective labyrinth geometry than state of art labyrinth sealing so that the sealing effectiveness approaches that of contact sealing. Specifically, the use of the proposed labyrinth sealing in combination with non-contacting pistons in concentric cylinder assemblies will provide similar sealing effectiveness to that of piston ring sealing. The latter requires oil lubrication and imposes significant friction losses on the compressor or internal combustion engine system and results in wear and emissions as previously mentioned. The friction and wear of labyrinth seals are minimal and close to zero in contrast to the friction and wear of contact piston rings.

In the following Description and Claims relating to labyrinth sealing of non-contacting pistons, 'piston skirt_ generally refers to most of the peripheral area beneath the piston crown as the absence of piston rings enables the labyrinth pattern to commence at the very top of the piston, or very close to the top of the piston, depending on the use of micro-labyrinth cavities, as described with reference to Figures la and 1 b.

Main Claim In its broadest interpretation, the invention is a labyrinth sealing pattern, for a compressible fluid in a volume formed by a non-contacting piston moving in a cylinder bore, the sealing being formed between the small clearance of the non-contacting surface of the piston and the non-contacting surface of the cylinder bore, in which the labyrinth pattern comprises a multiplicity of longitudinal flow channels, containing multiple cavities separated by dams within the longitudinal flow channels, said flow channels starting at the upstream pressure area on at least one of these surfaces and the labyrinth pattern having the major axis of each flow channel at a non-orthogonal angle to the main direction of the overall pressure gradient across the surfaces, so that there are high velocity flow interactions with energy dissipation between the fluid flow in the angled longitudinal flow channels and flow across and between said longitudinal flow channels arising due to the fluid leakage flow along the shortest path between the upstream and downstream pressure zones.

This invention and other embodiments are now described with particular reference to concentric sealing surfaces such as those of cylindrical pistons in cylinder bores, albeit the invention applies to the sealing surfaces of other prismatic and concentric male and female surfaces which can operate with small clearances between the surfaces.

The invention may be used in combination with conventional state of art type of labyrinth sealing systems.

Figures F igure la shows a stepped piston with prior art conventional labyrinth sealing circumferential cavities and dams applied to a non-contacting portion of the piston.

Figure lb shows an expanded upper corner portion of the piston (from Figure la) with smaller scale labyrinth cavities and dams at the top of the piston.

S

Figure 2 shows a typical two-dimensional section view and fluid flow patterns through a single circumferential labyrinth groove of Figures la and 1 b, with a preceding groove and a following groove, and an adjacent boundary cylinder bore Figure 3 shows one embodiment of the claimed invention with two examples of longitudinal and helical pattern labyrinth paths spiralling in one direction around the skirt of a non-contacting stepped piston.

Figure 4a shows an enlarged and diagrammatic sketch of the claimed invention with an example of a single longitudinal and helical pattern labyrinth.

Figure 4b shows multiple longitudinal and helical labyrinths of the claimed invention spiralling in opposite directions to each other, as applied to the skirt surface of a stepped piston.

Figure 5 shows a two-dimensional projected plan view of several parallel longitudinal labyrinths with multiple cavities on the skirt of a non-contacting piston, also indicating noti onal leakage flow directions.

Figure 6 shows multiple longitudinal and helical pattern labyrinths with multiple cavities disposed in parallel to each other along a first helical angle around the piston skirt 2 of the non-contacting piston 30, and longitudinal and helical pattern labyrinths with multiple cavities disposed in parallel to each other along a second helical angle around the piston skirt 2.

All figures include a '2000_ and '1000_ annotation; 2000 indicates upstream (higher) pressures relative to piston assembly and the labyrinth sealing pattern, while 1000 indicates downstream (lower) pressures relative to piston assembly and the labyrinth sealing pattern.

Description

Figure 1 a, which is used to explain the state of art labyrinth sealing as applied to cylindrical concentric surfaces, shows a stepped piston with labyrinth sealing on the portions 1 and 2 of the upper piston or 'smaller diameter_ piston 20 which is as described in the Definitions. The piston crown 1 is designed to withstand the maximum pressure above the piston and to transmit the resultant force into the remainder of the piston structure. With a conventional crank slider mechanism, the piston skirt 3 guides the piston and transmits the side force, due to the angularity of the connecting rod, onto the larger cylinder bore 12 via an oil film. Gases above the piston crown 1 will tend to escape between the cylindrical surfaces of the outer diameters of the piston crown 1 and piston skirt 2 and the surfaces of the inner diameter of the cylinder wall 11. With conventional pistons, contacting piston rings (not shown) are fitted to the piston crown 1; these substantially reduce gas leakage from the volume above the piston crown 1 to the volume below the piston, which in conventional engines or compressors is usually the engine or compressor crankcase.

However, in this stepped piston example, with reference to Figure la, the guidance of the upper piston crown 1 and skirt 3 is performed by the larger diameter piston 30 which is attached rigidly, in some cases, to the upper smaller diameter piston, and in other cases with some degree of controlled compliance. The larger diameter piston 30 slides with clearance between its skirt 3 and a cylinder bore 12 and is equipped with lubricant oil control piston rings 4 and 5 which limit the oil flow into and out of the clearance between the piston skirt 3 and the cylinder bore 12. //At least one of these piston rings, for example piston ring 4, and/or piston ring 5, also prevent escape of any leaking fluid from the upper volume of the larger diameter piston 30 to the volume below the larger diameter piston 30. The cylinder bore surface has oil retention features that prevent migration of the lubricating oil to the smaller diameter piston so that the latter can operate oil free, also known as 'dry_. Due to the guidance of the larger diameter piston 30, the smaller diameter piston 20 can operate with a small radial clearance between its skirt 2 and the cylinder wall 11; no oil is required as the piston skirt 2 does not touch the cylinder bore wall 11 during movement of the piston 20. The non-requirement of oil for the upper piston 20 prevents any oil contamination of the working fluid above the piston. This is important, particularly for engines and compressors where oil ingress into the cylinder air in the volume above piston 20 will result in hydrocarbon emissions in the exhaust or outlet port.

With continued reference to Figure la, also Figure lb and Figure 2, piston 20 has circumferential cavities, also described as annular grooves, also known as channels or trenches, such as 6, 7 and 8, and more if required to control the leakage rates to acceptable levels, the major axis of each of these annular grooves or circumferential cavities being orthogonal to the pressure gradient from the upstream condition to the downstream condition. The conventional circumferential cavities 6, 7 and 8 (seen in section in Figure 2) are separated by circumferential dams such as 201 and 202 (Figure lb and Figure 2); these darns have a very small clearance relative to the cylinder bore wall 11, typically of the order of 0.01-0.1% of the cylinder bore diameter. The darns between circumferential grooves such as 201 and 202 have a maximum length in a range between 0.05mm to 0.5mm. The circumferential and annular cavities typically have a length (311) to depth (312) ratio (Figure 2) in excess of three to one (3:1).

Although not shown in Figures la, Figure 1 b, Figure 2 or any other Figures, the grooves or cavities and darns described in these and other Figures may either extend continuously around a circumference, also known as 'fully circumferential, i.e. fully annular, or may be arranged with at least one discontinuity, which is also a dam, in the groove or cavity. The latter arrangement is also called a 'partial_ circumferential or partial annular groove or cavity; there may be multiple partial grooves or cavities and dams along a circumference, with darns in between the consecutive grooves.

As can be seen in Figure 2, the walls forming the dams in the annular cavities are at an angle (313) of at about 90 degrees to the bottom of the cavity 210 so that the cavity sections are substantially rectangular. In other labyrinth designs, the cavities in the flow channels are formed by arcuate walls so that the cavity sections are substantially part circular.

With continued reference to Figure 2 and Figure lb, the prPcsure reducing characteristic of the circumferential standard cavities 6, 7, 8 and others is achieved by leakage entry flow 301, approaching from the top in Figure 2 and passing over the circumferential dam 201 and bounded by the cylinder bore surface 11. This flow separates into flow path 302 which follows the contour of the adjacent cylinder wall 11 and flow path 303 which begins a re-circulatory flow in the cavity 7. The flow 302 adjacent to the cylinder wall 11 is important as it acts as at boundary layer effectively reducing the leakage path clearance between the cavity 7 and the cylinder wall 11. The re-circulatory flow 303 into the cavity] is also important, with appropriate cavity proportions, as it continues its re-circulatory path as shown diagrammatically by multiple flow paths 304, 305, 306, 307 and 309, effectively slowing the leakage flowrate from top to bottom by loss of kinetic energy via turbulence degradation and dissipation of the re-circulatory fluid flow paths. The residual leakage flow 308 leaves cavity 7 and transfers over the circumferential dam 202, bounded by the cylinder wall 11, into cavity 8 and the flow process is repeated with further reductions in the kinetic energy of the fluid and in the reduction in leakage flowrate from top to bottom. The angle 313 of the cavity walls to the bottom surface of the cavities, which form the inner diameter of the circumferential groove, are important as they increase cavity flow recirculation and turbulence degradation and dissipation of the kinetic energy of the leakage flow. Cavity wall angles, i.e. the angle subtended between two adjacent surfaces, of approximately 90 degrees will promote the most rapid loss of flow energy.

The preceding explanation describes the general fluid flow behaviour within cavities, over darns and adjacent to the cylinder walls common to all labyrinth sealing patterns. In conventional or prior art labyrinth sealing patterns, the leakage flow direction in Figure 2 is predominantly top to bottom; there is little or no transverse flow in the cavities, i.e. orthogonal to this page.

With reference to Figure lb, this shows an expanded detail of an alternative labyrinth design which can be used in conditions where the dams 101a, 101b and 101c may make slight contact with the cylinder wall 11 due to thermal expansion and/or angular tipping of the piston 1 from dynamic loads. Though the shallower or micro labyrinth cavities la, lb, lc, etc, and the smaller dams 101a, 101b, 101c and others generate smaller scale and more local ised turbulence than the larger standard labyrinth cavities 6, 7 and others, they are more robust mechanically than the circumferential dams 201, 202 and others adjacent to the larger standard labyrinth cavities 6, 7 and others. Any damage to the micro labyrinth darns 101a, 101b, 101c from contact with the cylinder walls 11 usually results in tolerable swaging of the edges of the darns into the micro labyrinth cavities la, lb, lc, etc. with no serious damage or malfunction of the piston in cylinder. However, the sealing effectiveness of micro labyrinth cavities la, 1 b, lc and others is much lower than that of the larger standard labyrinth cavities 6, 7 and others, mainly because there can be more turbulent eddies and vortices in the larger scale annular grooves.

Although labyrinth sealing of pistons in cylinders may use a variety of cavity and dam geometries, these circumferential, also known as 'annular_, cavities and dams of state of art conventional labyrinths are arranged to be orthogonal to the main direction of the overall pressure difference and sequential along the main direction of the overall pressure difference. Other than local turbulence and recirculation effects within each cavity, the bulk flow is one-dimensional from the entry of the leakage fluid at the upstream condition of the piston and cylinder bore to the exit of the leakage fluid at the downstream condition of the piston and cylinder bore.

With reference to Figure 3, this shows a similar non-contacting piston arrangement to that of Figure la and Figure lb but with the addition of at least one longitudinal and, in this embodiment, helically arranged flow channel and labyrinths 70h and 80h of sequential and contiguous dams and cavities which emanate from an upstream junction with the circumferential cavity 6 and terminate either at some downstream point between the circumferential cavity 6 and the bottom of the skirt 2, or the sequential dams and cavities of the longitudinal channel(s) terminate at a downstream point of the piston skirt surface 2. The helical flow channel(s) may have a helix angle in the range of 20-70 degrees relative to the circumferential cavity 6, i.e. spiralling in one direction, or the helical labyrinth pattern may have a helix angle in the range of 110-160-degrees relative to the circumferential cavity 6, i.e. spiralling in the opposite direction to the aforementioned 20-70 degree helix angle. These longitudinal channels of the labyrinth pattern are on axes that are non-orthogonal to the pressure gradient across the non-contacting surfaces, i.e. they are at an angle to the main pressure gradient across the piston skirt The longitudinal flow channels are arranged to begin upstream on the piston skirt surface from the last dam, in the direction of reducing precsure, of the circumferential cavities. For a piston with a single circumferential cavity, the longitudinal flow channel pattern begins at the downstream dam of the single circumferential cavity. In the case of the piston having several circumferential cavity labyrinths, the longitudinal flow channel pattern begins at the downstream dam of the last circumferential cavity in the direction of reducing pressure.

By arranging the labyrinth longitudinal flow channels along paths that are at an angle to the direction of the main pressure differential across the conduit formed by two opposed and non-contacting surfaces, the channel flow path length is firstly extended and enables a higher number of cavities and darns than the circumferential cavity pattern, and secondly the angular direction of the longitudinal labyrinth channel flow paths will create side leakage from the cavities in one labyrinth path which will create additional turbulent energy losses in the cavities of adjacent downstream helical labyrinth paths of the leakage fluid.

With reference to Figures 3, 4a and 4h, there may be several helical labyrinths in clockwise direction such as 70h, 80h and 90h and others emanating from the downstream dam of the annular cavity 6, also known as a 'groove, and terminating either at a downstream point between the annular cavity 6 and a lower pressure downstream location towards the bottom of the skirt 2 or terminating at the bottom of the skirt 2. These several labyrinths 70h, 80h and 90h may all spiral along parallel paths or some, such as 70h and 80h may spiral in one direction while others such as 110h, 120h and 130h spiral in the opposite direction as shown in Figure 4b.

With reference to Figure 5, this two-dimensional surface view diagram shows three adjacent longitudinal and helical labyrinths 110, 120 and 130 and their fluid flow paths which are part of multiple longitudinal and helical labyrinths and fluid flow paths on the skirt of a non-contacting piston, each labyrinth emanating from a circumferential groove located near the upstream pressure end of the non-contacting piston. In this diagram, the continuous lines and solid shapes are the aspects of the labyrinth that are discussed in detail. The dashed lines depict similar aspects that are peripheral to the continuous line aspects that are described and these dashed are intended to show that the described features are part of a pattern that extends around and along the piston skirt. To simplify the diagram, only some of the continuous line features are described; the other similar shaped continuous lined features behave in the same manner as those described. The fluid flow behaviour is described for contiguous cavities 71, 72 and 73 of longitudinal helical path 130, these cavities having transverse sequential turbulence generating dams 7201, 7202 and 7203 along the main longitudinal flow direction of this labyrinth path. Cavities 71, 72 and 73 are bounded on their left side, in this diagram, by a longitudinal and helical dam 142, and these same cavities are bounded on their right side, in this diagram, by a longitudinal and helical darn 132. The adjacent set of cavities to the right of 71, 72 and 73 are similarly bounded to their left and right respectively by longitudinal and helical darns 132 and 122.

The longitudinal flow 7301 (grey arrow depiction) on entering the cavities 71, 72 and 73 over the dams 7201, 7202 and 7203, cascades into turbulence, depicted in a very simplified manner, by rotational arrows 7307. The turbulence within the cavities causes flow separation and recirculation as described earlier with reference to Figure 2. This turbulence depletes the energy and momentum of the longitudinal flow 7301 so that the flow velocity reduces progressively between successive cavities, as depicted by the reduced sized longitudinal arrows in the direction of flow.

The flow paths 7308 (solid white arrow depiction) indicate side leakage flow vectors from the cavities bordering the longitudinal side dams (122, 132 and 142). These flows are due to a combination of side leakage from the cavities, arising from to the longitudinal pressure gradient along the piston skirt and cylinder bore, and the effects of turbulent flow within the cavities resulting in non-longitudinal flow within and from the cavities.

The flow paths depicted by 7308 will impinge and interfere on the longitudinal flows 7301, resulting in further turbulence and dissipation of the leakage flow energy, momentum and fl owrate With further reference to Figure Sand Figure 2, the longitudinal and helically arranged cavities each have a length, in the direction of flow, to depth ratio (311/312, in Figure 2) greater than three to one (3:1), and a width to length ratio (316/311 in Figure 5) greater than approximately one to two (1:2).

Each of the dams between cavities, such as 7201, 7202 and 7203, have a maximum length in the direction of flow between 1% to 25% of the cavity length (311).

With continued reference again to Figure 5, each longitudinal and helical labyrinth experiences some leakage flow in the direction of the helical path and experiences some leakage flow at angles to the direction of the helical path. The cavities are therefore subjected to cross flows from adjacent cavities, increasing flow re-circulation and turbulence within each cavity. The relative split of flow along the helix labyrinth path and at right angles to this path is dependent on the angle of the helix, the total length of the helical path, the number of cavities in the helical path, the clearance between the darns and the cylinder walls, the length of the darns and the width of the cavities, and the helix angle at the junction with the annular groove 6; the invention covers helix angles of the helical labyrinth(s) relative the annular groove between approximately 20-160 degrees. In some embodiments as previously stated, some helical labyrinths have helix angles of approximately 20-70degrees relative to the annular groove 6, and other helical labyrinths have helix angles of approximately 110-160degrees relative to the annular groove 6, so that the labyrinth paths intersect each other, as shown in Figure 6, further increasing the level of turbulence generation and energy dissipation at the intersecting junctions, further reducing the leakage flow.

It will be noted in Figure 5 that cavities of adjacent longitudinal and helical labyrinths are offset from each other in order to promote more crossflows and turbulence generation.

With reference to Figure 6, 70, 80 and 90 are examples of the multiple longitudinal labyrinths with multiple cavities disposed in parallel to each other along a first helical angle around the piston skirt 2 of the non-contacting piston 30, the longitudinal labyrinth paths commencing from the downstream dam of the circumferential cavity 6 and ending in this embodiment near the lowest downstream pressure end of the piston skirt 2. Other embodiments of multiple longitudinal labyrinths 110, 120 and 130 with multiple cavities are disposed in parallel to each other along on a second and different helical angle around the piston skirt 2 of the non-contacting piston 30, the longitudinal labyrinth paths commencing from the downstream dam of the circumferential cavity 6 and ending in this embodiment near the lowest downstream pressure end of the piston 30. Although not visible in Figure 6, the cavity sequence in the parallel longitudinal flow channels may be offset longitudinally by up to one half cavity length as shown in Figure 5. The embodiment of the invention shown in Figure 6 also has optional micro labyrinth dams 1 as described with reference to Figure 1 b.

A further embodiment of the invention comprises a series of cavities such that the leakage fluid passes from one cavity to the next over a short darn, said cavities and dams being disposed contiguously and following a prescribed geometrical pattern around the piston surface, such as a zig-zag arrangement, there being a multiplicity of these zig-zag labyrinths arranged with the defined pattern around the piston skirt, commencing upstream near the crown of the piston from a circumferential cavity from a downstream dam and terminating partway, or at the bottom of the piston skirt. In this labyrinth sealing arrangement, the forward path of each zig-zag labyrinth has an angle of approximately 10-80 degrees relative to the circumferential cavity, and the reverse path of each zig-zag labyrinth has an angle of approximately 10-170 degrees relative to the plane of the circumferential cavity.

The previously described labyrinths may extend from the circumferential groove 6 to the bottom of the piston skirt 2 (Figure 3), or may terminate part way along the piston skirt.

In all embodiments, the aforementioned labyrinths may start upstream near the piston crown without a circumferential groove following a defined pattern around the piston towards downstream portion of the piston surface.

The previously described inventions may optionally have either a partial circumferential groove surrounded by dams, or a fully circumferential groove with dams only on the upstream and downstream sides. The partial circumferential groove or grooves may be truncated in at least one section around the circumference of the piston or cylinder bore, with a plain surface at the dam locations.

All the aforementioned longitudinal labyrinth patterns may be applied to the male sealing surface, such as the piston, or to the female surface, such as the cylinder bore, or applied to both surfaces. Furthermore, when applied to both male and female surfaces, the disposition of the longitudinal labyrinth patterns on the male and female may be arranged to create maximum flow interference and turbulence between the labyrinth patterns on each surface. This could be achieved, for example, by arranging a helical flow direction pattern on the male surface to be in a clockwise direction, and a helical flow direction pattern on the female surface to be in an anticlockwise direction, or vice-versa. In another arrangement, the angular dispositions of the longitudinal labyrinth patterns on the male surfaces may be at first inclination to the main axis of the piston or cylinder bore, and the angular dispositions of the longitudinal labyrinth patterns on the female surfaces may be at a second inclination to the main axis of the piston or cylinder bore, and vice-versa.

In this aforementioned embodiment with labyrinth patterns on both the piston and cylinder bore surfaces, the longitudinal labyrinth flow channels on the piston start from an upstream location near the crown of the piston from a first circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam and said longitudinal labyrinth channels terminating at a downstream location partway along, or at the bottom of the piston, and in which the flow channels on the cylinder bore start at entry to the cylinder bore from a circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam, and said channels terminating at a downstream location partway along, or at the bottom of the cylinder bore.

The helix angle of the longitudinal helical flow channels may be between 20-160 degrees relative to the plane of the circumferential cavities on the surfaces of the piston and the cylinder bore. For example, some helically disposed longitudinal fl ow channels on the cylinder bore surface have a helix angle between 20-70 degrees relative to plane of the circumferential cavity, and other helically disposed flow channels have a helix angle between 110-160 degrees relative to the plane of the circumferential cavity.

In all these labyrinth sealing embodiments, each circumferential groove or each cavity is formed by walls or dams that are at least 70 degrees to the floor of the cavity so that the cavity sections are substantially rectangular.

Alternatively, the sectional shape of cavities in the longitudinal flow channels may be formed by arcuate walls so that the cavity sections are substantially part circular.

All these labyrinth sealing embodiments may be used with a stepped piston in which the larger diameter of the stepped piston guides the smaller diameter piston skirt with the labyrinth sealing pattern and having a non-contacting clearance relative to the cylinder bore.

The longitudinal labyrinth pattern, such as the helical path labyrinth pattern, may be used in combination with one or several of the circumferential grooves which are generally disposed near the crown of the piston. In other arrangements, the helical path pattern may be used with some circumferential grooves at the crown of the piston, and some intermediately located circumferential grooves along the piston skirt so that the helical labyrinths intersect the ci rcumferenti al grooves All these multiple longitudinal Iabyrinths with sequential cavities and dams, as previously described for the invention and its embodiments, may be used in compressors or engines with either a crosshead supported piston, or a rectilinear drive supported piston, or a stepped piston or an articulated piston or any other arrangement that enables the piston skirt and cylinder bore to operate with contacting each other and with a controlled clearance.

Novelty There are at least four significant novel and non-obvious aspects of the invention that are not previously used in prior art labyrinth seal arrangements.

The first novel aspect is the bulk leakage flow of the invented labyrinth pattern which has a substantially longer flow path than prior art labyrinths where the bulk flow follows the shortest path from the upstream pressure to the downstream pressure. With this longer flow path, the invention reduces pressure gradients, versus state of art conventional labyrinths, and this reduces leakage leading to higher sealing effectiveness compared to conventional ci rcumferenti al labyrinths.

The second novel aspect is the overall flow patterns of the proposed labyrinths are multidimensional because the leakage flow paths of the labyrinths are at angles to the shortest flow path, generating cross flows. By contrast the major flow pattern of state of art conventional circumferential labyrinths is one-dimensional along the shortest route from the upstream pressure to the downstream pressure. The invented multi-dimensional flow routes result in more energy and momentum losses than the conventional one-dimensional flow patterns, producing more rapid pressure reduction in the leakage areas The third novel aspect is the designed cross flow situation of intersecting longitudinal flow paths of the invention which generates more turbulence, more momentum losses and more flow energy dissipation in the dams and cavities compared to state of art conventional labyrinths where turbul ence is only generated by one-dimensional flow.

The fourth novel aspect is the much higher number of cavities and dams along the flow paths of the invention, when compared to conventional circumferential labyrinths, resulting in greater turbulence levels and also greater high frequency turbulence content and dissipation; it is generally accepted that high frequency turbulence is the most effective form of turbulence dissipation for reducing momentum and energy flows and increasing pressure losses.

Although the above inventive geometrical aspects represent application of common principles, these aspects do not exist in any products or published information relating to labyrinth sealing. The absence of these inventive features from the public domain may either have resulted from prior manufacturing limitations whi ch are now substantially overridden by modern manufacturing methods, or state of art conventional labyrinths perform satisfactorily for their current applications with low pressure differentials across the piston. However, as mentioned in the Background, prior art labyrinth sealing is inadequate for pressure differentials in compressors and reciprocating engines that are several times higher or an order of magnitude higher than the current pressure differentials.

Summary

In summary, the invention is a labyrinth sealing arrangement with various embodiments, for a volume of a compressible fluid formed by a non-contacting piston moving in a cylinder bore, the labyrinth pattern being formed between the small clearance of the non-contacting surface of the piston and the non-contacting surface of the cylinder, in which the labyrinth pattern comprises a multiplicity of longitudinal flow channels, with multiple cavities separated by dams, starting at the upstream pressure area on at least one of these surfaces and the labyrinth pattern having the major axis of each longitudinal flow channel at a non-orthogonal angle to the main direction of the overall pressure gradient across the surfaces, such that there are high velocity flow interactions between the fluid flow in the cavities of the longitudinal channels, and leakage flow across and between said longitudinal channels, these flow interactions creating a loss of fluid momentum and therefore a reduction in pressure and leakage flow. The longitudinal flow channels comprise a series of cavities and darns such that the fluid leakage passes from one cavity to the next over a dam, said cavities and darns being disposed contiguously along each flow channel, said channels commencing at or near to the points of the upstream leakage fluid flow entry to the two non-contacting surfaces, and said channels terminating part way along, or at the downstream flow exit of the two surfaces. These flow channels may be either on the piston surface, or on the cylinder bore surface or on both the piston and cylinder bore surfaces.

In the case of the labyrinth sealing on the piston surfaces, the longitudinal flow channels start at an upstream location near the crown of the piston from a first circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam upstream of each longitudinal flow channel, said channels terminating at a downstream location partway along, or at the downstream portion of the piston skirt.

In another embodiment each flow channel on the piston commences from or near the downstream dam of the last circumferential cavity below the crown of the piston, this cavity being itself a single circumferential groove receiving leakage flow across a fully peripheral dam from the preceding circumferential cavity between the last circumferential groove and the piston crown.

In a further embodiment, the labyrinth sealing system has at least one or more circumferential cavities on the piston between the said first circumferential cavity and the said last circumferential cavity, this one of more additional cavities being themselves labyrinth cavities receiving leakage flow from a circumferential dam of the preceding upstream circumferential cavity, and delivering leakage flow via a circumferential dam to the following downstream circumferential cavity.

In one embodiment the multiple longitudinal flow channels are disposed helically around the piston skirt, each flow channel commencing upstream near the crown of the piston from the last circumferential cavity, and said flow channels terminating downstream partway along, or at the bottom of the non-contacting piston skirt. The helix angle of the helical flow channels is typically between 20-160 degrees relative to the plane of the circumferential cavity. Some of the helically disposed flow channels may have a helix angle between 20-70 degrees relative to the plane of the circumferential cavity, and other helically disposed flow channels may have a helix angle between 110-160 degrees relative to the plane of the circumferential cavity so that the flows in the intersecting longitudinal cavities interfere and create turbulence with subsequent energy and momentum loss, thus reducing the leakage flow.

In another embodiment of the invention, the multiple longitudinal flow channels are disposed in zig-zag patterns around the non-contacting piston skirt, each flow channel commencing upstream near the crown of the piston from the dam downstream of the last circumferential cavity, and said flow channels terminating downstream partway along, or at the bottom of the piston skirt. The forward path of each zig-zag flow channel may have an angle between 10-70 degrees relative to the plane of the circumferential cavity, and the reverse path of each zig-zag labyrinth may have an angle between 110-160 degrees relative to the plane of the circumferential cavity.

The zig-zag labyrinth multiple fl ow channels may be disposed in multiple differing patterns around the piston skirt, each flow channel commencing at an upstream location near the crown of the piston from the dam downstream of the last circumferential cavity, and said flow channels terminating downstream partway along, or at the bottom of the piston skirt.

Claims

Claims 1 A labyrinth sealing pattern, for a volume of a compressible fluid formed by a non-contacting piston in a cylinder bore, the sealing being formed between the small clearance of the non-contacting surface of the piston and the non-contacting surface of the cylinder, in which the labyrinth pattern comprises a multiplicity of longitudinal flow channels, with multiple cavities separated by dams within the longitudinal flow channels, said flow channels starting at the upstream pressure area on at least one of these non-contacting surfaces and the labyrinth pattern having the major axis of each longitudinal flow channel at a non-orthogonal angle to the main direction of the overall pressure gradient between the upstream and downstream of the leakage flow.
2 A labyrinth sealing arrangement as in Claim 1, in which each longitudinal flow channel comprises a series of cavities and dams such that the fluid leakage passes from one cavity to the next over a dam, said cavities and dams being disposed contiguously along each flow channel, and said channels terminating between the upstream and downstream locations of the leakage flow.
3 A labyrinth sealing arrangement, as in Claim 2, with flow channels on both the piston surface and the cylinder surface.
4 A labyrinth sealing arrangement, as in Claims 1 and 2, in which the longitudinal flow channels start upstream near the crown of the piston from the downstream dam of a first circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam, and said longitudinal channels terminating downstream partway along, or at the bottom of the piston skirt.
A labyrinth sealing system as in Claims 1 and 2, in which each longitudinal flow channel on the piston commences upstream from the downstream dam of the last circumferential cavity below the crown of the piston, this cavity being itself a labyrinth groove receiving leakage flow across a circumferential dam from the preceding circumferential cavity between the previous upstream circumferential groove and the piston crown.
6 A labyrinth sealing system as in Claim 4, which has at least one or more circumferential cavities on the piston between the said first circumferential cavity and the said last circumferential cavity, these additional cavities being themselves circumferential labyrinth cavities receiving leakage flow via a circumferential dam from the preceding upstream circumferential cavities, and delivering leakage flow via a circumferential dam to the following downstream circumferential cavity.
7 A labyrinth sealing arrangement as in Claims 4, 5 and 6, in which the multiple longitudinal flow channels are disposed helically around the piston outer surface, each flow channel commencing upstream near the crown of the piston from the downstream dam of the last circumferential cavity, and said longitudinal flow channels terminating downstream partway along, or at the bottom of the piston skirt.
8 A labyrinth sealing arrangement as in Claim 7, in which the helix angle of the helical flow channels is between 20-160 degrees relative to the plane of the circumferential cavity.
9 A labyrinth sealing arrangement, as in Claim 8, in which some helically disposed flow channels have a helix angle between 20-70 degrees relative to the plane of the circumferential cavity, and other helically disposed flow channels have a helix angle between 110-160 degrees relative to the plane of the circumferential cavity.
A labyrinth sealing arrangement as in Claim 4, Claim 5, Claim 6 and Claim 7, in which the multiple flow channels are disposed in zig-zag patterns around the piston outer surface, each flow channel commencing upstream near the crown of the piston from the circumferential dam downstream of the last circumferential cavity, and said longitudinal flow channels terminating downstream partway along, or at the bottom of the piston skirt.
11 A labyrinth sealing arrangement, as in Claim 10, in which the forward path of each zig-zag flow channel has an angle of between 10-70 degrees relative to the plane of the circumferential cavity, and the reverse path of each zig-zag labyrinth has an angle between 110-160degrees relative to the plane of the circumferential cavity.
12 A labyrinth sealing arrangement as in Claim 4, Claim 5, Claim 6 and Claim], in which the multiple flow channels are disposed in multiple differing patterns around the piston surface, each flow channel commencing upstream near the crown of the piston from the circumferential dam downstream of the last circumferential cavity, and said longitudinal flow channels terminating downstream partway along, or at the bottom of the piston skirt.
13 A labyrinth sealing arrangement, as in Claim 12, in which the forward paths of the different pattern flow channels have angles in the range of 10-70 degrees relative to the circumferential cavity, and the reverse paths of the different pattern flow channels have angles in the range of 110-160 degrees relative to the circumferential cavities.
14 A labyrinth sealing arrangement, as in Claims 1 -13, in which the cylinder and piston are cylindrical.
A labyrinth sealing arrangement, as in Claim 3, in which the direction of the longitudinal labyrinth channels on the cylinder bore are locally arranged to be in a cross flow direction to the adjacent longitudinal labyrinth channels on piston.
16 A labyrinth sealing arrangement as in Claim 15, in which the longitudinal labyrinth flow channels on the piston start upstream near the crown of the piston from a circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam, and said longitudinal Iabyrinth channels terminating downstream of the piston skirt, and in which the flow channels on the cylinder bore start at an upstream location on the cylinder bore from a circumferential cavity, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam, and said channels terminating downstream of the cylinder bore.
17 A labyrinth sealing arrangement, as in Claims 1 and 2, in which the longitudinal flow channels start upstream of the cylinder bore surface from a first circumferential cavity on the cylinder bore surface, also known as a groove, with a circumferential upstream dam, a circumferential downstream dam, and said longitudinal flow channels terminating at a downstream location of the cylinder surface.
18 A labyrinth sealing system as in Claims 1 and 2, in which each longitudinal flow channel on the cylinder bore commences from the downstream dam of the last circumferential cavity on the cylinder bore surface, this cavity being itself a circumferential labyrinth groove receiving leakage flow across a circumferential dam from the preceding circumferential cavity between the last circumferential groove and upstream of the cylinder surface.
19 A labyrinth sealing arrangement as in Claim 18, in which the multiple flow channels are disposed helically around the cylinder bore surface, each flow channel commencing upstream near the innermost point of piston travel on the cylinder surface from the dam downstream of the last circumferential groove on the cylinder surface, and said flow channels terminating at a downstream location of the cylinder surface.
A labyrinth sealing arrangement, as in Claim 19, in which the helix angle of the helical flow channels is between 20-160 degrees relative to the plane of the circumferential groove.
21 A labyrinth sealing arrangement, as in Claim 20, in which some helically disposed longitudinal flow channels on the cylinder surface have a helix angle in the range of 2070 degrees relative to plane of the circumferential groove, and other helically disposed flow channels have a helix angle in the range of 110-160 degrees relative to the plane of the circumferential groove.
22 A labyrinth sealing arrangement, as in all Claims, in which circumferential grooves have a length in the direction of flow to depth ratio in excess of three to one (3:1).
23 A labyrinth sealing arrangement, as in all Claims, in which each of the longitudinal cavities has a length in the direction of flow to depth ratio in excess of three to one (3:1).
24 A labyrinth sealing arrangement, as in all Claims, in which each of the longitudinal cavities has a length in the direction of flow to width ratio at least of one to one (1:1).A labyrinth sealing arrangement, as in all Claims, in which each of the darns between cavities has a length in direction of flow of between 0.05mm to 5mm 26 A labyrinth sealing arrangement, as in all Claims, in which the cavities in the longitudinal flow channels are forn led by walls that are at an angle of at least 70 degrees to the floor of each cavity so that the cavity sections are substantially rectangular.27 A labyrinth sealing arrangement as in all Claims excepting Claim 26, in which the cavities in the longitudinal flow channels are formed by arcuate walls so that the cavity sections are substantially part circular.28 A labyrinth sealing arrangement or embodiment as shown in Figure 3.29 A labyrinth sealing arrangement or embodiment as shown in Figure 4a.A labyrinth sealing arrangement or embodiment as shown in Figure 4b.31 A labyrinth sealing arrangement or embodiment as shown in Figure 6.32 Labyrinth sealing arrangements or embodiments as in all Claims when applied to a compressor.33 Labyrinth sealing arrangements or embodiments as in all Claims when applied to an engine.