WO2012113349A1

WO2012113349A1 - Hydraulic cylinder and spool type hydraulic control valve with metallic seal ring

Info

Publication number: WO2012113349A1
Application number: PCT/CN2012/071603
Authority: WO
Inventors: Lok Kin LEE; Kyong Tae Chang
Original assignee: INNOZEAL TECHNOLOGY Ltd
Current assignee: INNOZEAL TECHNOLOGY Ltd
Priority date: 2011-02-25
Filing date: 2012-02-24
Publication date: 2012-08-30
Anticipated expiration: 2013-08-25

Abstract

A hydraulic actuator comprises a metal helical coiled multilayer seal (8, 12) for sealing between two relatively moving parts. The hydraulic actuator may include a hydraulic cylinder assembly in which the metal helical coiled multilayer seal is configured for piston sealing and piston rod sealing. The hydraulic actuator may also include a spool type hydraulic control valve in which the metal helical coiled multilayer seal is configured for spool sealing. The present invention overcomes the temperature limitation and pressure limitation and allows the removal of all of the rubber O-rings in hydraulic actuators in conventional art.

Description

HYDRAULIC CYLINDER AND SPOOL TYPE HYDRAULIC CONTROL VALVE

WITH METALLIC SEAL RING

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates generally to sealing of moving parts in hydraulic systems, and in particular, to sealing of pistons in hydraulic cylinders, and sealing of spools in spool type hydraulic control valves.

Description of Related Art

In conventional hydraulic cylinder, the sealing of the piston and the piston-rod is achieved by rubber O-rings. Sealing of the piston and piston-rod by rubber O-ring can be done only when the rubber O-ring has a certain range of elasticity which means the ambient temperature should be within the range between -50 degree C and +250 degree C.

The elasticity of rubber O-ring is an essential characteristics to perform sealing. Nevertheless, the elasticity of rubber O-ring is lost below -50 degree C due to freezing of rubber molecules. In addition, the elasticity of rubber O-ring is lost above +250 degree C due to carburizing of rubber molecules.

The elasticity of rubber O-ring is essential but it also causes the pressure limitation to apply in hydraulic cylinder. In other words, the rubber O-ring is usable only below a certain pressure limit, e.g.: 450 kg/square-cm, because the seal will be destroyed when rubber is squeezed out of the gap between the cylinder and the piston. This is referred as extrusion phenomenon when the rubber O-ring is exposed to the pressure above a certain limit, e.g. : 450 kg/square-cm.

To summarize, rubber O-rings used for piston in conventional art suffer from many disadvantages including typically temperature limitation and pressure limitation.

Modern industry requires faster and accurate operations of the machine devices which are possible only when such operations are under higher pressure. There is also need that these machine devices are able to be operated and accessible at more extreme condition such as at the North Pole and close space of melting furnace.

In general, about 8 to 11 different functioning O-rings are used on one piston as the seal in conventional art to overcome those low temperature condition and high temperature condition and to withstand higher pressure with rubber O-rings.

Rubber O-rings cannot withstand high pressure alone and need one or two assisting rings to help withstand high pressure. Wear ring made of hard polymer such as glass fiber reinforced phenol resin are also needed to provide the rubber O-rings longer life. Other hard polymer ring are also needed to overcome friction of rubber O-rings and thereby make sliding action easy. As a result, a total of around 10 assisting O-rings are required according to conventional art.

In conventional art, all of the hydraulic actuators including power cylinder, hydraulic motor, accumulator, pump and so forth must be controlled to have goes and stops accordingly under the control of sequence control system. The hydraulic system along with progressing of all other surrounding technology also needs to have faster and more accurate actuations under higher load. Higher load, higher speed and higher accuracy in the hydraulic system are attainable only with higher fluid pressure. Generating high pressure fluid is already difficult but controlling the higher pressure is even more difficult due to the difficulties of sealing related parts including control valve.

One of the most demanded parts in high pressure control systems is spool type direction control valve. The spool type direction control valve for high pressure hydraulic system in conventional art has no sealing rings on spool. The sealing of spool in conventional art relies only upon the precise dimension control approaching submicron grade and finer finishing of the surface of the bore and surface of the spool to minimize leakage. There are no practical sealing devices in between the bore and the spool.

Some types of elastomeric material such as polyamide could withstand 500 bar pressure before it is extruded but the elastomeric material cannot be employed on the spool as sealing ring.

In constructing spool type valve there must be two parts, the valve block and the spool. There must be at least 5 ports in a valve block of spool type control valve:

• Main power fluid supply port

• Output port A

• Output port B

• Return port of output port A

• Return port of output port B. It needs to drill 5 holes from outer surface of the valve block into cylinder to penetrate into cylinder bore to connect 5 ports from outside with cylindrical bore inside through which controlling fluid should flow.

Drilling a hole that penetrates the metal wall creates unavoidable burs on the opposite side of the metal wall which should be removed using proper tool such as chamfer tool to undergo subsequent processes safely since the burs are always sharp and could damage other contacting parts and can be cause of the sticking of other mating part.

When both sides of the metal on which holes are drilled are in open condition it is easy to remove drill hole burs and also could easily be chamfered to avoid sharp corner edge of the drilled holes but if one side of the drilled hole remains in closed location as inside of the cylinder bore where the chamfer process is not accessible the sharp corner edge of the drilled hole has to be left not chamfered.

In producing spool type control valve it is essential to drill 5 holes into the valve block cylinder bore from outside where the chamfering process is not possible so the sharp corner of the drilled hole remain as cutting edge of the metal.

Besides, the hole inside the cylinder is not true circle but in oval shape as the drilled hole from outside is connected to the cylindrical surface of the cylinder bore that makes even sharper edge if not chamfered.

Low pressure application spool valves such as pneumatic control systems applicable pressure under 30 bar are using elastomeric O-rings for spool sealing ring in the pneumatic spool valve since the rubber O-ring has enough strength to overcome sharp edge of drilled hole not chamfered remaining inside of the cylinder bore of the spool valve when the pressure is very low.

But it is impossible to have elastomeric sealing rings that provide enough high strength to overcome 300 bar or higher pressure which is average pressure in current hydraulic system, without torn off at sharp corner edge of the drilled hole not chamfered left inside of the high pressure hydraulic control spool valve.

Accordingly, all of the spool type high pressure hydraulic control valves in conventional art are made without sealing rings on spool. BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to overcome or substantially ameliorated at least one of the above disadvantages. In particular, it is an object to overcome those temperature limitation and pressure limitation by introducing metallic dynamic sealing ring called CFS (Coiled Felt Seal) both on the piston and on the piston-rod of hydraulic cylinders. The present invention allows the removal of all of the rubber O-rings in hydraulic cylinder pistons according to conventional art. The present invention results in simplicity in structure, higher performance, the ability of withstanding extreme high temperature, extreme low temperature, and extreme high pressure, and in the meantime provides minimum friction loss and substantially zero leak seal.

It is a further object of the present invention to provide metallic seal ring on the spool of high pressure hydraulic spool valve and thereby removing the pressure limitation in conventional art, as long as the metal constructing the sealing ring could withstand the applied pressure, that usually could go up many thousand bars.

According to an aspect of the present invention, there is provided a hydraulic actuator. The hydraulic actuator includes a metal helical coiled multilayer seal for sealing between two relatively moving parts.

Advantageously, the hydraulic actuator further includes a hydraulic cylinder assembly. The metal helical coiled multilayer seal is configured for piston sealing and piston rod sealing.

Advantageously, the hydraulic actuator further includes a spool type hydraulic control valve. The metal helical coiled multilayer seal is configured for piston sealing.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are described hereinafter, by way of example only, with reference to the accompanying drawings in which:

Fig-1 shows the cut out view of over all schematic of hydraulic cylinder assembly according to an embodiment of the present invention.

Fig-2 shows the cut out view of overall schematic of hydraulic cylinder assembly in accordance with the conventional art.

Fig-3 shows the enlarged detail of the rubber O-rings before and after inserted in the cylinder according to an embodiment of the present invention.

Fig-4 shows the cutout view of spool type pneumatic valve that uses rubber O-rings as seal ring for sealing and isolates or connect each port in each given control condition. Left side drawing depicts the condition of piston pushed out and right side drawing depicts the condition of piston pulled in by control of hydraulic fluid.

Fig-5 is the enlarged cutout view of valve body spool, rubber O-rings that shows how the rubber O-ring could be torn out by the sharp edge of the drilled hole into valve body when the sharp edge of the drilled holes are not chamfered.

Fig-6 shows the cutout view of spool type high pressure hydraulic valve according to an embodiment of the present invention, that uses metallic seal rings for sealing that isolate or connect each port in each given control condition. Left side drawing depicts the condition of piston pushed out and right side drawing depicts the condition of piston pulled in by control of hydraulic fluid.

Fig-7 is enlarged cutout view of valve body, spool, metallic O-ring seal that shows how the metallic O-ring seal according to an embodiment of the present invention could withstand extreme high pressure without distorted or being damaged by high pressure in the high pressure hydraulic system.

Fig-8 shows a Coiled Felt Seal that is adopted on a hydraulic cylinder piston or on a spool of a spool type hydraulic control valve in accordance with the embodiments of the present invention.

Fig-9 shows the partial rings for constructing the Coiled Felt Seal (CFS) that is adopted on a hydraulic cylinder piston or on a spool of a spool type hydraulic control valve in accordance with the embodiments of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hydraulic Cylinder with CFS Sealed Piston CFS seal, Coiled Felt Seal is a metallic helical coiled dynamic seal that is applied to the technical field of the present invention. It is aimed to improve the performance of the hydraulic cylinder by using CFS on both piston and piston rod.

Applying CFS on piston and piston-rod of the hydraulic cylinder assembly of conventional art improves not only the performance of the hydraulic cylinder but also the durability. It also cut the manufacturing cost due to the unique sealing performance of the CFS.

Fig-1 shows the cut out view of the hydraulic cylinder assembly structure in accordance with an embodiment of the present invention. In Fig-1, only one CFS seal(08) on piston(05) instead of 11 different functioning rubber O-rings in conventional art. There is also only one CFS seal(12) on piston-rod seal block(04) instead of 5 different functioned rubber O-rings in conventional art.

CFS piston seal(08) is mounted on piston block(06) and the compression spring(09) that inserted in the spring holes on compression ring(09) provides force on CFS to keep the source rings of the CFS piston seal(08) tightly contacted.

Sealing between piston block(06) and piston-rod(05) is done by rubber O-rings(20) and the bolts(lO) hold piston block(06) and compression ring(09) together tightly, and the rod nut(l l) holds piston block (06) and compression ring(09) on the piston rod(05).

Link-end(02) of the cylinder(Ol) is fastened to the cylinder by tie bolts(17).

Link-end(03) of the piston-rod(05) is fastened to the piston-rod(05) by own screw thread made both on the tie-end(03) and the piston-rod(05).

The piston-rod seal block(04) is fastened to the cylinder(Ol) by tie bolts(16).

The piston-rod seal(12) is installed on the inside of the piston-rod seal block(04) and the compression spring(14) that inserted in the spring holes on compression ring(14) provides force on CFS piston-rod seal(12) to be strongly compressed to keep the source rings of the CFS tightly contacted.

Fig-2 shows the cut out view of overall schematic of hydraulic cylinder assembly in accordance with the conventional art. In Fig-2, there are 11 different functioning O-rings on piston block(25) instead of only one CFS seal(8) in the embodiment of the present invention. In addition, there are 5 different functioning O-rings on piston-rod-seal-block(50) instead of only one CFS seal(12) in the embodiment of the present invention.

Fig-2 shows 11 different functioning O-rings on piston block(25) each of which is retaining ring(34), seal ring(35), seal ring(36), back-up ring(37), slip ring(38), cushion ring(39), wear ring(40), cushion ring(41), back-up ring(42), seal ring(43) and retaining ring(44).

Fig-2 also shows 5 different functioning O-rings on piston-rod-seal-block(50) instead of only one CFS seal ring(12) according to the present invention each of which is retaining ring(45), seal ring(46), U-packing(47), retaining ring(48) and dust wiper(49).

Fig-3 shows the enlarged detail of the rubber O-rings before and after inserted in the cylinder according to an embodiment of the present invention. The lower part of Fig-3 shows two rubber O-rings installed in the O-ring groove to have sealing function seal ring(35) and another seal ring(36) which shows perfect natural circle which shall be forced press flattened to insert in between cylinder tube(24) and piston block(25) with back-up ring(37) in conventional art.

The upper part of Fig-3 shows two rubber O-rings installed in the O-ring groove to have sealing function seal ring(35) and another seal ring(36) which shows flattened oval circle with back-up ring(37) after insert in between cylinder tube(24) and piston block(25) in conventional art.

The flattening of rubber O-ring is creating rubber recovering force to return to its perfect circle by the nature of the rubber which creates sealing function between two mating surfaces, cylinder tube(24) and piston block(25) in conventional art .

This recovering force of rubber also causes the friction between cylinder tube(24) and piston block(25) in conventional art during functioning of sealing.

Those 6 rubber O-rings on the piston block(25) of conventional art each of which is retaining ring(34), seal ring(35), seal ring(36), cushion ring(39), wear ring(40) and another seal ring(43) creates tremendous friction during high speed reciprocation of piston in the cylinder which causes loss of power and also causes shorter life of hydraulic cylinder by conventional art.

To summarize, the use of CFS seal in hydraulic cylinder assembly on piston seal and piston rod seal reduces the friction loss during reciprocation of piston, thereby resulting in longer life of the hydraulic cylinder and lowering manufacturing cost due to reducing the number of parts.

Spool Type Hydraulic Control Valve with Metallic Seal Ring

Fig-4 is the schematic cutout view of a spool type control valve which is currently used in control of pneumatic system for pressure not higher than 30 bar.

On the left side of Fig-4 piston pushed out condition is depicted.

A long cylindrical hole(19) is made inside of the valve block(Ol) in which the valve spool(02) shall be inserted which has six grooves(17) and on each groove(17) rubber 0-ring(18) shall be assembled to isolate or connect valve ports by shifting of spool(02) location by the logic controller of compressed air in the pneumatic system.

Supplying the compressed power air by air flow arrow(12) into supply port(03) creates air flow arrow(14) through spool neck(20) and through tube(09) that connected to the actuator cylinder(lO).

Piston(l l) is pushed outward as direction arrow(16) by the air in the cylinder(lO) by the force of air flow arrow(14).

By the forward moving of piston(l l) as direction arrow(16) the original air inside of the cylinder(lO) is pushed out as air flow arrow(15) through tube(08) that connected to port(06) through spool neck(21) and discharges out as air flow arrow(13) through the port(04).

On the right side of Fig-4 piston pulled in condition is depicted.

Supplying the compressed power air by air flow arrow(12) into supply port(03) creates air flow arrow(22) through spool neck(21) and through the tube(08) that connected to port(06) pushes the piston(l l) of actuator cylinder(lO) inward as direction arrow(25).

By the backward moving of piston(l l) as direction arrow(25) the original air inside of the cylinder(lO) is pushed out as air flow arrow(23) through tube(09) that connected to port(07) through spool neck(20) and discharges out as air flow arrow(23) through the port(05). Thus the Fig-4 shows how the piston(l l) could be moved to have actuator motion to either direction forward arrow(16) direction and backward arrow(25) direction by the shifting of the spool(02) location in the valve block(Ol).

Fig-5 is the enlarged cutout view of valve body, spool, rubber O-rings that shows how the rubber O-ring could be torn out by the sharp edge of the drilled hole in valve body when the sharp edge of the drilled holes are not chamfered.

Rubber O-rings are assembled on the grooves(31) of the valve spool(29) and the rubber O-ring must be compressed as shown compressed 0-ring(32) that became oval shape cross section to make the outside diameter smaller to force insert into the valve bore(30) that is smaller diameter than the free condition of rubber O-ring so as to let rubber O-ring have 3 dimensional expanding force to keep contact under certain contacting force simultaneously with bore(30) and spool(29) that called sealing.

In some instance the rubber 0-ring(34) could come to the location as drawing in Fig-5 right on the drilled hole(34) location which makes rubber O-ring return to original true circle as shown by 0-ring(38) on the position where there is no wall of bore(30) so if the spool(29) is pushed to rightward direction to make the edge of the rubber-O-ring (37) as depicted to meet sharp corner(36) of the drilled hole(35) the 0-ring(37) will be sheared by the sharp corner(36) of bore(30) and 0-ring(37) will be torn out at the point of sharp corner(36) which damages sealing function of spool.

When the system is in low pressure under 30 bar the rubber O-ring can maintain its shape but if the pressure of the system is high up at 300 bar the O-ring can not maintain the shape without torn off, this is the reason why high pressure system can not use rubber O-ring.

Sealing the spool inside of the spool valve in high pressure system rely upon only the viscosity of the fluid used in the system so the clearance between the spool and bore wall must be kept as small as possible unless the spool is stuck inside of the bore due to too small clearance.

The valve bore must pass all the procedures from boring, reaming, grinding and honing through out entire processes.

The alloy of the valve body should be selected that could maintain lowest thermal expansion coefficient to keep possible for least dimensional change under wide range of temperature change to prevent the spool in the bore from stick in the position.

The valve body should pass the extreme grade heat treatment to maintain lowest thermal deformation along with wide variety of temperature that causes high cost from the first and those alloys passing extreme heat treatment having extra high strength and hardness that makes difficult in all subsequent process from drilling and boring that causes another cost push and difficulties in quality control.

All those difficult factors are caused by the sharp edge of the drilled hole left inside of the bore not chamfered.

But metallic O-ring is completely free from shearing off by not chamfered sharp edge of the drilled hole left inside of the valve bore.

Fig-6 shows the cutout view of the valve assembly with metallic O-ring seal on the spool for any high pressure application.

On the left side of Fig-6 piston pushed out condition is depicted.

A long cylindrical hole(42) is made inside of the valve block(39) in which the valve spool(40) shall be inserted.

Six pieces of metallic O-rings(60) are mounted on the spool(40) and those O-rings(60) are kept on each predetermined location by the separation sleeves(41).

Metallic O-ring(60) is constructed by 3 different functioning layer of rings each of which are cylinder seal layer, absorption layer and shaft seal layer constructed all in one not separable single piece of O-ring(60).

The cylinder seal layer seals the cylinder wall only without contacting shaft in any condition, absorption layer absorbs any and all dimensional variations during dynamic movement of the shaft and the shaft seal layer seals shaft only without contacting cylinder in any condition.

Supplying the compressed power hydraulic fluid flow arrow(51) into supply port(45) creates hydraulic fluid flow arrow(56) through tube(69) that connected to the port(50) supplying hydraulic fluid to the actuator cylinder(43) which pushes piston(44) outward as direction arrow(59).

By the forward moving of piston(44) as direction arrow(59) the original hydraulic fluid inside of the cylinder(43) is pushed out as hydraulic fluid flow arrow(57) through tube(61) that connected to port(49) discharges out hydraulic fluid to return to tank as flow arrow(58) through the port(46).

On the right side of Fig-6 piston pulled in condition is depicted.

Supplying the compressed hydraulic fluid by flow arrow(51) into supply port(45) creates hydraulic fluid flow arrow(52) through the tube(61) that connected to port(49) pushes the piston(44) of actuator cylinder(43) inward as direction arrow(55).

By the backward moving of piston(44) as direction arrow(55) the original hydraulic fluid inside of the cylinder(43) is pushed out as hydraulic fluid flow as arrow(53) through tube(69) that connected to port(50) through port(47) and the hydraulic fluid return to tank.

Thus Fig-6 shows how the piston(44) could be moved to have actuator motion to either direction forward arrow(59) direction and backward arrow(55) direction by the shifting of the spool (40) location in the valve block(39).

Fig-7 shows the enlarged cutout view of the valve block(62) with the inserted spool(63) on which separation sleeves(64) and metallic sealing 0-rings(65 and 67) are assembled and located right at the location to meet drilled hole(66) of the valve that is not chamfered.

The metallic sealing 0-ring(65 and 67) has radial tension which means the ring could be expanded to have slightly bigger diameter or contracted to have slightly smaller diameter by its radial tension but each points on the ring circumference of metal ring can not rise or dimple down like the rubber O-ring surface which should be changed its surface shape when the contacting surface changes.

So even though the surface of the metallic seal 0-ring(65 and 67) comes right at the hole, it will not be changed by the contacting surface, meaning that the metallic 0-ring(65 and 67) will not be torn or scratched by the meeting with the hole. Thus the sealing function of the metallic seal 0-ring(65 and 67) will be maintained and the performance of the valve with metallic seal 0-ring(65 and 67) will last very long. Coiled Felt Seal

Fig-8 shows a Coiled Felt Seal (CFS) that is adopted on a hydraulic cylinder piston or on a spool of a spool type hydraulic control valve in accordance with the embodiments of the present invention.

The CFS consists of 3 different functioned layers each of which are piston seal layer (801), absorption layer (802), and cylinder seal layer (803). The outside diameter of piston seal layer (801) is made smaller (e.g.: 1% less) than cylinder bore to keep away from cylinder wall and the inside diameter is made slightly smaller (e.g. : 0.1% less) than the piston to keep contact of piston at all time. The outside diameter of the absorption layer (802) is made smaller (e.g.: 1% less) than cylinder bore and the inside diameter is made larger (e.g. : 1% more) than the piston to keep the absorption layer (802) from contacting the cylinder wall and the piston surface. The outside diameter of cylinder seal layer (803) is made slightly larger (e.g.: 0.1% more) than cylinder bore to keep contact wall at all time but the inside diameter is made larger (e.g.: 1% more) than the piston diameter to make it never be able to contact the piston.

This invention uses CFS to replace the rubber O-rings from conventional art. The CFS is able to provide all of the functions that rubber O-rings from conventional art provides but having minimal operating friction and able to provide substantially zero leak function. Unlike existing rubber O-ring that relies all of its performance on a single contact line, CFS has multiple lines of seal as failsafe system with substantially zero-leak-seal to ensure perfect performance. In an embodiment of the present invention, CFS is made of fast heat transmitting bronze or brass that cools more effectively and the soaked lubricant between layers of CFS guarantee best form of lubrication for friction free seal.

CFS is a helical metal seal constructed by joining of partial rings (804). The partial rings are connected by complementary interlocking structure (805), for example, dovetail connection. By nature, it has expanding radial tension when twisted to make smaller diameter, and contracting radial tension when it twisted to make larger diameter. It provides two main advantages: 1.) minimal friction lost between the piston and cylinder wall. 2.) no internal leakage.

Fig-9 shows the partial rings for constructing the Coiled Felt Seal (CFS) that is adopted on a hydraulic cylinder piston or on a spool of a spool type hydraulic control valve in accordance with the embodiments of the present invention. The partial rings are connected by complementary interlocking structure (901), (902) at the end of each partial ring. The complementary interlocking structure (901), (902) offsets towards the exterior circumference of the partial ring differently for identifying itself as the corresponding layer in the Coiled Felt Seal.

In an exemplary embodiment, the CFS is made of helical coiled metal tube that is constructed by connecting individual C-rings. Each of these C-rings has male and female dovetails at both ends and they are to be connected progressively to construct a helical coiled tube. The location of the dovetail joint on the C-ring is different on each of the 3 different functional layers. On the piston seal layer, the dovetail joint is adjacent to the inner circumference, while on the cylinder seal layer, the joint is adjacent to the outer circumference. On the absorption layer, the dovetail joint is in the middle of the ring. The location differences are for easy identification of each layer during the manufacturing process, as the C-rings of different layers are very difficult to distinguish once they are mixed together.

The foregoing description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configurations of the present invention. Rather, the description of the exemplary embodiments provides those skilled in the art with enabling descriptions for implementing an embodiment of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the claims hereinafter.

Where specific features, elements and steps referred to herein have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. Furthermore, features, elements and steps referred to in respect of particular embodiments may optionally form part of any of the other embodiments unless stated to the contrary.

The term "comprising", as used herein, is intended to have an open-ended, non-exclusive meaning. For example, the term is intended to mean: "including principally, but not necessarily solely" and not to mean "consisting essentially of or "consisting only of. Variations of the term "comprising", such as "comprise", "comprises" and "is comprised of, have corresponding meanings.

Claims

1. A hydraulic actuator, comprising a metal helical coiled multilayer seal for sealing between two relatively moving parts.

2. The hydraulic actuator according to claim 1, further comprising a hydraulic cylinder assembly, wherein said metal helical coiled multilayer seal is configured for piston sealing.

3. The hydraulic actuator according to claim 1, further comprising a hydraulic cylinder assembly, wherein said metal helical coiled multilayer seal is configured for piston rod sealing.

4. The hydraulic actuator according to claim 1, further comprising a spool type hydraulic control valve, wherein said metal helical coiled multilayer seal is configured for piston sealing.

5. The hydraulic actuator according to claim 1, wherein said metal helical coiled multilayer seal further comprises:

a piston seal layer;

an absorption layer; the outside diameter of said piston seal layer is larger than that of said absorption layer, and the inside diameter of said piston seal layer is same as that of said absorption layer; and

a cylinder seal layer; the outside diameter of said cylinder seal layer is same as that of said absorption layer, and the inside diameter of said cylinder seal layer is smaller than that of said absorption layer.

6. The hydraulic actuator according to claim 1, wherein said metal helical coiled multilayer seal further comprising a plurality of partial rings, wherein said partial rings are connected by complementary interlocking structure at the end of each said partial ring.

7. The hydraulic actuator according to claim 6, wherein said complementary interlocking structure offsets towards the exterior circumference of said partial ring differently for identifying itself as the corresponding layer in the metal helical coiled multilayer seal.