GB2426312A - A seal arrangement for a piston of a piston and cylinder shock absorber - Google Patents

A seal arrangement for a piston of a piston and cylinder shock absorber Download PDF

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Publication number
GB2426312A
GB2426312A GB0615647A GB0615647A GB2426312A GB 2426312 A GB2426312 A GB 2426312A GB 0615647 A GB0615647 A GB 0615647A GB 0615647 A GB0615647 A GB 0615647A GB 2426312 A GB2426312 A GB 2426312A
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GB
United Kingdom
Prior art keywords
piston
seal
seal member
cylinder
cylinder assembly
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB0615647A
Other versions
GB0615647D0 (en
GB2426312B (en
Inventor
King-Song Yu
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Leado Door Controls Ltd
Original Assignee
Leado Door Controls Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Leado Door Controls Ltd filed Critical Leado Door Controls Ltd
Publication of GB0615647D0 publication Critical patent/GB0615647D0/en
Publication of GB2426312A publication Critical patent/GB2426312A/en
Application granted granted Critical
Publication of GB2426312B publication Critical patent/GB2426312B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
    • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
    • F16F9/32—Details
    • F16F9/44—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction
    • F16F9/46—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction allowing control from a distance, i.e. location of means for control input being remote from site of valves, e.g. on damper external wall
    • F16F9/461—Means on or in the damper for manual or non-automatic adjustment; such means combined with temperature correction allowing control from a distance, i.e. location of means for control input being remote from site of valves, e.g. on damper external wall characterised by actuation means
    • F16F9/462—Rotary actuation means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
    • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
    • F16F9/10—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium using liquid only; using a fluid of which the nature is immaterial
    • F16F9/14—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect
    • F16F9/16—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts
    • F16F9/18—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts with a closed cylinder and a piston separating two or more working spaces therein
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
    • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
    • F16F9/32—Details
    • F16F9/36—Special sealings, including sealings or guides for piston-rods
    • F16F9/368—Sealings in pistons
    • E—FIXED CONSTRUCTIONS
    • E05—LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05F—DEVICES FOR MOVING WINGS INTO OPEN OR CLOSED POSITION; CHECKS FOR WINGS; WING FITTINGS NOT OTHERWISE PROVIDED FOR, CONCERNED WITH THE FUNCTIONING OF THE WING
    • E05F5/00—Braking devices, e.g. checks; Stops; Buffers
    • E05F5/06—Buffers or stops limiting opening of swinging wings, e.g. floor or wall stops
    • E05F5/10—Buffers or stops limiting opening of swinging wings, e.g. floor or wall stops with piston brakes
    • E—FIXED CONSTRUCTIONS
    • E05—LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05Y—INDEXING SCHEME RELATING TO HINGES OR OTHER SUSPENSION DEVICES FOR DOORS, WINDOWS OR WINGS AND DEVICES FOR MOVING WINGS INTO OPEN OR CLOSED POSITION, CHECKS FOR WINGS AND WING FITTINGS NOT OTHERWISE PROVIDED FOR, CONCERNED WITH THE FUNCTIONING OF THE WING
    • E05Y2201/00—Constructional elements; Accessories therefore
    • E05Y2201/20—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore
    • E05Y2201/21—Brakes
    • E—FIXED CONSTRUCTIONS
    • E05—LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05Y—INDEXING SCHEME RELATING TO HINGES OR OTHER SUSPENSION DEVICES FOR DOORS, WINDOWS OR WINGS AND DEVICES FOR MOVING WINGS INTO OPEN OR CLOSED POSITION, CHECKS FOR WINGS AND WING FITTINGS NOT OTHERWISE PROVIDED FOR, CONCERNED WITH THE FUNCTIONING OF THE WING
    • E05Y2201/00—Constructional elements; Accessories therefore
    • E05Y2201/20—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore
    • E05Y2201/252—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore characterised by type of friction
    • E05Y2201/254—Fluid or viscous friction
    • E05Y2201/256—Fluid or viscous friction with pistons or vanes
    • E—FIXED CONSTRUCTIONS
    • E05—LOCKS; KEYS; WINDOW OR DOOR FITTINGS; SAFES
    • E05Y—INDEXING SCHEME RELATING TO HINGES OR OTHER SUSPENSION DEVICES FOR DOORS, WINDOWS OR WINGS AND DEVICES FOR MOVING WINGS INTO OPEN OR CLOSED POSITION, CHECKS FOR WINGS AND WING FITTINGS NOT OTHERWISE PROVIDED FOR, CONCERNED WITH THE FUNCTIONING OF THE WING
    • E05Y2201/00—Constructional elements; Accessories therefore
    • E05Y2201/20—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore
    • E05Y2201/262—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore characterised by type of motion
    • E05Y2201/264—Brakes; Disengaging means, e.g. clutches; Holders, e.g. locks; Stops; Accessories therefore characterised by type of motion linear

Abstract

A piston and cylinder assembly for a hydraulic hydraulic damper 2 comprises a piston 6 and a piston cylinder 4 the piston having a peripheral groove 110 containing a seal 112, the seal comprising radially inner and outer annular seal members 114, 116. The inner seal member 114 abuts the outer seal member 116 and the base of the peripheral groove 110, and the outer seal member 116 engages the inner wall of the cylinder 4.

Description

76674.70 Hydraulic Damper The present invention relates to hydraulic
dampers at more particularly but not exclusively, to hydraulic dampers for use in door closing mechanisms.
Door closing mechanisms typically include a hydraulic damper which, when the door is being opened, provide relatively little resistance to movement of the door, but which provide a greater resistance to movement when the door is being closed, allowing the door to close more slowly. The present invention seeks to provide a new hydraulic damper which accomplishes this.
From a first aspect, therefore, the invention provides a hydraulic damper comprising a piston and piston cylinder, said piston cylinder defining a chamber for hydraulic fluid, said piston dividing said chamber into first and second compartments, said piston comprising a valve arranged so as to permit hydraulic fluid to flow through said piston from one compartment to the other in one direction only as the piston moves in one direction in the cylinder, and a bypass passage arranged to permit fluid to flow between the compartments when the piston moves in the opposite direction in the cylinder.
Accordingly, in accordance with this aspect of the invention, a bypass passage is provided to allow hydraulic fluid to bypass a valve in the piston to allow it to flow between fluid compartments.
Preferably the passage is configured to provide a different, preferably higher, resistance to flow than the return valve through the piston thereby providing a greater resistance to flow of hydraulic fluid thereby providing a greater damping effect.
In the preferred embodiment, the damping effect is variable, so preferably the bypass passage comprises has a valve to control the resistance to flow of hydraulic fluid therethrough.
In the preferred embodiment, the bypass passage comprises a valve orifice which can closed and opened by a valve member. Preferably, the valve orifice is provided in an end closure of the piston cylinder and the valve member mounted within that end closure.
Preferably the orifice opens into a bore of the closure, with the valve member being mounted within that bore.
Most preferably the valve member is arranged to move axially of the damper cylinder.
Preferably the valve member is formed with a threaded region which cooperates with a corresponding region of the bore such that rotation of the valve member will cause axial movement of the valve member and opening and closing of the orifice.
Preferably the bypass passage is formed within the body of the cylinder wall. Most preferably the cylinder wall comprises an outer wall and an inner sleeve within which the piston moves, the bypass passage being formed between the outer wall and the inner sleeve.
The outer wall or inner sleeve may have a groove formed therein to define the passage, but in a preferred embodiment one or other, most preferably the sleeve is formed with a flat to define a passage between it and the surrounding outer wall.
In addition to the above, it is quite often difficult to produce a satisfactory seal around the..
piston in a hydraulic damper. Normally the seal is arranged within a groove extending around the periphery of the piston head, the seal projecting proud of the piston surface. It is important, however, that the seal should not be subject to undue distortion when the piston is moved within the piston cylinder so as to prevent leakage around the seal or to prevent movement of the seal itself within the groove leading to unwanted undamped movement of the piston. From a further aspect, the invention seeks to provide an improved piston sealing arrangement. From a second aspect, therefore, the invention provides a piston and cylinder assembly comprising a piston having a peripheral groove containing a seal, said seal comprising radially inner and outer annular seal members, the inner seal member abutting the outer seal member and the base of the piston head groove, and the second seal member engaging the cylinder wall.
With such an arrangement, the material of the outer seal member may be chosen so that it is more resistant to deformation by the pressurised liquid within the piston cylinder while the inner seal member may be chosen to provide sufficient resilience so as to maintain the outer seal member in close contact with the cylinder wall.
Preferably, therefore, the outer seal member is less resilient than the inner seal member.
Preferably the outer seal member is generally rectangular in crosssection. Preferably the walls of the outer seal member preferably are a close fit or sliding fit within the groove.
In order to reduce the friction of the seal against the cylinder wall, the outer seal member may be made of a low friction material such as PTFE.
The inner seal member may be of a standard 0 ring construction acting both to bias the outer ring against the cylinder wall and also to prevent any fluid which enters the groove around the walls of the outer seal member passing through the groove.
Typically the 0 ring can be a standard material such as nitrile rubber (NBR).
Some preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which; Figure 1 shows a general assembly of a damper in accordance with the invention; *1 Figure 2a shows an end view of a component of Figure 1; Figure 2b shows a view along arrow A of Figure 2a; Figure 2c shows a view along arrow B of Figure 2a; Figure 2d shows a view along arrow C of Figure 2a; Figure 3 shows a further component of Figure 1; Figure 4 shows a yet further component of Figure 1; and Figure 5 shows a detail of the piston sealing arrangement of Figure 1.
With reference to Figure 1, a hydraulic damper 2 for use in a door closing mechanism comprises a piston cylinder 4 and a piston 6 moveable along the piston cylinder 4. The piston cylinder 4 comprises a metallic outer sleeve 8 and a metallic inner sleeve 10 which is a close sliding fit within the outer sleeve 8.
One end of the cylinder 4 is closed by a seal arrangement 12 and the other end by a closure 14 which will be described in further detail below. The cylinder 4, seal 12 and closure 14 form a fluid chamber 16.
The piston 6 comprises a piston shaft 18 and piston head 20 which is received within the inner sleeve 10.
The shaft 16 of the piston 6 passes through the seal 12 as will be discussed further below. The piston head 20 divides the fluid chamber 16 into compartments A and B. In greater detail, the inner sleeve 10 of the cylinder 4 locates at one end against the seal arrangement 12.
The seal arrangement 12 comprises a metallic e.g. iron stop ring 22 having a tapered bore 24 for receiving the piston shaft 18. The ring 22 is an interference fit within the inner sleeve 10.
Behind the stop ring 22 are arranged a washer 26 and ferrule 28, e.g. of copper. The ferrule 28 receives respective inner and outer 0-ring seals 30. 32 which make sealing contact with the piston shaft 18 and outer sleeve 8 respectively. The ferrule 28 is retained by a rolled over flange 34 of the outer sleeve 8. The washer 26 and ferrule 28 are formed with central bores to allow passage of the piston shaft 18 which slidingly and sealingly engages the seal 30.
The closure 14 at the other end of the cylinder comprises a plug member 36 e.g of aluminium, which locates inside the end of the outer sleeve 8. The plug 36 has a shoulder 38 which abuts the end of the inner sleeve 10.
The closure plug 36 is retained in the end of the outer sleeve 8 by virtue of a cap (not shown) which engages an end piece 40, e.g of aluminium, and which is secured to a screw thread 42 formed on the outer surface of the outer sleeve 8.
The plug member 36 comprises a first section 44 which fits within the inner sleeve 10 and is sealed relative thereto by an 0-ring seal 46 and a larger diameter second portion 48 which engages the inside surface of the outer sleeve 8 and which is sealed relative thereto by a further 0-ring seal 50.
The plug member 36 also comprises an orifice 52 which extends through one side of the plug 36 into the central bore 54 of the plug member 36 (see Figure 3).
The plug member 36 receives a valve member 56 (see Figure 4) which is provided with a screw thread 58 which engages with a complementary screw thread 60 provided on the plug member 36. The plug member 36 is provided with a tapering front section 62 which receives a taperthg section 64 of the valve member 56. The rear of the valve member 62 is provided with a cross groove 66 for receiving a screw driver or the like for rotating the valve member 56, thereby moving it in and out of the plug member 36. The valve member 56 is sealed relative to the plug member 36 by a seal 68 arranged in a seal grooves 70.
As the valve member 56 moves, its tapering section 64 moves in and out of the tapering section 62 of the plug member 36, thereby increasing or decreasing the flow resistance therethrough. The effect of this will be described further below.
As can be seen most clearly from Figures 2a and 2b, the inner sleeve 10 is provided with a flat surface 72 running along its outer surface. This forms a bypass passageway between the flat surface 72 and the surrounding circular cylindrical inner surface 74 of the outer sleeve 8.
The ends 76, 78 of the flat surface open into generally semi-circular slots 80, 82 which extends through the wall of the inner sleeve 10. This places one end 76 of the bypass passageway in fluid communication with the chamber B via the slot 80. The other slot opens opposite the valve orifice 52 in the plug member 36, thereby placing the other end of the bypass passageway in fluid communication with the valve member 56.
A through hole 86 extends through wall of the inner sleeve 10 nearer the end 76 of the slot 72 adjacent the stop ring 22. This provides a further fluid communication between the chamber B and the bypass passageway formed between the inner and outer sleeves,8, 10.
Two further flats 88, 90 are provided as shown in Figures 2c and 2d. Smaller through holes 92 than the hole 86 extend through the wall of the inner sleeve 10 at opposite ends of the flats. This permits limitec circulation of hydraulic fluid between the inner sleeve 10 and outer sleeve 8.
As stated above, the piston 6 comprises a piston shaft 16 and a piston head 18. The piston head 18 is fabricated from a material such as stainless steel or the like and is threadedly mounted in a blind bore 94 provided at the end of the piston shaft 16. The piston head 18 is provided with a through bore 96 having an opening 98 into chamber A of the piston cylinder 4. A -7-.
valve seat 100 is formed to receive a ball valve 102 which is urged against the valve seat 100 by a coil spring 104 which is arranged within the bore 92 and which reacts against the base of the piston shaft blind bore 90. The piston head 18 also comprises a side bore 106 which extends between the bore 96 of the piston head 18 and its outer peripheral surface.
The piston head 18 further comprises a peripheral groove 110 which receives a seal 112. As is seen in greater detail in Figure 5, the seal 112 comprises an inner seal member 114 and an outer seal member 116. The inner seal member 114 is an 0 ring constructed of, for example, NBR whilst the outer seal member 116 is generally rectangular in section and is made from a material such as PTFE. As can be seen from Figure 5, the outer seal member 116 is a close fit within the groove 110.
Operation of the damper as described above will now be explained.
When the piston 6 moves to the right in the sense of Figure 1, the ball valve 102 will be lifted from its seat 104 against the force of the spring 104 to allow hydraulic fluid to pass from compartment A to compartment B through the bores 96, 106 formed in the piston head 18. This will present relatively little resistance to flow, so the piston 6 will be able to move quite easily in this direction. If the damper is connected to a door closing mechanism, this means that the door can be opened quite easily.
However, when the piston is moved from right to left in the sense of Figure 1 (for example under the action of a return spring mechanism (not shown)), then the ball valve 102 will be thrust against its seat 100, preventing fluid flow from compartment B back into compartment A through the piston head 18. In this condition, hydraulic fluid will, however, be able to pass from compartment B to compartment A through the bypass passageway formed by the flat 72 between the outer sleeve 8 and the inner sleeve 10. Initially flow into this passage way will be by way of the slot 80 and the hole 86, and flow out of it will be via the plug member 36 and the valve member 56.
As explained above, by moving the valve member 56 axially inside the plug member 36, the flow restriction tormed between the plug member 36 and the valve member 56 can be varied, thereby varying the resistance to flow of hydraulic fluid through the bypass passage. In this way the resistance of the damper can be varied. In any event, the resistance to flow through the bypass passage will, in general, be greater than that through the piston head valve 98, thereby providing a greater damping effect.
Flow of hydraulic fluid around the piston head 18 is prevented by the seal 112. The 0 ring 114 acts to support the outer seal ring 116 against the inner wall of the inner sleeve 8, as well as sealing between the outer seal member 116 and the base of the piston head groove 110. The outer member 116 is of PTFE and therefore can slide easily within the sleeve 8, but on the other hand is more resistant to deformation which might otherwise lead to leakage around the seal 112.
It will be appreciated that various changes may be made to the described embodiment without departing from the scope of the invention. For example, the bypass passage in the damper may be formed in an alternative manner and a different variable valve arrangement might be provided. For example, the opening 86 may be sole or main opening into the bypass passage. Also, the seal arrangement disclosed may be used in any type of damper arrangement where improved sealing is required.

Claims (6)

  1. Claims: 1. A piston and cylinder assembly comprising a piston having a
    peripheral groove containing a seal, said seal comprising radially inner and outer annular seal members, the inner seal member abutting the outer seal member and the base of the piston head groove, and the second seal member engaging the cylinder wall.
  2. 2. The piston and cylinder assembly as claimed in claim 1 wherein the outer seal member is less resilient than the inner seal member.
  3. 3. The piston and cylinder assembly as claimed in claim 1 or 2 wherein the outer seal member is generally rectangular in cross- section.
  4. 4. The piston and cylinder assembly as claimed in claim 1, 2 or 3 wherein the walls of the outer seal member preferably are a close fit or sliding fit within the groove.
  5. 5. The piston and cylinder assembly as claimed in any preceding claim wherein the outer seal member may be made of a low friction material.
  6. 6. The piston and cylinder assembly as claimed in any preceding claim wherein the inner seal member is a standard 0-ring construction.
GB0615647A 2003-01-06 2003-01-06 Hydraulic damper Expired - Lifetime GB2426312B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0300204A GB2396901B (en) 2003-01-06 2003-01-06 Hydraulic damper

Publications (3)

Publication Number Publication Date
GB0615647D0 GB0615647D0 (en) 2006-09-13
GB2426312A true GB2426312A (en) 2006-11-22
GB2426312B GB2426312B (en) 2007-08-01

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GB0615647A Expired - Lifetime GB2426312B (en) 2003-01-06 2003-01-06 Hydraulic damper
GB0300204A Expired - Lifetime GB2396901B (en) 2003-01-06 2003-01-06 Hydraulic damper

Family Applications After (1)

Application Number Title Priority Date Filing Date
GB0300204A Expired - Lifetime GB2396901B (en) 2003-01-06 2003-01-06 Hydraulic damper

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Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT12440U1 (en) * 2010-10-06 2012-05-15 Blum Gmbh Julius FURNITURE SHOCKS

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0896174A2 (en) * 1997-08-08 1999-02-10 Yamaha Hatsudoki Kabushiki Kaisha Piston ring arrangement for shock absorber
JPH11210622A (en) * 1998-01-27 1999-08-03 Japan Science & Technology Corp Cylinder part sealing structure
JP2002156045A (en) * 2000-11-20 2002-05-31 Yamaha Motor Co Ltd Piston sealing structure of hydraulic equipment
WO2005010395A1 (en) * 2003-07-22 2005-02-03 Vauth-Sagel Holding Gmbh & Co. Kg Air damper

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB676313A (en) * 1949-09-22 1952-07-23 Dowty Equipment Ltd Improvements in telescopic seat stays
DE4410522C2 (en) * 1994-03-26 1997-04-17 Fichtel & Sachs Ag Hydraulic, adjustable vibration damper
DE4424433C1 (en) * 1994-07-12 1995-10-12 Fichtel & Sachs Ag Intermediate tube for vibration damper with variable damping force
US6244398B1 (en) * 1997-05-15 2001-06-12 K2 Bike Inc. Shock absorber with variable bypass damping
US6102170A (en) * 1998-05-07 2000-08-15 Tenneco Automotive Inc. Passive anti-roll system
US6390257B1 (en) * 2000-02-16 2002-05-21 Delphi Technologies, Inc. Suspension damper having piston plate with coined, continuously curved bypass

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0896174A2 (en) * 1997-08-08 1999-02-10 Yamaha Hatsudoki Kabushiki Kaisha Piston ring arrangement for shock absorber
JPH11210622A (en) * 1998-01-27 1999-08-03 Japan Science & Technology Corp Cylinder part sealing structure
JP2002156045A (en) * 2000-11-20 2002-05-31 Yamaha Motor Co Ltd Piston sealing structure of hydraulic equipment
WO2005010395A1 (en) * 2003-07-22 2005-02-03 Vauth-Sagel Holding Gmbh & Co. Kg Air damper

Also Published As

Publication number Publication date
GB2396901A9 (en) 2005-01-27
GB2396901A (en) 2004-07-07
GB2396901B (en) 2006-10-25
GB0615647D0 (en) 2006-09-13
GB0300204D0 (en) 2003-02-05
GB2426312B (en) 2007-08-01

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PE20 Patent expired after termination of 20 years

Expiry date: 20230105