WO2008085097A1

WO2008085097A1 - Framgaffel med tätningsfunktion / front fork with sealing

Info

Publication number: WO2008085097A1
Application number: PCT/SE2007/050990
Authority: WO
Inventors: Atsushi Ishii
Original assignee: Ohlins Racing AB
Current assignee: Ohlins Racing AB
Priority date: 2007-01-10
Filing date: 2007-12-13
Publication date: 2008-07-17
Anticipated expiration: 2009-07-10
Also published as: SE531829C2; SE0700033L

Abstract

The invention relates to a front fork (1) having an inner first volume (1a), which is at least partially filled by a first fluid medium (01) in the form of an oil. The outer structure of the front fork (1) is made up of an outer leg (2) and an inner leg (3), which move telescopically relative to each other when subjected to an external force. The movement is controlled by a main spring (4) and is dampened by a damping device (5). The damping device is in the form of a damping cylinder (6) sealed off from the inner first volume (1 a) of the front fork and filled with a second fluid medium (O2) in the form of an oil pressurized at a basic pressure higher than the atmospheric pressure. The damping cylinder (6) has a second volume (13) and is divided into two damping chambers (R, C) by a piston (7) fixed to a piston rod (8). The piston rod (8) extends through a first sealing head (10) fixed at one end (6a) of the damping cylinder. Outside the damping cylinder (6), directly adjacent to the first sealing head (10), there is disposed a third volume (21) delimited by a body (20) and filled with a gas (G3), preferably air. The demarcations between the gas-filled third volume (21) and the inner oil-filled first volume (1 a) of the front fork and between the gas-filled third volume (21 ) and the oil-filled second volume (13) of the damping cylinder (6) comprise at least one seal (10a, 25) each, suitable for sealing between fluid medium and gas. The seal is preferably an X-ring or a lip seal with necessary back-up rings.

Description

Front fork with sealing function

Technical field

The invention is applied to a front fork in which a pressurized damping system is disposed in the outer legs of the front fork. The damping system is filled with a fluid damping medium in the form of, for example, oil with known additives, and in order to maintain the pressurization it is delimited from the environment by one or more seals.

Background of the invention

A front fork for a two-wheeled vehicle is made up of an outer leg and an inner leg in which there is disposed a damping cylinder filled with damping medium. The damping cylinder is divided into two damping chambers by a piston fixed to a piston rod joined together with the outer leg. The piston rod extends through one end off the damping cylinder and the damping medium in the damping cylinder is delimited from the inner volume of the front fork by a seal placed in a sealing head. In order to minimize the friction between the outer and inner legs of the front fork and prolong the working life of the parts incorporated in the fork, the interior of the front fork is also partially filled with oil. When the front fork is subjected to an external force, the outer leg moves telescopically relative to the inner leg, so that the piston fixed in the piston rod is made to operate in the damping medium in the damping cylinder. The damping medium is then pressed, via a duct and a restriction in the form of, for example, an adjustable valve, from the first to the second damping chamber. As a result of this restriction of the damping medium flow, the speed of movement of the front fork is dampened. In order to reduce the cavitation risk and improve the damping characteristics, a reservoir is pressurized by an external pressurizing member coupled with the interior of the damping cylinder, so that the damping medium is always subjected to a certain pressure. The reservoir can be coupled with one or both damping chambers. If both damping chambers are coupled with the reservoir, the damping during a return and compression stroke respectively can be adjusted independently of each other via two separate adjustable valves.

An example of the last type of pressurized front fork is described in the Applicant's own patent EP1666348, in which a damping-medium-filled damping cylinder operates in an oil-filled inner and outer leg. A sealing head having seals and bushings effects a seal between the pressurized damping cylinder and the oil-filled volume in the interior of the fork leg.

When these types of front forks are operating, the seal disposed in the sealing head is subjected to high pressures, whilst, at the same time, it has to effect a seal between a pressurized oil and a non-pressurized oil. It has proved to be a problem to effect a seal between two oil-filled spaces under the conditions prevailing in a front fork. Oil either leaks out from the pressurized space or is sucked into it, in which case the pressure ratios in the front fork are no longer optimal.

Object of the invention

The present invention aims to solve the problem of oil leaking out of or being sucked into a damping cylinder in a pressurized oil-filled front fork. The invention also aims to solve this problem in a simple and economical manner by using a new type of seal design and by utilizing components already present in the fork leg to prevent the leakage.

Summary of the invention

The invention relates to a front fork having an inner first volume which is at least partially filled by a first fluid medium in the form of an oil. The outer structure of the front fork is made up of an outer leg and an inner leg, which move telescopically relative to each other when subjected to an external force. The movement is controlled by a main spring and is dampened by a damping device. The damping device is in the form of a damping cylinder, sealed off from the inner first volume of the front fork, having a second volume filled with a second fluid medium, also in the form of an oil, which is pressurized at a basic pressure higher than the atmospheric pressure. The damping cylinder is divided into two damping chambers by a piston fixed to a piston rod. The piston rod extends through a first sealing head fixed at one end of the damping cylinder. Outside the damping cylinder, directly adjacent to the first sealing head, there is disposed a third volume, delimited by a cylindrical body filled with a gas, preferably air, and disposed around the piston rod. The first sealing head is fixed to a first end of the cylindrical body, preferably to the internal face of the cylindrical body. The gas-filled third volume prevents direct contact between the first and the second fluid medium. The demarcations between the gas-filled third volume and the inner oil-filled first volume of the front fork, and between the gas- filled third volume and the oil-filled second volume of the damping cylinder, comprise at least one seal each, suitable for sealing between fluid medium and gas. The seal is preferably an X-ring or a lip seal with necessary backup rings.

By creating in the front fork a condition such that sealing only needs to be made between fluid medium and gas, existing well-working seals may be used in the system. Oil is thus prevented from leaking out of or being sucked into the pressurized damping system.

In a second embodiment of the front fork, at least one groove for the boundary seal is machined directly in the cylindrical body which encloses the gas-filled volume.

In a second embodiment of the invention, at least one groove for the seal is machined in a second sealing head disposed on a second end of the cylindrical body. - A -

In a further embodiment, the first sealing head, or if a second sealing head is also used, both these sealing heads, is/are connected to the internal face of the cylindrical body.

In one embodiment, the internal connection between sealing head(s) and the cylindrical body can be provided by means of a joint in which at least one ring made of an elastic material is disposed in a first groove in the respective sealing head and cooperates with a second groove disposed in the cylindrical body. In further embodiments, the internal connection can also be provided by means of a threaded joint or by means of a press fit between the parts.

In a further embodiment, the outer face of the cylindrical body is also arranged to control the movements of the main spring and centre its position in the interior of the front fork. To reduce the friction between the outer face of the cylindrical body and the main spring and/or the piston rod, the cylindrical body is made of a polymer, preferably polyamide with various additives. Preferably, the cylindrical body is also made of an existing spring support material.

The invention is described in greater detail below with references to accompanying drawings.

List of figures Fig. 1 shows a pressurized front fork according to a first embodiment of the invention,

Fig. 2 shows an enlarged view of a first sealing head in the front fork,

Fig. 3 shows an enlarged view of a first embodiment of a second sealing head in the front fork, and Fig. 4 shows an enlarged view of a second embodiment of a second sealing head in the front fork. Detailed description of the invention

Figure 1 shows a front fork 1 according to a first embodiment of the invention. The front fork 1 has an inner first volume 1a, which is filled to between 75% and 90% with a first fluid medium 01 in the form of an oil with necessary additives. The remaining part of the inner first volume 1a is filled with a first gas G1 , preferably air. The outer structure of the front fork is made up of an outer leg 2 and an inner leg 3, which move telescopically relative to each other when subjected to an external force. The external force is absorbed by a main spring 4 disposed in the inner first volume 1a and is dampened by a damping device 5. The damping device 5 is disposed in the inner first volume 1a, but is delimited from the first fluid medium O1 therein. The inner first volume 1a is delimited at its upper end by a fork head 7 secured in the outer leg 2. The first end 8a of a piston rod 8 is secured in the fork head 7. At the second end 8b of the piston rod there is disposed a first piston 9, which divides a damping cylinder 6 in the damping device into two damping chambers C, R. The piston rod 8 extends also through a first sealing head 10 fixed at the first end 6a of the damping cylinder. The damping cylinder 6 is filled with a second fluid medium 02, this too in the form of an oil.

The oil 02 in the damping cylinder 6 is pressurized on both sides of the first piston 9 in a manner already known through the Applicant's so-called TTX technology. The TTX principle in this front fork can briefly be described as follows. A member 11 pressurized with a second gas G2, which member in Figure 1 has the form of a second piston, disposed in a pressurizing reservoir 12, pressurizes a second volume 13 common to both damping chambers C, R. Coupling of the two damping chambers C, R is enabled by first and second flow ducts 14, 15, which extend between the common second volume 13 and the respective damping chamber C, R. The first flow duct 14 extends from the common second volume 13, between the damping cylinder 6 and a further pipe 16 enclosed around this, and is terminated in the return chamber R. Between the common second volume 13 and the respective damping chamber C, R, valves 17, 18 are arranged to adjust the flow in the flow ducts 14, 15, i.e. with these valves the damping characteristics of the front fork can be determined. The pressurizing reservoir 12 is fixed to a bottom piece 19 intended to be fixed to a wheel (not shown). The bottom piece 19 is fixed to the lower part 3a of the inner pipe 3 and incorporates within it the common second volume 13, the adjustable valves 17, 18 and the sub-ducts 14a, 15a linking the flow ducts 14, 15. Since the two damping ducts C, R are coupled with the pressurized common second volume 13, the pressure is never less than zero in any of the chambers C, R.

Of course, the invention can also be applied to a front fork which is based on the older de Carbon principle, as the damping system is only pressurized by the pressurizing reservoir on one side of the piston.

In Figure 2 an enlarged view of the sealing head 10 is shown. The sealing head 10 delimits the inner volume 5' of the damping device 5, filled with damping medium O2, with one or more seals 10a, 10b arranged to seal off both against the piston rod 8 and against the inner leg 3. Adjacent to the upper end 10' of the sealing head 10 there is disposed a cylindrical body 20. This body 20 encloses a third volume 21 filled with a gas G3, preferably air. The body 20 is fixed at a first end 20a to the sealing head 10, and between these parts, too, one or more seals 10c are provided. The seals 10a, 10b, 10c are suitable for effecting a seal between the fluid medium O1 , O2 and the gas G3, preferably an O-ring, X-ring or a lip seal with necessary backup rings being able to be used. Between the piston rod 8 and the sealing head 10 there is also provided a bushing 23, for reducing the friction when the parts 2, 3 of the front fork move in relation to each other.

In the embodiment shown in Figure 2, the body 20 is fixed to the sealing head 10 by the fact that the seals 10c rest in grooves 22a, 22b milled in both the sealing head 10 and the body 20. During assembly, the seals 10c are pressed into the grooves and thereby hold the body in place. Moreover, this assembly method can be adapted so as to optimize the sealing of the inner volume 21 of the body. Other securing methods, too, may be used, for example the parts 10, 20 can be fixed together with a threaded joint or with a simple press fit.

According to the embodiment in Figures 1 and 3, a second sealing head 24 is pressed in inside the body 20 at its second end 20b. In a groove in the inner side of this sealing head 24, at least one seal 25 is arranged to effect a seal between the inner gas-filled third volume 21 of the body 20 and the inner oil-filled first volume 1a of the front fork. A bushing 26 is also provided on the inner side of the sealing head 24 to reduce the sliding friction against the piston rod 8. The second sealing head 24 is securely held and is sealed against the body 20 in the same way as the body 20 is fixed to the first sealing head 10, i.e. with elastic rings, for example seals 27 in grooves 22a', 22b'. Of course, other securing methods, such as, for example, a threaded joint, may also be used.

In the embodiment according to Figure 4, at least one groove for the seal(s) 25 is machined directly in the body 20. If the body 20 is made of a low- friction material such as a polymer, preferably polyamide with various additives, the bushing between the piston rod 8 and the body 20 can be omitted.

The body 20 can also have other fields of application, given that it controls the movements and centred position of the main spring 4 in the interior 1a of the front fork. The outer face 20c of the body 20 has a small diametrical clearance s, preferably of between 0.2 and 2 mm, against the inner face of the main spring 4. As a result of this clearance, the spring 4 does not lock against the body, but instead slides against the outer face 20c. The cylindrical body 20 according to the invention is made of a polymer spring support material. The spring support is modified only by the fact that, at its two ends, the sealing head(s) 10, 24 are secured and/or a groove is milled for a seal 23. This simple modification of the pre-existing spring support means that the inventive problem of sealing off a pressurized damping system is solved in an economical and resource-saving manner.

The invention is not limited to the embodiment shown above by way of example, but can be modified within the scope of the following patent claims and the inventive concept. For example, the assembly of the front fork can be facilitated and/or the production cost can be reduced by the sealing head 10 being composed of a plurality of parts fitted together by means of threaded joints or a press fit.

Claims

Patent claims

1. Front fork (1) having an inner first volume (1a), which is at least partially filled by a first fluid medium (01) in the form of an oil and the outer structure of which is made up of an outer leg (2) and an inner leg (3), which move telescopically relative to each other when subjected to an external force, in which the movement is controlled by a main spring (4) and is dampened by a damping device (5) in the form of a damping cylinder (6), sealed off from the inner first volume (1a) of the front fork, having a second volume (13), which is divided into two damping chambers (C, R) by a first piston (9) fixed to a piston rod (8) extending through a first sealing head (10) fixed at one end (6a) of the damping cylinder and in which the damping cylinder (6) is filled with a second fluid medium (O2) in the form of an oil subjected to a certain basic pressure higher than the atmospheric pressure, characterized in that outside the damping cylinder (6) there is disposed a third volume (21) which is filled with gas (G3), preferably air, and prevents direct contact between the first (01) and the second (02) fluid medium, in which the third volume (21) is delimited by a cylindrical body (20) disposed around the piston rod (8) and in which a first end (20a) of the cylindrical body (20) is fixed to the first sealing head (10).

2. Front fork (1) according to Claim 1 , characterized in that the demarcations between the third volume (21), filled with gas (G3), and the inner first volume (1a), filled with first fluid medium (01), of the front fork, and between the third volume (21), filled with gas (G3), and the second volume (13), filled with second fluid medium (02), of the damping cylinder (6), comprise at least one seal (26) each, suitable for sealing between fluid medium (01 , 02) and gas (G3), preferably an O-ring, X-ring or a lip seal with necessary back-up rings.

3. Front fork (1) according to Claim 2, characterized in that at least one groove for the seal (26) is machined directly in the cylindrical body (20) which encloses the gas-filled volume (21).

4. Front fork (1) according to Claim 3, characterized in that at least one groove for the seal (26) is machined in a second sealing head (24) disposed on a second end (20b) of the cylindrical body (20).

5. Front fork (1) according to any one of Claims 2-4, characterized in that the first sealing head (10) is connected to the internal face of the cylindrical body (11).

6. Front fork (1) according to Claim 4, characterized in that the first

(10) and/or the second sealing head (24) is/are connected to the internal face of the cylindrical body (20).

7. Front fork (1) according to Claim 5 or 6, characterized in that the internal connection between the sealing head(s) (10, 24) and the cylindrical body (20) is provided by means of a joint in which at least one ring (10c, 25) made of an elastic material is disposed in a first groove (22a, 22a') in the respective sealing head (10c, 25) and cooperates with a second groove (22b, 22b') disposed in the cylindrical body (20).

8. Front fork (1) according to Claim 5 or 6, characterized in that the internal connection between the sealing head(s) (10, 24) and the cylindrical body (20) is provided by means of a threaded joint.

9. Front fork (1) according to Claim 5 or 6, characterized in that the internal connection between the sealing head(s) (10, 24) and the cylindrical body (20) is provided by means of a press fit between the parts.

10. Front fork (1) according to any one of the above claims, characterized in that the movements and centred position of the main spring (4) in the interior (1a) of the front fork are arranged to be controlled by the outer face (20c) of the cylindrical body (20).

11. Front fork according to any one of the above claims, characterized in that the cylindrical body (20) is made of a polymer, preferably polyamide with various additives, to reduce the friction between the outer and inner face (20c) respectively of the cylindrical body (20) and the piston rod (8) and/or the main spring (4).

12. Front fork according to Claim 11 or 12, characterized in that the cylindrical body (20) is made of en existing spring support material.