GB2458456A

GB2458456A - Adjustable piston damper to fit in an OEM telescopic suspension fork

Info

Publication number: GB2458456A
Application number: GB0804886A
Authority: GB
Inventors: Kenneth Charles Summerton
Original assignee: TECH SUSPENSION Ltd K
Current assignee: TECH SUSPENSION Ltd K
Priority date: 2008-03-15
Filing date: 2008-03-15
Publication date: 2009-09-23
Anticipated expiration: 2028-03-15
Also published as: GB2458456B; GB0804886D0; EP2268938A1; WO2009115791A1

Abstract

A solid piston damper 1,15 for a telescopic leg 20 of a motorcycle may be a rebound only damper 15 or compression only damper 1. The damper 1,15 may be substantially tubular and have a cylindrical central piston chamber that is in fluid communication with an outer chamber 10 at a first end and a second end. A valve 5 controls the fluid flow between a first end of the piston chamber 2 and a first end of the outer chamber 10. The damper 1,15 further comprises an expansion chamber 9, which may be annular and formed substantially around the piston chamber 2. The expansion chamber 9 is sealed at a second end and in fluid communication with either the first end of the piston chamber 2 or outer chamber 9 at a first end. The expansion chamber 9 contains a separation piston 11 sealingly and slidingly mounted therein and resilient means between the first end of the expansion chamber 9 and the separation piston 11 such that the expansion chamber 9 may accommodate any changes in volume of the fluid within the piston chamber 2 caused by the movement of a piston 3. The damper 1,15 can directly replace the OEM damper and can be adjusted without removing it from the telescopic leg.

Description

TITLE

A Damper for a Telescopic Fork

DESCRIPTION

Field of Invention

The present invention relates to telescopic forks, such as those found on motorcycle front fork arrangements. In particular, the present invention provides a telescopic fork and dampers for telescopic fork legs

Background

Conventional telescopic fork legs, such as those found on motorcycles, include a suspension system. Generally, such telescopic legs will comprise inner and outer tubes that are arranged telescopically and are fitted between parts that may move relative to one another, for example the wheel and chassis of a motorcycle. They will further comprise a main suspension spring fastened to the inner and outer tubes and a damper substantially contained within the inner and outer tubes. Dampers damp the movement of the telescopic leg by forcing fluid contained within one or more sealed chambers through one or more valves as the leg is moving. Individual dampers are usually capable of damping both compression and rebound of a single telescopic leg.

That is, the flow of fluid within a single damper may function to damp the movement of the piston in both directions.

Many designs of dampers for telescopic legs have been proposed. In a common design the damper substantially comprises a piston formed within a fluid filled chamber. When the damper is extended or compressed the piston is moved within the chamber and the fluid is thereby forced through valves formed in the piston, thus providing a damping action. In these valved piston dampers the fluid within the chamber is not moved substantially around the damper, it simply passes from one side of the piston to the other. For example, the fluid may be forced through shims that form the valves when the piston is displaced within the chamber.

In an alternative design of damper the piston is solid and, instead of forcing fluid through valves formed in the piston, movement of the solid piston forces fluid through valves formed at one or both ends of the fluid chamber, around an external passage and back into the opposite end of the fluid chamber. The major advantage of solid piston damping systems is that the valves through which the fluid is forced may be formed in readily accessible positions and thus may be adjusted or replaced easily.

Solid piston dampers may have a first valve at a first end of the fluid chamber that may control the flow of fluid around in the damper in a first direction, and a second valve at a second end of the fluid chamber that may control the flow of fluid around the damper in a second direction. Furthermore, the first valve and the second valve may be individually adjustable such that the rebound and compression characteristics of the damper may be individually altered. For this reason solid piston damping systems may be preferred for use in situations where precise control of the damping characteristics is required. However, in order to adjust the damping characteristics of such dampers it is necessary to access both ends of the damper. This may not be possible when the damper is mounted substantially within a telescopic fork leg.

Solid piston dampers also have generally quicker response times than valved piston dampers and are thus preferred when more responsive damping is required, for example in racing situations.

Many dampers are capable of dual regime operation and include at least one leak flow passage for the fluid. The at least one leak flow passage may be formed within valves at the end of the fluid chamber or within the piston, depending upon the specific construction of the damper. In such dampers, when the piston is moved at low speeds, for example less than 0.1 ms', the fluid may be free to move through the damper through at least one leak flow passage. Thus, at these low speeds, the damper will provide negligible damping. However, when the piston is moved at higher speeds, above a choke limiting flow rate, the fluid flow through the leak flow passage will be choked due to the size of the passage and the fluid will be forced to flow through the valves and the damper will damp the movement of the piston. The choke limiting flow rate of any leak flow passage may be controlled by a metering device, for example an adjustable needle that protrudes into the passage and may be externally adjusted.

In many dampers the piston will be attached to a first end of a piston rod. The second end of the piston rod will then be attached to the telescopic fork leg. This arrangement results in a change of volume of the fluid within the damping system when the piston is displaced. This change of volume arises due to the length of piston rod contained within the fluid chamber varying as the piston rod is displaced. The change of volume produces a variation of the fluid pressure within the damping system. Furthermore, changes in temperature of the fluid within the system, for example during operation of the damping system, also result in a variation of the fluid volume and therefore the fluid pressure. Pressure changes are undesirable as they may affect the performance of the damping system, for example by causing aeration of the fluid or cavitation.

Cavitation will usually occur adjacent to any valves within a damper and is particularly undesirable as it may damage the valves. Cavitation results in poor damper performance, which may be evidenced in increased hysteresis of the damper and a degrading of the damper fluid.

In order to avoid significant pressure changes within a damper it may be necessary that the damper includes an expansion chamber. Expansion chambers are generally external to and in fluid communication with the fluid chamber. They usually consist of a chamber that is sealed at a first end and is fluid communication with the fluid within the damper at a second. A slidable sealing piston is mounted within the expansion chamber between the first end and a second end. A resilient means, for example a gas or a spring, is provided between the first end of the chamber and a first side of the sealing piston and the fluid within the damper presses against a second side of the sealing piston. In this manner the resilient means and the sealing piston accommodate any change in volume of the fluid within the damping system and thereby avoid the problems set out above. Expansion chambers are usually mounted substantially externally to the telescopic leg that the damper is contained within.

Production motorcycles with telescopic front forks are provided with original equipment manufacturer (OEM) dampers within each of the legs of their front forks.

These dampers are usually suitable only for general road driving. Racing motorcycles may require more specialised dampers. In particular, they may require dampers that are finely adjustable or that are more responsive. The need for easy adjustability means that solid piston dampers are often preferred in racing motorcycles. However, as most solid piston dampers require expansion chambers that cannot be contained within the telescopic forks of production motorcycles it is not currently possible to* simply replace OEM dampers with suitable solid piston racing dampers. Instead it is usually necessary to completely replace each telescopic fork of the motorcycle with a racing fork.

In light of the above, there is a need for a damper for a telescopic leg that is highly responsive and adjustable and is capable of simply replacing OEM dampers within the telescopic legs of production motorcycles. Preferably the damping characteristics of any such damper should be easily adjustable without the need to completely remove the damper.

Summary of Invention

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� 1L. �11 IJ1 FL.? Y L'.4%,., t4 UwLL}Jl.t 1.JL U JUL'.. .ULAJL L.)U%. U piston chamber having a first end and a second end and a solid piston slidingly mounted therebetween; an outer chamber having a first end and a second end, the second end of the outer chamber being in substantially unrestricted fluid communication with the second end of the piston chamber; an expansion chamber being in fluid communication with either the piston chamber or the outer chamber substantially at a first end; a slidable piston member mounted within the expansion chamber and resilient means within the expansion chamber between the piston member and a second end of the expansion chamber; and at least one valve member substantially at the first end of the piston chamber and forming at least one controlled flow passage between the first end of the piston chamber and the first end of the outer chamber, wherein the valve member or members control fluid flow in one direction through the controlled flow passage but allow substantially unrestricted fluid flow in the opposite direction.

Preferably, the first end of the outer chamber is in restricted fluid communication with the first end of the piston chamber via a leak flow passage. In this manner a leak flow may be provided between the first end of the outer chamber and the first end of the piston chamber when the damper is extended or compressed.

Advantageously, if the damper includes a leak flow passage, the flow of fluid through the leak flow passage may be controllable using an adjusting member. A suitable adjusting member may be a parabolic needle or other suitable means that is adjustably mounted at least partially within the leak flow passage. For example, the adjusting member may be a parabolic needle that is mounted through the end of the damper adjacent the first end of the piston chamber such that the end of the needle protrudes into the leak flow passage. The needle may be mounted in the damper by means of a screw thread and have an outer end that is substantially external to the damper. By screwing the needle into or out of the leak flow passage the fluid flow through the leak flow passage may be controlled.

The damper of the present invention is provided with at least one valve member at only the first end of piston chamber. There is no valve member at the second end of the piston chamber. As a result any damper according to the present invention may act either as only a rebound damper or as only a compression damper, depending upon its precise construction. A compression damper will only substantially damp the compression of the telescopic leg and will provide negligible damping to the extension of the telescopic leg. Conversely, a rebound damper will only substantially damp the extension of a telescopic leg and will provide negligible damping to the compression of the telescopic leg.

Having valve members at only one end of the piston chamber is particularly advantageous as it means that only the first end of the piston chamber need be accessed in order to adjust or change the or each valve member and thereby alter the damping characteristics of a damper. There is no need to access both ends of the piston chamber or to access the piston itself to adjust the damping characteristics, as is

necessary in the prior art.

If the expansion chamber is in fluid communication with the piston chamber and the or each valve member controls fluid flow from the first end of the outer chamber to the first end of the piston chamber but allows substantially unrestricted fluid flow in the opposite direction the damper will function as a rebound damper. Conversely, if the expansion chamber is in fluid communication with the outer chamber and the or each valve member controls fluid flow from the first end of the piston chamber to the first end of the outer chamber but allows substantially unrestricted fluid flow in the opposite direction the damper will function as a compression damper.

A compression damper according to the present invention will function in the following manner. If the damper has a leak flow passage, when the damper is compressed at very low speeds, for example less than 0.1 ms', the movement of the piston will force fluid within the piston chamber to pass through the leak flow passage to the first end of the outer chamber, similarly fluid within the outer chamber will pass freely from the second end of the outer chamber into the second end of the piston chamber. When the speed of movement of the piston is increased the flow of fluid through the leak flow passage will be choked and the fluid within the piston chamber will be forced through at least one valve member formed at the first end of the piston chamber. If the compression damper does not have a leak flow passage the fluid will be forced through at least one valve member formed at the first end of the piston chamber at all compression speeds. Forcing the fluid through a valve will damp the movement of the piston and therefore the compression of the fork leg in which the damper is mounted. When a compression damper is extended the fluid within the damper will flow freely from the second end of the piston to the second end of the outer chamber and from the first end of the outer chamber to the first end of the piston chamber. Fluid will freely flow from the first end of the outer chamber to the first end of the piston chamber through any the leak flow passage and/or through at least one valve member. In this maimer extension of a compression damper is not damped.

A rebound damper according to the present invention will function in the following manner. If the damper has a leak flow passage, when the damper is extended at very low speeds, for example less than 0.1 ms, the movement of the piston will force fluid within the piston chamber to pass from the second end of the piston chamber into the second end of the outer chamber and fluid within the outer chamber to pass through the leak flow passage to the first end of the piston chamber. When the speed of movement of the piston is increased the flow of fluid through the leak flow passage will choke and the fluid within the outer chamber will be forced through at least one valve member formed at the first end of the piston chamber. If the rebound damper does not have a leak flow passage the fluid will be forced through at least one valve member formed at the first end of the piston chamber at all extension speeds. Forcing the fluid through a valve member will damp the movement of the piston and therefore the extension of the fork leg in which the damper is mounted. When a rebound damper is compressed the fluid within the damper will flow freely from the second end of the outer chamber to the second end of the piston chamber and from the first end of the piston chamber to the first end of the outer chamber. Fluid will freely flow from the first end of the piston chamber to the first end of the outer chamber through either the leak flow passage or through at least one valve member. In this manner compression of a rebound damper is not damped.

During compression and extension of a compression damper according to the present invention the displacement of the fluid within the piston chamber resulting from the piston rod entering and leaving the piston chamber is accommodated by the expansion chamber. During compression the length of piston rod contained within the piston chamber will increase and therefore a volume of fluid equal to the additional volume of the piston rod contained within the piston chamber will be displaced from the piston chamber. The displaced volume of fluid flows into the expansion chamber from the outer chamber thereby pushing the piston member towards the second, sealed end of the expansion chamber against the pressure provided by the resilient means. The action of the resilient means ensures that a constant pressure is maintained in the fluid of the damper during compression despite the change of volume of the piston rod contained by the piston chamber.

When a compression damper is extended the length of piston rod contained within the piston chamber will decrease, which will result in a pressure gradient that will draw a volume of fluid equal to the reduction in volume of the piston rod contained within the piston chamber into the piston chamber. However, the pressure of the fluid within the damper will be maintained as an equal volume of fluid will be displaced from the expansion chamber into the outer chamber by the action of the resilient means on the piston member. In this manner the action of the resilient means ensures that a constant pressure is maintained in the fluid of the compression damper during extension.

As will be appreciated by a person skilled in the art, in a rebound damper according to the present invention the fluid pressure is maintained by the resilient means in the expansion chamber in substantially the same manner except that the expansion chamber is in fluid communication with the first end of the piston chamber rather than the outer chamber. In both embodiments it is important that the piston member is in sealing engagement with the expansion chamber such that the fluid within the damper cannot pass the piston member and the expansion chamber properly accommodates changes of volirnie of the fluid within the piston chamber.

The expansion chamber will also accommodate changes in the volume of the fluid within the piston due to changes in temperature of the fluid. This is particularly important as use of the damper will necessarily heat the fluid within the damper thereby increasing its volume. If the expansion chamber were not present these volume changes could cause a hydraulic lock and could be detrimental to the performance and durability of the damper.

The expansion chamber is preferably in fluid communication with either the outer chamber or piston chamber of the damper, depending whether the damper is a rebound or compression damper, through a plurality of small apertures formed in the wall of the outer chamber or piston chamber. In a compression damper according to the present invention the apertures may be formed around an outer wall of the expansion chamber substantially adjacent to the first end of the outer chamber. In a rebound damper according to the present invention the apertures may be formed around an outer wall of the piston chamber substantially at the first end of the piston chamber and adjacent to the, or each, valve member.

The resilient means in the expansion chamber may comprise a gas. If the resilient means is a gas it will be sealed within the expansion chamber between the second end and the piston member such that when the piston member is displaced along the expansion chamber the volume of gas within the expansion chamber is correspondingly compressed or expanded. Alternatively or additionally, the resilient means may comprise a spring that is contained within the expansion chamber between the second end and the piston member.

The fluid contained within the damper may be conventional damper oil.

The, or each, valve member may be formed in any manner apparent to the person skilled in the art. If the piston chamber is substantially tubular there may be only one valve member substantially at the first end of the piston chamber. The valve member may substantially comprises a solid body having a plurality of return bores and control bores formed therethrough wherein fluid flow through the bores is controlled by at least one shim clamped to at least one end of the valve member such that fluid flow through the control bores is prevented in a first direction and controlled in a second direction and fluid flow through the return bores is prevented in the second direction and substantially unrestricted in the first direction. The valve member may have a leak flow passage formed axially through its centre. One or more shims may be clamped to either or both sides of the valve member to control the flow of fluid through the bores in a manner that would be understood by those skilled in the art.

Alternatively, one or more shims may be clamped to the valve and the bores may be arranged such that the shims control the flow of fluid through the controls bore only and one or more one-way valves may control the flow of fluid through the return -10-valves. As will be understood, the size and positioning of the bores within the valve member may be modified to alter the flow characteristics of the damper.

As explained above, when a rebound damper according to the present invention is compressed the fluid within the damper will flow freely from the second end of the outer chamber to the second end of the piston chamber and from the first end of the piston chamber to the first end of the outer chamber. Although the fluid is substantially free to flow when the damper is compressed it is still possible that a pressure difference is created across the piston. That is, it is possible that fluid at the side of the piston nearest the first end of the piston chamber will be at a higher pressure than the fluid at the side of the piston nearest the second end of the piston chamber. This may be a particular problem when the damper is compressed rapidly and the fluid is not given enough time to flow around the damper to equalise the pressure difference. A pressure difference across the piston is undesirable as it can result in unwanted hysteresis and possibly cavitation of the piston or piston chamber.

Thus, in order to ensure no significant pressure difference is created across the piston during operation of a rebound damper according to the present invention, it may be preferable that at least one one-way valve is provided through the piston. Suitable one-way valves will be provided in such a manner to allow fluid to flow through the piston from the fiSt end of the piston chamber to the second end of the piston chamber but not in the opposite direction. The result of this construction is that fluid would be allowed to flow through the piston when the rebound damper is compressed but will not be allowed to flow through the piston when the rebound damper is extended.

It may also be preferable to provide one or more one-way valves through the piston of a compression damper according to the present invention. As explained above, when a compression damper according to the present invention is extended the fluid within the damper will flow freely from the second end of the piston chamber to the second end of the outer chamber and from the first end of the outer chamber to the first end of the piston chamber. Although the fluid is substantially free to flow when the damper is extended it is still possible that a pressure difference is created across the piston.

That is, it is possible that fluid at the side of the piston nearest the second end of the piston chamber will be at a higher pressure than the fluid at the side of the piston nearest the first end of the piston chamber. This may be a particular problem when the damper is extended rapidly and the fluid is not given enough time to flow around the damper to equalise the pressure difference. A pressure difference across the piston is undesirable as it can result in unwanted hysteresis and possibly cavitation of the piston or piston chamber.

Thus, in order to ensure no significant pressure difference is created across the piston during operation of a compression damper according to the present invention, it may be preferable that at least one one-way valve is provided through the piston. Suitable one-way valves will be provided in such a manner to allow fluid to flow through the piston from the second end of the piston chamber to the first end of the piston chamber but not in the opposite direction. The result of this construction is that fluid would be allowed to flow through the piston when the compression damper is extended but will not be allowed to flow through the piston when the compression damper is compressed.

As will be understood, the, or each, one-way valve may be provided through the piston in any manner that will be apparent to the person skilled in the art.

As each damper of the present invention will only function as either a rebound or a compression damper it is necessary that any telescopic fork utilising dampers according to the present invention contains a rebound damper in a first leg and a compression damper in a second leg. In this manner the telescopic fork may be properly damped in both compression and extension.

A damper according to the present invention may be formed such that the expansion chamber is formed around the piston chamber and the outer chamber is formed around the expansion and the piston chamber. Dampers formed in this manner will -12-not require a substantially external piston chamber and will thus be significantly more compact that most current solid piston dampers.

In a preferred embodiment of the present invention the damper comprises a substantially tubular cartridge that can be simply inserted into OEM motorcycle telescopic fork legs. In this preferred embodiment the piston chamber may be substantially cylindrical. The expansion chamber may be substantially annular and formed around the piston chamber. The outer chamber may also be annular and formed around the expansion chamber and the piston chamber. An outer wall of the outer chamber may be formed by the wall of the telescopic leg. A cartridge damper according to the present invention may be designed to be contained within a telescopic fork leg such that the first end of the piston chamber and the outer chamber, and therefore the, or each, valve member, is at the lower end of the leg. This may enable the, or each, valve member to be easily accessed and adjusted without the need to entirely remove the damper from the telescopic leg. Furthermore, any adjusting member of any leak flow passage may also be easily accessed and adjusted.

However, it is to be appreciated that it is also possible for a cartridge damper according to the present invention may also be designed to be contained within a telescopic fork kg in the opposite orientation. That is, the cartridge damper may be contained within a telescopic fork leg such that the first end of the piston chamber and the outer chamber, and therefore the, or each, valve member is at an upper end of the leg.

If the expansion chamber is annular the piston member may be an annular separation piston substantially formed of low friction nylon and having annular 0-rings mounted in grooves formed on its outer and/or inner surface. The grooves may be sized so as to allow the 0-rings to partially roll within the grooves and thereby reduce the friction between the separation piston and the walls of the expansion chamber when the separation piston is moved small distances. For example, the grooves may be sized to allow the 0-rings to roll up to 45 degrees in either direction.

-13 -If the damper is tubular its cylindrical walls may be substantially formed from commercially available high quality seamless steam tube. In order to minimise friction it is preferable that the walls of the tubes are polished.

Further features and advantages of the present invention will be apparent from the specific examples illustrated in the drawings and described below.

Drawings Figure 1 is a schematic diagram of a compression damper according to the present invention; Figure 2 shows a cross-section through a first end of telescopic leg containing an extended compression damper according to the present invention and a first end of a telescopic leg containing a compressed compression damper according to the present invention; Figure 3 shows a cross-section through a complete telescopic leg containing an extended compression damper according to the present invention and a complete telescopic leg containing a compressed compression damper according to the present invention; Figure 4 is a schematic diagram of a first embodiment of a rebound damper according tO the present invention; Figure 5 shows a cross-section through a first end of telescopic leg containing an extended rebound damper according to the present invention and a first end of a telescopic leg containing a compressed rebound damper according to the present invention; Figure 6 shows a cross-section through a complete telescopic leg containing an extended rebound damper according to the present invention and a complete telescopic leg containing a compressed rebound damper according to the present invention; Figure 7 is a cross-section through a second embodiment of a rebound. damper according to the present invention; Figure 8 is a close up cross-section of the piston of the rebound damper of Figure 7; -14-Figure 9, is a cross-section through a damper according to the present invention showing the spring assembly.

A schematic of a compression damper I according to the present invention is shown in Figure 1. The damper 1 is substantially cylindrical and includes a central piston chamber 2 that has a solid piston 3 slidably mounted therein. The piston 3 is attached to a first end of a piston rod 4 that extends partially through the piston chamber 2 and extends out of a second end of the piston chamber. An expansion chamber 9 is formed around the piston chamber 2. An outer chamber 10 is formed around the expansion chamber 9. The outer chamber 10 is in fluid communication with the piston chamber 2 at first and second ends. The expansion chamber 9 is in fluid communication with the outer chamber 10 at a first end and is sealed at a second end. The expansion chamber 9 is in fluid communication with the outer chamber 10 via a plurality of small diameter fluid communication apertures 13 formed through its outer wall. An annular separation piston ii is sealingly and slidably mounted within the expansion chamber 9. A resilient means (not shown) is located in the expansion chamber 9 to urge the separation piston 11 away from the sealed second end. The remainder of the damper I is substantially filled with damper fluid.

A valve member S is mounted at the first end of the piston chamber 2. The valve member 5 has a leak flow passage 6 formed through its centre. The leak flOW passage 6 communicates between the second end of the piston chamber and the second end of the outer chamber 10. An adjusting member 12 protrudes from the outside of the damper 1 into the leak flow passage 6. A plurality of bores 7, 8 are formed through and circumferentially spaced around the radially outer portions of the valve member 5. Half of the bores are control bores 7, another half of the bores are return bores 8.

The control bores 7 are formed such that fluid will pass through the control bores only when the pressure on the bore exceeds a minimum pressure. Furthermore, fluid can only flow through the control bores 7 from the piston chamber 2 to the outer chamber 10. In contrast the return bores 8 are simple one-way valves in that they allow fluid to flow substantially freely from the outer chamber 10 to the piston chamber 2 but do not allow fluid flow in the opposite direction.

The damper I may be mounted within a telescopic leg of a motorcycle fork (not shown). The damper I will be mounted such that the valve 5 is substantially at the wheel end of the fork. The tubing of the telescopic leg may form the outer wall of the outer chamber 10 and the adjusting member 12 and valve member 5 may be attached to a lower portion of the telescopic leg. The piston rod 4 may be attached to an upper portion of the telescopic leg.

The damper I operates in the following manner. When the piston 3 is forced towards the first end of the piston chamber 2, for example by compressing a cooperating telescopic leg, it moves fluid around the damper 1. When the piston 3 is moved at low speeds, for example less than 0.1 ms', the fluid will pass freely from the first end of the piston chamber 2, through the leak flow passage 6 into the outer chamber 10. The fluid will also pass freely from the second end of the outer chamber 10 to the second end of the piston chamber 2. As the piston 3 is solid, fluid cannot pass through the piston. When the piston 3 is moved at higher speeds the fluid flow through the leak flow passage 6 will be choked and fluid will be forced through the control bores 7 of the valve member 5. The action of the fluid flowing through the control bores 7 damps the fluid flow and therefore the movement of the piston 3.

When the piston 3 moves in the opposite direction, for example when an attached telescopic leg is extended, fluid is free to move around the damper 1 and substantially no damping is provided. Fluid will flow freely from the second end of the piston chamber 2 to the second end of the outer chamber 2 and from the first end of the outer chamber 10 to the first end of the piston chamber 2 via the return bores 8 and leak flow passage 6.

When the piston 3 is moved within the piston chamber 2 the length of the piston rod 4 contained within the piston chamber 2 will vary. Therefore, the volume of fluid that is contained by the piston chamber 2 must also. vary. This change in volume is accommodated by the expansion chamber 9. If fluid is displaced from the piston chamber 2 by the piston rod 4 the separation piston 11 will be forced towards the second end of the expansion chamber 9 by the displaced fluid. This movement will be opposed by the resilient means, which thereby acts to maintain the fluid pressure within the damper. Similarly, fluid may be expelled from the expansion chamber 9 by the resilient means moving the separation piston II when the piston rod 4 is being withdrawn from the expansion chamber 9. The expansion chamber 9 will also accommodate any changes in the volume of the fluid due to variations in the temperature.

The adjusting member 12, which may be a parabolic needle threaded through a base portion of a telescopic leg, may be inserted further into or withdrawn from the leak flow passage 6 to alter the flow characteristics of the leak flow. This will alter the damping characteristics of the damper I at slow speeds. The valve member 5 may be adjusted or replaced to further alter the damping characteristics of the damper 1 at high speeds.

The first embodiment of a rebound damper 15 shown in Figure 4 is substantially the same as the compression damper 1 of Figure 1 except that the expansion chamber 9 is in direct fluid communication with the piston chamber 2 rather than the outer chamber and the control bores 7 and return bores 8 are in the opposite orientation. The fluid communication apertures 13 are formed in the outer wall of the piston chamber 2 near the first end of the piston chamber. The return bores 8 allow fluid to flow freely from the piston chamber 2 to the outer chamber 10, whilst the control bores 7 allow fluid to flow from the outer chamber 10 to the piston chamber 2 when the pressure of fluid on them exceeds a minimum threshold. Thus the rebound damper 15 will only provide substantial damping when the piston 3 is being moved towards the second end of the piston chamber 2. The rebound damper 15 will not provide any substantial damping when the piston 3 is moved towards the first end of the piston chamber 2.

Figures 2 and 3 show a compression damper 1 according to the present invention mounted in a telescopic leg 20. Figures 4 and 5 show a rebound damper 15 according to the present invention mounted within a telescopic leg 20. The rebound damper 15 and compression damper I may be mounted into separate legs of a single telescopic fork to provide suitable damping for the fork, which may be a motorcycle front fork,

for example.

The telescopic leg 20 comprises an inner tubular part 22 and an outer tubular part 23.

The inner tubular part 22 is slidingly mounted within the outer tubular part 23 in a conventional maimer with a main suspension spring (not shown) mounted between them. A wheel mounting base portion 24 is attached to a lower end of the inner tubular part 22. The inner tubular part 22 forms the outer wall of the outer chamber 10 of the damper 1. The valve 5 and adjusting member 12 are fixed within the base portion 24. The valve is bolted to the base portion 24 using bolt 25. The leak flow passage 6 is formed partially through the bolt 25 and the adjusting member protrudes into the leak flow passage. The control bores 7 and return bores 8 are formed through the valve 5. The control bores 7 and return bores 8 are formed as simple through bores and the flow of fluid therethrough is controlled by a plurality of shims 26 mounted on either side of the valve 5 in a maimer that will be immediately apparent to those skilled in the art.

The resilient means within the annular expansion chamber 9 is a spring 27. The separation piston 11 is a substantially annular low friction nylon piston that is slidingly mounted within the expansion chamber 9 arid scalcd by two rubber O-z'iiigs 28.

in the compression damper I the expansion chamber 9 is in fluid communication with the outer chamber 10 by means of small apertures 13 formed in the outer wall of the expansion chamber 9 adjacent to the first end of the expansion chamber. In the rebound damper 15 the expansion chamber 9 is in fluid communication with the piston chamber 2 by means of small apertures 13 formed in the outer wall of the piston chamber 2 adjacent the first end of the piston chamber.

The dampers 1, 15 are, shown fully compressed at the top of Figures 2, 3, 5 and 6 and fully extended at the bottom of those Figures. in these Figures it is easy to see the variation in the position of the separation piston 11 within the expansion chamber 9 in the compressed and extended dampers. In the compressed dampers the piston rod 4 takes up a relatively large volume within the piston chamber 2 and thus the fluid has been forced into the expansion chamber 9 and the separation piston 11 has moved towards the second end of the expansion chamber. Conversely, in the fully extended dampers the piston rod 4 takes up substantially no volume within the piston chamber 2 and there is very little fluid contained within the expansion chamber 9. Thus the separation piston 11 is substantially at the first end of the expansion chamber 9.

It is also clear from Figures 2, 3, 5 and 6 that, as the expansion chamber 9 of the dampers 1, 15 is formed between the outer chamber 10 and the piston chamber 2 the dampers are contained within cylindrical outer walls and thus may be easily housed within a telescopic leg 20. Therefore the dampers 1, 15 of the present invention are particularly suitable for replacing OEM dampers supplied with production motorcycle telescopic forks.

As can be seen in Figures 3 and 6 the piston rod 4 is attached to a top end of the telescopic leg 20. Thus the displacement of the piston 3 relative to the piston chamber 2 will mirror the displacement of the inner part 22 of the telescopic leg 20 relative to the displacement of the outer part 23 of the telescopic leg. The piston rod 4 is attached to the telescopic leg 20 by the top cap 21, which screws into the outer tubular part 23 of the telescopic leg.

In order to facilitate the mounting of a compression or rebound damper 1, 15 within a telescopic leg 20 the damper substantially comprises four constituent and separate assemblies, These assemblies can be assembled within a telescopic leg 20 to form a damper 1, 15 and may be disassembled therefore when required.

Specifically, the damper 1, 15 comprises a cartridge assembly, a damper rod assembly, a spring assembly and a top cap 21. The cartridge assembly substantially comprises the valve 5 and the expansion chamber 9. The damper rod assembly substantially comprises the piston rod 4 and piston 3. As shown in Figure 9, the spring assembly substantially comprises a spacer tube 40 and spring 41 that serve to bias the inner tubular part 22 of the telescopic leg 20 from the outer part 23 of the telescopic leg.

A compression or rebound damper 1, 15 may be mounted within a telescopic leg 20 in the following manner. First the cartridge assembly is fixed in position in the telescopic leg 20. This is done by sliding the cartridge assembly into position within the inner tubular part 22 of the telescopic leg 20. The valve 5 of the cartridge assembly is then fixed in position using the bolt 25, which extends through the base portion 24 of the telescopic leg 20. The telescopic leg 20, including both the inner and outer tubular parts 22, 23 and containing the cartridge assembly are then filled with the damper oil and all air is bled out in a manner that will be immediately apparent to the person skilled in the art.

After this has been done, the damper rod assembly is then inserted within the cartridge assembly and telescopic leg 20 using appropriate tools in a manner that will be apparent to those skilled in the art. The oil level within the assembly is then topped up to the desired level. The spring assembly is then inserted into the telescopic leg 20 until the spacer tube 40 rests upon the piston 3. The spring assembly and damper rod 4 are then locked within the telescopic leg 20 by the top cap 21. First the top cap 21 is fixed to the damper rod 4. Then the top cap 21 is fixed to the outer part 23 of the telescopic leg 20 in a conventional manner. In this manner the damper I, iS is mounted and contained within the telescopic leg 20. When this has been done the damping characteristics of the damper 1, 15 may be adjusted as required, for example by using the adjusting member 12.

A cross-section through a second embodiment of a rebound damper 15' according to the present invention is shown in Figure 7. The rebound damper 15' of Figure 7 is substantially identical to the rebound damper 15 shown in Figures 4 to 6 and discussed above except that a plurality of one-way valves 30 are provided through the piston 3. The one way valves 30 allow fluid to flow through the piston 3 from the side of the piston nearest the first end of the piston chamber 2 to the side of the piston -20 -nearest the second end of the piston chamber 2 but does not allow fluid to flow through the piston in the opposite direction.

As explained above, when a rebound damper 15, 15' is compressed fluid will also be substantially free to flow around the damper. However, in the first embodiment of the rebound damper 15 it is still possible that a pressure difference will be created in the fluid across the piston. That is, as a result of the compression, the fluid on the side of the piston 3 nearest the first end of the piston chamber 3 may be at a higher pressure than the fluid on the other side of the piston.

In the second embodiment of the rebound damper 15' the presence of the one way valves 30 means that when this rebound damper is compressed fluid may flow through the piston 3 and thereby balance the pressure difference that would otherwise be created across the piston by the compression. As the one-way valves 30 allow fluid to flow through the piston in one direction only, when the rebound damper 2 is extended fluid is not allowed to flow through the piston 3 from the side of the piston nearest the second end of the piston chamber to the side of the piston nearest the first end of the piston chamber. Therefore, the presence of one-valves do not interfere with the damping provided by the rebound damper when the damper is extended.

Claims

CLAIMS1. A damper for a telescopic leg comprising: a piston chamber having a first end and a second end and a solid piston slidingly mounted therebetween; an outer chamber having a first end and a second end, the second end of the outer chamber being in substantially unrestricted fluid communication with the second end of the piston chamber and the first end of the outer chamber being in restricted fluid communication with the first end of the piston chamber via a leak flow passage; an expansion chamber being in fluid communication with either the piston chamber or the outer chamber substantially at a first end; a slidable piston member mounted within the expansion chamber and resilient means within the expansion chamber between the piston member and a second end of the expansion chamber; and at least one valve member substantially at the first end of the piston chamber and forming at least one controlled flow passage between the first end of the piston chamber and the first end of the outer chamber, wherein the valve member or members control fluid flow in one direction through the controlled flow passage but allow substantially unrestricted fluid flow in the opposite direction.
2. A damper according to claim 1, wherein the first end of the outer chamber is in restricted fluid communication with the first end of the piston chamber via a leak flow passage
3. A damper according to claim 2 further comprising an adjusting member for controlling the fluid flow through the leak flow passage.
4. A damper according to claim 3, wherein the adjusting member is a needle adjuster that may protrude into the leak flow passage.-22 -
5. A damper according to any preceding claim, wherein the expansion chamber is formed substantially around the piston chamber and the outer chamber is formed substantially around the piston and expansion chambers.
6. A damper according to claim 5 wherein the piston chamber is substantially cylindrical and the expansion chamber and outer chamber are substantially annular.
7. A damper according to claim 6, wherein the piston member is an annular separation piston.
8. A damper according to any preceding claim, wherein the resilient means comprises a spring.
9. A damper according to any preceding claim, wherein the resilient means comprises a gas medium, and wherein the expansion chamber is substantially sealed at its second end and by the piston member such that the gas medium is contained between the second end and the piston member.
10. A damper according to any preceding claim having a single valve member that substantially comprises a solid body having a plurality of return bores and control bores formed therethrough wherein fluid flow through the bores is controlled by at least one shim clamped to at least one end of the valve member such that fluid flow through the control bores is prevented in a first direction and controlled in a second direction and fluid flow through the return bores is prevented in the second direction and substantially unrestricted in the first direction.
II. A rebound damper according to any of claims I to 10, wherein the expansion chamber is in fluid communication with the piston chamber and the or each valve member controls fluid flow from the first end of the outer chamber to the first end of the piston, chamber but allows substantially unrestricted fluid flow in the opposite direction.
12. A rebound damper according to claim 11, further comprising at least one one-way valve member provided through the piston to allow fluid to flow through the piston from the first end of the piston chamber to the second end of the piston chamber but that substantially prevents fluid flow through the piston in the opposite direction.
13. A compression damper according to any of claims 1 to 10, wherein the expansion chamber is in fluid communication with the outer chamber and the or each valve member controls fluid flow from the first end of the piston chamber to the first end of the outer chamber but allows substantially unrestricted fluid flow in the opposite direction.
14. A compression damper according to claim 13, further comprising at least one one-way valve member provided through the piston to allow fluid to flow through the piston from the second end of the piston chamber to the first end of the piston chamber but that substantially prevents fluid flow through the piston in the opposite direction.
15. A telescopic fork for a motorcycle including a rebound damper according to claim 1 1 in a first leg and a compression damper according to claim 13 in a second leg.
16. A damper substantially as described herein and as illustrated in the drawings.