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Title:
ARRANGEMENT FOR TELESCOPIC FORK LEG WITH PARALLEL DAMPING
Document Type and Number:
WIPO Patent Application WO/2007/046750
Kind Code:
A1
Abstract:
A device for telescopic fork legs, preferably for a motorcycle or bicycle. The damping system comprises two damping system components that are both acted upon by the flow of medium created by the compression and expansion movements of the piston. The damping system components together form a compact unit in the form of a removable insert system, that comprises medium flow passages that are parallel in relation to each other and that run between the upper and lower sides of the piston. This insert system forms a compact unit that is simple to adapt to suit different front fork dimensions and to use as a kit for providing an existing front fork with parallel damping. Parallel damping achieves, for example, simple adaptation of the damping characteristics to different types of terrain.

Inventors:
SINTORN, Torkel (Hallmans allé 1, Skarpö, Vaxholm, S-185 91, SE)
Application Number:
SE2006/001187
Publication Date:
April 26, 2007
Filing Date:
October 18, 2006
Export Citation:
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Assignee:
ÖHLINS RACING AB (Box 722, Upplands Väsby, S-194 27, SE)
SINTORN, Torkel (Hallmans allé 1, Skarpö, Vaxholm, S-185 91, SE)
International Classes:
F16F9/512; B62K25/08; F16F9/06
Attorney, Agent or Firm:
IPENDO AB (Nygatan 25, Linköping, S-582 19, SE)
Download PDF:
Claims:
CLAIMS

1. A device for telescopic fork legs (1), preferably for a motorcycle or bicycle, where the telescopic fork leg (1) comprises outer and inner legs (9, 7) and a damping system with a piston and piston rod arrangement (15, 16) arranged within these, where the damping system comprises two damping system components (13, 14) that are both acted upon by a flow of medium created by compression and expansion movements of the fork legs, where the damping system components (13, 14) together form a compact unit that comprises medium flow passages (29, 30) that are parallel in relation to each other, and that run between the upper and lower sides of the piston (15), characterized in that the compact unit forms a removable insert system that comprises two concentric tubes (13, 14) between which the medium flow passages (29, 30) run parallel in relation to each other and in that the medium flow passages (29, 30) can also be adjusted or selected by means of setting devices, for example valves (12a, 12b, 12a', 12b')/ in order to adapt the damping characteristics to different types of terrain.

2. The device as claimed in claim 1, characterized in that insert system comprises a first tubular part (13) that is enclosed in a second tubular part (14), a tube end (23) and a head (10) comprising setting devices (12a, 12b, 12a', 12b') and medium passages (29, 30) which are connected to a pressurizing location that is common to both passages (29, 30) and that is pressurized by a pressurizing organ (19)

3. The device as claimed in claim 2, characterized in that the setting devices (12a, 12b, 12a', 12b') are arranged in the head (10) in such a way that a first adjustable device (12a, 12b) affects the flow of the

medium in the medium passage (29) during the compression movements and in that a second adjustable device (12a', 12b') affects the flow of the medium in the medium passage (30) during the return movements, in such a way that the adjusting capabilities are independent of each other.

4. The device as claimed in any one of claims 1-3, characterized in that the insert system is inserted in the outer leg (9) and the head (10) belonging to the insert system is mounted on one end of the outer leg (9) .

5. The device as claimed in any one of the above claims, characterized in that the piston rod (16) is sealed against and extends through the tube end (23) of the insert system.

6. The device as claimed in claim 5, characterized in that one end of the piston rod is attached to a bottom unit (9) that is connected to the inner leg (7) and the piston (15) is attached to the other end of the piston rod, which piston operates in the first tubular part (13) .

7. The device as claimed in any one of the above claims, characterized in that the pressurizing device (19) is a piston that is pressurized by means of gas, a spring or the like, or a gas-filled rubber bellows.

8. The device as claimed in any one of claims 1-7, characterized in that the pressurizing device (19) is comprised in a separate external container (20).

9. The device as claimed in any one of claims 1-7, characterized in that the pressurizing device (19) is

incorporated between the outer legs (9) of the front forks and the insert system.

Description:

ARRANGEMENT FOR TELESCOPIC FORK LEG WITH PARALLEL DAMPING

The present invention relates to a device for telescopic fork legs, preferably on a motorcycle or bicycle, where the telescopic fork leg comprises outer and inner legs and a damping system with a piston and piston rod arrangement that is arranged within these.

A front fork for a motorcycle or a bicycle can be subjected to wheel speeds in the whole range of 0-lOm/s and stroke lengths of up to 300 mm. In order to be able to absorb such high speeds and such large strokes, great demands are made of the front fork. It must be able to absorb forces and be strong, while at the same time it must be able to handle a large flow of oil. It is also desirable to have good control in the whole range of speeds and for the damping to be adjustable. A compact and light system that can be adapted to fit several different front fork dimensions is also required. Reference is made, for example, to patent US6260832, that shows a front fork of the type described above. US6260832 does not, however, have the desirable build-up of pressure that is described below.

Current systems can be represented by a damper of the De Carbon type, see for example FR1055443A, and have a serial damping force construction that is based on a principle of pressurizing two locations in series in order to avoid cavitation or the admixture of air into the damping medium. This system has limitations in that the pressures in the two pressurizing locations must more or less harmonize with each other, as the drop in pressure (δPl=Pi ow -P mid , δP2=P midt -P g as) across the two pressurizing pistons should be greater than zero in order not to create cavitation. See Figure 1. As the drop in pressure across the piston is dependent upon the flow resistance through the piston in combination

with the force that acts on the piston, the flow resistance, controlled for example by a shims stack, can only be adjusted within a certain limited range which thus also results in a limited area of use for the damper. It is then also necessary to dimension pistons, piston rod and damping tubes so that the force absorption agrees with the pressures that have been built up, in order to obtain the required damping. With serial damping, the oil is forced through both the valves in series, which results in high flow speeds. With high flow speeds and high piston speeds, the design of the pistons is limited in order not to obtain an unwanted uncontrollable build-up of pressure due solely to the flow resistance.

A system with parallel damping solves the abovementioned problem. Examples of such dampers can be found in the patent documents EP1505315A2 and EP0322608A2. The parallelism in the damping arises through the damping medium being pressurized by two pressurizing pistons that are arranged parallel to each other in the damping chamber and in a space arranged outside the damping chamber. The pressurized outer space is interconnected with both the compression chamber and the return chamber. With parallel damping, the pressure on the low-pressure side of the damping piston is always as large as possible, irrespective of whether the front fork is subjected to a compression or a return stroke. The definition of the low-pressure side of the damping piston is the side of the piston where the volume of the chamber increases. Due to the fact that the pressure is never allowed to become zero on that side, cavitation is prevented. This parallel arrangement also means that the damper can be pressurized and the pressure, that is the damping, can be adjusted, without having to take into account the drop in pressure across the piston (s) . The increase in

pressure, as well as the increase in force, now takes place without cavitation, irrespective of the setting.

The designs according to EP1505315A2 and EP0322608A2 are adapted for shock absorbers that are not subjected to the same forces and impacts as a front fork. A device is thus required for a front fork that comprises adjustable parallel damping. It is also advantageous if the device is able to be adjusted to suit different front fork dimensions and can be used as a kit for modifying an existing front fork.

The telescopic fork leg according to claim 1 of the invention meets the abovementioned requirements and comprises an outer and an inner leg and a damping system arranged within these. The damping system comprises damping system components that are acted upon by the flow of medium caused by the compression and expansion movements of the main piston. The damping system components together form a compact unit that comprises parallel medium flow passages for the flow between the upper and lower sides of the main piston and the flow that is caused by the pressurizing device that pressurizes the whole damping system. The medium flow passages are arranged parallel to each other in order to ensure low flow speeds between the said sides of the main piston and thereby prevent the uncontrollable build-up in pressure and force on the sides of the piston as a result of the rapid movements and large strokes of the front fork. In each damping system component, the flow through one or both of the respective medium flow passages can be arranged so that it can be adjusted or selected by means of devices, for example valves, in order to achieve, for example, matching of the damping characteristics to different types of terrain, by means of an exceptionally wide range of settings. This wide range of settings is

achieved by the medium flow passages comprising separate connections to a common pressure build-up location where the pressure is created by the abovementioned pressurizing device.

The essential characteristics of the invention are that the damping system components comprise two concentric tubes in the form of a damping tube and an outer tube that is arranged around the damping tube, that together form a removable insert system in the front fork. The insert system creates a double tube function in which the damping medium can flow in parallel as a result of the duct between the damping tube and the outer tube being used to connect together the two chambers and the common pressurizing location. The pressurizing location is connected to the medium flow passages between the damping cylinder and the outer tube via a head that also comprises valves for adjusting the flow of the medium. This insert system forms a compact unit that is simple to adapt to different front fork dimensions and that can also be used as a kit for providing an existing front fork with parallel damping. Additional further developments will be apparent from the following claims.

The invention is described in greater detail in the following, with reference to the attached drawings.

Figure 1 shows a damper according to previously-known technology (De Carbon)

Figure 2 shows a front fork mounted on a vehicle

Figure 3 shows a view of the front fork in cross section

Figure 4 shows a detail view of the lower part of the front fork

Figure 4a shows a detail view of the hydraulic stop

Figure 5a shows a simplified view of the front fork in cross section with arrows illustrating the flow during a compression stroke

Figure 5b shows a simplified view of the front fork in cross section with arrows illustrating the flow during a return stroke

Figure 6 shows an alternative embodiment of the front fork with internal pressurized bellows as pressurizing device Figure βa is a detail view of a pressurizing device in the form of a movable piston pressurized by gas Figure 6b is a detail view of a pressurizing device in the form of a movable piston pressurized by means of a spring

Figure 2 shows the front fork (1) described in the application mounted on a vehicle, in this embodiment a motorcycle of which only the front part is shown. Fork legs (1) are arranged on each side of a steering pillar (2) . The lower parts of the fork legs (1) are attached to the wheel (3) and the upper ends are connected to the frame (4) via the top yoke and bottom yoke (5a, 5b) . According to this embodiment, the front fork has an external pressure chamber (6a, 6b) that is attached to the fork leg (1). Other fixing locations for the pressure chamber are of course possible, for example in the yoke, in the frame or on the steering pillar.

Figure 3 shows the front fork in cross section and its construction and function are described below in greater detail. The front fork consists of a lower inner leg (7) arranged on a bottom unit (8) and an upper outer fork leg (9) that terminates in a head (10) that is sealed against the fork. A spring (11) is arranged in the lower inner leg (7) and the damping system is arranged in the upper outer leg. The damping system is constructed of a damping tube (13) and an

outer tube (14) that together create the double tube function that contributes to the parallel flow. A shimmed damping piston (15) is arranged in the damping tube (13) on a piston rod (16), which piston (15) divides the damping chamber into a return chamber (18) and a compression chamber (17) . The return chamber and the compression chamber alternate in being the high- pressure and low-pressure side.

At the upper end of the front fork, opposite to the bottom unit, the double tube function is attached to the sealed-off head (10) that comprises valves (12, 12') that adjust the pressure in the damping system at both high and low speeds and during both compression and return strokes. The valves (12, 12') are connected via separate connectors to a common pressurizing location comprising a pressurizing device (19). In this embodiment, the pressurizing device (19) is a container

(20) divided by a piston (21) and pressurized by gas. A hose (22) is screw-fixed to one end of the container, which hose connects together the container (20) and the head (10) of the front fork.

The damping tube (13) and the outer tube (14) together with the head (10), the tube end (23) and the pressurizing device (19) create the said insert system that is simple to assemble and compact in size. The insert system can be adapted to be mounted in existing front forks on many different types of vehicle, in order to obtain, in a simple way, a system with the advantages of the parallel damping without having to buy a completely new product. With the compact insert system, it is also easy to dismantle and service the product.

One end of the piston rod (16) is attached to the bottom unit (8) on the front fork and the piston (15)

is mounted at the other end. The piston rod (16) is thus sealed against and extends through the tube end (23) of the insert system.

Figure 4 shows an enlarged part of the lower part of the front fork. In order to support the piston rod at the joint, a spring support (24) is arranged around the piston rod. The spring support (24) fulfils two important functions, namely to give the piston rod an extra point of support and to provide a low-friction surface for the spring to move against.

A metallic part (25) is arranged at the end of the spring support (24). This part (25) interacts with, that is can be inserted into, a cylindrical part (26) that is attached to the bottom unit (8), in such a way that a hydraulic stop is created, which prevents the front fork from bottoming in the event of unusually strong compressions.

The fact that the insert system is easy to dismantle from the front fork is also illustrated by Figure 4a which shows the lower part of the front fork. The figure shows that the lower part (26a) of the hydraulic stop (26) is pressed down into the bottom unit (8) of the front fork by pressure force. A thread (26b) is arranged in the internal diameter of the hydraulic stop, so that a bottom part (27) can be screwed into the thread (26b) . The bottom part (27) also comprises a seal (28) that prevents leakage from the front fork. The bottom-most part of the bottom part (27) is designed to be able to be attached or to be screwed in and out using a hexagonal key, so that the front fork is easy both to assemble and to dismantle. A piston rod holder (28) is also threaded into this bottom part (27). The piston rod (16) is attached in a recess in the piston rod holder (28a) and the other part of the

holder (28) is screwed down from above into the abovementioned bottom part (27) . Due to the fact that the holder (28) can be screwed out of the bottom part (27), the front fork is simple to dismantle by withdrawing the whole insert in an upward direction.

Figures 5a and 5b show the flow in the front fork through the different medium flow passages (29, 30), the flow areas in which are adjusted by means of valves (12a, 12b, 12a', 12b'). The valves are divided into high-speed valves (12a, 12a') and low-speed valves (12b, 12b') and standard non-return valves (12c, 12c'). The different types of valve are already well known and will not be described in greater detail in this document. The medium flow passages (29, 30) are arranged in such a way that they are parallel in relation to each other and are connected to the common pressurizing location, that consists here of the pressurizing device (19). As the passages (29, 30) are parallel, the flow is divided up between the two medium-flow passage areas and the flow speeds in the system can essentially be reduced, for example halved, in relation to the actual speed of the longitudinal displacement movements. The flow speed in the medium is determined by the frequency of the movements or the size of the impacts and, with a lower flow speed, the uncontrollable build-up of pressure and forces that can otherwise arise in the system is prevented.

In addition, in Figures 5a and 5b, the parts that are included in the previously-described insert are indicated with grey shading. The high-pressure and low- pressure sides of the damper change with the direction of the stroke. As a result of the flow paths and the position of the valves, the pressure on the low- pressure side is always as high as possible and cavitation is avoided.

During a compression stroke, Figure 5a, the damping medium flows through the damping system as shown by the flow arrows in the figure. The solid arrows represent the compression flow when the front fork is subjected to a force with high speed and the broken arrows represent the compression flow when the speed of the force that is applied is low. That is, at high speeds, when parts of the damping medium on the high-pressure side (H) are pressurized by the shimmed piston (15), the remaining quantity of medium flows via a passage (illustrated in a simplified form by (29) ) in the head (10) through the adjustable high-speed valve (12a) and the non-return valve (12c) through the space between the tubes (13 and 14) to the other side, that is the low-pressure side (L), of the piston. At low speeds, that do not cause sufficient pressure to open the shim stack and the high-speed valve, the medium flows via the adjustable low-pressure valve (12b) via the same non-return valve (12c) to the low-pressure side (L) .

Pressurizing of the medium, by means of the pressurizing device (19), takes place parallel with the flow. The medium that is displaced by the piston rod

(16) can be taken up by the container or volume that acts as a pressurizing device (19).

During a return stroke, the damping medium flows according to the same principle but in the opposite direction to the compression direction described above, according to the flow arrows shown in Figure 5b. The flow is thus partially directed straight through the piston (15) from the high-pressure side (H), and partially up through the space between the tubes (13, 14), via the passage (30) in the head (10), through the valve (12a' or 12b') dependent upon high or low speed, and then on to the low-pressure side (L) of the piston.

Pressurizing of the medium is also carried out here parallel with the flow.

As the compression and return adjustments are separated, the valves (12a, 12a', 12b, 12b') can be adjusted independently of each other. The pressure can therefore be controlled in such a way that the build-up is greatest during the return or compression stroke, depending upon the external circumstances . The damping characteristics can thus be maximally adapted to suit the terrain, as a result of the large range of adjustment that the valves (12a, 12a', 12b, 12b') now have. The large range of adjustment of the valves means an adjustment of the medium flow area from anywhere between maximal and minimal area depending upon the damping force reguirements .

By means of the parallel passages (29, 30) described above, the flow speed to a specific valve can also be reduced if the pressure on this valve becomes critically high. As the damping medium will take the easiest path (the lowest pressure) in the system, this adjustment capability means that a wide range of pistons (15) and pressurizing devices (19) can now be utilized. An advantage of this is that larger pistons can be used and, with larger pistons, the pressure does not need to be so high in the system and the damper has a smoother characteristic. By a smoother characteristic is meant that the increase in pressure, and also the increase in force, can take place without cavitation, irrespective of the setting.

Figure 6 shows a second embodiment of the invention without an external pressurized container. In this embodiment, the front fork also consists of a lower inner leg (7) arranged on a bottom unit (8) and an upper outer fork leg (9) terminating with a head (10)

that is sealed against the fork and upon which head the damping system is arranged. The valves (12, 12' (here drawn in a simplified way) ) are arranged in the sealed head (10) and ducts in the head interconnect all the pressurized spaces. The damping system is also here constructed of a damping tube (13) and an outer tube (14) that together create a double tube function. A pressurizing part (19), for example a floating piston or bellows, is arranged in a divided space outside the outer tube (14) . The pressurizing part must be able to take up the volume of damping medium that the piston rod (16) displaces during maximal compression. The reverse side of the floating piston is pressurized by gas (Figure 6a), a spring (Figure 6b) or the like and the bellows are pressurized by means of a compressible gas or the like. Due to the fact that the whole damping unit can be removed, the gas pressure that pressurizes the damper can also be adjusted in a simple way, for example by having a filling valve (31) connected to the divided space or to the interior of the bellows (not shown) . The bellows can, for example, be in the shape of a toroid that is sealed against the surroundings or a cylinder sealed against any one of the double tubes. As the pressurization of the front fork can now be carried out without the use of an external container, the front fork is easier to assemble and takes up less space .

The invention is not limited to what is described above, but can be modified within the scope of the protection provided by the claims .