SPRING UNIT

Abstract

The present invention relates to a spring unit (1) for a shock absorber (100) intended for a vehicle. The shock absorber (100) comprises a damping cylinder (101), wherein the damping cylinder (101) is adapted to be telescopically arranged within the spring unit (1). The spring unit (1) comprises a hollow body (2) comprising at least one compression chamber (2b) and at least one additional chamber (3) arranged to be in fluid communication with the compression chamber such that at least a first flow of fluid (F1) is adapted to be allowed between the compression chamber (2b) and the additional chamber (3) when a threshold value is met. The invention further relates to a shock absorber (100) comprising such a spring unit (1), and a front fork comprising such a shock absorber (100) as well as a method for filling the shock absorber (100).

Claims

1. A spring unit (1) for a shock absorber (100) suitable for a vehicle, said shock absorber comprising a damping cylinder (101), wherein said damping cylinder is adapted to be telescopically arranged within said spring unit, said spring unit comprising: a hollow body (2) comprising at least one compression chamber (2b) or at least one return chamber (2a); at least one additional chamber (3), said additional chamber being arranged to be in fluid communication with said compression chamber or return chamber such that at least a first flow of fluid (F1) is adapted to be allowed between said compression chamber or return chamber and said additional chamber; wherein said first flow of fluid is allowed when a threshold value (THV) is met.

2. The spring unit according to claim 1, wherein said spring unit comprises a first valve (4), adapted to allow said first flow of fluid from said compression chamber or said return chamber to said additional chamber, said first valve being adapted to allow fluid to pass from said compression chamber or said return chamber to said additional chamber when said threshold value is met.

3. The spring unit according to claim 1, wherein said first flow of fluid from said compression chamber to the additional chamber is allowed during a compression stroke, or wherein said first flow of fluid from said return chamber to the additional chamber is allowed during a rebound stroke.

4. The spring unit according to claim 1, wherein said threshold value is a pressure differential between said chamber (2a, 2b) and said additional chamber.

5. The spring unit according to claim 1, wherein said threshold value is a pressure level prevailing in said chamber (2a, 2b).

6. The spring unit according to claim 1, wherein said threshold value is adapted to be dependent on the relative positions between said damping unit and said chamber (2a, 2b).

7. The spring unit according to claim 1, wherein said chamber (2a, 2b) at a first end is delimited by a sliding seal (5a) adapted to be slidably arranged between an outer surface of said damping cylinder and an inner surface of said hollow body and said chamber (2a, 2b).

8. The spring unit according to claim 1, wherein said chamber (2a, 2b) at a second end is delimited by a dividing wall (6).

9. The spring unit according to claim 8, wherein said additional chamber is arranged adjacently to said chamber (2a, 2b), such that said additional chamber is delimited by said dividing wall.

10. The spring unit according to claim 8, wherein said dividing wall is arranged at a fixed position with respect to said spring cylinder wall.

11. The spring unit according to claim 1, further comprising a second valve (7) allowing a second flow of fluid from said additional chamber into the chamber (2a, 2b), wherein said second valve is a check valve.

12. The spring unit according to claim 11, wherein said first and/or said second valve is/are integrated in said dividing wall.

13. The spring unit according to claim 1, wherein said spring unit comprises a return chamber (2a).

14. The spring unit according to claim 13, wherein said return chamber is arranged in fluid communication with at least said compression chamber such that at least a first flow of fluid is adapted to be allowed between said return chamber and said compression chamber.

15. A shock absorber (100) intended for a vehicle, said shock absorber comprising: a damping unit and a spring unit according to claim 1, said damping unit comprising, a damping fluid cylinder (101) and a piston (102) movably arranged within said damping fluid cylinder, wherein said damping cylinder is adapted to be telescopically arranged within said spring unit.

16. The shock absorber according to claim 15, said shock absorber comprising a return chamber, adapted to be arranged in fluid communication with at least said compression chamber such that at least a first flow of fluid is adapted to be allowed between said return chamber and said compression chamber.

17. The shock absorber according to claim 15, wherein said damping cylinder is telescopically arranged within said spring unit such that an annular space is formed between an outer surface of the damper cylinder and an inner surface of the hollow body of the spring unit.

18. The shock absorber according to claim 17, said shock absorber further comprising: a first sealing structure (5b) slidably arranged between an outer surface (105) of said damping cylinder and an inner surface (104) of said hollow body; and a second sliding seal (5a) slidably arranged between an outer surface of said damping fluid cylinder and an inner surface of said hollow body, such that said hollow body is divided into a first and a second portion, wherein said first portion is arranged in said annular space and delimited by said first and second seal and said second portion is delimited at least by said second sliding seal.

19. The shock absorber according to claim 18, wherein said first seal is carried by the hollow body and arranged in sliding contact with the outside of the fluid cylinder.

20. The shock absorber according to claim 18, wherein said second seal is carried by the damping fluid cylinder and arranged in sliding contact with the inside of the hollow body.

21. The shock absorber according to claim 15, wherein said first portion corresponds to said return chamber and said second portion corresponds to said compression chamber.

22. The shock absorber according to claim 15, further comprising an external chamber (8) arranged on the outside of said gas cylinder, said external chamber arranged to be in fluid communication with at least one of said compression chamber and said return chamber, such that a pressure equalization between the external space and said compression chamber and/or said return chamber takes place.

23. The shock absorber according to claim 22, wherein said external chamber is arranged on the outside of said gas cylinder, such that said external chamber is in fluid communication with at least one of said first and second portions when the second seal is situated at a predetermined position, such that a pressure equalization between the external space and the at least one first or second portion takes place.

24. The shock absorber according to claim 22, wherein said external chamber is exclusively in fluid communication with said first portion when said second seal is positioned at a first predetermined position, such that a pressure equalization between the external space and the first portion takes place, and exclusively in fluid communication with said second portion when the second seal is positioned at a second predetermined position, such that a pressure equalization between the external chamber and the second portion takes place.

25. A front fork for a two wheeled vehicle comprising a shock absorber according to claim 15.

26. A method for filling a shock absorber according to claim 15, said method comprising the steps of: providing a first pressure in the additional chamber; allowing a pressure equalization between said additional chamber and said first portion of the hollow body by means of said first fluid flow; and allowing a pressure equalization between the first and second portion of the hollow body.

27. The method according to claim 26, wherein the pressure equalization between the first and second portion of the hollow body is allowed by means of a bypass at least at a first predetermined relative position of the damping unit and/or the damping piston and the additional chamber.

28. The spring unit according to claim 1, wherein the additional chamber comprises means for receiving a fluid.

29. The spring unit according to claim 28, wherein said means for receiving a fluid is a fluid connection adapted to allow a filling of the additional chamber.

30. The spring unit according to claim 1, further comprising means adapted to allow a defined, adjustable pressure drop between the chamber and the additional chamber, such that energy is absorbed by means of said first flow of fluid allowed from the chamber to the additional chamber after the threshold value is met.

Description

SHORT DESCRIPTION OF THE APPENDED DRAWINGS

[0071] The invention is described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawings, wherein:

[0072] FIG. 1 is cross sectional view of a shock absorber comprising a spring unit according to a first aspect of the present invention.

[0073] FIG. 2 is a cross sectional view of the additional chamber according to one embodiment of the invention.

[0074] FIG. 3 is a detailed view of the second valve according to one embodiment of the invention.

[0075] FIG. 4 is a detailed cross sectional view of an embodiment of the shock absorber comprising an external chamber in selectable fluid communication with the compression chamber and the return chamber.

[0076] FIG. 5 is a diagram showing the damping response curve, according to one embodiment of the invention, in comparison with spring units according to the prior art.

[0077] FIG. 6 is a diagram showing how different threshold values of the first valve influences the damping response curve.

[0078] All figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested. Throughout the figures the same reference signs designate the same, or essentially the same features.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0079] FIG. 1 shows a shock absorber 100 comprising a spring unit 1. The shock absorber further comprises a damping cylinder 101. A piston 102 is arranged within the damping cylinder, said cylinder is adapted to be filled with a fluid. A piston rod 103 is adapted to extend through a first end of the damping fluid cylinder and through the spring unit. Further, the damping cylinder is telescopically arranged within the spring unit. Other aspects of the damping fluid cylinder are known in the art and will not be described in greater detail.

[0080] The spring unit 1 comprises a hollow body 2, in the illustrated case a spring cylinder 2. The hollow body shown in FIG. 1 comprises a compression chamber 2b and a return chamber 2a, the latter arranged at a first end of the hollow body 2. Further, an additional chamber 3 is arranged at a second end of the hollow body 2. Accordingly the compression chamber 2b is arranged between the return chamber 2a and the additional chamber 3. The additional chamber further comprises a fluid connection, such that a fluid such as gas, or air, may for be received by the third chamber.

[0081] The compression chamber 2b and the additional chamber 3 are arranged in fluid communication such that at least a first flow of fluid F1 from the compression chamber 2b to the additional chamber 3 is allowed. The flow F1 is allowed to flow via a first valve 4. A second flow of fluid F2 is allowed to flow from the additional chamber 3 to the compression chamber 2b via a second valve 7. In the illustrated case, the additional chamber is arranged in fluid communication with the compression chamber 2b, however, in other embodiments (not shown), the additional chamber may instead be arranged to be in fluid communication with the return chamber 2a, or the spring unit may have a first additional chamber in fluid communication with the compression chamber 2b and a second additional chamber in fluid communication with the return chamber 2a.

[0082] The compression chamber 2b is delimited at a first end by a sliding seal 5a, the seal is arranged to slide between the inner wall 104 of the hollow body 2 and the outer surface 105 of the damping cylinder 101. At a second end, the compression chamber 2b is delimited by a dividing wall 6. Due to the arrangement of the additional chamber 3 adjacent to the compression chamber 2b, the additional chamber 3 is also delimited by the wall 6.

[0083] In the illustrated embodiment, the wall 6 is arranged at a fixed position P with respect to the wall of the spring cylinder unit 2. This arrangement is designed such that a fluid tight seal is achieved by the dividing wall 6. Since the additional chamber 3 is delimited at the other end of the end wall of the hollow body, the illustrated additional chamber 3 has a fixed volume.

[0084] The return chamber 2a is delimited on the one hand of the sliding seal 5a, and on the other side of a second seal 5b sealing the compression chamber 2b from the surroundings. Accordingly, in the illustrated case, the return chamber 2b is formed by the annular space between the hollow body 2, or spring cylinder, and the fluid cylinder.

[0085] The dividing wall 6, the valves 4, 7 and the fluid flows F1 and F2 will now be described in greater detail with reference to FIG. 2. FIG. 2, shows a detailed view of the additional chamber 3 delimited by the diving wall 6 and an end face of the spring unit cylinder 2. Both valves 4, 7 are integrated in the dividing wall 6.

[0086] The first valve 4 is adapted to allow the first flow of fluid F1, illustrated by the solid arrow, to flow from the compression chamber 2b to the additional chamber. This valve, in the illustrated case, is adapted to allow the flow F1 to flow during a compression stroke CS. The first valve 4 is further designed such that this first flow F1 is allowed when a threshold value THV is met. In the illustrated case, the threshold value is a predetermined pressure differential. Valves adapted to open at a predetermined threshold value as such are known in the art and the first valve 4 will therefore not be described in greater detail.

[0087] In the illustrated case, the wall 6 is arranged at a fixed point P on the hollow body wall. The compression chamber 2b is delimited by the wall, and by the second seal 5b and the end face of the damping fluid cylinder. Consequently, the pressure in the compression chamber 2b is dependent on the relative position between the damping unit and the hollow body 2, the damping unit 101 telescoping within the hollow body. Accordingly, the pressure level in the compression chamber 2b will rise during a compression stroke when the damping unit and the spring unit move towards one another. The first valve 4 is adapted to open when the threshold level, i.e. the pressure differential over the dividing wall 6, is sufficiently large. In other words, the first valve is adapted to open during a final stage of the compression stroke. Hereby, the additional chamber 3 gets connected to the compression chamber 2b at a predetermined pressure and the progressive pressure increase at the end of the stroke is thereby decreased. As a further consequence, the pressure drop between the compression chamber 2b and the additional chamber 3 is defined and adjustable, and when the valve opens the fluid flow from the compression chamber 2b to the additional chamber 3 acts like a damper, in the sense that the energy is absorbed and no “kick back” will occur.

[0088] The second valve 7 is adapted to allow the second flow of fluid, illustrated by the dotted arrow, from the additional chamber 3 to the compression chamber 2b. The illustrated valve 7 is a check valve allowing only a flow F2 in this direction and FIG. 3 shows a detailed view of a check valve according to one embodiment. The flow F2 will occur due to the resulting pressure levels during the return stroke. Further, this flow comprises a much lower pressure drop that is not meant to absorb energy in a noticeable amount.

[0089] FIG. 4 shows a detailed view of an embodiment comprising an external chamber 8. The external chamber is arranged on the outside of the cylinder 2 and is in the illustrated embodiment in fluid connection with the compression chamber 2b or the return chamber 2a, depending on the position of the sealing 5a. This fluid connection is achieved via at least one passage 9, or channel 9. The fluid passage 9 extends through the wall of the spring cylinder 2 and connects the external chamber 8 to the compression chamber or to the return chamber 2a depending on the telescoping movement between the damping cylinder 101 and the spring unit cylinder 2, in other words the positioning of the sealing 5a. The fluid connection may be referred to as a bypass. In the present case two passages are arranged to extend through the wall of the spring cylinder. The reciprocal, or telescopic motion, of the fluid cylinder with respect to the hollow body will in the illustrated case cause one of the channels 9 (and therefore the chamber 8) through the hollow body wall to be in fluid communication exclusively with the first portion or the second portion depending on the relative motion and hence the position of the second seal. Hereby, a pressure equalization between the external chamber 8 and the chamber 2a, 2b presently in fluid connection with the external chamber takes place.

[0090] FIG. 5 shows a diagram of the damper response, which shows the damping characteristics of the spring unit according to one embodiment, in comparison with two spring units according to the prior art. The diagram schematically shows the difference between a conventional air spring S1 having only one compression chamber, a coil spring S2 and the air spring comprising two compression chambers S3, i.e. one compression chamber 2b and one additional chamber 3, according to the present invention. As seen in the figure, compared to the air spring S1, the progressive pressure increase at the end of the compression stroke is decreased.

[0091] The pressure difference between the compression chamber 2b and the additional chamber 3 is controlled by the first valve 4. Thus, the pressure drop over the first valve 4 controls at which moment during the stroke the first valve 4 opens and lets damping fluid into the additional chamber 3.

[0092] At the starting point, the compression chamber 2b and the additional chamber 3 has essentially the same pressure. One advantage with the present invention is that when filling the damper, in order to achieve a desired pressure in the chambers, it is only necessary to fill the spring unit at one single point, i.e. in the additional chamber 3. Since the additional chamber 3 and the compression chamber 2b are interconnected via said second valve 7, which is a so called check valve, the damping medium will also enter the compression chamber 2b, via the second valve, such that the additional chamber 3 and the compression chamber 2b gets essentially the same pressure initially. Subsequently, pressure equalization between the first and second portion of the hollow body (i.e. between the compression and return chambers) may be allowed by means of a bypass. As described in detail with reference to FIG. 4, the bypass may be designed such that the pressure equalization is allowed when the distance between the damping unit and/or the damping piston and the additional chamber (i.e. the relative position there between) correspond to a certain value.

[0093] Depending on the size of the additional chamber 3, the size of the compression chamber 2b, and the pressure drop over the first valve 4, i.e. at which pressure difference between the chambers 2b, 3 the valve 4 opens, it is possible to decide how the damping response curve will look. FIG. 6 illustrates how the pressure drop over the first valve 4 influences the damping characteristics of the spring unit. Preferably, the pressure differential between the compression chamber 2b and the additional chamber 3 is approximately between 30-70% at the moment when the first valve 4 opens. In other words, during the compression stroke, the pressure is approximately 30-70% higher in the compression chamber 2b with respect to the additional chamber 3 at the moment the first valve 4 opens. Thus, the threshold value THV may preferably be set to be a pressure differential, between the additional chamber and the compression chamber, between 1:1,3 and 1:1,7. As an example, if chambers 2d, 4 are initially pressurized to 10 Bar, the first valve 4 may be arranged to open when the pressure is raised to 14 Bar in the compression chamber during the compression stroke (cf. lower pressure drop curve in FIG. 6). Furthermore, if the first valve 4 is set to open at a higher pressure, e.g. about 16 Bar, the damping response curve will look more like the higher pressure drop curve. Naturally, the valve 4 may be set to open at any other threshold value, i.e. at a higher or lower pressure differential, i.e. the between 1:1,2 and 1:1,8, or even higher depending on how a desired damping response curve looks.

[0094] While specific embodiments have been described, the skilled person will understand that various modifications and alterations are conceivable within the scope as defined in the appended claims.

Itemised List

[0095] Item 1. Spring unit (1) for a shock absorber (100) suitable for a vehicle, said shock absorber comprising a damping cylinder (101), wherein said damping cylinder is adapted to be telescopically arranged within said spring unit, said spring unit comprising: [0096] a hollow body (2) comprising at least one compression chamber (2b) or at least one return chamber (2a); [0097] at least one additional chamber (3), said additional chamber being arranged to be in fluid communication with said compression chamber or return chamber such that at least a first flow of fluid (F1) is adapted to be allowed between said compression chamber or return chamber and said additional chamber; [0098] wherein said first flow of fluid is allowed when a threshold value (THV) is met.

[0099] Item 2. Spring unit according to item 1, wherein said spring unit comprises a first valve (4), adapted to allow said first flow of fluid from said compression chamber or said return chamber to said additional chamber, said first valve being adapted to allow fluid to pass from said compression chamber or said return chamber to said additional chamber when said threshold value is met.

[0100] Item 3. Spring unit according to any of items 1-2, wherein said first flow of fluid from said compression chamber to the additional chamber is allowed during a compression stroke.

[0101] Item 4. Spring unit according to any of items 1-2, wherein said first flow of fluid from said return chamber to the additional chamber is allowed during a rebound stroke.

[0102] Item 5. Spring unit according to any of items 1-4, wherein said threshold value is a pressure differential between said chamber (2a, 2b) and said additional chamber.

[0103] Item 6. Spring unit according to any of items 1-5, wherein said threshold value is a pressure level prevailing in said chamber (2a, 2b).

[0104] Item 7. Spring unit according to any of items 1-6, wherein said threshold value is adapted to be reached during a compression stroke when said chamber is a compression chamber (2b), and wherein said threshold value is adapted to be reached during a return stroke when said chamber is a return chamber (2a).

[0105] Item 8. Spring unit according to any of items 1-7, wherein said chamber (2a, 2b) has a volume and said threshold value is dependent on a change of volume of said chamber (2a, 2b).

[0106] Item 9. Spring unit according to any of items 1-8, wherein said threshold value is adapted to be dependent on the relative positions between said damping unit and said chamber (2a, 2b).

[0107] Item 10. Spring unit according to any of items 1-9, wherein said threshold value is dependent on the temperature in said chamber (2a, 2b) and/or said additional chamber.

[0108] Item 11. Spring unit according to any of the preceding items, wherein said chamber (2a, 2b) at a first end is delimited by a sliding seal (5a) adapted to be slidably arranged between an outer surface of said damping cylinder and an inner surface of said hollow body and said chamber (2a, 2b).

[0109] Item 12. Spring unit according to any of the preceding items, wherein said chamber (2a, 2b) at a second end is delimited by a dividing wall (6).

[0110] Item 13. Spring unit according to item 12, wherein said additional chamber is arranged adjacently to said chamber (2a, 2b), such that said additional chamber is delimited by said dividing wall.

[0111] Item 14. Spring unit according to item 12 or 13, wherein said dividing wall is arranged at a fixed position with respect to said spring cylinder wall.

[0112] Item 15. Spring unit according to any of the preceding items, wherein said additional chamber has a fixed volume.

[0113] Item 16. Spring unit according to any of the preceding items, wherein said additional chambers comprises at least one internal dividing wall, such that at least two sections are formed in the additional chamber.

[0114] Item 17. Spring unit according to any of the preceding items, further comprising a second valve (7) allowing a second flow of fluid from said additional chamber into the chamber (2a, 2b).

[0115] Item 18. Spring unit according to item 17, wherein said second flow of fluid is allowed during a rebound stroke or a compression stroke.

[0116] Item 19. Spring unit according to any of items 17-18, wherein said second valve is a check valve.

[0117] Item 20. Spring unit according to any of the preceding items, wherein said first valve is adapted to allow a flow of fluid from said chamber (2a, 2b) to said additional chamber at a final stage of said stroke.

[0118] Item 21. Spring unit according to any of the preceding items when dependent on any of items 17-18, wherein said first and/or said second valve is/are integrated in said dividing wall.

[0119] Item 22. Spring unit according to any of the preceding items, wherein said threshold value is manually adjustable.

[0120] Item 23. Spring unit according to any of the preceding items, wherein said threshold value is automatically adjustable.

[0121] Item 24. Spring unit according to any of the preceding items, wherein said chamber (2a, 2b) comprises an elastic member.

[0122] Item 25. Spring unit according to any of the preceding items, wherein said additional chamber comprises an elastic member.

[0123] Item 26. Spring unit according to any of the preceding items, wherein said spring unit comprises a return chamber (2a).

[0124] Item 27. Spring unit according to item 26, wherein said return chamber is arranged in fluid communication with at least said compression chamber such that at least a first flow of fluid is adapted to be allowed between said return chamber and said compression chamber.

[0125] Item 28. Spring unit according to item 26 or 27 wherein said return chamber is arranged in said hollow body.

[0126] Item 29. Spring unit according to any of the preceding items 26-28, wherein said return chamber comprises an elastic member.

[0127] Item 30. Shock absorber (100) intended for a vehicle, said shock absorber comprising: [0128] a damping unit and a spring unit according to any of items 1-29, said damping unit comprising, a damping fluid cylinder (101) and a piston (102) movably arranged within said damping fluid cylinder, wherein said damping cylinder is adapted to be telescopically arranged within said spring unit.

[0129] Item 31. Shock absorber according to item 30, said shock absorber comprising a return chamber, adapted to be arranged in fluid communication with at least said compression chamber such that at least a first flow of fluid is adapted to be allowed between said return chamber and said compression chamber.

[0130] Item 32. Shock absorber according to item 30 or 31, wherein said damping cylinder is telescopically arranged within said spring unit such that an annular space is formed between an outer surface of the damper cylinder and an inner surface of the hollow body of the spring unit.

[0131] Item 33. Shock absorber according to item 32, said shock absorber further comprising: [0132] a first sealing structure (5b) slidably arranged between an outer surface (105) of said damping cylinder and an inner surface (104) of said hollow body; and [0133] a second sliding seal (5a) slidably arranged between an outer surface of said damping fluid cylinder and an inner surface of said hollow body, such that said hollow body is divided into a first and a second portion, wherein said first portion is arranged in said annular space and delimited by said first and second seal and said second portion is delimited at least by said second sliding seal.

[0134] Item 34. Shock absorber according to item 33, wherein said first seal is carried by the hollow body and arranged in sliding contact with the outside of the fluid cylinder.

[0135] Item 35. Shock absorber according to item 33 or 34, wherein said second seal is carried by the damping fluid cylinder and arranged in sliding contact with the inside of the hollow body.

[0136] Item 36. Shock absorber according to any of item 33-35, wherein said first portion corresponds to said return chamber and said portion corresponds to said compression chamber.

[0137] Item 37. Shock absorber according to any of items 33-36, wherein said second portion is further delimited by a dividing wall.

[0138] Item 38. Shock absorber according to item 37, wherein said additional chamber is arranged adjacently to said compression chamber, such that said additional chamber is delimited by said dividing wall.

[0139] Item 39. Shock absorber according to any of the preceding items 30-38, wherein said additional chamber is further delimited by a first end of said hollow body.

[0140] Item 40. Shock absorber according to any of the preceding items 30-39, further comprising an external chamber (8) arranged on the outside of said gas cylinder, said external chamber arranged to be in fluid communication with at least one of said compression chamber and said return chamber, such that a pressure equalization between the external space and said compression chamber and/or said return chamber takes place.

[0141] Item 41. Shock absorber according to item 40, wherein said external chamber is arranged on the outside of said gas cylinder, such that said external chamber is in fluid communication with at least one of said first and second portions when the second seal is situated at a predetermined position, such that a pressure equalization between the external space and the at least one first or second portion takes place.

[0142] Item 42. Shock absorber according to item 40 or 41, wherein said external chamber is exclusively in fluid communication with said first portion when said second seal is positioned at a first predetermined position, such that a pressure equalization between the external space and the first portion takes place, and exclusively in fluid communication with said second portion when the second seal is positioned at a second predetermined position, such that a pressure equalization between the external chamber and the second portion takes place.

[0143] Item 43. Shock absorber according to any of the preceding items 30-42, wherein said shock absorber is a gas spring shock absorber.

[0144] Item 44. Front fork for a two wheeled vehicle comprising a shock absorber according to any of the preceding items 30-42.