WO1999058392A1 - Damping and spring system for suspension system - Google Patents

Abstract

A suspension system is provided for use in one or both fork struts (14, 16) of a bicycle suspension fork (12). The fork struts (14, 16) have first tubes (18, 20) in telescoping, sliding engagement with second tubes (22, 24). The suspension system includes a shock absorbing arrangement (30) disposed in one or both of the fork struts (14, 16), which comprises a spring assembly (32) and a damping assembly (34). The spring assembly (32) includes a compression spring (36), a spring spacer (38) and an air spring which is defined by a pressurized air pocket. The damping assembly (34) includes a damper rod (46), a damping piston (48), and a valve (50). A damper dome (72) is mounted to the damper rod (46) for deflecting and directing fluid during operation of the system.

Description

DAMPING AND SPRING SYSTEM FOR SUSPENSION SYSTEM

This application claims priority of U.S. Provisional Patent Application No. 60/084,917, which was filed May 11, 1998. BACKGROUND OF THE INVENTION

The invention disclosed in the present patent application relates to the design of damping and spring systems for use in suspension systems, and particularly for use in bicycle suspension systems. In the past, suspension systems have been designed for use in connection with automobiles, motorcycles, aircraft, towing apparatuses, snowmobiles, all-terrain vehicles, as well as other vehicles and machinery. Recently, suspension systems have been specially designed and adapted for use in connection with bicycles for cushioning impacts or vibrations experienced by a rider when the bicycle contacts bumps, ruts, rocks, pot holes or other obstacles, and for maintaining the bicycle wheel in contact with the ground, thus improving the rider's steering and braking control over the bicycle. Indeed, bicycle suspension systems have been incorporated into front and rear bicycle forks, head tubes, seat tubes, rear-wheel swing-arm assemblies, as well as other locations. The popularity of such suspension systems has been increasing rapidly, particularly in connection with "mountain bikes", i.e., bicycles designed to be ridden over rough, off-road terrain. Mountain bikes are intended to be ridden frequently over demanding, punishing terrain which often is distant from a repair shop or other facility needed to perform major repairs should the bike's suspension system fail. Accordingly, there is an ongoing need for a suspension system that is reliable and requires a low level of maintenance. At the same time, particularly with mountain bikes, the demands of riding over rough terrain require suspension systems that deliver high quality suspension performance. Currently available suspension systems have attempted to address these requirements for vehicles such as mountain bikes. For example, the suspension used in connection with the 1998 Judy SL® brand manufactured by RockShox, Inc. is a popular high performance suspension system proven to have a high degree of reliability and a low maintenance requirement. However, this suspension system and systems that compete with it for sales are undesirably expensive to manufacture and, as a result, are not affordable by many mountain bike riders. Accordingly, there is a need for a high performance suspension system for vehicles such as mountain bikes which is reliable, has a low maintenance requirement and is not undesirably expensive.

One reason in particular why such suspension systems are expensive to manufacture is that, though the designs may incorporate a damping system and compression and/or rebound damping adjustment mechanisms, such adjustment mechanisms are difficult (and therefore expensive) to add to the suspension system. For example, in several such designs, the compression chamber of the damping system directly feeds the rebound chamber when the suspension system is compressed or expanded, either through a piston valve dividing the two chambers or through the damper rod to which a dividing piston is connected. During compression of the suspension system, the fluid in the compression chamber will take the path of least resistance to exit that chamber and enter the rebound chamber. Thus, if a valve is placed in the damper rod to restrict flow out of the compression chamber, for example, then the fluid will tend to flow through the piston valve and to thereby short-circuit the compression adjuster. Conversely, if the piston valve is made stiffer to force fluid through the damper rod, then the rebound chamber may become starved for fluid, resulting in cavitation and reduced damping performance. Accordingly, there is a need for a high performance suspension system for vehicles such as mountain bikes which is reliable, has a low maintenance requirement and is readily adaptable to incorporate a compression and/or rebound adjustment mechanism.

Another reason why currently available suspension systems are undesirably expensive to manufacture is that they are not specifically designed to have low-cost manufacturability . Thus, there is a need for a high performance suspension system for vehicles such as mountain bikes which is reliable, has a low maintenance requirement and is specifically designed for low-cost manufacturability. In addition, many fluid-damped suspension systems incorporate a damping cartridge which contains a damping fluid as well as other damper parts, is insertible as a unit into the suspension system and, preferably, is replaceable. Although such damping systems have many advantages to recommend them, they suffer from the disadvantage that the damping fluid is isolated from the non-damping components of the suspension system and therefore cannot be used to lubricate those components. As a result, the non-damper components either remain unlubricated or must be lubricated by a separate lubrication system. Either condition is undesirable. Thus, there is a need for a high performance suspension system for vehicles such as mountain bikes which is reliable, has a low maintenance requirement and has a system which both damps and lubricates the suspension system.

Another disadvantage of many suspension systems, and of mountain bike suspension systems in particular, is the fact that such systems typically include inefficient and/or ineffective bottom-out prevention mechanisms. With respect to typical suspension systems having two telescoping tubes, "bottom- out" occurs when the first tube has moved its furthest possible extent into the second tube, such that the tubes themselves, or components attached to the tubes, may collide and prevent the suspension system from compressing further. If cushioning is not provided, bottom-out can be abrupt and harsh, potentially resulting in damage to the suspended load, or in the case of vehicles such as bicycles, discomfort, loss of control and/or a loud "clunk" or "thunk". Typical bottom-out cushioning mechanisms comprise a thin resilient pad positioned so as to buffer contact between the moving parts as they approach bottom-out . Not only do such systems require the unwanted addition of one or more parts to the suspension assembly, but they typically are insufficient to prevent one or more of the undesirable bottom-out effects mentioned above. Accordingly, there is a need for a high performance suspension system for vehicles such as mountain bikes which is reliable, has a low maintenance requirement and has a bottom-out cushioning mechanism which requires no additional parts and can prevent damage, discomfort, loss of control or the loud "clunk" or "thunk" that may result from bottom- out of the suspension system.

SUMMARY OF THE INVENTION

The present invention provides an improved suspension system which is particularly suited for use in a suspension fork assembly for bicycles. When used in a pedal-driven vehicle such as a bicycle, the assembly may comprise a fork having at least one fork strut, and usually two such struts, the fork strut having a first tube in telescoping, slidable engagement with a second tube. The first tube is typically positioned above the second tube, and slides within the second tube, although this positioning is not critical to the invention. The first and second tubes are mounted in a fork crown assembly which also mounts a steerer tube for connecting the tubes to a bicycle frame. A shock absorbing arrangement is provided within the strut.

The shock absorbing arrangement comprises a spring assembly and a damping assembly. The spring assembly is comprised of a compression spring which may include one or more springs such as metal or plastic coil springs, air bladders or other air springs, arcuate spring discs, or any other spring medium either alone or in combination, and preferably comprises a metal coil spring. Preferably, the spring assembly also comprises an air assist spring. The damping assembly preferably operates in parallel with the spring assembly. In one embodiment, the damping assembly comprises a bi-directional damping system providing a different damping rate on the suspension system's rebound stroke than on its compression stroke. The damping assembly preferably provides a hydraulic bottom out. Generally, the spring assembly provides a mechanism for energy shortage while the damping assembly dissipates energy imparted to the suspension system.

The accompanying drawings, incorporated in and forming a part of this patent application, illustrate several aspects of the present invention, and together with the description herein, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a bicycle suspension fork containing the shock absorbing arrangement of the preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of one of the struts of the bicycle suspension fork of FIG. 1;

FIG. 3 is a detailed view of the operation of the damping assembly during compression of the bicycle suspension fork of FIG. 1;

FIG. 4 is a detailed view of the operation of the damping assembly during rebound of the bicycle suspension fork of FIG. 1;

FIG. 5 is an elevational view of the damper rod of the damping assembly of the preferred embodiment of the present invention;

FIG. 6a is a disassembled view of the damper piston, and check plate and spring washer assembly, of the preferred embodiment of the present invention; FIG. 6b is a view illustrating the assembly of the preferred embodiment of the damper piston and check plate and spring washer assembly of the present invention;

FIG. 7 is a cross-sectional view of the damper rod of the damping assembly of the preferred embodiment of the present invention, illustrating the preferred roll-crimped connection of the damper rod and threaded insert ; FIG. 8a is a partial cross-sectional view showing the placement of the rod guide retainer of the preferred embodiment of the present invention in relation to the first telescoping tube; and

FIG. 8b is a partial cross-sectional view showing the engagement of the rod guide and rod guide retainer of the preferred embodiment of the present invention in relation to the first telescoping tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The suspension system of the present invention will now be described with reference to the figures. The shock absorbing arrangement of the present invention may be used in one or both struts of a bicycle suspension fork of the type illustrated in FIG. 1. As shown in FIG. 1, fork 12 has a first fork strut 14 and a second fork strut 16, fork struts having first tubes 18, 20 in telescoping, slidable engagement with second tubes 22, 24. In fork 12, first tubes 18, 20 are positioned above second tubes 22, 24 and slide within second tubes 22, 24. First tubes 18, 20 are mounted in a fork crown 26 which is mounted to a steerer tube 28 for connecting first and second fork struts 14, 16 to a bicycle frame (not shown) . A shock absorbing arrangement 30 is provided within one or both fork struts 14, 16.

As shown in FIG. 2, the preferred embodiment of shock absorbing arrangement 30 is comprised of spring assembly 32 and damping assembly 34. In the preferred embodiment of FIG. 2, spring assembly 32 is comprised of compression spring 36, a spring spacer 38 and an air spring (described in detail below) . Compression spring 36 preferably is a steel coil spring. As will be apparent to those having skill in the art, however, other types of combinations of springs or spring materials may be used for spring assembly 32, based upon performance needs or user preferences. For example, the spring or springs used in spring assembly 32 may be exchanged for a softer (lower spring rate) , harder (higher spring rate) , or less or more progressive spring or springs to vary the performance of the suspension system. Spring spacer 38 is used to enable the compression of compression spring 36 between first tube 20 and second tube 24. In addition, spring spacer 38 is used to decrease the volume in first tube 20 that must be filled with fluid. Spring assembly 32 serves to store energy imparted to the suspension system during compression of the system, and returns the energy to the system during rebound. As shown in FIG. 2, a preload adjuster 40 preferably is attached to a top cap 42. Top cap 42 is threadably and sealingly attached to a first end 43 of first tube 20. Preload adjuster 40 includes an external adjustment knob 44 and is adjustably connected to and depends from top cap 42 to contact, and be preferably releasably attached to, a first end 37 of spring spacer 38.

Damping assembly 34 is a fluid damping system comprised of damper rod 46, damping piston 48, and valve 50. Damper rod 46 is fixed at a second end 55 to second tube 24 so as to move therewith, and its first end 53 extends into first tube 20. Damper rod 46 has a port 54

(see FIG. 4) at about the first end 53 and a port 52 (see

FIG. 3) at about the second end 55. Port 52 is preferably larger than port 54, as will be described.

Damping piston 48 is fixed at about the first end 53 of damper rod 46 and positioned within first tube 20. Damping piston 48 has a groove in its circumference in which is seated a glide ring 56 to form a seal between damping piston 48 and the inner surface of first tube 20. Damping piston 48 also has one or more ports 58 extending therethrough. Valve 50 is disposed on the underside of damping piston 48 to provide for one-way flow (during compression only) through ports 58. Valve 50 may be comprised, for example, of a check plate which is easily displaced from damping piston 48, but preferably is comprised of a check plate 60 biased against damping piston 48 by a spring washer 62. As illustrated in FIGS. 2-4 and 7, damper rod

46 preferably is hollow, and the hollow portion of damper rod 46 provides a fluid passage. A damper dome 72 preferably is placed on first end 53 of damper rod 46 to provide a spring perch for compression spring 36 and to deflect radially or to the side fluid flowing toward first end 53 of damper rod 46 during compression. The benefit of such deflection will be discussed in detail below.

The arrangement of the first tube 20, second tube 24, and damping assembly 34 forms three chambers in the shock absorbing arrangement 30. A compression chamber 64 is formed within second tube 24 between a second end 45 of first tube 20 and the second end 65 of second tube 24. A rebound chamber 66 is formed within first tube 20 between damping piston 48 and second end 45 of first tube 20. An air/oil reservoir chamber 67 is formed within first tube 20 between damping piston 48 and top cap 42. Compression chamber 64, rebound chamber 66 and air/oil reservoir chamber 67 contain a fluid, preferably a common grade of hydraulic oil. In the preferred configuration of the present invention as shown in FIG. 1, compression chamber 64 and rebound chamber 66 are filled with fluid, whereas air/oil reservoir chamber 67 is partially filled with fluid and has a gas chamber disposed between the fluid and top cap 42. This oil bath design is used both in the operation of damping assembly 34 to damp the movement of the suspension assembly, as will be described in more detail below, and to provide lubrication to the moving parts of fork strut 16.

Attached to the second end 45 of first tube 20 are a rod guide 68 and rod guide retainer 70. Rod guide 68 and rod guide retainer 70 operate to guide damper rod 46 as it moves within first tube 20. Rod guide 68 also seals the interface between damper rod 46 to prevent fluid leakage between compression chamber 64 directly into the rebound chamber 66.

A top-out spring 74 is attached to the underside of damping piston 48 to cushion the "top-out" of fork strut 16, i.e., to cushion the impact of first tube 20 and second tube 24 when first tube 20 and second tube 24 extend to their furthest possible extent during rebound. In addition, as shown in FIG. 2, top-out spring 74 also enables fork strut 16 to extend during rebound beyond its unloaded, equilibrium position to a limited extent. As used in the fork 12 of FIG. 1, such added extension enhances the ability of fork strut 16 to rapidly return the bicycle wheel to the ground, thus enhancing controllability of the vehicle. In the illustration of FIG. 3, second tube 24 is moved in the direction of arrow C (upward) with respect to first tube 20 during compression of fork strut 16. This motion reduces the internal volume of compression chamber 64, thus pressurizing compression chamber 64. The hydraulic oil in compression chamber 64 is forced through port 52 in damper rod 46. The fluid travels upwardly inside damper rod 46 and out damper dome 72, as shown. At the same time, the volume in rebound chamber 66 is increased as damper piston 48 moves away from rod guide 68. This reduces the pressure of the fluid in rebound chamber 66, drawing fluid in through valve 50. Air/oil reservoir chamber 67 also undergoes a reduction in chamber volume during compression of fork strut 16 as damper piston 48 moves further toward first end 43 of first tube 20.

As can be understood from FIG. 1, the rate at which the oil level will rise in air/oil reservoir chamber 67 during compression of fork strut 16 when measured with respect to top cap 42 does not vary linearly with the distance that fork strut 16 is compressed. This is evident in that the total change in the volume of compression chamber 64 is greater than the total change in the volume of rebound chamber 66 by the volume of fluid displaced from compression chamber 64 by first tube 20. Thus, the volume of fluid displaced from compression chamber 64 by first tube 20 is moved during compression through damper rod 46 into air/oil reservoir chamber 67 so that the fluid in that chamber rises at a rate greater than the compression rate of fork strut 16.

The oil level rise in air/oil reservoir chamber

67 creates a high pressure zone in air/oil reservoir chamber 67 which is position-sensitive. The greater the compression of fork strut 16, the greater the pressure in air/oil reservoir chamber 67.

The increase in air/oil reservoir chamber pressure serves three functions. First, it creates a high pressure differential across damper piston 48 and thus across the valve 50, forcing fluid into rebound chamber 66 through the valve 50. This is important because, if a sufficiently large pressure differential does not occur, rebound chamber 66 will become starved for fluid, resulting in cavitation. In addition, the increase in pressure creates a high pressure zone against which the compression fluid moving from compression chamber 64 to air/oil reservoir chamber 67 must do work. This creates position-sensitive compression damping. That is, as fork strut 16 compresses, its movement will be met with progressively increasing resistance.

The third function served by the increase in the pressure of the air/oil reservoir chamber 67 is to form a gas-assist spring. As described previously, air/oil reservoir chamber 67 is partially filled with hydraulic oil, on top of which is disposed a volume of gas, preferably air. As the volume of air/oil spring reservoir chamber 67 is decreased, the air volume is pressurized, creating an air spring which acts on the fluid surface and assists compression spring 36 in resisting compression of fork strut 16. By virtue of the gas-assist spring, the spring rate of compression spring 36 can be tuned to be more progressive by increasing the amount of oil in fork strut 16. In addition, the spring- assist provides a "hook" or transition to a stiffer spring rate as fork strut 16 approaches bottom-out. This "hook" acts as part of a bottom-out cushioning mechanism (described in more detail below) and ensures a smoother transition of the suspension system to rebound.

Damper dome 72 is highly beneficial in that it regulates the action of fluid flowing into air/oil reservoir chamber 67 during the compression of fork strut 16. In the absence of the damper dome 72, the fluid rushing through damper rod 46 from compression chamber 64 to air/oil reservoir chamber 67 normally would be ejected directly toward top cap 42 during compression. This would drive fluid near damping piston 48 upward, while forcing the air disposed above the fluid downward. Air near damping piston 48 would be drawn into rebound chamber 66, causing a reduction or even elimination in damping and, as a result, a potentially extreme deterioration in suspension performance. Damper dome 72 is designed to deflect the fluid to reduce the speed of, or otherwise inhibit, its movement toward the air chamber. Damper dome 72 preferably is designed to eject the fluid sideways keeping it near the top of damper piston 48. Alternatively, however, damper dome 72 may be formed to deflect the fluid in a radial direction trajectory at a low aspect from the top of damper piston 48.

A hydraulic bottom-out cushioning mechanism is provided to avoid potentially damaging and dangerous effects from the bottoming-out of strut 16 during compression. As first tube 20 and rod guide 68 move toward second end 65 of second tube 24, they close off port 52 in damper rod 46. As port 52 is being restricted as bottom-out is approached, damping increases until port 52 is fully closed off. At this point, the fluid no longer has an exit path from compression chamber 64 effectively preventing strut 16 from compressing further. In addition, the gas-assist spring described previously aids to progressively increase the resistance of the suspension system to compression as bottom-out is approached. This hydraulic bottom-out cushioning mechanism allows for a smooth transition to bottom-out without damage, discomfort, loss of control and/or the loud "clunk" or "thunk" that may result in suspension systems using typical bicycle suspension bottom-out cushioning mechanisms.

During the rebound stroke, compression spring 36, aided by the gas-assist spring formed in air/oil reservoir chamber 67, drives first tube 20 away from second tube 24 (in direction R as shown in FIG. 4) . As this occurs, rebound chamber 66 decreases in volume and compression chamber 64 increases in volume. This produces high pressure in rebound chamber 66 and low pressure in compression chamber 64. The fluid in rebound chamber 66 is prevented from flowing through the piston by valve 50, and instead flows through ports 52 and 54 in damper rod 46. In the preferred embodiment of the present invention, port 52 is larger than port 54, and the size of port 54 determines the amount of damping provided in rebound. The size of port 54 is selected based on the particular suspension system configuration, travel requirements, and user weight and preferences.

The low pressure in compression chamber 64 and the high pressure in oil/air reservoir chamber 67 during rebound force fluid back down through damper dome 72, through damper rod 46 and into compression chamber 64.

It will be appreciated that one of the strongest attributes of the suspension system of the present invention is that it has been designed to have a low cost of manufacture. Specifically, damper rod 46 preferably is made from thin-walled drawn steel or aluminum tubing. Damper piston 48 is press-fit onto damper rod 46, and first end 53 of damper rod 46 is swaged over (indicated by "S" on FIG. 5) to prevent damper piston 48 from being pulled off of damper rod 46. As shown in FIG. 5, a knurl K may also be added at about first end 53 of damper rod 46 to prevent the possibility of damper piston 48 sliding down damper rod 46. Ports 52, 54 are punched into damper rod 46. This design lends itself to screw machine manufacturing. A drawn surface finish is acceptable for damper rod 46.

In addition, damper piston 48 preferably is a plastic injection-molded part. As illustrated in FIG. 6a, second end 76 of damper piston 48 preferably is flexible prior to being pressed into engagement with damper rod 46. This flexibility is desirable to allow valve 50, preferably including check plate 60 and spring washer 62, to be placed over ridge 82 of second end 76 of damper piston 48 prior to assembling damper piston 48 and piston rod 46. Slotted section 84 in damper piston 48 also aids in permitting second end 76 of damper piston 48 to collapse. Once damper piston 48 is pressed onto damper rod 46, valve 50 cannot be removed.

As illustrated in FIG. 7, an insert 85 may be used to connect damper rod 46 to second end 65 of second tube 24. Preferably, insert 85 is threaded and is a screw machine part. Insert 85 is designed to be crimped, such as by roll-crimping, as shown at "X" in FIG. 7, into second end 55 of damper rod 46. Insert 85 preferably interfaces with second end 55 of damper rod 46 by means of an 8mm bolt. The use of an insert such as insert 85 permits the use of thin-walled tubing for damper rod 46. Rod guide 68 and rod guide retainer 70 may be plastic injection-molded parts. Rod guide 68 preferably has a second end 86 that is flexible so that it can pass through an opening 88 in second end 45 of first tube 20. Rod guide 68 has a slotted section 90 which aids in permitting second end 86 of rod guide 68 to collapse for fitting second end 86 through opening 88 in first tube 20. Second end 86 of rod guide 68 has a flange 92 designed to matingly engage a recess 94 formed on rod guide retainer 70. Once second end 86 is placed through opening 88, it is pressed through rod guide retainer 70 and snaps into place as flange 92 seats in recess 94, as illustrated in FIG. 8b. The insertion of damper rod 46 through rod guide 68 prevents second end 86 of rod guide 68 from collapsing, thereby securing rod guide 68 and rod guide retainer 70 in place.

Rod guide retainer 70 preferably has a hemispherical surface 96 which allows damper rod 46 to rock inside first tube 20 to a limited extent. This allows for misalignment in true position between damper rod 46, first tube 20 and second tube 24.

While there are shown and described herein certain specific structures comprising aspects of the invention, it will be clear to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept, and that the same is not limited to the particular forms herein shown and described.

Claims

WHAT IS CLAIMED IS;

1. A bicycle suspension system comprising: a first tube having a first end mounted to a portion of the bicycle, and a second open end; a second tube having a first open end and a second end, wherein said first tube is disposed to extend through said first end of said second tube and be in telescoping slidable engagement with said second tube; biasing means for resisting sliding movement of said second end of said second tube towards said second end of said first tube; a hollow, tubular damper rod mounted to said second end of said second tube and extending through said second end of said first tube to define a free damper rod end within said first tube, said damper rod having an inner passageway; and a damper dome having spaced-apart axial first and second ends and a peripheral surface extending therebetween, said second axial end being mounted on or adjacent to said free damper rod end, wherein said damper dome is formed with at least one passage extending from said peripheral surface and through said second axial end to communicate with said inner passageway of said damper rod.

2. A bicycle suspension system as in claim 1, further comprising a fluid partially filling said first tube to define an air pocket therein.

3. A bicycle suspension system as in claim 1, wherein said first end of said first tube is mounted to a fork crown of the bicycle.

4. A bicycle suspension system comprising: a first tube having a first end mounted to a portion of the bicycle, and a second open end; a second tube having a first open end and a second end, wherein said first tube is disposed to extend through said first end of said second tube and be in telescoping slidable engagement with said second tube; biasing means for resisting sliding movement of said second end of said second tube towards said second end of said first tube; and a hollow, tubular damper rod being mounted to said second end of said second tube and extending through said second end of said first tube into said first tube, said damper rod being formed with at least one port, wherein said port being located in proximity to said second end of said second tube such that said first tube may be telescopically slid into said second tube sufficiently to have said second end of said first tube be interposed between said port and said second end of said second tube with said port being fully enclosed by said first tube.

5. A bicycle suspension system as in claim 4, further comprising a fluid partially filling said first tube to define an air pocket therein.

6. A bicycle suspension system as in claim 4, wherein said first end of said first tube is mounted to a fork crown of the bicycle.

7. A bicycle suspension system as in claim 4, wherein said damper rod defines a free damper rod end within said first tube.

8. A bicycle suspension system as in claim 7, wherein said port being located in proximity to said second end of said second tube being a first port, and wherein said damper rod being formed with at least one second port in proximity to said free damper rod end.

9. A bicycle suspension system as in claim 8, wherein said first port is larger than said second port.

10. A bicycle suspension system as in claim 7, further comprising a damper dome having spaced-apart axial first and second ends and a peripheral surface extending therebetween, said second axial end being mounted on or adjacent to said free damper rod end, wherein said damper dome is formed with at least one passage extending from said peripheral surface and through said axial end to communicate with an inner passageway of said damper rod.

11. A bicycle suspension system comprising: a first tube having a first end mounted to a portion of the bicycle, and a second open end; a second tube having a first open end and a second end, wherein said first tube is disposed to extend through said first end of said second tube and be in telescoping slidable engagement with said second tube; biasing means for resisting sliding movement of said second end of said second tube towards said second end of said first tube; a hollow, tubular damper rod mounted to said second end of said second tube and extending through said second end of said first tube to define a free damper rod end within said first tube; a damping piston mounted on or adjacent to said free damper rod end, said damping piston being in sealing engagement with said first tube; and, sealing means disposed between said damper rod and said second end of said first tube to prevent fluid passage therethrough; wherein a first chamber is defined between said second end of said second tube and said second end of said first tube, a second chamber is defined between said second end of said first tube and said damping piston, and a third chamber is defined between said damping piston and said first end of said first tube, and wherein a fluid is disposed to fully flood said first and second chambers, and to partially flood said third chamber with an air pocket being defined therein.