Background of the Invention

Field of the Invention

The present invention relates to a shock absorbing system for the front fork of bicycles. More specifically, the present invention relates to such a shock absorbing system having a spring stop that is interchangeable to adjust the spring rate and thus, the resistance of the shock absorbing system.

Description of Related Art

Front fork suspensions have been known for motorcycles for a long time and with the invention of Turner U.S. Patent No. 4,971,344, became practical for use on bicycles, and have since found widespread use, particularly on mountain bicycles. In the suspension of the Turner patent, air pressure is used to adjust the hydraulic fork to compensate for rider weight variations or to produce a firmer or softer ride. However, because the extension damping performance of the suspension is directly related to the amount of air pressure in the system, adjusting of the air pressure to compensate for a rider's weight could adversely affect the

extension damping charaαeristics of the suspension, and no other means existed to vary the performance charaαeristics of the suspension, nor was the suspension designed to produce differing performance charaαeristics under different loading conditions apart from an ability to "lockout" low level forces of the type produced by pedaling while allowing the fork to react to high impact forces.

In Turner U.S. Patent No. 5,186,481, the fork suspension of the above-mentioned Turner patent was improved to enable varying of the preload on a coil-type compression spring, that aαs to hold a compression valve plate of a metering valve located between upper and lower hydraulic chambers in a closed position until a predetermined force level is reached at which time it pops open to allow flow through the valve. In particular, by turning of an adjustment rod so as to screw it more or less into the metering valve, the coil-type compression spring is caused to contract or expand, thereby changing the force required to open the compression metering valve, and allowing a wide range of adjustments for adapting the suspension to widely differing circumstances of rider weight and riding experience. However, this adjustability does not affeα the suspension beyond setting the threshold level at which compression of the fork will commence.

Other shock absorbing bicycle forks have since been developed which allow for personalized adjustment of the performance charaαeristics of the fork. For example, Wilson et al. Patent No. 5,269,549, discloses a suspension for the front wheel of bicycles in which a spring aαion is used for shock absorbing purposes and is obtained by a rod-mounted arrangement of stacked elastomeric pads which are disposed between the ends of the fork strut tubes to absorb shocks by

deformation thereof. By using different combinations of pads of different duro meters, resilience characteristics and/or lengths, the shock absorbing characteristics can be changed in accordance with the rider's weight and the conditions under which the bicycle will be ridden. However, such an arrangement simply is incapable of achieving the same kind of ride as a shock absorber having two or more springs arranged in series, and with which a different combined spring rate charaαeristic is achieved during a first compression period than during a subsequent, second compression period. Chen U.S. Patent No. 5,284,352 discloses a compression-adjustable bicycle shock absorbing front fork which, like that of Wilson et al., utilizes a rod-mounted arrangement of interchangeable stacked elastomeric pads, to which a compression coil spring is added. In addition to the adjustability afforded by the ability to change elastomeric pads, the initial compression characteristics and the travel length which the strut can be compressed can be adjusted by rotating of a mounting member which aαs to reduce or expand the initial height of the stacked pads and spring. Furthermore, washers are disposed between the rubber pads to distribute the external loading to the pads when the forks struts are compressed. Although, the Chen reference provides a multiple spring design using different types of spring elements, the device disclosed in Chen does not allow the user to adjust the spring rate characteristics of the shock absorber as a function of fork compressive travel.

Furthermore, it is recognized that coil springs and elastomeric pads have compression response characteristics that are different. Since a coil spring has a constant spring rate and an elastomeric pad has a spring rate which increases as it is compressed, a coil spring will provide a linear

increase in force per unit of compression, while an elastomeric pad will produce an exponential increase in force per unit of compression. Thus, for some riders (weight or skill level) and/or riding conditions, a coil spring might produce a more suitable ride while in others an elastomeric pad or pads might prove more desirable. However, neither the Wilson et al. nor the Chen suspensions are designed to effectively alter the spring rate charaαeristics of the suspension by removing the effeα of one spring of a two spring design at a controllable point in the compression stroke of the telescopic fork suspension. The Chen suspension is provided with a coil spring in addition to the rod-mounted pad arrangement, however, its function is primarily to allow the permissible degree of fork travel to be adjusted, and does not change the compression characteristics as a funαion of fork travel in a least one spring of a two spring design. By adjusting the spring force as a funαion of fork travel a user can more effectively adjust the stiffness of the front fork suspension and achieve the desired amount of front fork resistance.

In UK Patent No. 677,058 to Kronprinz, a motorcycle suspension is disclosed which includes a piston which acts on a column of rubber or a similar elastϊcally deformable material and a coil spring which are stacked in one of a pair of telescoping tubes, the piston being conneαed to the other of the telescoping tubes. This suspension system is designed so that the piston presses directly on the rubber column after a partial stroke so that the metal spring is then cut out and the heavier shocks are absorbed by the rubber column alone. The suspension system of Kronprinz, however, does not allow a user to adjust the degree of compressive travel which occurs before the coil spring component is rendered inactive. Moreover, the system is not designed to allow the

plunger or any other parts to be interchanged to adjust the firmness of the suspension and thus, accommodate different levels of rider skill or terrain roughness.

One suspension system which allows such an adjustment of the spring component is found in commonly owned U.S. Patent Application No. 08/341,134 filed November 16, 1994. This application discloses a front fork for a bicycle having both a spring type shock absorbing unit and a hydraulic shock damping unit with variable and adjustable damping characteristics. The spring elements of spring type absorbing unit may be of elastomeric pad or coil spring type. In one embodiment, the spring type shock absorbing unit includes a plurality of interchangeable spring elements with a spacer between them. An adjustment device has a stop sleeve that can be displaced toward or away from the topmost spacer to increase or decrease the amount of travel required to render the top spring element inaαive during compression due to engagement of the stop sleeve on the topmost spacer. Although this suspension system allows the user to adjust the travel point at which the spring rate is increased by the rendering of one spring elements inactive, the .amount of adjustment is limited and the adjustment mechanism itself is relatively complex and costly.

Thus, there is still a need for a shock absorbing system for a bicycle fork which allows a user to adjust the spring force of a series-type multi-spring design to desirably controllably alter the performance charaαeristics of the shock absorbing system as a function of compressive travel in a simple and inexpensive manner. Furthermore, there is a need for a shock absorbing system which allows for a wide range of spring rate adjustments to adapt the suspension to widely differing circumstances of

terrain, rider weight and riding experience, yet, at the same time being practical and economic for use on bicycles by the average rider thereof.

Summary of the Invention

It is a primary object of the present invention to provide a front fork suspension for bicycles which has a shock absorbing system having a spring assembly with at least a first and second spring element arranged in series, wherein one spring element can be rendered inaαive, resulting in an increase in the stiffness of the spring assembly, at a point in the compressive travel of the suspension which is adjustable so as to adapt the suspension to widely differing circumstances of rider weight and riding experience, as well as the type of riding terrain anticipated.

It is a further objeα of the present invention to provide a front fork suspension for bicycles that allows a user to effeαively modify the performance characteristics of the suspension, yet, at the same time being practical and economic for use on bicycles by the average rider thereof.

It is a more specific objeα of the present invention to provide a bicycle suspension which utilizes interchangeable spring stops of various sizes which engage a spacer between two spring elements to effeαively adjust the resistance of the fork to further compression. These and other features of the present invention are obtained in accordance with preferred embodiments in which a shock absorbing system having a spring assembly formed of a series-type arrangement of at least a first and second spring element stacked with a spacer therebetween, and further, wherein a spring stop is either attached to the

tube end cap of the front suspension fork or the spacer positioned between the first and second spring element, and which may be interchanged with a longer or shorter spring stop to adjust the point at which the resistance of the front fork suspension to further compression changes. The second spring element may be stiffer than the first spring element or may have a different type of spring rate characteristic. When a force is applied to the front fork, the first spring element, e.g., a coil spring, is compressed at a fairly linear rate until the spring stop abuts the tube end cap or the spacer between the first spring element and the second spring element. From this point on, only the second spring element (and any subsequent spring elements), e.g., an elastomeric column or pad stack, compresses with a spring rate that is substantially greater that the combined effect of the series arrangement prior to inaαivation of the first spring element. This changeover can also be used to cause the spring resistance increase to change from one that increases at linear rate to one that exponentially increases the resistance of the front fork suspension. A longer spring stop increases the spring rate sooner and a shorter spring stop delays the increase changeover.

In accordance with one embodiment, the first and second spring elements may be interchanged within each tube of the front fork.

These and further objeαs, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.

Brief Description of the Drawings

Fig. 1 is a perspective view of a front fork for a bicycle incorporating a shock absorbing system of the present invention;

Fig. 2 is a vertical cross-sectional view of one strut of the Fig. 1 fork including a shock absorbing system in a preferred embodiment;

Fig. 3 is a vertical cross-seαional view of one strut of the Fig. 1 fork including a shock absorbing system in an alternative embodiment;

Fig. 4 is a vertical cross-seαional view of one strut of the Fig. 1 fork including a shock absorbing system in another alternative embodiment;

Figs. 5a and 5 b are an exploded vertical cross-seαional view of the shock absorbing systems illustrated in Figs. 2 and 4, respectively;

Fig. 6 is a graph of the spring stop transitions as a function of spring force and fork travel in accordance with the preferred embodiment of the present invention; and

Fig. 7 is a graph similar to that of Fig. 6, but for the Fig. 3 embodiment.

Detailed Description of the Preferred Embodiments

Fig. 1 shows a shock absorbing front fork 1 for a bicycle of the type having a pair of telescoping struts 3, upper tubes 4 of which are interconnected by an upper crown 5 to a steerer tube 7 at their upper ends. The lower tubes 8 of struts 3 telescopingly receive the upper tubes

4 in the upper end thereof, and have mounting brackets 10 to which an

axle of a front wheel (not shown) is attached at the bottom end the struts.

A shock absorbing arrangement 15 is disposed within at least one of the telescoping struts 3, it having been found to be sufficient (and acceptable from a fork flexing standpoint) to provide shock absorption in only one strut 3 of fork 1, it also being possible to provide the same or a different type of shock absorption, or none at all, in the other strut 3. Referring now to Fig. 2, the shock absorbing arrangement 15 is disposed in upper tube 4 and includes a first spring system 17 and a second system 19. Although the first and second spring systems may be arranged in any order within tube 4, the preferred embodiment is discussed with the first spring system positioned above the second spring system.

In the preferred embodiment of Fig. 2, the first spring system 17 includes a coil spring 27 which is supported on a spacer 25, and a spring stop 29 formed of a rigid plastic material. Spring stop 29 may be formed as part of tube end cap 31 or may be detachably secured to it via, for example, a screw or snap-on conneαor.

Coil spring 27 can be any conventional spring having any desired spring force to provide adequate suspension for bicycle forks. Spacer 25 is positioned below coil spring 27 and includes a protrusion 25a which partially extends upward through the first winding of coil spring 27 to center spring 27. Spacer 25 may have any shape that will facilitate centering of the coil spring, as discussed above, and will provide adequate load distribution between the spring systems 17, 19. The spacer 25 is made from a rigid material, such as plastic or metal, that will not deform under the forces applied to it during use.

Second spring system 19, in the preferred embodiment, includes an elastomeric column 21 positioned in the lower portion of tube 4. Elastomeric column 21 may be a single rod of elastomeric material or maybe a series of elastomeric pads and spacers as known from the art mentioned in the Background portion of this application (such being represented by dash lines on column 21 in Fig. 2). The lower end of the elastomeric column 21 is supported on a spring compressor 23, the bottom end of which is rigidly connected to the lower tube 8 shown in Fig. 1, and the spacer 25 rests on the upper end of the elastomeric column 21.

Tube end cap 31 threadingly engages the top end of tube 4. This cap may be removed in order to retrieve or exchange the contents of tube 4. Tube end cap 31 is also made from a rigid material, such as metal or plastic, that will not deform under extreme pressure. When secured onto tube 4, tube end cap 31 is in an abutting relationship with coil spring 27, and applies an initial preload to the spring systems 17, 19.

Spring stop 29 is positioned in. the upper portion of tube 4 and is an essential component of first spring system 17. In the preferred embodiment, spring stop 29 is rigidly attached to the center of the bottom face of tube end cap 31. In this embodiment, spring stop 29 axially extends into the chamber of tube 4 and more specifically, into the inner passage of coil spring 27. Spring stop 29 is positioned direαly opposite spacer 25 and during compression of coil spring 27, moves towards spacer 25 until they abut, after which coil spring 27 is rendered inactive and further compression of the fork causes compression of only the second spring system 19, between the spring stop 29 and spring compressor 23.

The present invention is not limited by the shock absorbing system illustrated in Fig. 2. On the contrary, numerous other embodiments of the present invention are possible, some of which are discussed in detail below. Fig. 3 illustrates an alternative second spring system 19 design which may include a coil spring or other similar spring-type device. In the coil spring design, a spring 33 is provided on the spring compressor 34 and supports spacer 36. Spring compressor 34 is similar to spring . compressor 23 discussed above, however, the top face of spring compressor 34 is formed with a shoulder to receive and center spring 33. Spacer 36 is formed to receive and center both spring 33 at its bottom face and spring 27 of first spring system at its top face in the same manner as connector 25 discussed above.

Fig. 4 is directed to an alternative embodiment for the first spring system discussed in detail with respect to Fig. 2. In this design, a combined spring stop and spacer 35 is positioned in tube 4, so that its bottom face is supported on the top face of the elastomeric column 21. The bottom portion of coil spring 27 rests on and abuts the spacer portion of the spring stop and spacer 35, as shown in Fig. 4. Spring stop and spacer 35 includes a protrusion 35a which partially extends upward through the inner portion of spring 27 and serves the function of stop 29 in the first embodiment. Tube cap 37 is provided to secure the shock absorbing system within tube 4. The tube cap 37 threadingly engages the top end portion of the upper tube 4 and is removable to allow a user to access the components in tube 4. The upper portion of coil spring 27 is in an abutting relationship with the bottom face of tube cap 37. Moreover, in this embodiment, spring stop and spacer 35 moves toward

tube cap 37 during compression of coil spring 27, until they are in an abutting relationship, at which point the coil spring 27 is rendered inactive as in the first embodiment.

Figs. 5a and 5b are exploded vertical cross-sectional views of the shock absorbing systems illustrated in Figs. 2 and 4, respectively. These drawings reflect the interchangeability of the present invention which is discussed in detail below. The spring stop spacers and the second spring system of present invention may be changed by the user to alter the performance of the front fork suspension. Referring to Fig. 5a, spring stop 29 is rigidly attached to the tube end cap 32 when secured within tube 4. However, the spacer may be interchanged with a longer or shorter stop depending the performance desired by the user (the different lengths being represented by dashed lines on stop 29 in Fig. 2). The effect of the different length spring stops on performance is discussed in detail with respect to Figs. 6 & 7. Spring stop 29 may either be permanently attached to tube end cap 31 or removably attached thereto as noted, above. In the former design, the user would unscrew and remove the entire end cap and spring stop arrangement and replace it with an end cap having a different length spring stop affixed thereon. The present invention allows for easy removal and replacement of the end cap and shock absorbing components to avoid undesirable downtime. In the latter design discussed above, the user would simply detach the spring stop 29 from tube end cap 31 and replace it with a different length spring stop. The end cap and stop arrangement would then be threadingly secured back onto tube 4. One skilled in the art should appreciate that any means for attachment of the spacer to the end cap may be used on order to facilitate a quick and

effective exchange of the spring stop spacer components. Likewise, springs 27 of different spring constants or elastomeric pads of different durometers may be interchangeably used as well, in combination with the exchanging of the spring stops. Fig. 5b illustrates the alternative embodiment of the present invention shown in Fig. 4, wherein the spring stop is combined with the spacer. In this embodiment, a user would unscrew tube cap 37 from the upper tube 4 to remove or exchange spring stop and spacer 35. The user would then remove spring 27 and spacer 35 from tube 4. At this point, the user would replace stop and spacer 35 with one of a different length and then replace spring 27 and tube cap 37. The interchangeability of the present invention allows a user to quickly adjust the performance characteristics of the front fork suspension.

As mentioned in the Background portion above, coil springs and elastomeric pads have compression response characteristics that are different, a coil spring having a constant spring rate and an elastomeric pad having a spring rate which increases as it is compressed, so that a coil spring will provide a linear increase in force per unit of compression, while an elastomeric pad will produce an exponential increase in force per unit of compression. Thus, for some riders (due to weight or skill level) and/or riding conditions, a coil spring might produce a more suitable ride while in others an elastomeric pad might prove more desirable, a coil spring being preferable for less severe riding conditions and an elastomer or stiffer spring for more severe conditions. Furthermore, the use of only an elastomer spring for larger shocks takes advantage of the damping characteristics of such a spring as compare to a coil spring.

Furthermore, when springs are arranged in series, the spring rate of the series arrangement is less than that of the individual springs. For example, if springs 27 and 29 both had a spring rate of 20 lbs/in., arranged as shown in Fig. 3, the combined spring rate would be only 10 lbs/in., so that rendering of spring 27 ineffeαive eliminates the series arrangement so that the effeα of the 20 lbs./in. spring rate of spring 33 acts against compression of the fork.

From these standpoints, the use of different length spring stops in accordance with the present invention is used to change the performance of the front fork suspension after a predetermined amount at fork travel.

The effect of varying the spring stops is illustrated in Figs. 6 and

7 which show the stiffness of a front fork suspension incorporating, respectively, the Fig. 2 and 3 embodiments of the present invention as a function of spring force and fork travel. As depiαed in Fig.6, a longer spring stop prevents further compression of the coil spring 27 and thus, stiffens the front suspension fork faster, i.e., with less fork travel than a short or medium length one. A medium length spring stop increases the amount of fork travel before the coil spring is rendered ineffective, softening the ride of the front fork suspension. To further soften the ride and postpone implementation of the stiffness increase, a short stop should be used.

A spring stop allows the coil spring to travel a predetermined distance until the stop "bottoms out" or abuts another part of the suspension system, i.e. spacer or top cap, such that the spring 27 is no longer allowed to compress. Additionally, in each case represented in Fig. 6, since only the elastomeric spring of second spring system 19 remains active once the stop terminates compression of the first spring

system, the stiffness of the shock absorbing system then increases on an exponential basis instead of a linear one. While the spring force is substantially linear during initial compression of shock absorbing arrangement 15, i.e., while the coil spring in the first spring system 17 is able to compress, after the coil spring is no longer able to travel, the elastomeric column 21 works alone to resist additional compression forces applied to the shock absorbing system, doing so at a spring rate that increases exponentially. Thus, the advantage of this embodiment of the present invention is that fork travel point at which a changeover between spring systems occurs can be adjusted to achieve the desired performance from the front suspension simply by replacing the spring stop with another in terms of both an increase in the stiffness the fork suspension and the rate at which it continues to stiffen.

In the case of the use of two coil springs as shown in Fig. 3, as represented in Fig. 7, the fork can still be caused to stiffen at an adjustable point. However, in this case, the further stiffening of the suspension is less pronounced since the resistance coil spring 33 increases at a linear rate instead of the exponential one of an elastomeric spring. Thus, the ability to use two coil springs in series instead of a coil spring and elastomer spring in series further adds the degree to which the compression characteristics of the fork suspension can be customized to the particular rider the terrain conditions anticipated on a specific ride or portion thereof.

While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. For example, in

the illustrated embodiments, the spring stop 29, 35 is a rod inserted in and surrounded by the coil spring 27 of the first spring system. However, it is also possible for the stop to be a hollow cylindrical member within which the coil spring 27 telescopingly is received as a fixed length counterpart to the expansible and contractible stop shown in the Fig. embodiment of the above-described co-pending U.S. Patent Application No. 08/341,134. Therefore, this invention should not be viewed as being limited to the details shown and described herein. Instead, this invention includes all such changes and modifications as are encompassed by the scope of the appended claims.