GB2316047A - Shock absorber for a bicycle front fork - Google Patents

Abstract

A shock absorber mechanism 10 is mounted between the handlebar stem 4 and the fork stem 5 of a bicycle and includes a sleeve 11, a spring 18 and a friction member 20. The sleeve 11 is mounted to the lower end of the handlebar stem 4. The upper portion of the fork stem 5 slides freely but does not rotate relatively to the sleeve 11. The spring 18 is arranged between the sleeve 11 and the fork stem 5. The friction member 20 is mounted at the lower end of the sleeve 11 and can be freely installed and removed as well as slide on the outer peripheral surface of the fork stem 5. One purpose of the present invention is to allow for easy adjustment of the buffering and/or dampening characteristics depending on bicycle riding conditions and rider requirements.

Description

SHOCK ABSORBER FOR A BICYCLE FRONT FORK The present invention relates to a shock absorber to be incorporated into the mechanism that supports the front wheel of a bicycle on the frame of the bicycle. In particular, the invention pertains to a damping and buffering shock absorber mechanism mountable between the stem of a bicycle handlebar and the front wheel fork of a bicycle.

Shock absorber mechanisms for motorcycles are well-known. For instance, shock absorber mechanisms have been mounted to the portion of the front of the motorcycle frame which supports the front fork and the handlebar stem.

Further, such shock absorber mechanisms have been provided as a part of the handlebar stem and the fork stem.

On a motorcycle, the shock absorber mechanism typically requires two parallel units because of the size, weight and complexity of the motorcycle itself. However, bicycles are smaller and lighter, generally, than motorcycles and therefore the complexity and massiveness of motorcycle shock absorber systems are inappropriate.

Mountain bikes, in particular, experience shocks due to uneven surfaces and benefit greatly from shock absorbers.

However, motorcycle shock absorber systems, being massive and complex are difficult to arrange properly on a mountain bike frame.

Conversely, a handlebar stem type shock absorber mountable between the handlebar stem and the fork stem of the front of a mountain bike could absorb impacts using one shock absorber mechanism, if one would fit into the small dimensions of a bicycle frame. Such a mechanism would have the advantage of less parts and lighter weight. A well-known example of this type of shock absorber mechanism is the HeadShokm manufactured by the American company Cannondale. In the HeadShok > , there is an oil/air pressure system and a urethane rubber system. The oil/air pressure system obtains a buffering effect using an air pressure cylinder and a dampening effect using an oil pressure cylinder. Further, the urethane rubber system obtains a buffering effect and a dampening effect using urethane rubber.

Because the conventional oil/air pressure system shock absorber mechanism uses an oil cylinder, if an oil leak occurs due to deterioration with age or damage to the packing, the packing must be replaced. This is something that makes maintenance difficult. Moreover, the urethane rubber characteristics of the urethane rubber system change due to deterioration with age. Further, only one material is used for both the buffering effect and the dampening effect. Consequently, the dampening and buffering characteristics cannot be independently changed. Settings for the buffering effect and the dampening effect, depending on the road surface and usage conditions, cannot be changed or fine tuned.

One of the purposes of the present invention is to make it easy to change the characteristics of a buffering and dampening assembly depending on riding conditions or requirements of a bicycle rider.

According to the present invention, a shock absorber mechanism comprises: a sleeve rotatably mountable into a head tube of a bicycle frame, said sleeve having upper and lower holes formed therein, with a handlebar stem being mountable in said upper hole and a fork stem for supporting a front wheel being slidably but non-rotatably mountable in said lower hole; a removable elastic member disposed axially in said lower hole, said elastic member being compressible and extensible within said lower hole in response to slidable movement of said fork stem; a removable friction member retained at a lower end of said lower hole at least partially within said sleeve, said friction member producing friction in response to sliding movement of said fork stem; and a removable drop-check member being disposed at the lower end of said lower hole and retaining said fork stem and said elastic member within said lower hole.

The elastic member may be, for instance, a removable spring disposed axially in the lower hole. A removable cap ring may be disposed at a lower end of the drop-check member, the friction member being disposed within the dropcheck member and being retained therein by the cap ring.

The sleeve may include bottom and top end bearing assemblies for rotatably positioning and supporting the sleeve within a bicycle head tube, with the friction member being retained in the bottom end bearing assembly.

In use, the fork stem mounted to the front wheel slides inside the sleeve in response to a load from the road surface. The buffering characteristics during this time can change depending on the elasticity constants of the elastic member. Further, the sliding motion of the fork stem is controlled by the friction member. Because of this, the dampening characteristics can change depending on the type of friction material for the friction member, and can also change by changing the shape of the friction material for the friction member and altering the sliding condition. Consequently, the buffering characteristics and the dampening characteristics can separately and freely change depending on the conditions by replacing the elastic member and the friction member.

Maintenance can be simple.

The attention of the reader is here directed to the fact that the present application has been divided from application no. 9501440.3 (publication no. 2286566) which has claims directed to the provision of a friction member retainer adjustably fastened into a bottom end of the lower hole such that the friction member retainer can variably deform the friction member.

An embodiment of a shock absorber mechanism, in accordance with the present invention, will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary side elevation of a mountain bike provided with a front fork shock absorber mechanism in accordance with the present invention; Fig. 2 is a fragmentary, partial cross-section of the shock absorber mechanism taken along the line II-II in Fig.

1, on a slightly enlarged scale, looking in the direction of the arrows; and Fig. 3 is a fragmentary isometric view of a lower portion of the shock absorber mechanism, showing several of the parts of the mechanism partially disassembled.

In the accompanying drawings, where like reference numerals denote corresponding parts throughout, Fig. 1 represents a front portion of a mountain bike 1. The front of a main frame 3 of the mountain bike 1 includes a head tube 2. A handlebar stem 4 is rotatably disposed within the head tube 2 which supports handlebars 8. A fork stem 5 is coupled to the lower portion of the handlebar stem 4 via a shock absorber mechanism 10, which is described further below with reference to Fig. 2. A front fork 6 extends from the fork stem 5 and supports a front wheel 7 in a manner well known in the art.

Fig. 2 shows the shock absorber mechanism 10 supported in the head tube 2. The shock absorber mechanism 10 includes a sleeve 11, rotatably supported by bearings 12a, 12b disposed along the top and bottom rims of the head tube 2. The sleeve 11 includes a first hole lla in its upper portion, open to the upper end of the sleeve 11. The sleeve 11 also includes a second hole llb formed in its lower portion, open to the lower end of the sleeve 11. A bearing cup 12c for the bearing 12a is screwed onto the periphery of the upper portion of the sleeve 11.

The handlebar stem 4 is retained in the hole lla of the sleeve 11 and may be installed and removed via an elevating wedge 13 within the upper end of the sleeve 11.

The hole llb of the sleeve 11 is grooved with internal splines 14. The upper end of the fork stem 5 extends into the hole llb and is provided with external splines 15 which engage the splines 14. The fork stem 5 is thus slidably but non-rotatably joined with the sleeve 11, and thereby coupled with the handlebar stem 4.

The shock absorber mechanism 10 also includes cushions 16, 17, preferably made of an elastic material such as urethane, rimming upper and lower ends of the internal splines 14 along the interior of the sleeve 11. The shock absorber mechanism 10 further includes a compressed spring 18 acting as a damper between the sleeve 11 and the fork stem 5.

A threaded drop-check sleeve 19 of the shock absorber mechanism 10, for retaining the fork stem 5 from dropping out of the sleeve 11, is screwed into the opening at the lower end of the sleeve 11. A bearing cup 12d is formed along a rim of the drop-check sleeve 19 corresponding to the bearing 12b. A free bushing 20 is disposed as a buffering friction material along the inner peripheral surface of the drop-check sleeve 19.

As shown in Fig. 3, the free bushing 20, which can be made of urethane rubber, for example, is generally tubular, but is slit by an axial notch 22. The free bushing 20 is in slidable contact with the outer peripheral surface of the fork stem 5, and by friction, the free bushing 20 serves as a buffer to limit the movement of the handlebar stem 4 relative to the fork stem 5. A cap ring 21, supplied to provide independent access for replacing the free bushing 20, is fastened into the lower end of the drop-check sleeve 19 by any of a variety of means, such as screws (not shown) which may extend through holes 21a into corresponding holes (not shown) in the threaded drop-check sleeve 19.

Alternatively, the cap ring 21 may be provided with threads (not shown) and unscrewed from the drop-check sleeve 19.

Procedures for replacing the spring 18 and the free bushing 20 are as follows.

To replace the spring 18, and in order to change the dampening characteristics of the shock absorber 10, peripheral parts on the front of the bike 1 such as the brake cable are first removed, as necessary. Without unfastening the cap ring 21, the drop-check sleeve 19 can then be unscrewed as an assembly containing the free bushing 20 and withdrawn from the sleeve 11. Consequently, the fork stem 5 can be dropped from the sleeve 11. With the fork stem 5 removed from the sleeve 11, the spring 18 can be easily drawn out and replaced. The fork stem 5, housing a new spring 18, is then inserted into the sleeve 11. To complete the operation replacing the spring 18, the drop-check sleeve 19 is screwed into the lower end of the sleeve 11.

To replace the free bushing 20, on the other hand, in order to restore frictional dampening characteristics lost to abrasion, the cap ring 21 is unfastened from the drop-check sleeve 19, as shown in Fig. 3. The cap ring 21 can then be lowered to rest on the fork 6 at the base of the fork stem 5. Using a suitable tool, the free bushing 20 is then extracted from the drop-check sleeve 19. At this point, since the free bushing 20 is broken by the notch 22, it can be opened and easily removed from the fork stem 5.

A fresh free bushing 20 can be installed inside the drop-check sleeve 19 by first simply spreading it apart and pushing it onto the fork stem 5. The cap ring 21 is then slid to press the free bushing 20 into the drop-check sleeve 19, and refastened to the drop-check sleeve 19.

As the foregoing illustrates, both the spring 18 and the free bushing 20 are easily replaceable, and furthermore enable ready changing of the buffering and dampening characteristics of the shock absorber mechanism 10. For instance, if altered dampening characteristics are desired, a stiffer or more flexible spring 18 may be installed.

Further, the free bushing 20 may be made of differing thicknesses or materials providing differing degrees of friction contact with the fork stem 5 in order to alter the buffering characteristics of the invention.

Claims (4)

1. A shock absorber mechanism comprising: a sleeve rotatably mountable into a head tube of a bicycle frame, said sleeve having upper and lower holes formed therein, with a handlebar stem being mountable in said upper hole and a fork stem for supporting a front wheel being slidably but non-rotatably mountable in said lower hole; a removable elastic member disposed axially in said lower hole, said elastic member being compressible and extensible within said lower hole in response to slidable movement of said fork stem; a removable friction member retained at a lower end of said lower hole at least partially within said sleeve, said friction member producing friction in response to sliding movement of said fork stem; and a removable drop-check member being disposed at the lower end of said lower hole and retaining said fork stem and said elastic member within said lower hole.

2. A shock absorber mechanism according to claim 1, wherein a removable cap ring is disposed at a lower end of said drop-check member, said friction member being disposed within said drop-check member and being retained therein by said cap ring.

3. A shock absorber mechanism according to claim 1 or claim 2, wherein said sleeve includes bottom and top end bearing assemblies for rotatably positioning and supporting said sleeve within a bicycle head tube, and said friction member is retained in said bottom end bearing assembly.

4. A shock absorber mechanism substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.