WO2009027681A1

WO2009027681A1 - Bicycle seat post

Info

Publication number: WO2009027681A1
Application number: PCT/GB2008/002916
Authority: WO
Inventors: Richard Thorpe
Original assignee: Karbon Kinetics Limited
Priority date: 2007-08-31
Filing date: 2008-08-29
Publication date: 2009-03-05
Also published as: GB0717001D0

Abstract

There is described a bicycle seat post (2) having at its lower end to an expandable plug (9) for fixing the seat post (2) relative to the seat tube (22) of a bicycle frame (20). The expandable plug (9) is preferably formed from elastomeric material, and is radially expanded by axial compression of the plug between a pressure surface (7) of the seat post (2) and a pressure plate (8) movable relative to the seat post (2) by means of a cam (6,12) mounted at the upper end of the seat tube and connected to the pressure plate (8) by a tension member (11).

Description

Bicycle Seat Post

For many years, bicycle frames have been fitted with an adjustment mechanism to change the height of the seat relative to the frame of the bicycle. Changing the height of the seat is important for rider comfort as it means that the distance from the pedals to the seat can be matched to the length of the rider's legs.

This enables efficient pedalling and comfortable riding.

Typically, the seat of a bicycle is rigidly fixed to a seat post, which is a sliding fit inside the seat tube of the frame of the bicycle. The seat post moves in a direction that changes the distance of the seat to the pedals. The mechanisms used to permit adjustment of the post relative to the seat tube conventionally involve forming a longitudinal slot in the upper end of the seat tube of the bicycle frame, and providing a clamping collar around the slotted portion of the seat post tube.

When the external clamping collar is tightened, usually by a screw or over-centre cam, the diameter of the slotted part of the seat tube is reduced. The longitudinal slot in the bicycle frame seat tube at the end of the tube allows the bicycle frame seat tube to flex when the external clamping collar is tightened. This causes an inwardly acting compressive force to be applied to the seat post tube which increases the frictional force between the seat post and bicycle frame seat tube such that no relative movement of the seat post and seat tube will occur while the rider is seated on the bicycle.

However, external seat post clamps have the disadvantage that over-tightening the clamping collar can cause excessive inwardly acting compressive forces to be applied to the seat post. These forces can be high enough to crush the seat post tube, weakening it, and combined with the effect of the weight of the rider, can cause the seat post tube to bend or even break. To resist the crushing affect of an over- tightened external seat post clamping collar, seat post tubes are made with thickened tubular walls to provide an extra safety margin, but a disadvantage of this is that it increases the weight of the seat post.

The present invention seeks to provide a solution to this problem by replacing the external seat post clamping arrangement with an internal seat post height adjustment mechanism that produces a radial clamping action on the interior of the bicycle frame seat tube at a distance below its upper end. This outwardly acting radial force increases friction between the bicycle frame seat tube and the seat post assembly to prevent movement while avoiding the inwardly acting crushing force on the seat post. Thus the seat post can be made lighter with thinner wall sections. In one embodiment, the present invention provides a seat post with a height adjustment mechanism, the seat post including: an elongate tubular post; means for mounting a saddle at one end of the post ; an axially outwardly facing pressure surface at the other end of the post; a pressure plate mounted adjacent the pressure surface and movable axially relative to the seat post; an elastically deformable plug mounted between the pressure surface and the pressure plate; a tension member attached to the pressure plate and extending axially of the seat post; and means mounted to the seat post for applying a tension to the tension member, the arrangement being such that tension in the tension member urges the pressure plate toward the pressure surface and compresses the plug, causing radial expansion of the plug.

The plug is, in one embodiment, a cylindrical body of elastomeric material having a diameter substantially the same as the diameter of the tubular post when unstressed. The plug may have a central bore through which the tension member can pass.

The means for applying tension to the tension member may be an over-centre cam lever assembly, mounted adjacent the first end of the seat post tube so as to be accessible when the seat post is mounted to a bicycle frame.

A second aspect of the invention provides a bicycle frame having a seat post of the type described above mounted thereto. In a third aspect, the invention provides a bicycle having a frame and a saddle, the saddle being mounted to the frame by a seat post of the type described above.

The mounting arrangement of the seat post of the present invention is internal to the seat post tube. Operating the over-centre cam lever assembly such that the tension in the tension member increases will compress and deform the resiliently deformable plug in a radially outward direction against the internal wall of the seat tube of the bicycle frame, producing a frictional force between the plug and bicycle frame seat tube which locks the seat post in position relative to the frame

The tension member may be a rigid tie rod, or may be a flexible element such as a wire, fibre, or chain.

Operating the over-centre cam lever assembly such that tension in the connecting tension member is released will allow the deformable plug to resiliently return to its unstressed shape, thus relieving the frictional force between the plug and the bicycle frame seat tube, and allowing the seat post to slide within the seat tube enabling height adjustment of the saddle relative to the frame.

Preferably the deformable plug is made of an elastomeric material such as synthetic or natural rubber, silicone rubber, or a synthetic elastomer such that repeated height adjustment of the seat post will not permanently deform the plug.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a side view of a bicycle, with a saddle mounted thereto by a seat post according to the invention;

FIGURE 2 is a perspective view showing a seat post according to the invention assembled with a saddle;

FIGURE 3 is a longitudinal cross section of the seat post of the invention, seen from the side.

FIGURE 4 is a longitudinal cross section of the seat post of the invention seen from the rear, showing the rotating movement of the over-centre cam lever.

Referring now to FIGURE 1, there is seen a conventional bicycle having a frame 20. A seat post assembly 1 is attached to the bicycle frame 20 by introducing the seat post 1 into the open upper end 21 of seat tube 22. The seat post assembly 1 is fixed in position in the frame 20 by means of the expanding plug 9 at the lower end of the seat post, as will be described below.

FIGURE 2, shows a seat post 2 having a seat mounting fixture 4 at its upper end (as seen in the figure) for rigidly attaching a seat or saddle 3. Over-centre cam lever 6 is rotatably mounted to seat post 2 adjacent its upper end, and is rigidly attached to an over- centre cam bush 5.

At the lower end of the seat post, the seat post 2 has an axially-facing compression surface 7, a disc-shaped elastomeric plug 9, and a pressure plate 8 mounted there too. The diameter of the elastomeric plug 9 in its unstressed state is substantially the same as the director of the seat post 2, or may be slightly greater than the diameter of the seat post 2, provided that the unstressed plug may be introduced into the seat tube of a bicycle frame.

The pressure surface 7 in this embodiment is provided by a compression washer 7 fixed to the lower end of seat post 2.

Turning now to figure 3, the seat post assembly is shown in detail in this section or view scene from the side. At the upper end of the seat post, a cam assembly comprising cam lever 6, cam bush 5 and pin 12 is mounted to the seat post tube 2. The cam lever 6 and cam bush 5 are received in coaxial holes in the wall of the seat post tube, and rigidly connected together by the cam pin 12 which is received in coaxial bores 6a and 5a in the cam lever 6 and cam bush 5, respectively. The cam pin 12 is mounted eccentrically relative to cam lever 6 and cam bush 5, as will be described later.

At the lower end of the seat post tube 2, a compression washer 7 substantially closes off the end of the tube 2 to provide a downwardly-facing pressure surface at the lower end of the seat post tube. The compression washer 7 has a central opening 7a.

A resilient elastomeric bush or plug 9 is held against the compression washer 7 by a pressure plate 8. The plug 9 in this embodiment is generally disc-shaped, and has a central bore extending therethrough.

The pressure plate 8 is a disc having a central upstand which is receivable in the bore of the plug 9. The upstand is formed with an internal screw thread 8a, whose purpose will be described below. As can be seen in figures 3 and 4, the pressure plate 8 and plug 9 have a diameter substantially equal to the diameter of the seat post tube 2.

A tension member 11 extends axially of the seat post tube 2, and is connected at its upper end to the cam pin 12. At its lower end, the tension member 11 extends through the central opening 7a of the compression washer 7, and engages the pressure plate 8. The lower end 11a of the tension member is formed with a screw thread, which engages the thread 8a of the pressure plate 8.

The seat post assembly is prepared for fitting to a bicycle tube by the first rotating the cam lever 6 so as to place cam pin 12 in a lower position indicated by reference 12a in Figure 4, extending the tension member 11 to its greatest extent through the opening 7a in compression washer 7. In this position, the cam lever 6 may be at an upper position as indicated by reference 6 in Figure 4, or a lower position as indicated by reference 6a. Pressure plate 8 is then rotated so that the threaded engagement between the tension member 11 and the threaded upstand of the pressure plate brings the pressure plate 8 into close engagement with the plug 9, snugly fitting the plug 9 between the pressure plate 8 and the compression washer 7.

The seat post is then mounted to the bicycle frame by introducing the lower end of the seat post tube 2 into the open upper end 21 of the seat tube 22 of the bicycle frame 20. The seat post is moved into the seat tube until the saddle 3 is at the correct height relative to the bicycle frame 20.

Cam lever 6 is then rotated by hand through arc 14 to move the cam pin from the lower position 12a to the upper position 12b, the arrangement being such that during this movement the cam pin 12 passes through an uppermost position (not shown) before descending slightly to finish in the upper position 12b. Movement of the cam pin 12 draws the tension member 11 and pressure plate 8 upwards, axially compressing the plug 9 between the pressure plate 8 and the compression washer 7. The axial compression of the plug 9 causes the plug to expand radially into frictional engagement with the seat tube 22, locking the seat post in position.

To adjust the position of the seat post, cam lever 6 is returned to its starting position, moving cam pin 12, tension member 11 and pressure plate 8 first upwardly and then downwardly (as seen in figure 3) to release the compression of the plug 9. The plug resiliently returns to its original condition, expanding axially and contracting radially to release the frictional engagement between the plug 9 and the seat tube 22. The seat post 2 may then be slid within the seat tube 22 to the correct relative position, and cam lever 6 again operated to draw the tension member 11 and pressure plate 8 upwards to re-compress the plug 9.

Seat post 2 may be made of light metal alloy or composite resin and fibre material. Tension member 11 may be formed from wire such as steel wire, or from synthetic fibre such as polyester fibre, aramid fibre or carbon fibre. Alternatively, the tension member 11 may be a rigid rod able to support compression. Cam pin 12 could be press fitted or glued, threaded or otherwise fixed into over-centre cam lever 6, which itself could be made of light metal alloy or a plastics material such as glass reinforced moulded nylon. The rotating movement of over-centre cam lever 6 relative to seat post 2 could be aided by a lubricating film of grease or other friction reducing member. The deformable spring bushing member or plug 9 is preferably made of an elastomeric or rubber material, but may be provided by, for example, a series ^* of conical "Belleville" washers alternately placed over the end of the tension member 11 and compressible between the pressure plate 8 and compression washer 7.

FIGURE 4 is a rear view cross section of the invention and shows over-centre cam lever 6 in an upper position in which the seat post is fixed, and a lower position 6a in phantom lines, in which the seat post is slidable within the seat tube.

As an alternative to a rotary cam assembly, the tension member 11 may be urged upwardly by a mechanism or linkage comprising leavers, mounted at the upper end of the seat post and operable by a control member.

In a further alternative embodiment, not shown, the upper end of tension member 11 may be secured to a transverse bar extending out of the seat post tube through a pair of opposing longitudinal slots in the wall of the seat post tube, the ends of the bar being engaged by an internally-threaded ring mounted to the seat tube by means of an external screw thread on the seat tube, such that rotation of the ring relative to the seat tube can move the bar upwardly and thus exert a tension on the tension member 11.

Claims

Claims :

1. A bicycle seat post with a height adjustment mechanism, the seat post including: an elongate tubular post (2); means (4) for mounting a saddle (3) at one end of the post; an axially outwardly facing pressure surface (7) at the other end of the post; a pressure plate (8) mounted adjacent the pressure surface and movable axially relative to the seat post; an elastically deformable plug (9) mounted between the pressure surface and the pressure plate; a tension member (11) attached to the pressure plate and extending axially of the seat post; and means (6, 12) mounted to the seat post for applying a tension to the tension member, the arrangement being such that tension in the tension member urges the pressure plate toward the pressure surface and compresses the plug, causing radial expansion of the plug.

2. A seat post according to claim 1, wherein we means for applying a tension to the tension member comprises a rotary cam (6) mounted to the seat tube, the tension member (11) engaging and eccentric cam pin (12) which is movable axially of the seat post by rotation of the rotary cam (6) .

3. A seat post according to claim 1, wherein we means for applying a tension to the tension member comprises a toggle linkage.

4. A seat post according to claim 1, wherein we means for applying a tension to the tension member comprises a transverse bar extending out of the seat post tube through a pair of opposing longitudinal slots in the wall of the seat post tube, the ends of the bar being engaged by an internally-threaded ring mounted to the seat tube by means of an external screw thread on the seat tube

5. A seat post according to any of claims 1 to 4, wherein the tension member (11) is a flexible element.

6. A seat post according to claim 5, wherein the tension member (11) is a wire, fibre or chain.

7. A seat post according to any of claims 1 to 4, wherein the tension member (11) is a tie rod.

8. A bicycle seat post substantially as herein described with reference to figure 1, figure 2, figure 3 or figure 4 of the accompanying drawings