GB2329164A

GB2329164A - Bicycle suspension system

Info

Publication number: GB2329164A
Application number: GB9719627A
Authority: GB
Inventors: Jon Whyte
Original assignee: ATB Sales Ltd
Current assignee: ATB Sales Ltd
Priority date: 1997-09-15
Filing date: 1997-09-15
Publication date: 1999-03-17
Anticipated expiration: 2017-09-15
Also published as: GB9719627D0; GB2329164B

Abstract

The suspension system has an inner seat tube 24 which is slidably mounted within an outer seat tube 23. The lower end of the inner seat tube carries the bottom bracket 17 whilst the upper end is adapted to receive a seat post carrying a saddle so that the distance between the saddle and the bottom bracket remains constant. To prevent rotation of the inner seat tube within the outer seat tube an L shaped extension tube 30 projects from the bottom bracket to engage a short tube 31 fixed to the down tube 12. Springs or dampers 32 which provide the suspension to the saddle may be included between the inner and outer seat tubes, between the extension tube and the short tube or between both as shown. Instead of extension tube 30 and short tube 31 alternative arrangements may be used to prevent the relative rotation of the seat tubes such as rotation locking springs, a lug projecting from the inner tube which engages a slot in the outer tube or elongate ridges on one tube which cooperate with channels on the other. As shown, the chain stays 18 may be welded to the down tube 12 at a point along the tube's length rather that at the conventional position adjacent the bottom bracket.

Description

BICYCLE REAR SUSPENSION SYSTEM The present invention relates to a rear suspension system for a bicycle.

Suspension systems for bicycles are commonplace and have been applied to the front and rear wheels and the seat tube, providing suspension to the saddle. It is with improvements in or relating to this latter form of suspension with which the present invention is concerned.

In its broadest sense, the present invention provides a cycle suspension system comprising an inner seat tube having an upper end adapted to receive and retain a saddle post carrying a saddle, and a lower end upon which the bottom bracket is mounted; wherein the inner seat tube is slidably mounted within an outer seat tube forming a part of the frame of the cycle; suspension means being provided to suspend the inner seat tube within the outer seat tube; and wherein means are provided to prevent rotation of the inner seat tube within the outer seat tube during use of the cycle.

Typically, the suspension means comprises one or more spring or damper units.

In a preferred embodiment, the means to prevent rotation of the inner seat tube within the outer seat tube comprises an L-shaped extension leg extending from the lower end of the inner seat tube and engaging a tube provided in or on the frame of the cycle. Typically, the tube is provided within the down tube.

The above and other aspects of the present invention will now be described in further detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows, in side view, a conventional bicycle; and Figure 2 shows, in a part side schematic view, an embodiment of a cycle saddle suspension system in accordance with the present invention.

Referring to Figure 1, a conventional bicycle 10 comprises a frame including a crossbar or top tube 11, a down tube 12, a seat tube 13, front wheel 14, rear wheel 15, and chainset 16 through bottom bracket 17. Rear wheel 15 is rotatably mounted between twin chain stays 18 and upper support arms 19.

With reference to Figure 2, a cycle suspension system in accordance with the present invention adapts the conventional frame arrangement by replacing the single seat tube 13 with an outer seat tube 23, typically oversized, open at both ends and an inner seat tube 24 which is slidaf;le within the outer seat tube 23. The lower end of inner seat tube 24 carries the bottom bracket 17 and its associated bearings, axle and pedal cranks (omitted from Figure 2 for clarity). The upper end of the inner seat tube 24 is adapted to receive a conventional seat post carrying a saddle. A conventional grip 25 secures the seat post in position and allows adjustment to provide the appropriate leg adjustment between saddle and pedals as with a conventional bicycle.

It is important to provide some means for preventing rotation of the inner seat tube within the outer seat tube during use. Many suitable arrangements will be suitable, for example rotation-locking springs; one or more elongate ridges on one tube engaging corresponding channels on the other; a lug projecting laterally from the inner tube an engaging axial slot in the outer tube; and so on. In the preferred embodiment shown, rotation is locked by means of an L-shaped extension tube 30 projecting forwardly and upwardly from the bottom bracket engaging a short tube 31 'inserted' into down tube 12. Short tube 31 is orientated to be parallel to the seat tubes 23,24.

As shown, the chain stays 18 are welded to the down tube at a point some way along the tube, rather than the conventional position adjacent the bottom bracket. This is not, however, essential, and the stays may be welded to the lower end of the outer seat tube 23 in a more conventional position.

One or more suspension units, such as spring/damper units 32 are included in the system to provide the desired suspension to the saddle. This or these units may be included between the seat tubes 23,24 or between the extension tube 30 and the short tube 31, or both. Numerous alternative forms of suspension have been proposed in the prior art for bicycle saddles and many of these will be suitable for inclusion in the present invention with only minor modification if any.

The weight of the rider, whether seated or standing, is transmitted via the inner seat tube 24 to the spring or damper units 32, by which means the rider is cushioned from the roughness of the terrain experienced by the wheels and thereby the main frame.

Unlike other suspension designs, the system is unaffected by the rider shifting his weight between the pedals and the saddle and the distance between the saddle and pedal cranks centre remains constant, allowing for optimum pedalling efficiency.

It will be appreciated that as the inner seat tube 24 moves up and down within the outer seat tube 23, the separation of the bottom bracket 17 from the rear wheel axle 20 will vary. The spring tensioning system of a conventional derailleur gear mechanism will also take up of any undue slackening of the chain resulting from the inventive suspension system. Indeed, to a certain extent, the variation in chain length is a further advantage of the present system. The increase in chain tension during the power (downward) stroke of the pedal actually stiffens the suspension which prevents the shift in rider weight which occurs at this time from compressing the suspension. In this way, pedal-induced bobbing is reduced. When considering the tension forces in the chain, because of the non-vertical angle of the seat tube, there is a vertical component of this force which tries to lift the chain wheel up, thus counteracting the rider's downward force on the pedal.

Other suspension systems commonly use swing arms in place of conventional chain stays to support the rear wheel. The relative movement between such a swing arm and the main frame means that the fitting of luggage racks or mudguards is very complicated and difficult, often impossible. The suspension system of the present invention avoids such relative movement such that the fitting of accessories is straightforward. This means that touring bicycles can be provided with suspension for the comfort of the rider, whereas, in the past, suspension has, perhaps, been limited to off-road bicycles.

Claims

1. A cycle suspension system comprising an inner seat tube having an upper end adapted to receive and retain a saddle post carrying a saddle, and a lower end upon which the bottom bracket is mounted; wherein the inner seat tube is slidably mounted within an outer seat tube forming a part of the frame of the cycle; suspension means being provided to suspend the inner seat tube within the outer seat tube; and wherein means are provided to prevent rotation of the inner seat tube within the outer seat tube during use of the cycle.

2. A cycle suspension system as claimed in Claim 1 wherein the suspension means comprises one or more spring or damper units.

3. A cycle suspension system as claimed in Claim 1 or Claim 2 wherein the means to prevent rotation of the inner seat tube within the outer seat tube comprises an L-shaped extension leg extending from the lower end of the inner seat tube and engaging a tube provided in or on the frame of the cycle.

4. A cycle suspension system as claimed in Claim 3 wherein the L-shaped extension leg engages a short tube provided within the down tube.

5. A cycle suspension system as claimed in Claim 4 wherein suspension means are provided between the extension leg and the short tube.

6. A cycle suspension system as claimed in any preceding claim wherein suspension means are included between the inner and outer seat tubes.

7. A bicycle provided with a rear suspension system as claimed in anyone of Claims 1 to 6.

8. A cycle suspension system substantially as herein described with reference to accompanying Figure 2.

9. A bicycle substantially as herein described with reference to accompanying Figure 2.