WO1999015396A9

WO1999015396A9 - Suspension system for a bicycle frame

Info

Publication number: WO1999015396A9
Application number: PCT/NL1998/000532
Authority: WO
Inventors: Hendrik Marius Bremmer
Original assignee: Hendrik Marius Bremmer
Priority date: 1997-09-19
Filing date: 1998-09-15
Publication date: 2001-07-12
Also published as: WO1999015396A1; NL1008338C1; AU9097898A; EP1015302A1

Abstract

Suspension system for a bicycle frame which comprises a basic frame and chain stays pivotably connected thereto, the basic frame comprising a down tube and a head tube and seat tube which are connected to one another by the frame tube, and a bottom bracket being present at a connection between the frame tube and the seat tube, which suspension system is called into action when the chain stays pivot with respect to the basic frame, the suspension system comprising a cable which at one end is attached to the chain stays and of which another end is fixed with respect to the basic frame.

Description

SUSPENSION SYSTEM FOR A BICYCLE FRAME

The invention relates to a suspension system for a bicycle frame which comprises a basic frame and chain stays pivotably connected thereto, the basic frame comprising a down tube and a head tube and seat tube which are connected to one another by the frame tube, and a bottom bracket being present at a connection between the frame tube and the seat tube, which suspension system is called into action when the chain stays pivot about the bottom bracket . Bicycles generally comprise a frame composed of tubes, a head tube being present on the front side, in which head tube a front fork is pivotably accommodated on the underside, in which fork a front wheel is rotatably and pivotably mounted. On the top side of the head tube, there are handlebars, by means of which the front fork, and hence the front wheel, can be turned, so that the bicycle can be steered.

The head tube is connected, by one or more frame tubes, to a seat tube, on the top end of which a saddle is mounted. At the bottom end, the seat tube ends on a bottom bracket which is generally cylindrical and in which a crankshaft is rotatably accommodated. One end of the chain stays, in which a rear wheel is rotatably accommodated at the other end, is also connected to the bottom bracket. A driving sprocket over which a chain runs to a sprocket mounted on the rear wheel axle is mounted on the crankshaft . At the ends of the crankshaft, perpendicular thereto, there are fitted two cranks, and at the end of each of the cranks, perpendicular thereto, there is a pedal which can rotate with respect to the cranks . As a result of a rider who is sitting on the saddle pedalling on the pedals, the crankshaft is set in a rotational movement which is transmitted by the chain to the rear wheel, with the result that the rider propels the bicycle. Owing to the rigid connection between the chain stays and the frame, movements of the rear wheel up and down when the said wheel rolls over unevenness in the roadway, by way of example, are transmitted as shocks to the saddle and hence to the rider. Bicycle frames in which the chain stays can pivot with respect to that section of the frame to which the saddle is attached are known. In contrast to the situation with rigid frames, in this case the shocks which the rear wheel undergoes when passing over unevenness in the roadway are not transmitted directly to the rider sitting on the saddle, but rather are at least partly absorbed by the chain stays pivoting with respect to the frame. The result is a higher level of comfort when cycling. As a rule, means are also provided which check the pivoting movements of the fork with respect to the basic frame in a resilient and damping manner. The pivoting structure has to satisfy high demands with regard to stability and strength. In a large number of the known designs, the centreline about which the chain stays pivot is situated outside the centreline of the bottom bracket . This has the drawback that, as the chain stays pivot, the distance from the centreline of the bottom bracket to the centreline of the rear wheel varies and that the length of the drive chain has to be able to follow these variations. In the case of bicycles which are provided with a derailleur system, the chain tensioner incorporated therein takes care of the required extension and shortening of the chain. In systems without a derailleur, such variations in chain length cannot readily be dealt with.

Variations in the distance between the centreline of the bottom bracket and the centreline of the rear wheel are avoided if the chain stays can pivot about the centreline of the bottom bracket . Bicycles with a design of this nature are also known, for example from DE-A-44 27 409 and EP-A-673 , 382. In this case, a forked end of the chain stays, which is optionally supported, engages around the axial ends of the bottom bracket.

Most bicycle frames in which the chain stays can pivot with respect to the basic frame are provided with a suspension system which cushions and limits the extent of the pivoting of the chain stays with respect to the basic frame. Generally, the suspension system is arranged between the chain stays and the seat tube, between the rear wheel axle and the seat tube and/or between the rear wheel axle and a frame tube. Such designs are known per se, for example from DE-A- 44 27 409, FR-A-2 , 683 , 785 and US-A-5, 269, 552. A shock absorber is often incorporated in the suspension system. In the known suspension systems, the resilient action is obtained by a resilient component being compressed when the rear axle pivots with respect to the basic frame. A drawback of the known design is the complexity which it inevitably entails in order to be fitted in the existing frame structures. Additional side arms or complex stay designs are often required in order to be able to incorporate the suspension system in the frame .

The object of the invention is to provide a suspension system of simple design which is also easy to fit into current frame designs.

This object is achieved according to the invention by the fact that the suspension system comprises a cable which at one end is attached to the chain stays and of which another end is fixed with respect to the basic frame. The suspension system according to the invention is easy to install and fits entirely into virtually all conceivable frame structures, including those commonly used. At one end, the cable is attached to the chain stays, preferably in the vicinity of the crankshaft. The cable runs through or along one of the frame tubes which are connected to the bottom bracket . The said one end is, as viewed from the basic frame in the direction of the chain stays, attached to the chain stays below or behind the centreline of the crankshaft, with the cable running along or through the down tube or through or along the front of the seat tube. The other end is fixed with respect to the basic frame, preferably to the down tube or the seat tube or to some other frame component in the vicinity thereof, for example to the head tube or the top tube. When the chain stays are forced upwards as a result of the rear wheel travelling over an uneven surface, the cable is subjected to tensile load and the pivoting movement is resiliently checked as a result of the inherent extension. The suspension system according to the invention has the further advantage of increased stability. This is achieved as a result of the fact that the pivoting is checked by the cable being tensioned, while in the suspension system according to the prior art pivoting is checked by a spring being compressed, which spring under compression has a tendency to spring away sideways. A cable with a reversible elasticity of between 1 and 4%, preferably between 1.5 and 2.5%, is particularly suitable for use in the invention. Instead of a cable, it is also possible to use some other elongate body with sufficient elasticity and sufficient tensile strength to withstand the forces exerted on it by the pivoting of the chain stays around the bottom bracket during a bicycle ride on uneven surfaces and by the load of the driver, for example a chain or a tie rod, in which case, depending on the elasticity of the chain or rod, the latter may also be attached to the frame parts via disc springs, also known as Belleville springs, which provide extra elasticity, or a combination of the said components . In stead of the preferred disc springs also other elastic elements can be applied, for example a piece of rubber. In case a tie rod is applied the said other end preferably is fixed to the down tube in the vicinity of the bottom bracket rather than near the head tube. Where the following and preceding description mentions a cable, this is also to be understood as meaning the said alternatives, as well as other possible functional alternatives. The elasticity of the cable, in conjunction with its length, which is determined by the location where the other end of the cable is attached to the basic frame, may be selected in such a way that the desired suspension characteristics are achieved.

In order to limit the pivoting of the chain stays in the direction in which this is not checked by subjecting the cable to tensile load a stop made of a resilient material, for example, is arranged on the bottom bracket or in or on one of the frame tubes, against which stop the chain stays can rest when no tensile force is exerted on the cable.

The cable may run inside the said tubes or along the outside thereof. A very suitable design is a suspension system which comprises a cable which runs through the down tube and which is attached at one end to the chain stays, and the other end of which is fixed with respect to the basic frame at the level of the connection between the frame tube and the head tube. In this case, suspension means with which the cable is in contact may also be arranged in the frame tube, which suspension means are called into action by the cable when the chain stays pivot about the bottom bracket . This design may be similarly used with the cable running through the seat tube and being fixed at the other end in that section of the seat tube which lies more in the direction of the saddle.

This design has the advantage that the suspension system is accommodated entirely inside the frame structure and is protected against dirt and damage, which is of benefit to the reliability and service life.

The cable is, for example, a steel or plastic cable of the required strength. At one end, the cable is attached to the chain stays, for example clamped to the underside thereof, for example by means of a metal plate which is screwed onto this underside. Furthermore, any method which is known per se for fixing a cable or cable end can be used. It is also possible to use two cables, for example one on each side of the frame.

The other end of the cable is fixed in the vicinity of the connection between the frame tube and the head tube, for example to a projection which is mounted on or in the frame tube or by allowing the cable to project outwards through a hole in the frame tube and providing its end with a bead which prevents it from slipping back into the tube through the hole . The corresponding design for the case in which the cable runs through the seat tube is easy for one skilled in the art to construct. If the cable runs through the down tube, the other end of the cable preferably projects into the head tube through a hole in the wall of the latter, and this end is provided with a bead which fixes the cable in the head tube, thus preventing it from slipping back into the frame tube. By selecting a suitable location for the hole in the head tube, it is possible, in conjunction with the location where the other end of the cable is fixed to the chain stays, to select the shortest possible path for the cable through the tube. This is important when using a preferred embodiment of the further suspension system, as will become clear below from the description of this embodiment. It is also possible to guide the cable from the connecting section of the chain stays, through the down tube and outwards through an opening therein in the vicinity of the head tube, then to wrap it around the outside of the head tube and guide it through a second opening in the frame tube back into this tube, and running it back through the frame tube to the chain stays. Both ends of the cable are then fixed to the chain stays . This avoids fixing the cable by means of a bead, which generally provides a connection which is weaker than the cable itself. Moreover, in this case the cable may be of less strong and also less heavyweight and thick construction. It is easy for one skilled in the art to determine the required strength of the cable, given the dimensions of the frame and the load which the bicycle must be able to resist. Additional suspension means may also be used in the suspension system according to the invention. As additional suspension means, the suspension system comprises, by way of example, a block of resilient material which is attached in the down tube or in the seat tube and is compressed by the cable running inside the tube in question when the chain stays pivot with respect to the basic frame. One example of such suspension means comprises a block of resilient material, which has been pushed into the tube in question through an opening in the wall of this tube. This block is, for example, incorporated in a metal container, from which it protrudes, over a certain length, on the side of the container facing the inside of the tube. The protruding length is hereafter referred to as the top part. In assembled condition, the cable runs along this top part. Preferably, the top part is provided with a groove through which the cable can run. The top part preferably extends beyond the centreline of the tube, so that the cable does not run through the tube along the shortest path from one fixing point to the other, but rather along a bent and therefore longer path. The extent to which the presence of the bend lengthens the distance along which the cable runs through the tube by comparison with the shortest, straight distance depends on the height to which the top part projects into the frame tube and on the location where the cable is fixed at the chain stays and with respect to the frame tube or the seat tube . When the chain stays are forced upwards as a result of the rear wheel travelling over an uneven surface, tension is applied to that end of the cable which is attached to the chain stays . Since the cable is fixed at both ends, the only possibility, apart from extension of the cable, for effectively lengthening the cable is for it to stretch, i.e. for the bend in the cable to become less sharp. This is achieved by the fact that the cable runs over the top part, preferably through a groove therein, and exerts a force on this top part, so compressing the elastic material. In this way, the pivoting of the chain stays is transmitted, with a low force transfer ratio, virtually perpendicular to the elastic material, bringing about a spring action since the elastic material offers resistance to compression. This suspension system operates progressively, owing to the fact that the transfer ratio decreases as the bend in the cable becomes smaller owing to the resilient component being compressed. As this component is com- pressed further, an increasingly greater tensile force is required in the cable in order to compress it still further.

Suitable elastic materials for use as a resilient component in the suspension system described above are, for example, coil springs, disc springs or blocks of rubbery material. By suitably selecting the elastic material, the suspension action can be made more or less stiff. Adaptation is easy and merely requires the replacement of the spring or the block of rubbery material by one with different spring characteristics.

If additional suspension means are used, it is possible to make do with a cable with very low elasticity, for example less than 1%.

In order to prevent any suspension movement brought about by the chain stays pivoting about the bottom bracket from continuing, it is advantageous to incorporate a shock-absorbing structure in the bicycle frame. This may, for example, be combined with the suspension system in a manner which is known per se from the abovementioned patent applications and patents. A stop as mentioned above and made from an elastic material can also ensure the desired shock-absorbing action.

The shock-absorbing system, if present, is situated in or on the down tube or the seat tube, and preferably the shock-absorbing system is situated at least partially inside the down tube or the seat tube in the vicinity of the bottom bracket and is called into action by the pivoting of the chain stays. This design has the advantage that the moving parts of the shock- absorbing system can be sealed off from the environment and are thus protected against damage and dirt . In a design of this kind, by way of example, a projection connected to the chain stays is in contact with a section of the shock-absorbing system which protrudes into the down tube, which system is called into action when the chain stays pivot. Shock-absorbing means which are suitable for use in such a shock-absorbing system are known per se. It is preferable to use a design which is similar to that described above for the suspension system, in particular the one in which a block of a material, which in this case is shock-absorbing, is used. Here too, it is possible, by suitably selecting the material, to adapt the shock-absorbing performance to the wishes of the rider.

A significant advantage of the bicycle frame according to the invention is therefore that, by selecting the cable elasticity and, if present, the materials in the suspension and shock absorber, the suspension characteristics can be adapted to the condition of the roadway and the weight and wishes of the rider and, as will become clear further below, in a preferred embodiment, also by adapting the stress under which the resilient or shock-absorbing material is placed in the suspension system or shock-absorbing system when fitted. Thus the bicycle frame according to the invention provides hitherto unachievable possibilities for adapting the performance of the bicycle to the wishes of - li ¬

the user and the condition of the road over which the bicycle is travelling.

The invention will be explained with reference to the following drawings, in which: Fig. 1 shows a partially cut-away side view of a bicycle frame containing a suspension system according to the invention;

Fig. 2 shows a cross-section on line A-A in Fig. 1 through additional suspension means as are present in the frame in accordance with Fig. 1;

Fig. 3 shows a cross-section on line B-B in Fig. 1 through a shock-absorbing system as is present in the frame in accordance with Fig. 1;

Fig. 4 shows a rear view of the basic frame from Fig. 1 at the location of the bottom bracket;

Fig. 5 shows a side view of the chain stays from Fig. 1;

Fig. 6 shows a top view of the chain stays in accordance with Fig. 5; Fig. 7 shows a bottom view of the chain tays from Fig. 5;

Fig. 8 shows a side view of a bicycle frame in which a second embodiment of the invention is present . Fig. 9 shows a side view of a bicycle frame in which a third embodiment of the invention is present.

Fig. 10 shows a top view of the chain stays from Fig. 9;

Fig. 11 shows a bottom view of the chain stays from Fig. 9;

Fig. 12 shows a side view of a bicycle frame in which a fourth embodiment of the invention is present .

Fig. 13 shows a side view of the chain stays from Fig . 12 ;

Fig. 14 shows a top view of the chain stays from Fig. 12;

Fig. 15 shows a bottom view of the chain stays from Fig. 12;

Fig. 16 shows a side view of a bicycle frame in which a fifth embodiment of the invention is present; and

Fig. 17 shows a partially cut-away side view of a bottom bracket with adjoining frame parts in which a sixth embodiment of a suspension system according to the invention is present.

In the figures, corresponding components are always denoted by numerals in which the final two digits coincide.

In Fig. 1, 1 denotes the basic frame and 2 the chain stays. The basic frame 1 comprises a head tube 3 , a seat tube 4 , a down tube 5 and a top tube 6. The connection between frame tube 5 and seat tube 4 is formed by bottom bracket 7, which is partially situated inside frame tube 5. Chain stays 2 comprise a connecting section 8 and a fork section 9. In this fork section 9, there is an opening 10 in which the axle of a rear wheel can be held and attached. A cable 11 runs from head tube 3 to connecting section 8 and, owing to the presence of the suspension system 12, is bent at the location of the latter. The cable 11 protrudes into the head tube 3 and is secured against being pulled out of the latter by a bead 13, the dimensions of which are larger than the opening in head tube 3 through which the cable enters the frame tube. On the other side, the cable 11 is attached to connecting section 8 by means of a clamping block 14 screwed onto it .

Cable 11 is in contact with top part 15 of suspension system 12 , which is shown in more detail in Figure 2. This top part is resiliently accommodated in housing 16 of suspension system 12. A sleeve 17, which preferably extends beyond the centreline of tube 5, is arranged in this tube. The centreline is understood here to mean the line which intersects the planes of symmetry of the tube. The sleeve 17 is preferably provided with an internal screw thread from the side which is open towards tube 5 down to the slots described below, into which housing 16 can be screwed. Two slots, which lie diametrically opposite one another and run parallel to the longitudinal axis of the sleeve, are present in the circumference in that end of sleeve 17 which faces towards the inside of tube 5, through which slots cable 11 runs in assembled condition. Sleeve 17 is preferably not perpendicular to tube 5, but rather forms a small angle for example between 3° and 7°, to the perpendicular to tube 5, with the section of the sleeve 17 which faces towards the inside of tube 5 being directed slightly at an angle towards the head tube 3. This has the advantage that when the suspension system 12 is compressed, the distance from the cable end at the head tube to the top of the top part 15 becomes greater, with the result that the extension of cable 11 under the load which also causes compression of the suspension system is compensated for. This reduces possible wear to top part 15, since movement of the cable under changing loads is prevented to a significant extent.

Part 18 of connecting section 8 which is situated furthest inside is in contact with a shock- absorber system 24 which comprises, inter alia, a sleeve 19 and is situated in the vicinity of seat tube 4 and protrudes through an opening in frame tube 5.

In Fig. 2, suspension system 12 comprises a housing 16 in which there are accommodated a body 20 made of resilient material and a top part 15, part of which projects beyond the housing 16 but, in assembled condition, is still situated inside sleeve 17, where it is in contact with the cable 11 running through the slots 20 in sleeve 17. A groove 21, in which, in assembled condition, cable 11 (not shown here) runs, is present in top part 15. Housing 16 on the side which projects outside the tube 5 is provided with a hexagonal projection 22, on which a spanner can engage in order to screw the suspension system into frame tube 5 with the aid of screw thread 23 in sleeve 17.

In Fig. 3, shock-absorber system 24 comprises a housing 25, in which a body 26 of shock- absorbing material is accommodated. Top part 27 is provided with a hexagonal projection 28 and screw thread 29, by means of which this top part can be screwed into sleeve 19 on frame tube 5 using a spanner which engages on projection 28. For this purpose, sleeve 19 is provided with an internal screw thread which is complementary to screw thread 29. In assembled condition, the underside 30 of housing 25 is in contact with part 18 of connecting section 8 which is situated furthest inside, as shown in Fig. 1. Fig. 4 shows a rear view of the basic frame, showing bottom bracket 7 with, on the top side thereof, the bottom end of seat tube 4 and, on the underside, opening 31 in the basic frame, through which the chain stays 2 can be pushed into the basic frame 1, after which it can pivot therein about the bottom bracket 7.

In Fig. 5, chain stays 2 comprise a connecting section 8, in which there is a recess 32, fitting around the bottom bracket of the basic frame (not shown here) , and chain stay 9, containing opening 10 for holding the axle of the rear wheel.

In Fig. 6, the components of chain stays 2 are denoted by the same numerals as in Fig. 5. Holes 33, which are provided with an internal screw thread, are present in connecting section 8, so that block 34, which for this purpose is provided with holes 35 whose positions correspond to holes 33, can be attached to the connecting section using bolts after the chain stays have been arranged in frame tube 5 around bottom bracket 7. This makes it impossible for the chain stays to come out of the frame tube and also encloses the bottom bracket over rather more than half its circumference. The advantage of this design over for example the design known from DE-A-44.27.409 is that the chain stays need not be disassembled into two halves when repairs need to be carried out or components need to be replaced and also that the further design and assembly are simple.

In the design described here the bottom bracket is situated at least partly within the bottom tube, one end of the chain stays being formed by a connecting section which is partly incorporated within the bottom tube and in which a recess is present in that part which is incorporated in the bottom tube, which recess at least partially encloses, and pivots about, that part of the bottom bracket which is situated within the bottom tube.

The chain stays can be mounted in the frame simply by placing the connecting section in the bottom tube and bringing the recess into contact with with that part of the bottom bracket which is incorporated within the bottom tube. To prevent the chain stays unintentionally coming out of the basic frame, it is advantageous to fit a provision preventing such detachment after the chain stays are attached to that part of the connecting section which projects beyond the bottom tube. An example of such a provision is a body of metal or other strong material which is attached, for example screwed, to the part of the connecting section which projects beyond tube in order to limit the angle through which the chain stays can pivot. It is preferred for such body to be shaped such that, in assembled condition, it links up with the circumference of the bottom bracket so that this bracket is enclosed by the body together with the connecting section over more than 50%, more preferably over more than 60% and even more than 70% of the circumference .

The bottom bracket is cylinder-shaped and the recess in the connecting section also has the shape of a part of a cylinder. The radii of the outside circumference of the bottom bracket and of the inside circumference of the recess are equal or at least so adapted to one another that the recess in the connecting section can pivot about the bottom bracket with minor play at the most. The radius of the recess may, for example, be chosen to be so much larger than that of the bottom bracket that a lubricating layer can be applied between the two cylinder surfaces or a friction-reducing coating can be applied to either or both surfaces. If desired, bearings, for example plain or ball bearings, may be applied in order for the stays to pivot about the bottom bracket with the least possible friction.

An additional advantage of the design described has to do with the large contact area between the recess and the bottom bracket, which ensures a highly stable design by which especially movements perpendicular to the axis of rotation are prevented. Also, because of the large contact area, the load per unit area is low so that the design can function without any additional bearings being necessary. The present design for connecting the chain stays to the basic frame can also be applied in combination with other suspension systems than those described herein, including those that are known per se and referred to herein. In Fig. 7, the components of chain stays 2 are denoted by the same numerals as in Fig. 5. 36 denotes a groove through which cable 11 (not shown here) runs in assembled condition. Furthermore, holes 37, which are provided with an internal screw thread, are present on the underside of the connecting section 8, so that clamping block 38, which for this purpose is provided with holes 39 whose position corresponds to the holes 37, can be screwed onto the connecting section 8 using bolts, in order to fix the cable 11 to this connecting section.

With reference to Figs . 1 and 4 , the chain stays 2 can easily be fitted to the basic frame 1 by firstly sliding part 18 of the chain stays into down tube 5, through opening 31, at an angle which is smaller than that illustrated with respect to seat tube 4, sufficiently far for recess 32 to come into contact with and fit around bottom bracket 7. After chain stays 2 have pivoted in the clockwise direction so that the angle to the seat tube increases, block 34 is fitted on connecting section 8, after which the chain stays can no longer be removed from frame tube 5.

Another possibility (not shown in the figures) is for a block similar to block 34 to be fitted on that part 18 of connecting section 8 which is situated furthest inwards. The shock-absorber system is then in contact with this block. The block can be fitted via the opening of the shock-absorber system, which has not yet been attached. Then, cable 11, which may optionally be guided through frame tube 5 before attaching the chain stays, is fixed to connecting section 8 by clamping block 38. This may be carried out before suspension system and/or shock-absorber system are fitted or, in any case, before the latter are tightened, so that the cable is not yet under stress, since this considerably facilitates assembly. Finally, the components of suspension system and shock-absorber system are attached and housing 16 and top part 27 are screwed in sufficiently far to place the cable under the desired stress and for the bicycle frame to have the desired suspension characteristics and shock-absorbing performance. It should be noted that this possibility of affecting the ride of the bicycle frame is an additional feature to the possibility already mentioned above of affecting this ride by selecting the material of suspension and shock-absorber bodies 20 and 26, respectively.

Figure 8 differs from Figure 1 owing to the absence of the additional suspension means and shock- absorbing means in the frame tubes. In this case, the suspension is supplied by cable 211. The pivoting of the chain stays 202 into the position in which no tensile force is exerted on the cable 211 is limited by a block 240 of resilient material which is arranged on that section of connecting section 208 which is situated furthest inside frame tube 205. As the chain stays pivot in the clockwise direction, this block 240 comes into contact with the inside of frame tube 205, thus preventing the rear axle from pivoting further in that direction.

In Fig. 9, the cable 311, as in the preceding embodiments, runs inside the frame tube 305. In the embodiment illustrated in Fig. 9, however, the chain stays are also connected to the ends of the bottom bracket. In this case, a half-ring section 341 of the connecting section 308 engages around the underside of the left-hand end (as seen in the direction of travel) of bottom bracket 307. A complementary half-ring closure piece 342 engages around the upper half of the left-hand end of the bottom bracket and is connected to section 341, for example by means of screws. An annular bearing may be present between bottom bracket and the enclosing parts 341 and 342. Although this cannot be seen in the figure, the chain stays are connected in a similar manner to the opposite end of the bottom bracket.

In Fig. 10, 341 is a half-ring part of connecting section 308 and 343 is the corresponding part on the opposite side of the chain stays 302. Section 344 of the connecting section which comes to lie inside the frame tube 305 is separated from the half-ring parts 341 and 343 by slots 345 and 346. A block 340 of resilient material is attached to one end of section 344, with the same function as described above. Fig. 11 shows a groove 336 through which the cable 311 (not present in the figure) runs in assembled condition. The cable is fixed with respect to the chain stays by means of the clamping block 314 which is to be screwed on. It is also possible, for the purpose of fixing one end, for the cable to be provided with a bead which fits into a widened section to be formed in groove 336.

In Fig. 12, the cable 411 runs outside the frame tubes. As in Fig. 9, half-ring section 441 engages around the bottom half of the left-hand end of the bottom bracket 407, and the half-ring closure piece 442, which is connected to section 441, engages around the top half of the left-hand end of the bottom bracket. As seen in the figure, cable 411 runs along the front side of the frame. On the other side, in a corresponding manner, there runs a second cable (not visible in the figure) . Cable 411 is connected at one end to seat tube 404 and at the other end to the chain stays 402, as can be seen in the following figures 13 , 14 and 15.

A resilient block 440, which has the same function as that described above for corresponding blocks 240 and 340, can be seen in Fig. 13, the block in this embodiment coming into contact with the bottom outside of frame tube 405. It can be seen in Fig. 14 that block 440 is mounted on a bridge 446 which connects half-ring sections 441 and 443. The two chain stays 409 are also connected by a second bridge 447. It can be seen in Fig. 15 that a groove 436 is provided on the underside of each of the half-ring sections 441 and 443 for the two cables which connect the chain stays to the frame. Here too, the cables are fixed by a clamping block 414.

In Fig. 16, cable 511 also runs on the outside of the frame tubes, in this case along the down tube 505. The connection between the chain stays and the bottom bracket corresponds to that shown in Figs . 9 and 12. In this embodiment, it is possible to use either one or two cables, it being possible for the connection to the chain stays to be similar to the embodiments described above.

In Fig. 17 a projection is present between the half-ring section 641 and the non-visible corresponding half-ring section that engages around the other end of the bottom bracket 607. A channel 651 is present in this projection. At the underside of down tube 605 there is present a projection 652 connected thereto, in which a channel 653 is present. When the chain stays are assembled and the bicycle is unloaded the channels 651 and 653 are in the same straight line. Through the channels 651 and 653 runs a tie rod 654 clear of the channel walls. The ends of the rod protrude from the channels . The end of the rod protruding from channel 653 is provided with a head 655 and the other end is provided with a screw thread onto which a nut 656 is screwed. The dimensions of the head and the nut are larger than the dimension of channels 651 and 653. Beneath the head and beneath the nut there is provided an assembly of two curved rings 657 and 658 that can act as a hinge in the case of tilting of tie rod 654 in channel 653 due to the pivoting of the chain stay around the bottom bracket. An elastic cushion 659 is present between projection 650 and projection 652. Nut 565 acts via the assembly of rings 657 and 658 on a ring 660, which fits in a cylindrical housing 661, which in its turn fits in a recess in projection 650. A plurality of disc springs 663 are locked up by nut 656 under a desired tension between ring 660 and bottom 662 of housing 661. When the chain stays 602 pivot counter- clockwise as a result of the bicycle riding over a bump, the disc springs 663 are compressed by the tensile force exerted on rod 654 and so flexibly dampen the movement . Pivoting of the chain stays in the opposite, clockwiswe, direction is restrained by elastic cushion 659.

The suspension characteristics of this embodiment can be controlled by the proper choice of the elastic characteristics of the disc springs and the elastic cushion and by tightening or loosening nut 656

The suspension system according to the invention, which is substantially characterized by the presence of a cable in the suspension system, can also be used for bicycles in which the chain stays are pivotably connected to the basic frame, even if the pivot axis does not lie in the centre of the crankshaft. It is also possible to use, besides the chain stays described above, stays which are known from the prior art, in particular those comprising a left-hand and right-hand half which are connected to one another using bolts or in some other manner to form a fork. In that case, it is advantageous not to connect the chain stays to the ends of the bottom bracket using two half-ring parts which are joined together, but rather, for one end of each chain stay to comprise a complete ring, with or without a bearing, which can be pushed over the end of the bottom bracket .

Claims

1. Suspension system for a bicycle frame which comprises a basic frame and chain stays pivotably connected thereto, the basic frame comprising a down tube and a head tube and seat tube which are connected to one another by the frame tube, and a bottom bracket being present at a connection between the frame tube and the seat tube, which suspension system is called into action when the chain stays pivot with respect to the basic frame, characterized in that the suspension system comprises a cable which at one end is attached to the chain stays and of which another end is fixed with respect to the basic frame.

2. Suspension system according to Claim 1, in which the other end is attached to the down tube.

3. Suspension system according to Claim 1, in which the other end is attached to the head tube.

4. Bicycle frame according to Claim 3, in which the other end of the cable protrudes into the head tube and is provided with a bead which fixes the cable in the head tube.

5. Suspension system according to one of Claims 2-4, in which the cable runs through or along the down tube.

6. Suspension system according to Claim 1, in which the other end is attached to the seat tube .

7. Suspension system according to Claim 6, in which the cable runs through or along the seat tube.

8. Suspension system according to one of the preceding claims 5 or 7, in which the cable runs through the frame tube or the seat tube, which suspension system comprises suspension means which are present in the frame tube or the seat tube and with which the cable is in contact, which suspension means are called into action by the cable when the chain stays pivot with respect to the basic frame.

9. Suspension system according to Claims 1 and 2 in which the cable is a tie rod and which comprises disc springs which are compressed when the chain stays pivot with respect to the basic frame as a result of the bicycle being loaded.

10. Bicycle frame which includes a suspension system according to one of Claims 1-9, in which shock- absorbing means are also present which damp the pivoting of the chain stays with respect to the basic frame.

11. Bicycle frame according to Claim 10, in which the shock-absorbing means are situated in or on the down tube or the seat tube in the vicinity of the bottom bracket and are actuated by the chain stays on the latter pivoting.

12. Bicycle frame according to Claim 10, in which the shock-absorbing means are arranged on the chain stays .