WO2004080786A2

WO2004080786A2 - Bicycle frame provided with a flexible seat tube

Info

Publication number: WO2004080786A2
Application number: PCT/FR2004/000508
Authority: WO
Inventors: Manuel Roure; Yvan Pesenti
Original assignee: Salomon S.A.
Priority date: 2003-03-05
Filing date: 2004-03-04
Publication date: 2004-09-23
Also published as: FR2851983B1; FR2851983A1; WO2004080786A3

Abstract

The invention relates to a bicycle frame comprising a head tube (20), a crankset housing (26), a post for a seat (38), a rear wheel crank axle (32), a rigid frame (12): The inventive frame is characterised in that the rigid frame (12, 28) connects at least the head tube (20) to the crankset housing, the seat post comprises a bent seat tube (40) connected to the rigid frame (12, 28) and the trajectory of the seat (38) is generally horizontal with respect to the rigid frame (12) as a result of the seat tube (40) bending.

Description

FLEXIBLE BEAM BIKE FRAME

The invention relates to the field of bicycle frames. According to the most conventional construction, a bicycle is made up of a rigid frame connecting a steering box (on which is articulated a fork carrying a front steering wheel), a bottom bracket, a saddle support, an axle of anchorage for the rear driving wheel. The rigid frame is generally made of metal, for example steel or aluminum alloy.

To increase comfort and / or trajectory holding, it is known to provide wheel suspension systems. These suspensions, inteφosed between a wheel and the rigid frame, are generally designed so as to collect a mainly vertical component of the shocks due to the passage of the wheels on irregularities or obstacles.

It is also known to interpose, between the saddle and the frame, a saddle support forming a vertical suspension, for example in the form of a telescopic seatpost. In all cases, it is difficult to choose the right firmness for the elastic elements associated with this kind of suspension. In fact, by using overly flexible springs and shock absorbers, pumping phenomena very quickly appear when the cyclist is in the middle of pedaling effort, which is very penalizing in terms of performance of the bicycle, and which therefore increases the cyclist fatigue. To eliminate this pumping phenomenon, it is therefore necessary to greatly increase the stiffness of the suspensions, so much so that they only very partially absorb the shocks due to rolling. If such firm suspensions remain interesting to absorb the big shocks encountered during the practice of mountain biking (MTB), they do nothing during small shocks caused by bitumen irregularities or encountered during the progression on the way stony earth. Document BE-439599 describes and represents a bicycle frame in which the part of the frame which supports the saddle extends from the bottom bracket without being connected to any other rigid element. In this bicycle, we note that the frame part which connects the steering box to the crankset and the frame part which supports the saddle are made up of the same part, in this case two parallel tubes. Those skilled in the art therefore deduce that these two parts of the frame have the same intrinsic rigidity. However, it is known that the part of the frame which connects the steering box to the crankset must be rigid, if only to support the weight of the cyclist without bending. If this part of the frame is not rigid enough, the steering box will not be guided well enough, so the steering will not be precise enough.

In document US Pat. No. 5,833,255, a saddle suspension system is described which comprises a deformable parallelogram structure which replaces the usual seat post. However, this system has the disadvantage of a large overall height, which greatly reduces any possibility of adjusting the seat height relative to the frame. In addition, the geometry of this structure is such that it is difficult to integrate therein an elastic return system which is sufficiently progressive over the entire travel of the saddle. Finally, the

- elastic return system described in this document generates very high stresses in the parallelogram, to the point of being able to cause the device to rupture and it very strongly limits the travel of the saddle.

The object of the invention is therefore to propose a new design for a bicycle, more particularly for its frame, in which suspension means make it possible to isolate the cyclist to a large extent from minor impacts.

To this end, the invention provides a bicycle frame, of the type comprising:

- a steering box;

- a bottom bracket; - a saddle support;

- an anchor axle for a rear wheel;

- a rigid frame; characterized in that the rigid frame connects at least the steering box to the bottom bracket, in that the saddle support comprises a flexing beam connected to the rigid frame, and in that the path of the saddle relative to the frame, due when the beam is bent, is mainly horizontal.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, as well as in the light of the appended drawings in which:

- Figure 1 is a schematic side view of a bicycle provided with a frame according to the teachings of the invention;

- Figure 2 is a partial perspective view of the frame of the bicycle of Figure 1;

- Figure 3 is a view similar to that of Figure 1 illustrating a variant of the invention in which the frame further incorporates a suspension system of the rear wheel; - Figure 4 is a view similar to that of Figure 1 illustrating a variant of the invention in which the frame incorporates a system for damping the movements of the saddle. There is illustrated in Figures 1 and 2 a bicycle 10 provided with a frame 12 according to the invention. The bicycle 10 has a rigid frame 12 to which are fixed a front steering wheel 14 and a rear driving wheel 16. The front wheel 14 is more particularly mounted on a front fork 18, which may or may not be provided with a suspension system, and which is rotatably mounted in a steering box 20 of the frame 12. Above the steering box 20, a handlebar 22 is linked to the fork 18 to allow the user to control the rotation of the front wheel 14, so steer the bike. The bicycle also has a crankset 24 which is rotatably mounted in a bottom bracket

26 of the frame 12 for controlling the drive of the driving wheel 16.

According to the invention, the frame comprises at least one rigid portion connecting the steering box to the bottom bracket. By rigid, it should be understood here that this part of the frame must not deform significantly when the bicycle is used. It goes without saying that the rigidity absolute does not exist and that this one is defined here according to what can be felt and seen by the user.

In the first exemplary embodiment illustrated in FIGS. 1 and 2, the rigid frame is produced in the form of a lattice of tubes. These tubes can for example be made of metal, or of high-performance composite materials, for example of carbon fibers embedded in a thermosetting resin. In addition, in this first example, the rigid frame extends to an axis for anchoring the rear wheel.

In this first example, the rigid frame 12 therefore comprises a main beam 28 which directly connects the steering box 20 to the bottom bracket 26, and two rear beams 30 which extend in the same plane from the bottom bracket 26 and whose the rear ends 32 form the anchoring axis of the rear wheel 16. The rigid frame also comprises two rectilinear diagonal beams 34 which directly connect the steering box 20 to each of the two rear ends 32 forming the anchoring axis of Rear wheel. The two diagonal beams 34 therefore have a transverse spacing, due to the transverse spacing of the two rear ends 32 on which the rear wheel are fixed 16. The spacing of the diagonal beams 34 and the direct connection between the steering box 20 and the anchor pin 32 of the rear wheel 16 provides this frame with very good torsional rigidity.

The rigid frame also has a central beam 36, one end of which is fixed to the bottom bracket 26 and the other end of which is connected to the two diagonal beams 34. The central beam 36 is substantially perpendicular to the diagonal beams 34.

The frame thus formed by the beams is perfectly rigid. It is rigid on the one hand by the intrinsic rigidity of the beams which constitute it. This rigidity is also due to the geometric character of the assembly of the beams, this geometry being a closed geometry. Of course, the different connections between the beams of the rigid frame are rigid connections similar to embedding. In the case of beams made of metal tubes, these connections are for example made in the form of welds.

The rigid frame which has just been described could take other forms. It could also be produced in a completely different way, for example in the form of a one-piece structure made of composite material. Of course, the bicycle frame according to the invention comprises a saddle 38 mounted on a saddle support.

According to the invention, the saddle support comprises a flexing beam 40 connected to the rigid frame. This beam is linked by its lower end to the main beam 28, at a point thereof which is advanced relative to the bottom bracket 26. It elongates in a general direction which is inclined upwards and towards the rear, and it carries at its upper end, the saddle 38 mounted at the end of a seat tube 42. Thus mounted, the saddle 38 is arranged in a conventional position relative to the bottom bracket and the handlebar 22.

According to the invention, the beam 40 is flexible enough to flex in use and for this flexion to result in a displacement of the saddle 38 which has a component mostly horizontal, in a vertical and longitudinal plane. This deflection, and the corresponding displacement, may appear under the simple weight of the user. However, the geometry of the beam 40 and its orientation may cause the simple weight of the user, when stationary, to not cause any displacement. This would for example be the case if the flexing beam was oriented in a substantially vertical direction, since the action of the weight on the beam would be a compression action which would cause almost no deformation. On the contrary, in use, the assembly formed by the cyclist and his bicycle will be subjected to an acceleration or micro-accelerations having a horizontal component. These accelerations, applied to the mass of the cyclist, will result in forces which will cause the beam 40 to bend in a direction substantially pe sensiblementendicular to its elongation.

The flexing beam 40 is constructed in such a way that, under the normal forces of using the bicycle, the saddle moves over a distance of at least one centimeter relative to the rigid frame 12, and if possible over a distance of 1 '' from 3 to 5 centimeters. Of course, for a given flexing beam, the amplitude of these displacements will depend, for example, on the mass of the cyclist and on the intensity of the accelerations or micro-accelerations to which he is subjected. In particular, the flexing beam 40 will be intrinsically significantly more flexible in bending than the rigid frame.

The path of the saddle 38 relative to the rigid frame is comparable to an arc of a large radius. This trajectory is mainly horizontal in the sense that the displacement of the saddle between the extreme positions (under normal conditions of use) has a horizontal component which is greater than its vertical component.

In the example illustrated in FIGS. 1 and 2, the beam 40 is fixed to the main beam 28 of the rigid frame 12 by a pivoting link 44 of transverse axis, and it abuts longitudinally towards the rear against a transverse bar 46 which extends between the two diagonal beams 34. This abutment support takes place in a predominantly horizontal direction, and it is located approximately halfway up the beam 40. It can also be seen that the flexing beam 40 passes between the two diagonal beams 34, which can be used to provide transverse guidance. One could also provide a stop forwards for the beam 40, for example in the form of a second transverse bar arranged just in front of the beam 40. Thanks to the illustrated construction, the beam bends over its entire length in the same direction .

As a variant, provision could be made for the flexing beam 40 to be directly embedded on the rigid frame 12, for example on the main beam 28. In this case, the longitudinal stop (s) could be eliminated. However, it would be necessary to carefully build in the two beams because it would be the site of very high concentrations of forces. Provision could also be made for the connection point between the flexing beam 40 and the rigid frame 12 to be at another location in the frame, for example at the bottom bracket 26. The beam 40 can be constructed in different ways, taking care, however, to give it sufficient flexibility in bending in the longitudinal and vertical plane, while taking care, on the contrary, to keep it good rigidity in the transverse direction. The beam could be made of metal with high elasticity, or even of wood. However, it appeared particularly advantageous to produce the flexing beam 40 in the form of a sandwich structure comprising a central core and two external skins. The central core can for example be made of foam, honeycomb or wood. The skins will advantageously be formed by a composite material comprising fibers (glass, carbon, metal, etc.) embedded in a thermosetting resin (polyester, epoxy, etc.). Such a structure makes it possible to fairly easily obtain the desired mechanical characteristics. In the example illustrated, the beam 40 has at rest a slightly curved shape. However, it could be carried out more simply in a rectilinear manner. Similarly, the section of the beam can take different forms, but it will be advantageous to use a beam of substantially rectangular section, elongated in the transverse direction of the bicycle like that illustrated in FIG. 2, which allows it to be given flexibility desired in the longitudinal direction and the desired stiffness in the transverse direction. In addition, the entire rigid frame being located below a line joining the steering box to the anchor axis 32 of the rear wheel 16, the center of gravity of the frame is particularly low.

In the example illustrated, it can be seen that the saddle 38 is fixed to the end of the flexing beam 40 by a conventional saddle tube 42, so that it is easy to adjust the height of the saddle 38 relative to the floor and pedal 24.

However, provision can be made for the flexing beam 40 to be dismountably mounted on the rigid frame, and for the frame to be equipped with different models of beams. These flexing beams may differ from each other for example by their height, by their characteristics of flexibility and stiffness, or by their geometry so as to define different positions of the saddle relative to the crankset (for example positions more or less advanced).

Thus the characteristics of the frame can be infinitely adapted according to the size of the cyclist, his weight, his style of practice, or even the nature of the terrain on which he plans to ride.

In the embodiment of the invention which is illustrated in Figure 3, we can see a bicycle frame in which the rear wheel 16 is connected to the rigid frame 12 by a suspension system. Thus, the two rear beams 30 can be articulated around the bottom bracket 26 and be supported by a combined spring-shock absorber 48 arranged in alignment with the diagonal beams 34 and resting on the latter. Of course, such a suspension of conventional design allows the rear wheel to describe a predominantly vertical trajectory relative to the rigid frame 12. This rear suspension could also be replaced by any type of known rear wheel suspension fulfilling the same function. In all cases, the frame will keep a rigid part connecting the steering box 20 to the bottom bracket 26, and a flexing beam 40 carrying the saddle 38. With such an embodiment, the rear suspension can be adjusted so that it collects and absorbs mainly large shocks, while small shocks and micro-accelerations will be absorbed by the deformation of the flexing beam 40. In FIG. 4, the possibility of providing a mechanism for damping the displacements of the saddle 38 has been illustrated. Indeed, even if the flexing beam can to some extent dampen the displacements of the saddle due at its own bending, it may be advantageous to provide the flexing beam with a damping mechanism sufficiently effective to avoid incessant oscillations of the saddle. Thus, provision can be made to use a damper 50 (for example a hydraulic damper) inteφosé between the rigid frame 12 and the vicinity of the free end of the flexing beam 40. In the example illustrated, it can be seen that the one of the rods of the hydraulic shock absorber 50 is connected to the diagonal tubes 34 while the other rod of the shock absorber is connected to the flexing beam 40 at a point situated between its upper end and the stop point on the transverse bar 46 rigid frame. The bicycle frame according to the invention therefore makes it possible to obtain a bicycle that is both rigid and nervous, which makes it possible to obtain very good performance and very good riding precision, while guaranteeing a level of comfort for the user hitherto not reached, especially in the ability to filter out small shocks due to driving. In addition, the suspension system of the saddle which is proposed is both very simple, therefore without risk of breakage or wear, and very light since the excess weight compared to a fully rigid bicycle is much less than that 'drives a classic suspension system.

Claims

1. Bicycle frame, of the type comprising: - a steering box (20);

- a bottom bracket (26);

- a saddle support (38);

- an anchor pin (32) for a rear wheel (16);

- a rigid frame (12); characterized in that the rigid frame (12, 28) connects at least the steering box (20) to the bottom bracket (26), in that the saddle support comprises a flexing beam (40) connected to the rigid frame (12 , 28), and in that the path of the saddle (38) relative to the rigid frame (12), due to the bending of the beam (40), is mainly horizontal.

2. Bicycle frame according to claim 1, characterized in that the flexing beam (40) has a lower end which is fixed to the frame (12, 28) and an upper end which carries the saddle (38).

3. Bicycle frame according to claim 2, characterized in that the lower end of the flexing beam (40) is fixed to the frame by a recessed connection.

4. Bicycle frame according to claim 2, characterized in that the lower end of the flexing beam (40) is fixed to the frame (12, 28) by a pivoting link (44).

5. Bicycle frame according to any one of the preceding claims, characterized in that the flexing beam (40) is supported on the rigid frame (12, 46) by a central region of the beam.

6. Bicycle frame according to any one of the preceding claims, characterized in that the rigid frame (28, 30, 34) connects at least the steering box (20), the bottom bracket

(26) and the axle (32) for anchoring the rear wheel (16).

7. Bicycle frame according to any one of the preceding claims, characterized in that the flexing beam (40) is made of composite material.

8. Bicycle frame according to any one of the preceding claims, characterized in that the flexing beam (40) is produced according to a sandwich technology.

9. Bicycle frame according to any one of the preceding claims, characterized in that the rigid frame (12, 34) provides transverse guidance of the flexing beam (40).

10. Bicycle frame according to any one of the preceding claims, characterized in that the rigid frame (12) extends below a line joining the steering box (20) to the anchor axis (32 ) for the rear wheel (16).

11. Bicycle frame according to any one of the preceding claims, characterized in that the rigid frame comprises at least one rigid beam (28) connecting the steering box (20) to the bottom bracket (26).

12. Bicycle frame according to any one of the preceding claims, characterized in that the rigid frame comprises several rigid beams (28, 30, 34, 36) assembled together rigidly according to a closed geometry.

13. Bicycle frame according to any one of the preceding claims, characterized in that it comprises at least one rigid beam (34) directly connecting the steering box (20) to the anchor pin (32) for the rear wheel (16).

14. Bicycle frame according to claim 13, characterized in that the rigid beam (34) directly connecting the steering box (20) to the anchor pin (32) for the rear wheel (16) comprises several coplanar elements .

15. Bicycle frame according to claim 11, characterized in that the flexing beam (40) is fixed on the rigid beam (28) connecting the steering box (20) to the bottom bracket

(26), in an area located between the two said housings (20, 26).

16. Bicycle frame according to any one of the preceding claims, characterized in that the frame comprises a system (50) for damping the movement of the saddle (38).

17. Bicycle frame according to claim 16, characterized in that it comprises a shock absorber (50) which is connected on the one hand to the rigid frame (12, 34) and on the other hand to the flexing beam (40).

18. Bicycle frame according to claim 17, characterized in that the flexing beam (40) has damping properties.