Patent Application
20250136235
The present invention relates to a frame for a bicycle and relates particularly, but not exclusively to a frame for a rear suspension mountain bicycle.
Rear suspension mountain bikes come with many design layouts each providing design different advantages and disadvantages to the rider. Most designs aim to provide a solution to the ideal rear axle path by minimizing or compromising rear suspension complications. Measuring the rear axle path is achieved by following the direction of the rear axle as the bicycle transverses over uneven ground and the suspension is activated.
Examples of the complications that arise from attempting to produce the ideal rear axle path include pedal kickback and pedal bob.
Pedal-kickback is a result of chain growth rotating the cranks backwards during suspension compression. Chain growth is the increase in the length of the chain line which is measured from the points at which the chain contacts the front and rear cogs in the drivetrain. On a rear suspension bike the front or main frame is able to move or pivot relative to the rear frame portion. When the front cog is attached to the main frame portion (via the bottom bracket) and the rear cog-set is attached to the rear frame portion, the distance between the front and rear cogs changes which in turn alters the length of the chain line. It is when the chain line grows significantly due to rearward movement of the rear axle, that excessive pedal-kickback can occur.
Pedal bob is initiated when the pedaling forces from the rider cause the rear suspension to ‘bob’ up and down. This can be caused both by the movement of the rider and by the forces exerted by the rider on the drivetrain. Pedal bob wastes the energy of the rider by compressing the suspension instead of driving the bike forwards.
Examples of the prior art are disclosed in the patent applications published under the numbers EP2420435 and WO2013/126968. Both documents disclose examples of the use of high idler mechanisms in rear suspension mountain bikes.
Preferred embodiments of the present invention seek to overcome or alleviate the above described disadvantages of the prior art.
According to an aspect of the present invention there is provided a frame for a bicycle, the bicycle including said frame, a drivetrain and a plurality of wheels, the frame comprising:
Having two counter-rotating linkages relative to the rear frame portion creates an instantaneous centre of rotation (virtual pivot) which is rearward of the bottom bracket. This is the pivot point that the rear axle is rotating around at any given instant during the action of the suspension, providing a very curved rearward axle path. This process causes the rear wheel to move predominantly backwards during the first part of suspension compression and more vertically during the second part of suspension compression. This is particularly advantageous as the distance between the rear wheel and the front wheel does not continue to lengthen during the second half of the compression, allowing the rider to control the bike more effectively.
Furthermore, having an element of the drivetrain, for example the idler or the bottom bracket, mounted on the second linkage provides additional advantages. The position of the idler on the second linkage allows for control of chain growth in a way that is most desirable for rider. During the first part of the suspension (rearward axle arc path, when the rear axle moves further from the bottom bracket) the idler allows for a small amount of the chain growth to counteract pedal bob during increased pedaling but decreases the amount of chain growth during the second half of the compression (vertical axle arc path) increasing the ability for the rear suspension to absorb bumps during less pedalling activity and reduces pedal kick-back. Furthermore, this location enables the chain to move over the idler along a smoother angle range therefore decreasing distortion and tension experienced by the chain. The chain line is comparatively undistorted compared to other high-pivot designs, as the position of the idler pulley wheel does not pull the chain to an acute angle.
Having the bottom bracket located on the second linkage also reduces complications caused by pedal kickback and pedal bob by enabling the rear axle to move rearwards during the first half of the suspension compression and vertically during the second half of the suspension compression.
In a preferred embodiment the mounting further comprises at least one idler mounting for receiving an idler.
In another preferred embodiment the idler mounting is moveable.
In another preferred embodiment the idler mounting further comprises an aperture for receiving an axle of said idler.
By allowing a single idler moveable or multiple possible locations for the idler within the linkage, the rider can adjust the idler and create the ideal balance between suspension performance and pedalling efficiency, according to the terrain and the rider.
In a preferred embodiment the second linkage is located below said first linkage.
The lower of the two linkages is the more effective place to locate the drivetrain element.
In a further preferred embodiment the mounting further comprises an aperture for receiving a bottom bracket.
In an additional preferred embodiment first and second location are at opposing ends of said first linkage and the third and fourth location are at opposing ends of the second linkage.
In another preferred embodiment the mounting allows the drivetrain component to be mounted to said second linkage at a plurality of locations.
In a further preferred embodiment the mounting comprises multiple mountings.
In an additional preferred embodiment the shock absorber has one shock absorber mount located at the first location and another shock absorber mount is located on the main frame mount.
In another preferred embodiment the shock absorber mount is located at a fifth location and another shock absorber mount is located on the main frame mount wherein, the fifth location is on said first linkage distal of said first location.
The rotation of the first and second linkages is preferably exclusively in said second rotational direction.
According to another aspect of the present invention there is provided a bicycle comprising:
In a preferred embodiment the drivetrain further comprises a plurality of gears.
In another preferred embodiment the drivetrain comprises an idler pulley and a chain.
In a further preferred embodiment the drivetrain comprises a bottom bracket mounted to the second linkage.
In an additional preferred embodiment the bicycle further comprises a crank assembly connected to the bottom bracket.
Preferred embodiments of the present invention will now be described, by way of example only, and not in any limitative sense with reference to the accompanying drawings in which:
Referring initially to
The rear frame portion 22 is located behind the seat tube and forms a triangle. The sides of the triangle are formed from a seat stay 32 (the longest side running from adjacent the seat to adjacent the axle of rear wheel 18) a beam 33 (which is next to the seat tube 28) and a chain stay 34 which is closest to the ground.
Located between the main frame portion 20 and the rear portion 22 are a pair of linkages. The first linkage 36 is pivotably connect to the rear frame portion 22, specifically on the beam 33, at a first location 38, and pivotably connected to the main frame portion 20, specifically on the seat tube 28, at a second location 40. The two locations being at opposing ends of the first linkage.
The second linkage 42 is pivotably connected to the rear frame portion 22, specifically at the chain stay 34, at a third location 44 and to the main frame portion 20, specifically at seat tube 28, at a fourth location 46. These locations are also found at opposing ends of the second linkage. This second linkage 42 is located below the first linkage 36. That is when the bike 12 is in standard use, with the wheels 18 and 19 in contact with the ground, the first linkage 36 is above the second linkage 42 being located closer to the top tube 24. The second linkage 42 is located closer to the drivetrain 14 and closer to the ground.
The second linkage 42 also includes a mounting 48. This mounting is used to mount a component of the drivetrain 14, for example the idler or the bottom bracket. In
In the embodiment shown in
Mounted to both the rear frame portion 22 and the main frame portion 20 is the drivetrain 14. The drive train includes a rear cog-set (or cassette) 50 and rear derailleur 52 both located at or adjacent the axle 18x of rear wheel 18 at the junction of the seat stay 32 and chain stay 34. In
Now referring to
The first linkage 136 has a first and second location, 138 and 140, located at distal ends. The first location is on the seat stay 132 of the rear frame portion 122 and the second location is on the seat tube 128. The first linkage also includes a fifth location 158 providing a mount for one end of the shock absorber 116 with the other end of the shock absorber 116 being connected to the down tube 126.
The main difference between the embodiment shown in
Referring now to
When the bicycle encounters a bump 62 (
It should be noted that some of the rotation of the linkages may reverse at the extreme ends of their movement. For example, as the rear frame portion 22 rotates in a clockwise direction the linkages 36 and 42 initially, and through the majority of their movement, rotate in an anti-clockwise direction as described above. However, there comes a position where the first (upper) linkage 36 becomes aligned with the beam 33 that forms the portion of the rear frame portion closest to the seat tube 28. That is, the linkage 36 and beam 33 are in a straight line. Any further movement of linkage 36 in the anti-clockwise direction pulls the beam 33 slightly upwards in turn causing the second (lower) linkage 42 to briefly and slightly begin to rotate in a clockwise direction. It is therefore the case that rotation of the rear frame portion 22 in a first rotational direction relative to the main frame portion 20 results in rotation of the first and second linkages 36 and 42 that is primarily in a second rotational direction opposite to the first direction and the rotation of the first and second linkages is not exclusively in the second rotational direction. In this instance the preferred movement of the idler under pedalling load in the initial part of the suspension travel is still achieved. However, if the linkage 36 and beam 33 do not pass the point of being aligned then the rotation of the first and second linkages is exclusively in the second rotational direction.
This motion initially drives the rear wheel backwards, increasing the distance between the rear axle 18x and bottom bracket 51. With additional reference to
If the idler 49 is located on or close to the fourth location 46, where the second linkage 42 is attached to the main frame portion 20, then the idler 49 is less able to influence chain line length as L1 remains substantially the same through the whole of the movement of the suspension. This is in part because the idler is located very close of the front chain ring 54 and because the anticlockwise movement of the second linkage about the fourth location 46 results in very little movement of the idler 49. However, the length L2 extends in a similar way to the way L3 would in the absence of an idler 49 because the rearward movement of the rear axle 18x results in movement of the rear cog-set away from the fourth location. As a result of the minimal movement of the idler, the impact of the increasing length of the chain line (chain growth) is not significantly compensated for by the idler. This location for the idler 49 is most beneficial in reducing pedal bob (extending the suspension during pedalling) because chain growth is useful in counteracting this problem. However, it is least effective in reducing pedal kickback where the sudden chain growth resulting from compression of the suspension passes that force into the pedals risking throwing the rider off balance. As a result, idler locations closer to the fourth location 46 will maximize pedalling responsiveness which is preferable for bikes intended to be ridden uphill or for full-suspension bikes where pedalling importance is the primary concern.
In contrast, if the idler 49 is located on or close to the third location 44, where the second linkage 42 is attached to the rear frame portion 22, then the idler 49 has significant impact on the chain line length as the idler moves when the suspension compresses. In particular, if the second linkage 42 is long enough the idler 49 is able to swing through a sufficiently large arc so that the idler moves to a position where it is not forming the sides L1 and L2 and the chain is extending substantially along the line L3 as through the idler were not present. This location of the idler 49 is most beneficial in reducing pedal kickback because there is little or no increase in the chain line length as the two sides of the triangle L1 and L2 flatten out during compression of the suspension. However, this location is the least effective at reducing pedal bob. As a result, this location or idler locations close to the third location 44 are preferable for bikes primarily designed to travel downhill using the suspension and are used less for pedalling uphill, for example, downhill mountain bikes.
If the idler 49 is located on the second linkage 42 between the third location 44 and the fourth location 46 then a compromise between the extreme positions set out above is provided. Furthermore, ideally the mounting 48 for the idler 49 can be changed allowing a rider to set up their mountain bike for the type of terrain they are expecting to encounter during that ride. This can be achieved by having an idler axle mounted in one of a series of apertures formed in the second linkage or by having an idler mounting which can be slid along the second linkage and fixed into a desired position.
As the rear wheel continues to ascend over the bump the suspension enters into the second part of compression. During this second phase the rear wheel axle begins to move in a more vertical direction compared to the rearward movement during the first phase on compression. This occurs due to combined effect of the two linkages meaning that the rear suspension portion is not pivoting around a single point but instead has a virtual pivot point which moves during the compression of the suspension. This motion is represented in
The choice of the position of the bottom bracket mounting 148 on the second linkage 142 impacts the amount of chain line length increase as follows. The closer the bottom bracket mounting 148 is to the third location 144 the smaller the amount of chain line length increase during the activation of the suspension. Less chain line length increase is better for reducing pedal kickback but assists less in overcoming pedal bob. As a result, this position for the bottom bracket mounting 148 is preferable where the suspension is going to be used significantly and pedalling is minimized such as downhill mountain biking.
In contrast, the closer the bottom bracket mounting 148 is to the fourth location 146 the longer the length of the triangle L4 and therefore the greater the chain line length increase during the suspension stroke. More chain line length increase is better for reducing pedal bob but risks increasing pedal kickback. As a result, this position for the bottom bracket mounting 148 is preferable where pedalling performance is more important.
It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the protection which is defined by the appended claims. For example, the rear frame portion is illustrated as a right-angled triangle however, the rear frame portion could also be a non-right-angled triangle (oblique triangle). In both the examples illustrated above the shock absorber is mounted on the first linkage at or close to the first location 38 and 138 at one end and mounted on the down tube 26 and 126 at the other end. These are provided merely as examples of a suitable shock absorber mounting location and many alternative arrangements for the shock absorber will also prove effective, including, but not limited to, the shock absorber being mounted directly between the front and rear parts of the frame, or where an arrangement of connecting struts and additional linkages could be used to situate the shock absorber in a plurality of positions. Furthermore, the shock absorber could be mounted to portions of the linkages that extend beyond the points at which the linkages mount to the frame. It should also be noted that the present invention is suitable for both standard pedal bikes, particularly mountain bikes, but is also suitable for electrically assisted bicycles commonly known as E-bikes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2202119.0 | Feb 2022 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2023/050365 | 2/17/2023 | WO |
