Phrases by Dan B. at Wheelbased
On this article, we’ll be discussing a Multi-Physique Automobile Suspension Linkage by Yeti, US publication 20200247500. The publication date is August sixth 2020 and the submitting date was Jan 31, 2020. This patent is said to quite a few provisional purposes.
Transient Abstract (tl;dr)
Yeti have created a brand new 6-bar suspension system that makes use of an analogous Change Infinity-type idea, the place the underside pivot strikes upward to an inflection level and again down on the finish of the journey. In contrast to the linear motion of the Change Infinity, the underside pivot of this method has a non-constant radius of curvature, in contrast to the linear system the place the radius of curvature is zero and in contrast to a round movement the place the curvature is fixed. Yeti declare this may increasingly enhance anti-squat and anti-rise numbers. Extra importantly, Yeti declare the 6-bar system will enable the designers extra freedom in separating kinematic dials equivalent to anti-squat, anti-rise, and leverage ratio.
Background
There are a number of rear suspension methods within the mountain biking business, equivalent to Horst-link, single pivot, VPP, and Yeti’s Change Infinity to call just a few. All these suspension methods present distinctive kinematic traits, permitting us, as customers, to argue about which design is the perfect. Every system turns each single kinematic dial in such a method to produce a motorcycle that can carry out how the producer desires the bike to carry out.
For a little bit technical background, we’ll outline some essential car dynamic phrases. Immediate velocity facilities (IVC), bodily on the spot velocity facilities (PIVC), and dynamic on the spot velocity facilities (DIVC) are utilized in all suspension design. An IVC is some extent of a shifting physique that doesn’t have a velocity at a cut-off date. Moreover, Yeti defines PIVC’s as:
 | PIVCs are outlined on the pivotal axes or digital pivotal axes of jointed linkage physique members. There are 4 PIVCs in a 4-bar linkage whereas there are seven PIVCs in a 6-bar linkage. |
In different phrases, the seven PIVCs are bodily pivots and don’t have to be derived. You’ll be able to view them on the bike because it sits. DIVCs are migrations of IVCs, so that they’re shifting IVCs. On this article, we’re solely going to speak specifics concerning the PIVCs, or else this text will probably be 5 occasions longer.
The variety of IVC’s of a suspension system may be calculated utilizing the equation:
the place N is the variety of whole variety of IC’s and is the variety of hyperlinks (bars). Within the case of a 4 bar system, there are 6 whole IC’s. Within the case of a 6 bar system, there are a whopping 15 IC’s. These IC’s are what controls the texture of our bikes.
Supposed novelty
The meant novelty of this a part of the invention is identical as the primary half. The underside pivot has a non-linear migration path, in contrast to the present Change Infinity system. The entire Yeti system is a 6-bar system, however the Chebyshev 4-bar system of this invention accommodates non-opposing hyperlinks driving a pivot in a non-linear migration path.
Why
From a practicality perspective, Yeti declare a number of benefits of this design. Yeti state:
The smaller envelope of the linkage design as disclosed herein can have a number of benefits structurally: For instance, there may be extra clearance between the rear tire and the suspended physique permitting for a shorter distance from the driving cog axis to the pushed wheel axis. This generally is a efficiency profit permitting for faster turning. The added tire clearance offers extra room for filth and dust that may construct up when using. This added clearance additionally permits room for a bigger “bridge” tying collectively the drive and non-drive sides of swingarm physique which aids in torsional stiffness. The added clearance in entrance of the driving cog axis offers extra room to suit a water bottle and different equipment inside the body of [front triangle].
From a kinematic perspective, Yeti additional declare that:
The smaller envelope of the linkage design as disclosed herein can have a number of benefits kinematically as a result of there may be extra freedom to find PIVC 45 and subsequently a better means to tune parameters equivalent to antisquat, anti-rise, and leverage fee which interprets to better efficiency. Additionally, PIVC migration paths are capable of have a particularly giant minimal radius of curvature, or distinctive curvature profiles with inflection factors inside this small linkage envelope. This isn’t doable with conventional hyperlinks and permits for elevated tunability of suspension habits”.
So, Yeti imagine it is a extra tunable, and refinable suspension system for the long run.
From a compliance perspective, in Fig. 2.16, Yeti present a rear view of the seat tube with each the present Change Infinity system and the proposed suspension system. They declare that
…6104 is horizontal distance of the linkage interface between swingarm physique 1002-E and hyperlink physique 1005-E. 5105 is horizontal distance of the linkage interface between swingarm physique 5002-E and hyperlink physique 5005-E. It’s clear 6104>5105. The broader interface as disclosed herein permits for a stiffer interface between swingarm physique 1002-E and hyperlink physique 1005-E which interprets to a stiffer interface between swingarm physique 1002-E and the suspended physique 2. This enables better efficiency by enhancing the dealing with accuracy of the car.
In brief, the broader profile of the proposed system would supply extra stiffness, main to higher dealing with. Be aware in determine 2.16 how a lot wider and shorter this new system is in comparison with the present Change Infinity system.
What
Yeti are introducing one other design for a similar concept of getting a non-linear migration path of the underside pivot. Once more, it is a 6-bar system with a pivot that isn’t concentric with the shock hyperlink pivot as a result of strong swingarm. The consequence must be just like the present Change Infinity system with an inflection level and a reversal of the underside pivot. The essential distinction is that the linear migration path of the underside pivot within the present Change Infinity system just isn’t the identical as this invention. Yeti aren’t 100% clear as to what benefits this design has over the primary instance.
Yeti state that this design is just like the design from the primary article, however not precisely the identical. Yeti say:
…embodiment 2 [example 2] reveals comparable anti-squat, anti-rise, and leverage fee properties, though not an identical. The upper anti-squat proportion is for pedaling effectivity at first of the journey whereas the decrease anti-squat proportion minimizes the anti-squat pressure the place bump absorption takes priority. Thus, suspension efficiency could also be improved by the interrelationship between the 15 IVC migration paths.
How
We’ll begin with some transient background. There are 3 completely different states of a Yeti bike; an prolonged state (E), an inflection state (I), and a compressed state (C). As with the Change Infinity system, Yeti like to make use of an inflection state, the place the underside pivot of their suspension system modifications route. The prolonged state is a static, no-load state. The compressed state is totally hucked to flat state.
Determine 2.1 reveals the proposed suspension system in a totally prolonged place. The swingarm (element 1002) is hooked up at PIVC 1045 and PIVC 1046. The higher pivot of the swing arm pivot is linked at PIVC 1046 and pivots round PIVC 42. The swingarm can also be hooked up to a backside pivot system. This backside pivot system is the novelty of this invention. It’s essential to keep in mind that PIVC 1045 is the underside pivot that’s linked to the swingarm and will probably be performing the up-down motion.
Determine 2.11 and a pair of.12 reveals two detailed views of the seat tube with the suspension in an prolonged state and a compressed state, with out the swingarm. Because the bike goes by its journey, the shock is compressed round PIVC 1042. Once more, the swingarm is pivoting about PIVC 1045 and 1046. Right here’s the place it will get tough. There may be binding within the system as a result of swingarm being a strong piece and the shortage of concentricity with the two pivots. That is solved (and was solved within the Change Infinity) through the use of a movable backside pivot (PIVC 1045). Yeti have just a few completely different configurations of this design that we’ll speak about on this part.
Determine 2.8 reveals a easy level schematic of the underside pivot system from Figures 2.11 and a pair of.12. Once more, observe the E, I, and C as prolonged, inflection, and compressed states. Because the bike goes into its journey, the swingarm PIVC 1045 travels upward to an inflection level then downward throughout a totally compressed state. Be aware the 2 strains marked with a ‘2’ are the swingarm. The one pivot factors that aren’t shifting are PIVCs 1040 and 1041 (hooked up to the entrance triangle). All different factors within the system transfer throughout wheel journey.
There’s a concentric rotation of the shock hyperlink physique 1006 round PIVC 1042. Consequently, as a result of the rear swing arm has zero pivots, this rotation just isn’t concentric across the pivot hyperlink physique 1005, which is constrained by hyperlinks 1003 and 1004. This whole proposed configuration relies on a system referred to as a Chebyshev 4-bar system. The Chebyshev 4-bar system constrains some extent (1045) with two non-opposing hyperlinks (1003 and 1004) in such a method that the purpose (PIVC 1045) strikes in an almost straight line, utilizing the 2 hyperlinks (1003 and 1004) rotating round two completely different pivots (1040 and 1041). Within the case of this invention, hyperlinks 1003 and 1004 transfer level 1045 practically linearly, however not fairly. Determine 2.26 reveals an instance migration path of PIVC 1045 by the bike’s journey. As you’ll be able to see, the migration path just isn’t fairly completely linear.
Yeti describe the migration path of PIVC 1045:
The radius of curvature just isn’t fixed and varies all through your complete migration path. This isn’t true with linear movement [old system] the place the curvature is 0, or with round movement the place the curvature is fixed [other manufacturer system].
Properly, that’s the geometry. Now let’s speak about how they’re implementing the idea on the bikes.
Apart from the standard shock linkage, there’s a small machine behind the seat tube, simply above the underside bracket. Determine 2.15 reveals an isometric view of one of many proposed methods put in on a motorcycle in comparison with the present Change Infinity system. Be aware how a lot smaller, wider, and easier this new system is.
Determine 2.14 reveals an exploded view of the identical system. As you’ll be able to see, the configuration seems to be smaller and presumably easier/lighter than the present Change system. There are two hyperlinks, 1003 and 1004, hooked up to the entrance triangle. These hyperlinks are then hooked up to hyperlink 1005. That is the Chebyshev 4-bar system.
Yeti don’t state any extra examples of this method, equivalent to versatile brackets or something of the type. It seems as if it is a easier system in comparison with the Watts system.
When?
When will we see this method launched on a brand new bike? Properly, in response to Yeti, not any time quickly – “We’re continuously growing and exploring new concepts. Nevertheless, not all R&D initiatives make it to manufacturing. We have now a number of take a look at mules of varied suspension designs that we’ve been on for years. At present, we’re deliberate out by 2023 and this patent isn’t in our manufacturing line.” All the identical, it is fascinating to get a glimpse at what’s being developed, and to look at the completely different components that make up a brand new suspension system.
