In this article, we’ll be discussing a Linear Derailleur Mechanism by Yeti, US patent number 10,894,575. The patent date is Jan. 19th, 2021 and the filing date is June 5th, 2018. This is a continuation of patent 10,011,325 from July 2018, which is a continuation of publication 2016/0167740 from June 2016, so this is not a new idea from Yeti. It’s just been under the radar for quite a long time.
Just like the last Yeti patent, this one is incredibly good. They’re the anthesis of Shimano patent documents. Here’s an interesting little anecdote: this patent is assigned to Yeti Design, while their bike suspension patent is assigned to Yeti Cycles. Not sure why, but here we are.
This patent has been granted as of Sept. 2020.
Brief Summary (tl;dr)
Yeti are implementing a new derailleur with a 6R linkage system that moves the derailleur in a perfectly linear movement. Yeti say this will be smaller, lighter, simpler, and allow for more freedom for designers. Additionally, Yeti say this will improve the performance of the derailleur system.
A derailleur is a mechanism used to change the gears of a multi-geared bike with a cassette-style gearing system. A chain is guided through the mechanism and aligned using a pulley system. Traditionally, a cable is attached from a shifting mechanism to the derailleur that, when activated, changes the tension of the cable to move the derailleur from gear to gear. There’s some hydraulic and electronic actuation methods that have the same end-results. I’d imagine this patent can also be used in all different actuations.
Derailleurs can be used in both a forward system at the crank and a rearward system at the rear hub, though the front systems have become nearly obsolete in mountain bikes. Road bikes are still using front systems, though. According to Yeti, current derailleur systems have an inherent flaw that they say they have solved.
Linear derailleurs are not a new concept. A commenter brought this example to my attention. White Industries created a very cool linear derailleur in the 90’s that utilized a pair of rods and a fancy bearing set up. It was a very simple concept, though this article explains some issues with it.
Yeti are introducing a derailleur with a linkage system that has a rectilinear path. So, the movement of the derailleur is perfectly linear. Typical derailleurs use a planar 4-bar link forming a parallelogram. The resulting movement of the derailleur is non-linear and constrains the design based on the path of the derailleur linkage. Below is a current SRAM system with the parallelogram highlighted. This is the system that Yeti say they’ve improved.
In short, Yeti state they’re using a 6R linkage system for their derailleur.
As an example, the linear derailleur includes an over-constrained 6R spatial linkage (e.g. a Sarrus linkage) which is capable of substantially linear motion of the floating link. As a result, the angles of the pulley axes and the wheel or crank axis remain constant relative to one another. This linear motion allows for either of a concentric or eccentric mounting of the derailleur cage on the linkage system.
Yeti also describe a 6R mechanism:
A 6R spatial mechanism is one that includes 6 links with revolute joints and at least one link axis is not parallel to another within the system.
Yeti’s intended novelty appears to be the use of a spatial linkage with a floating linkage having a linear path, where at least one component of the linkage moves in a linear path with the cassette axis or wheel axis.
Yeti state that the problem with the current derailleur system is wear and tear due to a non-linear shifting path.
The resultant path of the floating link 20 of this mechanism is non-linear, forming a curved or arcuate path. As a result, the angle of the derailleur pulley axes 17, 19 are not constant relative to the wheel axis 7 in at least one reference plane throughout the entire travel range, which can create undesirable forces and negatively affect performance and wear and tear on the components.
Like I said, Yeti’s patent documents are awesome. They even explain the issue with current systems in detail. Figure 1 shows a current system with a parallelogram-shaped link.
Yeti state some disadvantages to this design:
There are several disadvantages to this mechanism. For example, the resultant path this linkage defines is non-linear curved. As a result, the angular relationship of the derailleur pulley axes 17, 19 varies with respect to the wheel axis throughout the range of motion. The inherent geometry of the parallelogram leaves little freedom of the linkage mounting location relative to the rear wheel to achieve the desired linkage path. This limited freedom correspondingly limits frame designers options, whereas more freedom of this mounting location would give frame designer more options.
So, they’re doing this for design freedom.
With a parallelogram design, the mechanism’s linkage path is dependent upon the link lengths and axes geometry. In order to achieve an optimum linkage path and actuation ratio in a parallelogram mechanism, it is common to add additional complex features such as pulley wheels and extended links. These items add weight and complexity.
They’re also saying this is a lighter and less complex solution.
The inherent geometry of the parallelogram leaves little freedom to minimize the mechanism’s volume envelope and envelope position relative to the drive side frame dropout. It is desirable to have a compact mechanism located as inboard as possible to the frame to minimize the chance of hitting the derailleur on an obstacle while riding, which can prove difficult to achieve with this design.
Yeti state this is a smaller design.
By moving the [derailleur] in such a consistent manner, overall shifting and functionality of the derailleur is improved over traditional types.
Most importantly, Yeti state this will improve shifting. I’m not sure what ‘improved’ means here, but that’s what they say.
I’ll be honest, there’s a lot going on here, so I’m not going to dive super deep into each axis of rotation of each of the 6 links in this patent. I’ll try to keep it higher level.
Yeti have designed a derailleur that has an absolutely linear path throughout the entire range of motion of changing gears. Figure 3A shows the design in question. There are two parts to this derailleur (and probably all derailers); the cage assembly 30 and the movable connection 110. This design allows the movable connection 110 to move in a linear path.
The movable connection 110 is driven by a link system with 6 different parts, shown in Fig 4A. Each part has a very specific axis of rotation.
This link system is shown assembled in Fig 4B, below. Yeti also show the linear movement of this new link system, what they’re calling a ‘rectilinear’ path. Position A is the collapsed position, position B is an intermediate position, and position C is an expanded position. This is the over-constrained 6R spatial linkage.
The rectilinear path allows more freedom of design, where the links can be in various orientations and locations to achieve the same linear path.
With rectilinear actuation, the mechanism 110 can be rotated in any direction and the travel of the floating link 150 is the same linear path.
There’s an interesting line in this patent that breaks down the theory very concisely, though you’ll probably need to read it a few times to absorb what they’re saying. Referring to Fig. 4C:
… it is understood theoretically that in order for the spatial linkage to constrain the floating link 150 to a rectilinear path, certain conditions should be met. In one embodiment, with a 6R linkage, R denoting revolute joints or rotary hinges that allow one degree of freedom movement between links (see e.g. FIG. 4A), all three pivot axes of the first linkset 145a are be parallel to each other, all three pivot axes of the second linkset 145b are parallel to each other, and the first linkset’s pivot axes N, P, and Rare not parallel to the second linkset’s 145b pivot axes M, Q, and S. Such a system is illustrated in FIG. 4C. The floating link is constrained to a rectilinear path and may be suitable for use in one or more of the various linear derailleur embodiments as described in this disclosure.
Yeti also broaden the scope of this system:
…the linksets can be configured in a crossed configuration as illustrated in FIGS. 4E and 4F. Or in another example, the linksets can be configured in an open configuration as illustrated in FIGS. 4G and 4H.
This is the cool part for me. Yeti show some example graphs that compare their derailleur geometry to currently available systems. I’ve added some support for each graph.
Company 1 is the SRAM XX1 and Company 2 is the Shimano RDM9000. This graph shows the yaw and roll paths of both the SRAM and Shimano examples compared to the Yeti example during horizontal movement away from the bike as a rider upshifts. Note how the SRAM and Shimano derailleurs have a non-linear path and Yeti’s is perfectly flat.
Fig. 11 also show pulley axes angles and explain this graph:
…the pulley axes of linear derailleur are parallel to the wheel axis throughout the entire travel range throughout the entire travel range in pitch. However both of the parallelogram designs deviate from zero in pitch but [SRAM] does remain constant in pitch unlike [Shimano].
In FIG. 12 the pulley axes of the rectilinear linkage derailleur are set at an angle with the yaw at about -1.5 degrees and the roll at about -0.9 degrees. Still, the linear derailleur remains constant through the range of travel
…in FIG. 13 with the pitch set at about 90 degrees, the pulley axes of linear derailleur remain constant relative to their initial pitch.
Yeti’s injecting themselves in a market that has well-established players, but they’ve shown again that they are among the best in understanding geometry, and the intricacies and ramifications of geometry changes. If this can live up to the promises they’ve laid out, this might be a huge step forward in the derailleur market. I’ve been looking at Shimano and SRAM patents for a while now, and they appear to be heavily invested in electronic stuff and cassette/cog micro-improvements. I’ve found almost nothing on them trying to improve shifting with the derailleur geometry itself.
1/26 edit: I deleted this part about prosecution because after some digging, this has been granted. So, there’s no use in my assumptions on what the attorneys will do because it’s already happened and the USPTO has decided this is novel and Yeti now own the idea.
After a quick glance at the prosecution history, the USPTO rejected it once on a drawing rejection, a double patenting rejection, a 112 rejection, and a 102 rejection.
The drawing rejection was overcome by a clarification of some different planes in the claims/drawings. The double patenting rejection was based on Yeti’s own prior patent in view of 3,847,028 from 1973. A terminal disclaimer was filed to overcome the double patenting. A terminal disclaimer is a document stating that (Yeti’s) second patent expires when the original one expires.
The 112 rejection means Yeti had something in their claims that wasn’t supported in the specification. All they had to do was do change/add some language to the spec.
The 102 rejection is an actual rejection, based on 3,847,028 again. This patent is a leaf spring derailleur and was easily overcome because they’re not even close to similar.
Lastly, is Yeti going to actually make this? I’d think it would probably be more advantageous to license the design to companies like SRAM or Shimano, which have many years of derailleur experience. But who the fuck am I? I don’t know what they’re planning with this, but it’s cool to see.