In this article, we’ll be discussing a Multi-Body Vehicle Suspension Linkage by Yeti, US publication 20200247500. The publication date is August 6th 2020 and the filing date was Jan 31, 2020. This patent is related to numerous provisional applications.
This article is the fourth of a 4 part series. Please read the first article, second article, and third article for some background on this article. Some of this article is going to be a copy/paste of the other articles since they’re so similar, and I’m going to assume people are going to come straight here and not read the first article. This part of the patent is short so this article will be shorter.
Brief Summary (tl;dr)
Yeti are introducing an E-bike with a gearbox. As with every other bike, the motor and gearbox are located at the bottom of the downtube. This system is a 6-bar system that uses the Watts 4-bar system from the first article. One pivot of the 4-bar system is attached to the front triangle and the other pivot is attached to the gearbox housing. Yeti say this is a novel design that provides numerous advantages such as weight and manufacturability. Additionally, linkages can be placed more freely, allowing designers to fine tune more easily.
There are multiple rear suspension systems in the mountain biking industry, such as Horst-link, single pivot, VPP, and Yeti’s Switch Infinity to name a few. All these suspension systems provide unique kinematic characteristics, allowing us, as consumers, to argue about which design is the best. Each system turns every single kinematic dial in such a way to produce a bike that will perform how the manufacturer wants the bike to perform.
Yeti developed the Switch Infinity system a few years ago, and it looks like we’re getting an updated version with an electric motor and a gearbox. The first article speaks about a 6-bar system with a smaller 4-bar system located at the bottom pivot, where the bottom pivot moves in a linear migration path with small curvature at the ends of the migration path, allowing for better kinematic tunability.
For a little technical background, we’ll define some important vehicle dynamic terms. Instant velocity centers (IVC), physical instant velocity centers (PIVC), and dynamic instant velocity centers (DIVC) are used in all suspension design. An IVC is a point of a moving body that does not have a velocity at a point in time. Additionally, Yeti defines PIVC’s as:
“PIVCs are defined at the pivotal axes or virtual pivotal axes of jointed linkage body members. There are four PIVCs in a 4-bar linkage while there are seven PIVCs in a 6-bar linkage”.
In other words, the seven PIVCs are physical pivots and do not need to be derived. You can view them on the bike as it sits. DIVCs are migrations of IVCs, so they’re moving IVCs. In this article, we’re only going to talk specifics about the PIVCs, or else this article will be 5 times longer.
The number of IVC’s of a suspension system can be calculated using the equation:
where N is the number of total number of IC’s and n is the number of links (bars). In the case of a 4 bar system, there are 6 total IC’s. In the case of a 6 bar system, there are a whopping 15 IC’s. These IC’s are what controls the feel of our bikes.
E-bikes have really become a staple on the trails. I see at least one every time I’m out. Hell, I even saw one at the bike park… getting on a lift. Whether you like them or not, they’re here to stay, and as long as people are buying them, companies will be making them.
For those who don’t know, an E-bike is a bike with a small electric motor in or around the pedals. These systems aren’t like the electric motor bikes, they’re pedal assist. You still have to pedal, but the bike helps you pedal. There are different modes to the pedal assist, from an easy mode with high levels of assistance, to hard mode with low levels of assistance.
Personally, I think they’re amazing for certain situations. Unfortunately, they’ve gotten a bad wrap because they’ve been bought up by the perceived lazy and uninspired that don’t want to put in the work, and they’ve become the representation for this type of bike. But for those that are trying to lose weight, these bikes are excellent to get started. Someone may be older, their bones and muscle just can’t handle the stresses anymore, and just want to cruise the local trails. They’ve earned their spot on an E-bike. Most importantly, someone may have some kind of disability and a mechanical bike may never allow them to explore trails and reach these amazing places you and I enjoy every weekend. These E-bikes are a godsend to some people.
So the intended novelty of this one is, in part, the same as the first article. The migration path of the bottom pivot isn’t linear anymore. But the design from those articles may have been influenced by the known implementation of a motor and gearbox. The actual intended novelty of this part is that one of the PIVC’s of the small 4-bar system is integrated into the gearbox housing and another is integrated into the front triangle. So, the little Watts 4-bar has one pivot attached to the gearbox housing and another pivot is attached to the front triangle.
Yeti recognize their intended novelty very explicitly:
Note that… other combinations [are] possible in which PIVCs are located on modular bodies that form a rigid suspended body based on the disclosure herein. For example, a PIVC may be integrated into a motor and gearbox that is combined into one unit. These types of motor/gearbox assemblies are commonly used, but currently do not have integrated PIVCs. Another example could be a non-motorized two-wheel vehicle. Here the bottom bracket shell may be a separate modular component front the front triangle structure. In another non-motorized example, the gearbox may be a separate modular component front the front triangle structure but without motor assist. These types of gearbox assemblies are commonly used to replace traditional derailleur shifting systems, but currently do not have integrated PIVCs.
It’s pretty obvious why Yeti are getting into the E-bike game: money. But Yeti make it clear as to why they’re designing this bike the way they are:
In current electric bicycle or pedelec designs, PIVCs are not integrated into motor, battery or gearbox housings. Breaking up suspended body into modular components with PIVCs located on more than one such as gearbox housing and front triangle structure has several advantages. First, it allows for better packaging of suspension linkages. If PIVC 4040 was required to be part of front triangle structure rather than gearbox housing , it would be difficult to fit 4-bar linkage with other packaging constraints such as drive-train clearances. It would also be difficult to provide adequate clearance for linkage body 4003 and linkage body 4005. In addition, the front triangle structure would require a cantilevered “C” shape that extended over the gearbox housing to PIVC 4040. This type of structure may have inadequate strength, may be difficult to manufacture, and may be heavy. As a result of the modular PIVC design, both the gearbox housing and the front triangle structure can be better optimized for weight, strength, and manufacturability. It also allows for more freedom to place linkage bodies and therefore tune kinematics which allows for increased suspension performance as described above.
I’m not going to go into this one. They’re using a Watts 4-bar. Check out article 1 for that part. But they’re putting a motor, gearbox, and battery in the bike with the Watts 4-bar using an integrated PIVC in the gearbox and front triangle.
Figure 4.16 shows a side cross section of a bike with the gearbox 4099, motor 4700, and battery 4705. The motor drives a pinion gear 4701 that drives main gear 4702 connected to crank axle 4703. Yeti do state that this is a simplified drawing to show the general design. An optional clutch mechanism, used to separate the motor from the cranks, is not shown.
Figure 4.4 shows a close up of the gearbox and the Watts 4-bar system. The 4-bar system is attached to the gearbox and front triangle, allowing for a tighter and lighter package.
Figure 4.7 shows a pseudo-exploded view of the gearbox outside the front triangle.
Figure 4.17 shows a full exploded view of the proposed system.
Yeti have also put a removable downtube cover for the battery. I’d actually like to see this on all bikes. Assuming it doesn’t change frame flexibility too much, we could change these out after lots of rock strikes. Better yet, we if we take a hard case to the downtube or BB, there would be a smaller chance of breaking the front triangle and the cover may take the brunt of the force. Then we’d just switch out the cover and done with it. It would be a crush panel.
Yeti don’t state who’s gearbox, motor, or battery they’re using, so lets speculate wildly.
When will we see this system released on a new bike? Well, according to Yeti, not any time soon – “We are constantly developing and exploring new ideas. However, not all R&D projects make it to production. We have several test mules of various suspension designs that we’ve been on for years. At the present, we are planned out through 2023 and this patent isn’t in our production line.” All the same, it’s interesting to get a glimpse at what’s being developed, and to examine the different elements that make up a new suspension system.
Whether you like it or not, this is an absolutely incredible design. Yeti have managed to design a suspension system to allow for more compartmentalized kinematic dials, have made the system smaller/stiffer/lighter, and have managed to put in a motor and gearbox; all in the same design. I’ll speculate and also say this will probably get them off the Fox train too, hopefully saving them a few bucks, and in turn, saving us a few bucks. Alternatively, the gearbox housing may be made in house so that might bring the price back up. Fingers crossed on that one. This design is genuinely mind blowing and these guys and girls should be given their due credit. The wild speculation and criticism on complexity is far overblown and I think this will be a simpler system than the current Switch Infinity. Other manufacturers have 6 bar systems and I don’t see this kind of vitriol shown to them.
Well that’s it for this series. Thanks for reading! These articles saw more eyes than I ever thought they would have and I’m happy to have brought this to your phone or computer this last week or so. Please subscribe to something, I don’t care what, so I can justify doing this for the near future.