Erik Buell’s latest patent combines exhaust, swingarm

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Erik Buell likes to say that the motorcycles he makes, including the EBR 1190RS debuting this winter,  have only just caught up with designs he first penned 20 years ago. Here’s a rare glimpse inside some of his latest thinking, this patent for an exhaust-incorporating swingarm was just published.

Somewhat confusingly titled a “Movable Exhaust System” in the patent, the concept here is relatively simple: channel the exhaust through the swingarm, housing the components that usually form the exhaust canister inside that swingarm.

This dual role fits with the fundamental tenet’s of Erik’s designs. His frames hold fuel, swingarms in the past have held oil, Harley engines were fun to use and kept his evil corporate masters happy. By housing the exhaust within the swingarm, mass will be made more centralized, the motorcycle will stand up to crashes better, a major heat source will moved away from the rider and the overall number of parts will be reduced. We showed these drawings to an automotive engineer, who doesn’t believe there will be an appreciable increase in unsprung weight as most of the added components are housed directly under or forward of the spring mount. He went on to say that those components were very light anyways and, should there be a slight increase in unsprung weight, it would be more than made up for by losing the weight of an external canister and in reducing part counts.

But get this, the system shown in these patent drawings doesn’t just combine two roles, it adds a third which has never before been possible. When we exclusively unveiled the 2010 MotoCzysz E1pc, we saw that it used winglets to channel high pressure air through tunnels in the frame to the area above the rear wheel. This low pressure area is traditionally a huge problem for motorcycles, effectively pulling them backwards as speeds increase. Like the Moto Morini 500 Turbo before it, the E1pc filled in and broke up that low pressure area with high pressure air from the front of the bike. Taking dual-role parts to a ridiculous extreme, Erik has located the exhaust exit in an ideal location to use its gasses to break up and fill in that low-pressure area, achieving what should be a significant aerodynamic benefit.

Our automotive engineer buddy estimates that a motorcycle engine should be able to exhaust enough high-pressure gasses to have a measurable impact on aerodynamics. Using, say, a 1,200cc v-twin operating at a constant 8,000rpm, he roughly estimates that 1,200cc of high-pressure gas would be leaving the exhaust ever .0015 seconds.

These drawing show two potential methods for connecting the exhaust headers to the swingarm: a flexible pipe and a rotational coupling running through the swingarm pivot. it’s the former that will cause the most brow furrowing, but it shouldn’t. Flexible pipes capable of reliably dealing with extremely high temperatures have been around for years now. A nicely-designed cruiser by J.T. Nesbitt from New Orleans employed a flexible pipe made from a nickel-chromium alloy called Inconel to similarly channel its exhaust gasses through a swingarm.


Another potential criticism is also addressed in the drawings, two different solutions for service panels are shown, all of which would allow access to repair or replace the exhaust internals. What’s not clear is how that most possible of motorcycle modifications, the “performance enhancing” exhaust, could be accommodated. Presumably there’d be some sort of ability to reconfigure the gas flow through the swingarm internals.

The application for this patent lists “Erik Buell” as the inventor and includes this abstract:
“A motorcycle including a swingarm that movably mounts a rear wheel to a main frame of the motorcycle and defines a hollow portion through which exhaust gases are passed before being expelled from an outlet of the swingarm. A movable joint may be provided between a header and the swingarm, including a first portion fixed relative to the main frame, a second portion movable relative to the main frame, and a flexible conduit between the first and second portions. The movable joint may be coincident with the pivot axis. In some constructions, the hollow portion of the swingarm is divided into at least three chambers, and a plurality of pipes is configured to provide at least two flow direction reversals within the swingarm between an inlet and an outlet, with multiple volumetric expansions between the inlet and the outlet.”

Erik likes to say that he’s designed hundreds of motorcycles over the years, the vast majority of which remain un-realized. Only time and new EBR products will tell if we ever see the Moveable Exhaust System on a production bike.

Sources: Bad Weather Bikers, USPTO

Thanks for your help, Bill.

  • slowestGSXRever

    There is a rear tire warmer in that design somewhere. Quit being lazy and make it happen Buell!

  • Glenngineer

    The aero applications of such a design are likely worthless, in my opinion. Motorcycle exhaust is already funneled out the back of most bikes, where it doesn’t do much of anything. It isn’t ‘high pressure’ – the more pressure you throw out of an exhaust system, the more power you waste, and the more noise you make.

    • http://hellforleathermagazine.com Wes Siler

      As I understand it, there’s a specific and problematic low pressure area above the rear wheel that’s typically impossible to fill in or break up adequately. Traditional cans shoot out their gas too far to the rear or to the sides to contribute, but if you’re going to be sticking a significant amount of gas out somewhere, it may as well be directed at this area.

      It’s not like Buell’s are suddenly going to be setting speed records solely because of this, but I once talked to a car racer at Bonneville who reckoned doing this gave him 1 or 2mph extra.

    • jayspeed

      No, it’s not that the exhaust will be funneled out the back. It’s that it will be funneled over the area of the rear wheel, which is filled with low pressure that traditionally creates drag. No bike currently has this (which is one of the reasons why it is even patentable).

      • Glenngineer

        I can’t argue the point too hard, because I haven’t spent any time studying motorcycle aerodynamics, but a quick back of the envelope calculation shows an average sport bike displacing 150-200 times the amount of air it flows through it’s exhaust – 2 orders of magnitude more.

        I based the calculation on an R6 at 120 mph, assuming it’s frontal area is actually 2/3rd the rectilinear area calculated from it’s height and width. For bigger bikes and higher speeds, the case only gets worse for aero-friendly exhaust.

        I have the utmost respect for Erik Buell, and as an engineer and motorcycle guy, I would kill for the chance to work for him, but I think he puts a lot of faith into the theoretical 1% improvement that is in reality hard enough to realize that the implementation may actually cost you raw performance. Look at the belt drive – I love a belt drive, but off it comes for racing, for a variety of reasons.

    • Ducky

      Are you sure? The latest generation Hayabusa was also aerodynamically tested with the exhaust up at an angle for the same reason of reducing the low pressure area behind the bike (as well as shaping the air flow right behind the rider).

      Formula 1 cars too, use this effect. For a while they were able to direct exhaust gasses almost right underneath the cars in order to stimulate a low level ground effect; more recently they’ve been using it to shape the air as it encounters the rear wing of the cars.

      Pressure out of an exhaust isn’t wasted power. You want the cylinders to be scavenged of waste gas as fast as possible, particularly in racing applications (which is what this patent is for I assume).

      • Glenngineer

        Pressure out of your can is wasted energy – any power spent blowing shit through a tube is power not spent turning your rear wheel.

        Scavenging relies on AC pressure – waves. The exhaust has some DC pressure, which keeps it moving toward the outlet of your exhaust system, but there is a strong pressure wave rolling around in there which creates negative pressure at the valves, right when you need it in your exhaust stroke if done correctly.

        All I know about F1 cars is that they used to aim their exhausts at the aft diffuser, but stopped because it was making the cars handling too throttle position dependent. Having a wing, the diffuser, in the exhaust path made a big difference, because I figure the exhaust/displaced flow ratios are pretty similar for race bikes and F1 cars.

        Again, I’m not saying exhaust gases can’t or won’t improve motorcycle aerodynamics, I just don’t think there is much potential there for gain, either for the racer to use to win, or to sell the street rider.

        • Ducky

          I am not sure what to say to your first statement. So are you saying that we might as well all shove a fruit in the exhaust pipes of our vehicles for maximum performance? Or put on the most restrictive exhaust we can find?

          Or perhaps we are talking about different use of the term “pressure”? Because I am thinking about HFL’s use of “pressure” as more of “maximum mass flow rate”, rather than actual backpressure in an exhaust (which is, as you say, power robbing).

          Regardless, having an exhaust pushing out as much mass air flow (high velocity hot gasses too mind you), should thereotically affect the low pressure envelope behind a bike. Even if just a bit, it will help if the bike is optimized to direct air flow to take advantage of the effect.

          • Glenngineer

            You’re either over or under thinking it, I can’t tell.

            You don’t want to build an exhaust system that causes exhaust gas to get stuck in your engine – it needs to get out. The goal is to have an engine that operates efficiently. That means an engine that isn’t blowing a shit load of hot air out the valve every cycle, but also an engine that fully evacuates with every cycle.

            Power is proportional to the difference in pressure at the beginning and end of the power stroke. If there is back pressure from exhaust gasses in there, your power goes down. If your pressure hangs around on the exhaust stroke and doesn’t get utilized in the power stroke, it’s waste.

            I don’t want to shove fruit in my exhaust to plug up the power loss…the power is already wasted, and letting out becomes the best thing to do.

            Pressure is pressure – mass flow is mass flow. If you say pressure and mean mass flow, it becomes really hard to have a discussion rooted in engineering. What is more interesting, sometimes, is volumetric flow. Pressure times volumetric flow is power.

            • Ducky

              Hmm, I think I know what’s going on now. You and I are saying basically the same thing involving back pressure limiting power output. That’s why I made the joke about shoving a fruit in the exhaust pipe (a common -and expensive- prank if you’ve ever seen one), because I thought you literally were talking about high pressure in the exhaust system!

              However, what HFL meant wasn’t “pressure in the exhaust system” per se, they meant “high flow rate of high velocity exhaust gasses out the tailpipe”. They might have defined it wrong (well, they’re not engineers, just really crazy bike geeks =D), but I understood what they were trying to say.

              As for the discussion of Formula 1 cars, at one point it wasn’t just over the wings- before Formula 1 regulations disallowed it, exhaust gasses were actually output at an angle towards the ground, underneath the car. This cushion of hot air actually helped stimulate a small level of ground-effects, which greatly aided cars in high speed turns.

  • kneepuck

    So does this mean that your back and leathers with be permeated with the smell of motorcycle exhaust?

    • http://hellforleathermagazine.com Wes Siler

      Only if you don’t smell so strongly of beer and used engine oil that that’s a problem.

    • carcanal

      Hey is your gear doesn’t smell of exhaust and oil your doing something wrong. Last i checked we get blasted by all kind of exhaust from mopeds to semis.

      • kneepuck

        Not if you’re in front!

  • http://rohorn.blogspot.com rohorn

    I can’t wait to see what this gets bolted to.

    Predictably, those who “think” that their understanding of motorcycle design is eternally state of the art won’t approve of anything else Erik does, either – ’til everyone else copies it.

  • Sean

    Very cool. I for one am very much looking forward to what Eric can do now that he’s on his own and not trying to please any corporate masters.

  • seanslides

    I approve. Awesome.

  • Johndo

    Always nice to see some are still trying to think outside the box.

  • slowtire

    Loud swingarms save lives!

    • dux

      Hehe. Now how can we fit more chrome on it? That’s what it really needs.

  • DoctorNine

    Seems to me that the corrosive nature of the exhaust gas would be a problem with swingarm longevity. Also, the heat cycling would make metal expansion and dimensional changes an issue. I dunno. It’s weird enough that it might be interesting. But I’d definitely like to see how he solves those issues.

  • http://www.smartcycleshopper.com/author/doug-dalsing/ DougD

    I think the best part about an invention like this is the reduction of the number of motorcycle parts. The more simple a motorcycle can be made, the better. Unlike the gas/pressure argument folks are discussing above, you cannot argue against simplifying a design and reducing the parts count as long as the function and essence of the machine remain the same.

  • Stacey

    I spend some time over at one of the Buell boards, where a tuner spent a bunch of time and money doing a comparison of exhausts for the 1125.
    Dynos were posted, there was some grumbling as I recall, but one of the things I remember reading was that big (some say ugly) stock can is pretty free-flowing for an OEM piece. As tempting and aesthetically pleasing as some after market jobs are, I’m going to stick with my stock exhaust!

  • Cajun58

    Doesn’t Confederate already run the exhaust thru the swing-arm on one their creations guess he neglected to get a patent on it.

    • http://hellforleathermagazine.com Grant Ray

      Yep, JT Nesbitt’s second generation Hellcat ran the exhaust through the swingarm. Can’t give a definitive answer for why an engineering patent didn’t get filed.

  • Richard

    One possible caveat would be the exhaust heat affecting the lubrication of the swing arm bearings. This same heat effect on the steering head bearings was a major drawback of ‘oil in the frame’ designs.

  • http://rohorn.blogspot.com rohorn

    So how do bearings work in engines? Last time I checked, they got hot as well.

    • Richard

      It’s not the bearings themselves that’s the problem but the lubricant. Engine bearings are lubricated by a constant flow of pressurized oil, frame bearings by static grease. Hot grease doesn’t stay put.

      • http://rohorn.blogspot.com rohorn

        Very true – but:

        1) The SA bearing speed is very low.

        2) There is plenty of area radiating / mass conducting heat away.

        3) There’s a big hot freakin’ engine a fraction of an inch away from (and upstream of) ALL swingarm pivots.

        4) There’s usually an exhaust collector near swingarm pivots.

        5) Warm grease in the SA bearings improves suspension compliance (OK – that one is BS for the ad writers).

        Either way, I’ll bet some weirdo mil-spec high$ grease gets used.

  • Steve

    The swingarm bearing temperature was certainly one concern, but one there are readily available solutions. Compared to the grease-lubricated thrust-bearing in a F107 cruise missile engine, this is nothing. A much more difficult issue is sound radiation from the relatively flat surfaces of a swingarm side — reradiation was already an issue with the Buell 1125R; exhaust pulses nearby caused the swingarm to ring like a bell. This would likely have required either double-walling or a separation of the swingarm structural walls and the muffler wall. Also, keep in mind that this works better with an engine requiring a smaller muffler volume than a 1200cc Superbike Twin — say a middleweight Triple But overall, this solution is as sweet as Sugar.