Pneumatic Valves

[101N]

I was wondering about the pneumatic valve systems used and so I looked them up on wikipedia.org. They had a link to the following schematic...

http://scarbsf1.com/valves.html

Interesting stuff.

[yzr-m1]

Very interesting, thanks for the link.

I'm assuming that the MotoGP application still uses a cam to actuate the valve and uses gas pressure to return the valve rather than using gas pressure both ways. I'm also assuming the gas is applied with a constant pressure (ie no switching) and as such no gas is actually consumed.

[RatsMC]

This issue with gas leakage just doesn't make sense to me. I realize that we are talking about pressures much greater than those used in shocks but the principle is the same.

The elctro-hydraulic cam at the bottom of the page looks like the best idea.

[Albert]

Quite a while ago (and on another Forum) I wrote the following article in response to a question about Desmo v Pneumatics.
The original start to the thread had some fascinating stuff that I never came across -- many thanks!

After a couple of comments about the MotoGP Suzuki and Ducati valve systems I decided to dig a little deeper. I came up with the following - hope I don't bore you - and if there's anything I've got wrong then please feel free to correct me!

Pneumatics.

It's difficult to say for certain quite who is responsible for the pneumatic valve - although it's probably fair to say that Renault developed it into what we know today when they used it in their turbo-charged 1500cc F1 GP car. (the one that showed the bigger engined cars the way home many times!)
It's also more accurate to describe the system as Pneumatic Valve Springs, or Air Springs.

Put simply they are small metal bellows/cylinders filled with compressed gas and they probably take up a similar amount of space as the more usual metal valve springs.

By replacing the steel springs with light weight bellows/cylinders they can respond far faster thus letting the engine rev higher and produce more power. Basically they push the valve back up in much the same way as a conventional valve spring.

The only downside that I can see with this system is the need to keep it pressurised. Lost pressure must surely mean lost power and a small percentage of leakage is inevitable, which means the bike/car has to carry a pressurised cylinder to keep the system "topped up" in order to maintain efficiency.

However, Pneumatic valve springs have become pretty much standard in Formula 1 engines now so they're obviously able to engineer a way around their problems.



Desmodromics.

The word Desmodromic usually refers to mechanisms that have different controls for their activations. (Opening and Closing.)

Desmodromic valves are opened and closed by a cam and leverage system, rather than using conventional valve springs to close them. The system uses extra cam lobes which act on rocker arms to close the valves, instead of valve springs. This gives complete control of the opening and closing of the valves, and because there is no chance of the valves springs weakening at sustained high revs the sky is the limit. (theoretically!)

The only downside that I can see is that the desmo system must be a little heavier because of the need to add extra cam lobes and extra actuating rocker arms.

[yzr-m1]

I recall reading somewhere that with the spark plug removed it is possible to turn a Desmo engine over by hand which would be a lot more difficult with a normal 4 stroke.

This demonstrates the fact that the Desmo uses less power to open and close valves and as such should have a greater percentage of power available at the crank output shaft.

I'm not sure how much additional power this equates to though.

[Rusty Bucket USA]

All true.
There's another article I read last year by Kevin Cameron - which, unfortutely, has never been published on the Cycle World website - that talked about how the cam shafts start to twist in the rev range they're now running in MotoGP. The theoretically limitless top speed is one thing, but the movement up and down the tach wreaks havoc on valve timing because of this.

But, yes, the system is largely more efficient in that the parasitic losses from the extra rotating mass of the camshafts is less than the high compression from the valve springs (be they air or metal).

[CLX]

off-topic:

Just wondering, how many hp the the bikes make in 2001?
What about 2006?

[phil]

i've nothing to add other than i love the educational topics more than the personality/celebrity/team/manufacturer type topics.
thanks for the information and starting point to learn more.

[yzr-m1]

Some further reading...

Desmo for Dummies - straight from the horses mouth!

http://www.ducati.com/bikes/techcafe.jhtml?artID=2&detail=article&part=technical

[RatsMC]

All true.
There's another article I read last year by Kevin Cameron - which, unfortutely, has never been published on the Cycle World website - that talked about how the cam shafts start to twist in the rev range they're now running in MotoGP. The theoretically limitless top speed is one thing, but the movement up and down the tach wreaks havoc on valve timing because of this.

But, yes, the system is largely more efficient in that the parasitic losses from the extra rotating mass of the camshafts is less than the high compression from the valve springs (be they air or metal).

I read that article as I do everything from KC. Great stuff.

Just out of curiousity, how many here have held a valve spring and tried to compress it?. Now imagine that your engin has to exert that force4 to eight times for every power stroke. That is a significant amount of energy lost to just making the motor run. Desmo motors have an advantage here although it becomes insignificant when you get into the 200+ bhp range.

Total random note: the biggest energy waster in these engines is actually the pistons themselves. Even the lightest pistons are still a reciprocating mass that has to stop, reverse direction, move through its stroke, stop again, reverse direction, move through its stroke, stop, reverse direction, stroke, stop, reverse direction, stroke, stop again for each power stroke. I do wish rotary engines had caught on, do away with reciprocating mass and valve springs.

[OZintheDesert]

Hey guys whilst just over at Superbike planet I was looking at the article on the new R1,
It is saying that it has a 90 degree cam thing (sorry guys not a mech major) but I had read in a different article somewhere that this was basically the Screamer system where the power is delivered in a 'smooth constant motion' rather than a 'big bang' where the firing is staggered.
Rusty, as our resident engine guy, would I be correct in saying this? As I was interested that R1 would be a screamer as the article stressed so heavily that the bike had been 'taken straight out of MotoGp' but the M1 is a big banger isn't it??

Back on topic, would that mean that part of the Duc's bottom end power would be directly attributed to the desmo system as it doesn't need the extra force to get the valves closed, which in turn is even better that the spring system?

[RatsMC]

From what I am reading, the new R1 is somewhere between a screamer and a big-bang configuration but the concept is to take advantage of the big-bang power delivery. However, this will come at a loss of overall power as a result of longer gaps between firing. A big bang motor doesn't actually deliver torque more smoothly (as Yamaha claims), rather it delivers torque in big lumps. The important thing is that it is supposed to feel smoother to the rider.

A little more detail: The new R1 has a firing order that delivers power every 90 degrees of crank rotation and then must rotate another 360 degrees before the next piston fires which does actually make it a big bang but less radical that what is typical in racing which all pistons firing within about 70 degrees.

To your question about the desmo designs impact on bottom-end torque, I would say that there is some added power from the efficiencies of the desmo valves but it probably isn't significant or rather it probably isn't the race winning factor. Overall power delivery and torque curve which are impacted by all sorts of other design factors play the largest roll. Also, in failing to contain my inner nerd, I have to point out that the parisitic power loss from valve springs actually occurs during valve opening rather than closing (the cams have to compress the spring to open that valve whereas closing it just requires releasing pressure on the spring.

Of course, all of my points should be taken with a grain of salt as I don't actually know s**t.

[101N]

It would be interesting to compare the torque & Hp curves between the 2008 & 2009 R1s. I would expect you would see more torque at lower rpm with the new motor. I wonder if this different firing arrangement results in a different shape of the torque or Hp curve. If it doesn't, would there really be a discernible feel between the two motors?

[RatsMC]

The torque and horsepower curves are, to a large degree, a function of design compromises so if Yamaha wanted to have more low end, they could design it in with a cost to power elsewhere in the powerband. It is likley that the new motor actually has less low end as a result of the longer gap between piston firings which would be less noticable at higher RPMs.

Of course, the primary reason for a big bang motor and the reason for accepting the resulting performance loss is traction and I honestly don't think the average street rider is even going to notice the difference as they are rarely on the edge of breaking traction anywhere but on the track.

[Rusty Bucket USA]

Funny that you asked that question...
After I entered that post, I re-read this article:
http://www.superbikeplanet.com/2007/Dec/071217b.htm

I don't have access to the R1 details you guys are looking at (care to post a link?), so I'm just guessing... this does sound a bit unique; like a blurring of 2-stroke and 4-stroke.
"Smooth Bang/Long Bang"? Would love to hear it!

I wonder what "problem" is being "solved" with that... The only way it makes sense is if they think they've found something for WSBK or AMA SBK. Otherwise, it seems awfully complicated for street use...

[101N]

Here is a link to the Soup article on the new (2009) R1.

http://www.superbikeplanet.com/2008/Sep ... ronelv.htm

[RatsMC]

Rusty, I just read through a little more and I have to make it clear that I am making some guesses here as to exactly what Yamaha has done. I actually think I guessed incorrectly and the Yamaha is firing two pistons at 90 degrees to each other, cycling 180 degrees (rather than the 360 that I originally posted) then firing two more at 90 degrees from each other.

I do agree with you that I am not sure what problem they are trying to address. From what I can see this has more to do with racing rules and forcing World Superbike top to allow big-bang configurations.

[Rusty Bucket USA]

Reading that article didn't help (I'm not sure the writer gets it, either). I still can't say I have the firing order figured out, exactly, but this link is the coolest:
http://www.yamaha-motor.com/sport/msite/micro_v1.aspx
Click on the lowest highlighter box... and prepare to wet yourself!

I want one of these!

[101N]

Thank you for the link to Ryder's article. See below:

"Without doing the math, you can see how this variation of torque over each revolution might produce some small variations in the torque seen by the tire contact patch. On your 180-crank, four-cylinder road bike, you won't notice the effect because you don't use high enough revs, but as this inertia torque is proportional to rpm squared, you can see how a 17,000rpm MotoGP engine might have problems. At those sort of engine speeds, the 'noise' of the inertia torque is 'louder' than the 'signal' of the combustion torque. The rider's connection with what's happening at the rear tire's contact patch is lost both with the throttle open and with it closed."

I guess my question would be whether or not inertial torque matters really in a street going bike. Are guys going to wick these things up to the RPM levels at which inerial torque comes into play? Or is this something designed for production racing? (Is this meaningful trickle-down, or just bells & whistles?)

Either way, it's a beautiful bike!

(As an aside, this is a GREAT site. Nice work Krop!)

[jupiejupe]

i snap i have been waiting 3 years for this bike i thought it was suppose to have abs brakes as well, what a dreamy machine. time to up grade to 03 R!

[RatsMC]

This really means almost nothing to anyone but the most serious of track riders. Even without Ryders somewhat obtuse explanation, the engine speeds, torque output and lean angles required for a big bang engine to have any real benefit aren't often experienced on the road if ever.

As I mentioned, this is about World Superbike rules and marketing more than technology trickling down.

[OZintheDesert]

I must be way off the track here, as I thought that a firing order of 90, 180, 270, 360 was screamer territory? the point being that the firing was constant not off set which created the big bang?
Mind you I was also of the opinion that most of the road going sporst 4 bangers were screamers so this wouldn't be that new or revolutionary...
Now I am confused...

[yzr-m1]

One of the reasons big bang engines were introduced for 990cc was to decrease tyre wear. The power delivery on a 990cc screamer didn't give the tyre chance to recover from the power pulses as they were a lot closer together than on a big bang. The big bang delivers all of its power pulses close together (It's a bit like getting all of your post delivered on a Monday rather than spread over the whole week), this gives the remaining part of the tyre more time to recover and cool down. The big bang also allowed power to be put down more controllably when compared to the screamer and was allegedly easier to ride in this respect.

I don't think the R1 engine has been designed with these points in mind and it doesn't look to be a true big bang motor. It seems to be more about aligning the combustion torque and crank rotational torque to give a better throttle response.

The Yamaha site in the previous link is a great example of the marketing power of race bred technology.

[Rusty Bucket USA]

There's some murkiness in the language, now...
"Uneven firing order" is NOT synonymous with "Big Bang". It's important to realize how many more variables are opened up in an "uneven firing order". Even in an "even firing order" engine, there are a couple different ways to set up the crank to get different performance.

The true "Big Bang" was originally developed for V-motors, which is a whole different set of physics from trying to do a "Big Bang" in an inline motor.

The key understanding with this street bike is the phrase "derived from MotoGP" engines. The little bit that you can hear the engine on the website tells you it's different from other street bikes AND different than the M1. Obviously, they figured out something that they can mass produce that gets most of the benefits, which is good trickle-down technology for all of us. I'm sure it will be the best riding new bike - the variable-length intake runners and the firing order combining to make more torque and more top end - even if you do have to be leaned over and trying to twist the tach all the way around to exploit all the benefits.

Right after I win the lottery, I'm buying one!

[Rusty Bucket USA]

One of the reasons big bang engines were introduced for 990cc was to decrease tyre wear...

My "I'm not a team or manufacturing engineer..." disclaimer in place, I've never fully bought that theory. Right in the middle of the 15 year claim on that front, Garry McCoy was helping tire engineers discover that if you keep the rear over-heated by spooling it up all the time, you actually decrease core temperatures and help tire wear. The "pulse break", as it were, is a really short piece of time, even at 10,000 RPM.

Rossi kind of obliquely confirms in his book what I had always thought. He said he tested the two engines back to back (I think it was at Sepang) and said he wanted the Big Bang motor because the power was more tractable and predictable. I've always believed it is a function of the torque curve being more managable. Since then, it appears, based on what Furusawa is now saying, that they've developed some science to back up what Rossi's senses were telling him. When you get way past 10K, there are some peeky and spikey harmonics that show their unpredictable heads (especially in an in-line motor), and so Yamaha have managed to develop a competitive engine by going the other direction and around the problem.

Tire wear was not part of his considerations.