Panigale De-Compressor

In fact the press release for the Superquadro engine describes the decompressor system as being on the inlet cam side, but the diagrams show it on the exhaust side, and of course it should be on the exhaust as you wouldn't want gases being pumped back up the inlet tract... I've corrected this in the Superquadro feature.

I'm nore intrigued by the semi dry-sump oiling system with its sealed crankcase and oil pressure scavenge pump. I've got 2 motorcycles in my garage with the same design.

2008 CRF250X and 2010 VFR1200F.

The superquadro's crankcase vaccuum pump is almost identical to what Honda did in the VFR1200. The crankcase is sealed off from the sump and there is a second gerotor pump on the oil pump shaft that scavenges back into the sump.

I've had a look through the press info, and in the Honda's case it's clear that whoever wrote it didn't understand what was going on, hence there's very little anywhere else that makes sense either... From what I can see, the principle is the same between the VFR and Superquadro but there's a difference in scale. It is as I suspected and wrote further up this thread, the VFR uses the scavenge oil pump to draw air from the crankcase into the sump, where it's vented via a reed valve - the crankcase is sealed from the sump, as it has to be for this to work, so technically it's a semi wet sump design. The air pressure in the crankcase is therefore lower and this reduces pumping losses. The Superquadro uses a separate, more powerful dedicated vacuum pump in addition to its oil scavenging pump, and this creates a stronger vacuum with what seems to be significantly lower pressure than in the VFR, and this does seem to be a first on a production bike.

Thanks for the heads up on the VFR system, I'll refer to that when I'm writing about the Ducati one.

I was just coming back here to say that, the systems are indeed the same. The info from both Ducati and Honda isn't clear so I asked people at both companies for clarification, which actually muddied things further.

But you're absolutely right, Honda was first with the VFR's, this is simply following it. The impression I'd been given was that Ducati was using another pump in addition to the scavenge pump, specifically to draw out the air and do no other job. But that's incorrect, the scavenge pump removes oil and air in both designs.

I've written something for next week's MCN about it and I'll publish that on here a little bit later... or maybe I'll rewrite it for here sooner, depends on how busy I get!

Thanks for all that phobe, great to have people in this forum who keep you on your toes!

With regard to the de compressor, a light push down on the top of the “shimming clearance” spring would release the required valve from it’s seat. The force required would be very small. Obviously the spring could not be secured using the conventional split collet arrangement as it would all fall apart! Another method of retaining the spring would be needed, but I think the principle is ok, no? The mechanism could be released easily with a (small) centrifugal device.

Another idea might be to do away with the spring and take up the shimming clearance with oil pressure acting on a small rocker, via a small piston. By the time pressure has found it’s way to the top of the engine, it will have fired and got under way.

Some earlier designs used a separate little valve dedicated to the job I think. But with the desmo arrangement a lot more possibilities are opened up.

I have also been putting my head around this-being a mechanical design engineer from wayback it is giving me a headache just trying to work out how it is done.
The shimming clearance on a desmo engine is purely there to A/ allow the valve to rest on the seat without interference, and B/ allow the valve train to operate without any binding. The actual design and production of the cams is fantastic since you can rotate a desmo valve train very easily by hand-try and do that with a conventional engine. The other advantage is the well understood benefit of being able to use VERY aggressive opening and closing ramps-which again a spring valve train can't use since at high revs the springs cannot react quickly enough to keep the follower on the cam-and you get valve bounce.
So Kevin-if you can find out we will all be very gratefull.

John

Hi pete1950,

Fair hypothesis. I wish you luck!

I'm guessing that the shimming clearance must allow pressure loss as they have fitted light return springs. I wouldn't have thought they'd bother with the springs if the pressure loss was only tiny.

I'm staying with my own guess that it would be easier to just overcome the action of this spring via the opening rocker, without having to adjust the profile of both cams. I admit that, for this to work, there would need to be reasonable clearance between the two cams.

The closing cam in question appears to be thicker than the others but I suspect that is just so it is wide enough to support whatever mechanism is pivoting through it.

Is the Desmodromic system in general under patent? It has been used by a few manufacturers over the years so I assume not. Just wondering why other manufacturers of large capacity twins don't make use of it. In the case of BMW I suppose room is an issue.

Hee Hee. Good job we don't work for Ducati!

I have the hook shaped arm as the centrifugal weight, acting on that small pivoting latch. Where I'm coming a little unstuck is that I see the latch acting on top of the opening rocker via a spring. This spring would have to be stronger than the shimming clearance spring, to overcome it temporarily. I can see evidence of a spring poking through a hole in the cam but it looks too feeble for what I have in mind. ...? I don't have a problem with seeing the shimming clearance as large enough allow air to pass. They would need to build sufficient clearance in there to allow both cams a tolerance but just as important is ensuring the valve is never under preload. A large diameter valve would only need to drop a small amount to allow a reasonable amount of air to pass as it's circumference is large. Plus, at start up engine speeds the flow rate of air is low.

Okay, in Milan I spoke with Marco Sairu, engine design chief, and I've got it!

Mind you, it's so interesting seeing what theories people are coming up with here, it's tempting to wait for a bit longer, haha...

Okay okay, that'd be cruel, so here goes.

The arm on the end of the exhaust camshaft is indeed operated by centrifugal force. At very low engine speeds it's pulled in by a spring, pushing out a small lengthened ramp which sits above the profile of the exhaust cam's 'closed' circular face. This nudges the valve open by 0.2mm for some of the rotation period, enough to cause the required pressure loss in the cylinder. The desmos run at near zero clearance normally, nowhere near enough to lift the valve off its seat sufficiently to cause a useful pressure drop in the cylinder, so this 0.2mm lift is the minimum needed.

That's where we've all been getting headaches: how do you lift the valve off its seat by that much without it fouling the desmodromic closing cam? The trick took a bit of lateral thinking and some testing too: for the corresponding interval on the closing cam there is simply a dip in the profile of 0.2mm. As soon as the engine is running, the centrifugal force swings out the arm on the end of the camshaft, a pin rotates and the small lifting ramp drops below the cam profile... and that's that. It turns out, the 0.2mm dip in the desmo cam simply doesn't matter. So, during normal running, the rocker arm tracks the surface of the cam up to this section, then lifts off it so there's a brief 0.2mm gap between it and the cam, then it touches again on the other side. Over this interval, cylinder pressure is holding the valve closed anyway, and thanks to gentle ramps into and out of the dip in the cam face Ducati says there are no issues with unusual wear, rattling or anything else.

That make sense? For those of you who get MCN there's a longer explanation in the Tech Watch section I write, in the November 16 edition.

I wouldn't call it crude, just simple, as it's also a very clever piece of lateral thinking. It's true of desmo and normal cam lobes that they're not really exerting any pressure either way in the base circle sections, but it's a lot easier to grind the cam round all the way around rather than work out where it doesn't need to touch then grind that extra away, and there's not a lot of point as the friction is minimal when it's not opening or closing the valve anyway.

Kevin

You describe a "dip" in the closing cam. If it was too localised how could you be sure that the engine would come to rest in that exact spot?

I suppose you would then say that it doesn't matter, as it will have to pass over that portion in a fraction of a second as the engine is first cranked over, releasing any pressure. Further, that leads me to realise that there will only BE any pressure build up as the piston nears tdc. So I suppose it is a Localised "problem" after all. Once the engine is up and running gas pressure from combustion will have taken over at that point on the cam profile I assume.

Also, when you think about it, the shimming clearance is there to ensure there is no binding and no "negative clearance" when the valve is seated, causing bending forces on the rocker, stretching of the valve stem and high friction. My point being that if you build in, say, 5thou (125 microns for the younger amongst us) clearance, you may as well build in 0.2mm as a miss is as good as a mile.

No?