Renault and the damper story

[WhiteBlue]

http://www.madtv.me.uk/f1insight/defaul ... blogid=265
No wonder Renault are having such difficulty designing a competitive car when their engineers cannot grasp a new concept, even with a diagram of it in their hands. It is quite surprising that Flavio did not send them all back to school after that humiliating little exercise.

That's very harsh. Renault is definitely one the best teams on the grid and I don't think they deserve such comments from any F1 fans. I'm a Renault fan, and I didn't at all like this statement.

As for the mass damper, I strongly believe it would have been there. as someone rightly said F1 is all about innovations.

this is bad quoting. I have quoted the article but have not posted this opinion on the Renault engineers. people should take more care how they quote!

[HKS]

this is bad quoting. I have quoted the article but have not posted this opinion on the Renault engineers. people should take more care how they quote!

My fault. But I never pinpointed at you.

[Jersey Tom]

I can't imagine a "J-damper" being directly connected to the suspension. Doesn't make sense. If you had some rotational mass and extra spring connected to the torsion bar spring, you would just lower your wheel rate. You can do that with softer springs anyway. Doesn't gain you anything and would make for a bizarre setup. Unless adding that extra mass and spring system (to an already 2 mass 2 spring system at each corner.. plus 3rd spring) gives you some ability to tune out some resonance. A TMD though is not connected to the suspension at all. That's not how it works.

I could envision something similar to the linear TMD, being a cylinder with some mass, with its rotation axis lengthwise with the car. Torsion springs connect it to the chassis. Whereas the linear TMD "activates" by the chassis being kicked up vertically over a kerb, a rotational TMD would "activate" by the rotation of the chassis along the length of the car, by jumping up over a kerb or bump.

The difference between a J-damper and a linear TMD being that the TMD bounces up and down within the chassis. It translates. It moves. A rotational mass damper / J-damper as I described would sit in one spot and rotate. Instead of the degree of freedom being in the linear Z axis, its rotation about the X axis. At least that's what I suspect.

Regardless of how exactly its setup I don't think its as magical as some people are making it out to be.

[WhiteBlue]

I can't imagine a "J-damper" being directly connected to the suspension. Doesn't make sense. If you had some rotational mass and extra spring connected to the torsion bar spring, you would just lower your wheel rate. You can do that with softer springs anyway. Doesn't gain you anything and would make for a bizarre setup. ....

you should read Craig Scarbs essay on the J-dampers. he confirms that the damper is just a rotating mass on a ball screw. the ball screw is fixed to both primary dampers. so effectively it could be directly attached to the chassis because it only reacts to nick and not to roll movement. the rotary inertia provides a similliar effect to the linear tuned mass damper. you just convert the linear to a rotary action by the ball screw.

[zac510]

Typical, it's not in the print mag!

[RH1300S]

Can someone help a dimwit here

I understand (ish) how this works, but very simply

Why is a mass damper better than conventional damping for this role? P.S. I don't mean the individual wheel dampers, but a "normal" damper doing the job of a J-damper. Surely it could be tuned to damp out motion - or does the mass damper bit have other effects?

[WhiteBlue]

Typical, it's not in the print mag!

he offered it to us here by email. send him a pm. it worked for me.

[WhiteBlue]

.. Why is a mass damper better than conventional damping for this role? P.S. I don't mean the individual wheel dampers, but a "normal" damper doing the job of a J-damper...

the suspension has no influence on the springy tyre side wall. F1 tyres are having a big influence on the vertical movements of the cars. the suspension is usually very rigid. to influence the tyre deformation Renault originally used the linear mass damper that was tuned to the frequency of the tyres to provide a reciproke amplitude. you cannot do this with a normal suspension element. J-dampers basically do the same but they have the kinematic transformation from linear to rotary and a different mounting position to escape the ban of the linear TMDs.

[scarbs]

Typical, it's not in the print mag!

lol you should tell the mags editor that...! It might generate some work for me.

PM me with your email and I will send you a pdf of the autosport.com article.

[ReubenG]

I can understand from Scarbs' article how the J-damper is packaged, and from his description of "energy flow" I can easily see how translational kinetic energy from wheel movement is absorbed by rotational kinetic energy of the mass in the J-Damper.
As the mass moves on a power screw, there would be inherent damping from the friction between the threads.

However, what I cannot yet grasp is how they are tuning the frequency of the rotating system. Natural frequencies for rotating systems follow the same principle as linear systems - sqrt(Stiffness/Mass) vs sqrt(Torsional stiffness/Moment of inertia). The moment of inertia for the rotating mass is not a problem, but what I cannot see is where they have put the spring element. If the rotating mass is supported by bearings on either side, then there is no spring to restore the mass to its equilibrium position. i.e. if one slowly pushes the ends of the J-Damper together, then releases them at a certain displacement, what returns them to their original position? If there is no spring then how does one calculate the natural frequency?

Second question: much was made in earlier posts about the fact that Renault's TMD acted through the body work and that this was part of the reasoning that made it illegal. So if one attached a rod to the mounting point of the bell crank, and the other end to some point inside the chassis, and mounted the "mass damper" on this, it would no longer act through the body work but directly through suspension components. Would this also be illegal?

[WhiteBlue]

all the suspension members would act as springs, wouldn't they?

[ReubenG]

Yes, the suspension members can be treated as springs, with distributed masses but the stiffnesses and deflections would be different orders of magnitude: for instance the pushrod probably has a total deflection of the order of 0.1mm, for axial loads of the order of 150-200kg.Looking at the rough scale of the figure in Scarbs' article, the J-damper has deflections of the order of 10s of mm. I don't see how the combined compliance of the other suspension members (bell crank, pushrod etc) will provide sufficient motion to return the J-damper to its equilibrium position.

It has just occurred to me that maybe the designers don't want a system that returns to its original position, but do want the inertial resistance that the rotating system provides. But this is analogous to increasing unsprung mass, and still does not answer my original question: if there is no spring / elastic element to create stiffness, then how does one determine the natural frequency of the J-damper?

[WhiteBlue]

... how does one determine the natural frequency of the J-damper?

I was hoping that Scarbs would reveal something about the design resembling a spring in his write up but could not find it. I have since thought about the issue and I now think that the spring forces of the suspension return the rotating mass to its neutral position. they should also provide the spring rate for evaluating the frequency.

[rjsa]

I'm seriously missing something here. How is the mass (in understood it to be the red thingy) coupled to the screw????

1-Rigid, meaning it has threads inside of it?
2-Friction, it slides over something that has the threads inside?
3-Spring, it's sprung to something that has the inner threads?

All of these would be entirelly different beasts.

[checkered]

Having casually observed

the "J-damper" conversation for a while now, I noted that somewhere along the line scarbs asserted that McLaren had adopted the device some three years ago and alternatively called the device "Inerter". Thinking that this sounded like a much more plausible term for the kind of a function that had been described (and myself having loosely pictured as a "legal" alternative after Renault's debacle), I did a cursory web search along these lines.

What it yielded might well be the whole authoritative "low down" on the inerter. The trail led all the way to a University of Cambridge Dept. of Engineering, Control Group, professor Malcolm C. Smith and an IEEE Transactions on Automatic Control, Vol. 47, No. 10 (October 2002) article describing in great detail the problem setting and synthesis of a passive, mechanical one-point network. This seems to me to be the very paper that coins the term inerter, "the true network dual of the spring".

I have only briefly leafed through a number of PDF documents at this point (just venturing to post the links in my enthusiasm before really taking any time or effort as such), so I won't even attempt some half-a**ed representation of the theory or function. Anyway, obviously prof. Smith's papers make the most complete and concise case for the inerter by themselves. The links below, I believe, can have various F1T members occupied for some time.

Synthesis of Mechanical Networks: The Inerter
(PDF, IEEE ToAC, M.C.Smith, 2002)
The Inerter Concept and Its Application
(PDF, SICE Conference plenary lecture, M.C.Smith, 2003)
Performance Benefits in Passive Vehicle Suspensions Employing Inerters
(PDF, Vehicle System Dynamics, M.C.Smith & F-C.Wang, 2004)
Positive Real Synthesis Using Matrix Inequalities for Mechanical Networks: Application to Vehicle Suspension
(PDF, IEEE ToAC, C.Papageorgiou & M.C.Smith, 2006)

Prof. Malcolm C. Smith's university website profile, replete with these, and other, links

At this point it seems to me that references in F1 circles to the "J-damper" were, while legitimate in their own right, a bit of a red herring still to throw people off the inerter's trail. The information, after all, is in the public realm and has been so for at least six years now so it certainly isn't a great big secret as such. Doubtless the teams' engineers (and manufacturers') will be scouring academic records for just such innovations.

The inerter, from the get go, certainly wasn't among the obscurest ideas. Prominently described by a professor from a prominent university, three years' application time into F1 (by the first team) from having access to complete documentation isn't exactly lightning fast.