Hi guys,

I've been hearing about this mass damping thing for a while specifically about it being banned in F1. It is claimed that at certain tracks, they gain up to 0.3s using this system.

Please don't run away if you're not an engineer or hate this kind of stuff. The main question here is whether or not it can help us in our cars or do something similar.

What I'm posting here is the most theory behind it. I don't really know how it all applies to F1 cars or if it could be used in other applications. If any of you suspension guys can post your thoughts, hopefully we'll be able to shed proper light on the subject. If there is interest, I will, time permitting, post more complicated models as applicable.

Anyway, here goes....

What the 'mass damper' is can't be simpler. It's a mass on a spring. From what I've seen, it is mounted so that the mass can move vertically and it is mounted so that the axis of movement lies in the plane that contains the wheel centres (or thereabouts). Apparently, one system is mounted at the front and one at the rear.

What it does is kindda cool and useless at the same time. If we shake any sprung mass from low-high freq, there's a point at which things go a bit ape$hit. This is resonance. Obviously since F1 cars sit on 'springs' of some sort, this happens to them too. (Although dampers generally calm resosnance down). If you think of the car as a mass (say M) on a spring (stiffness K) and you're shaking the car, the mass damper is just like putting spring (stiffness k) on to the car and another mass (call it m) on top of that.

If you're shaking the car at a frequency near it's resonance, the car without the mass damper system will go a bit ape. If you have the system installed and you're clever and made k and m so that the little mass m resonates at the freq. you're shaking the car at, the car will remain absolutely still - while you're holding on to the car and heaving it up and down, the car will not move. It will be still. The mass m will effectively go beserk (well go up and down enthusiastically).

Now the 'useless' part. From the maths and all that stuff, while the original system (w/o mass damper) has one resonance freq (say f), the new system will actually have two as far as the car is concerned, f1 and f2. Where f1<f<f2. So we've got two points where it's problematic but we've got a point where the car is dead steady at f. How far apart f1 and f2 are depends on the ratio between m and M and k and K.

So, that's the most basic way of looking at it. There are other ways which I'll poke at tomorrow if I have time and see what the maths have to say (excitation at the tyre, tyre as spring, wheel mass, spring, car mass, small spring, small mass). At the moment, I'm picturing the F1 car bouncing on itstyres as they appear to do sometime. The stiffness K is the tyre stiffness, not the suspension springs.

Now my question is can anyone think why this is beneficial to a race car? You could perhaps use it to kill bounce from hitting a bump or something, but would that really have such a difference - and could you not use dampers instead?

Renault basically built their car around this system, so there must be some benefit. It also doesn't seem to be the most complicated of devices so if anyone thinks it might work with the evo, perhaps we can try it out?

Your thoughts....


much appreciated,

C

 

Well, you have to consider the aerodynamics of an F1 car more than mechanical grip generated by controlling the suspension. The amounts of down force it produces change drastically with minimal change in ride height and attitude. If you are able to produce a more stable ride height by controlling body movement through a mass dampening system it is a big advantage.

I went to the wind tunnel for the first time last week with the team I work for. You can't believe how much a difference 1" of ride height makes on a car that doesn't have wings and a flat bottom and it only gets bigger on cars with them.

 

That is what "active" suspensions were... kept the car where it needed to be to generate the most downforce, esentially making the whole car a "movable aerodynamic device." From what I understand with the Renault Damper, it essentially was an aero device in the same sort of way the active suspensions were..

First time I got to experience the rideheight/aero effect was in an F2000 car, where I bolted a new diffuser on, which didn't work with the "old" rideheight.. I kept lowering the car 2 turns on the spring perch at a time, and the difference was sudden. In a 120-mph kink I was having to breath the throttle and give probably 1/3rd turn on the wheel to make it, then two turns later, I was easily flat, and with half the input on the wheel than before (I actually turned in, then had to turn back out to not run off the track) .. so roughly 1/8th of an inch was all the difference...

Taking that into account, with a car that is more aero-sensitive than a F2000 car for sure, you can bet that it was a HUGE difference to keep the car in a range of movement/height.

Jon K

 

The system is basically mass suspeneded in oil. What it does is keep the front of the car from bouncing as it goes along. If you watch a lot of F1 (I'm a freakin addict), you can see in the slow-mo's that as cars go around turns, hit curbs, and accel/decell, the nose has a tendency to move up and down, like a diving board after the diver has jumped off. The mass damper steadies that tendency. It allwos the suspension to work better and give the car a better contact patch, more traction. I don't know how good this would be for a street application, but I definetly think it could help most cars on a track. Hope that helps.

 

I don't think it would be a any type advantage on a street car like the Evo even if it spends a lot of time on the track. Most of the Evo's grip comes from mechanical grip not aero and you need some compliance in the suspension. I would be willing to bet packaging and tuning it for the proper phase or phases would be a royal PITA if not impossible. You have to remember that they are operating in a relatively small range being on the track, no where near the variance we would see on the street.

I did read something about how on the RS4 they have linked the RF-LR and LF-RR shock reservoirs together to increase mechanical grip in a type of adaptive suspension that is totally mechanical. That might be doable and more practical for the Evo with a high dollar coilover setup.

 

We simulated a lab on this concept in a controls class in college (Purdue University Mech. Engineering) Basically it was a system comprised of a shaft with a weight suspended by a spring on the top and bottom with a cap plate on the top. The whole assembly was then placed on a shaker and brought up to the original springs natural frequency. With the second spring in place, the mass in the middle sat perfectly still and did not fluctuate at all. Quite interesting...

And no, in the world of non-solid bushings, reasonable ride heights, and only adequite tolerencing, this concept has few benefits for a production vehicle. Cool none the less.

 

Thanks for all your input guys. I'll think about it somemore and will post if I find anything interesting.

It's quite interesting how many people have posted about height sensitivity of aero parts. It is my understanding that this is so, but by the sounds of it, it's a much bigger issue than I had previously thought. With this in mind, might there be a situation where the wing (aero bits) it/themself/ves exaggerates the bounce? For example, if you go over the curb and basically give the car a series of jolts, is it possible for the car to bounce up and lose a bit of downforce, come down, compress the springs and doing so make more downforce to the spring is compressed even more, bounce up again due to the energy stored in the spring, go up again higher, come down again and repeat. It's kindda difficult for me to imagine the sort of damping that goes into these cars for obvious reasons plus they generate very significant amounts of downforce compared to the original load on the system (specially the front of the car).

racerjon1, can you remember typical figures on an F2000 car? Wheel rate and damping and so on. Or even perhaps a sort of general feeling - hard/soft that sort of thing? Did it bounce a lot? Thank dude.

 

Is it possible for a bouncing suspension to disrupt downforce levels, for sure. But this is why you see mugh higher spring rates on downforce cars. (for that reason, and the fact that a car producing 2500-4500 lbs of downforce and "normal" springs rates would be/are rendered useless. (also going over curbing, changes in the track that essentially make the car change pitch or yaw, all change downforce levels. (remember the flying Le Mans cars..)

when you design a car for downforce, you have to think about every system..

For a F2000 car / Formula Continental, some theories go with a need for spring rate = wheel rate, with the geometry in the cars, this leads to 900 - 1200 lb springs on a car with 250 - 350 lb corner weights.. the issue that pops up here with older cars (1990 and before) is that the a-arms/rockers only have lower spring rates and become flex points, which leads to breaking, and then crashing.. newer cars a-arms have an effective spring rate of 2000 lbs or so..

I do not remember figures off the top of my head, and my computer melted down last week so i would have to dig them off backup drives.. best thing to do to learn about this is go to www.apexspeed.com and the Formula Continental boards and do a search for wheel rate + spring rate and read the threads.. good stuff with multi-time SCCA champs and eingineers chiming in.

Do they bounce though.. no, not unless you hit something. even bodyroll is hardly detectable.

Some strange/interesting facts involving downforce cars...

An IndyCar on a 200-foot skidpad will pull about 1.2g (as can my "stock" class SCCA CRX) But when you put an IndyCar on a 1400-foot skidpad, it will pull 3.8g, where my CRX well.. doesn't even go that fast, but if it did, aero loads would make steering quite spooky if it happened at all... Why? Because the IndyCar is designed for high-speed cornering, not low speed.

Along those same lines, I have heard that a 120-hp 1100 lb Formula Ford 1600 is faster through turns 9-10 of the USGP course than a 900-hp 1320lb Formula One car.. Why? because turns 9 and 10 are 45-50mph corners, and the Formula Ford relies on mechanical grip not aero, where the F1 car has to compromise to go through faster corners as fast as it does.

(I heard this in 2001 or so, and since Tony George's nefew Kyle Krisilof won the SCCA Formula Ford national championship that year.. it isn't out of the rhelm of possibility that a formula ford has been driven on the road course at Indy, and there is hard data to compare it)

Jon K

 

racerjon1, thanks for the info.

Now, I've just read an interview with Pat Symonds, who knows a thing or two about these things. Interesting facts:

• three tenths a lap is confirmed.
• What he said : "For sure, although probably not as far as affecting tyre choice. But the whole thing about it is to reduce the variation of contact patch forces, so anything you do like that helps your tyres last better. There is no doubt about it. So it is not of a magnitude that you would have to use a different tyre, but for any given tyre it will perform better and longer with the mass damper fitted than with it removed." .... wow... So it's actually the vibration of the CONTACT PATCH we're talking about, so they're trying to reduce the amount the car 'bounces' on the tyres.
• The 'correct' term for these things is actually TMD's or Tunable Mass Dampers.
• The earliest application in a car was back in 1933 in an Alvis.
• Apparently the system is used in the Ford Explorer. If anyone's got one, can we have a picture or something?