armonic adsorber ?

[Ciro Pabón]

I was thinking along the same lines, Ciro. if you have some kind of free floating valve inside a shock, that opens and closes ports depending on the G's, it could damp out suspension movement in a like manner.
Since the shocks are usually mounted horizontal these days, maybe a sort of offset bobweight rotating around the shock shaft?

I am not totally sure you should have the damper moving vertically to allow patch contact: it only have to absorb the movement of the tire by inertia, counteracting it. I am thinking more about an "slider" that moves on a sleeve over the inner shaft of the shock absorber, tuned by springs like the image posted. After all, the valves in a shock absorber already work in the way you describe. Or (probably) I don't get your idea or Renault's idea...

[Ciro Pabón]

I was thinking along the same lines, Ciro. if you have some kind of free floating valve inside a shock, that opens and closes ports depending on the G's, it could damp out suspension movement in a like manner.
Since the shocks are usually mounted horizontal these days, maybe a sort of offset bobweight rotating around the shock shaft?

I am not totally sure you should have the damper moving vertically to get the same effect of increased patch contact: it only have to absorb the movement of the tire by inertia, counteracting it. As I see it, all you have to have is an element that is "moved by the bumps on the road", absorbing this energy, instead of moving the chassis (the feared by FIA "double chassis").

You could change the "direction" of the absorption, I'd guess, all you have is to do "something" with the energy, spending it.

I am thinking more about an "slider" that moves on a sleeve over the inner shaft of the shock absorber, tuned by springs like the image posted. After all, the valves in a shock absorber already work in the way you describe. Or (probably) I don't get your idea or Renault's idea...

Anyway, I'd say we need the equations. Can anybody post them and explain them?

[DaveKillens]

Due to current shock packaging requirements, both front and rear lay almost horizontally. It would take a complete redesign of the chassis and suspension to have vertical shocks.
Now imagine something similar to the present mass damper, but on a smaller scale. It would be integral to the shock absorber, part of the assembly. Since the shock absorbers are mounted to the chassis, any pitching G's would be felt in the shock. But instead of relying on the mass of the damper to counteract the chassis pitch, all this would have to do is move tiny guillitone valves inside the shock body.
A hard pitch up, and the mass would accelerate down, moving a valve that increases rebound. And a hard pitch down, a valve moves that increases compression. This mass would float between two springs, reacting only to G forces.

[yzfr7]

DaveKillens,

For my understanding, this device will not work, or have its desired effect, if attached to the shock absorber of the car.

The idea behind the "mass damper" is not to alter suspension stiffness to make the car more stable. Actually it has nothing to do with the suspension system, physically.

If you split the car in two parts, the famous unsprung and sprung masses, you have to let the unsprung mass move so it follows the irregularities of the road.

After you get through a bump, the chassis (sprung) will still go up and down untill the energy is "absorbed", usually one and a half cycle. During this period, the chassis is moving due to inertia.

It is when the "mass damper" works, after the bump. With a mass moving in the opposite direction, there will be a force against the movement of the car, slowing it until it stops. The trick is to make the mass vibrate at the same frequency of the car, but in opposite direction. This is done by knowing the average frequency the car vibrates and selecting mass and spring stiffness to produce an equal frequency, acording to

w²=k/m

w = frequency in Hz (or rad/s, it's the same)
k = spring stiffness in N/m
m = mass in kg

To make the mass go in opposite direction is pretty direct: mass-spring systems naturally causes a delay referred to the impulse. This means that, when the base moves, the mass will move after a certain time, and then vibrates at the given frequency. This delay can also be tuned by stiffness/mass ratio, so it is enough to make the mass go up while the base is already going down.

The result: when a mass (chassis) goes down, the other (mass damper) goes up, one cancelling each other. It is like the sum of waves we see at physics classes (the colored being the separated waves, black the result)



In the end it works on two distict times: 1) when the car is "in" a bump, it does nothing and let the suspension system work alone; 2) it produces an opposed force to the movement of the car after the bump, "damping" this movement.

So, it has to be attached to the chassis, and not to the suspension. If I get what you mean, you want a system that gets harder when through bumps, and this is completely undesirable. You want it to follow as much as possible the irregularities, and then dissipate the energy as fast as possible.

But to make a shock absorber sensible to acceleration ("depending on the G's"), as you said, is another story. The ususal shocks (viscous element shock absorbers) are sensible to velocity, their action proportional to the velocity of the compression/expansion.

[Ciro Pabón]

Thanks, yzfr7. Good explanation (well, good because I agree with it ).

Anyway, a shock absorber, I reiterate, works the way Dave describes.

I guess you all know this: the deflection valves (the picture I am posting is terrible, it has only one on the bottom chamber, I do not know why) are like round washers, but they are in the shape of a truncated cone (if you see them from the edge, they are not a line, the outer part of the circle is upwards of the center part). When the pressure in the liquid increases, the washer "clicks" and reverses its form, allowing the liquid to pass. The more pressure, the more clicks you'll get and more fluid will pass, absorbing with less resistance big movements while keeping the car "stiff" on small vertical movements of the tyre, when the valves are closed.



The racing shock absorbers I have worked with have a lot more valves than the ones in the picture (at least in the rebound side). What you regulate when you tune the car is the size of the holes and the size of the washers of this valves.

There are a couple of improvements to the basic shock absorber I know. The first are the gas charged ones. There you have a gas on a "third" chamber that has compressed nitrogen. This has two purposes: first, the increased pressure of the gas makes harder for the air and the liquid to mix. A mixture of gas an liquid is compressible, while a liquid is not. With less aireation the shock absorber is more consistent: normal shock absorbers get "mushy" after a while (not all the problems you get at the end of the race come from tyre degrading... ).

Actually, I do not know many people that can "feel" the difference: I have to convince some friends to test this "by hand", dismounting the part after a ride and asking them to compare the resistance with that of an "unshaked" part. Once you try to "feel the difference in the chassis" between the shock absorbers at the start and the end of the race, you find it. Actually, this also happens to gas absorbers, even if it is reduced compared to normal absorbers, not only because the gas, no matter the pressure, try to mix with the liquid, but because the liquid gets hotter and thus, more fluid.

Secondly, the gas pressure precharges the shock absorber, making it stiffer. This pressure will not help to increase the height of a car. The reason gas shock absorbers extend by themselves is a little more tricky: the area of the piston on the upper part of the valve is reduced (because of the shock absorber rod) and thus a differential pressure will develop.

Shock absorbers with a dual resistance have been devised. In this case, you have two shock absorbers, one inside the other (crudely speaking). The first one is "soft" and takes small irregularities of the road. The second one takes big bumps (is stiffer) and makes the car less prone to pitch an rolling. They also have tapered grooves on the pressure tube that allow the fluid to bypass the main valve while the shock absorber is in a middle zone and forces all the liquid to pass through the main valve when it is extended or compressed too much.

There are acceleration sensitive shock absorbers, that makes the suspension sensitive to G-forces, like Dave suggests: they have special valves that are sensitive, not only to the velocity of the fluid, like the dual resistance ones, but sensitive to G-forces. I know the Monroe Reflex. In this model, there is a "twin valve": the normal valve and a bypass around it, concentrical in what appears to be just one valve.

Finally, there is a speciall kind of acceleration sensitive shock absorbers, really ingenious (well, at least I didn't "get it" when I saw them for the first time... ). They are also called mono-chamber absorbers (at least in spanish). They only have a chamber. The chamber has a free-floating dividing piston, that separates compressed nitrogen gas in the lower section, from the liquid in the upper section, over the dividing piston. The pressure of the gas in this case helps to sustain the vehicle. The dividing piston moves freely keeping the liquid chamber full at all times, as the pressure piston (the normal piston of a regular shock absorber) moves up and down.



What makes me think about the possibility of a second free floating piston (not inside the chamber, but outside it) is this last design.

Perhaps somebody knows what kind of shock absorbers are used in F1 cars.

[DaveKillens]

You covered it well, Ciro, well done. Modern shock absorbers can be tuned for position, velocity, and acceleration. In the modern Formula One car they use shocks that are easily tuned by turning valves and screws. Once the shock has been "tuned" for that race, the shock engineers assemble shocks with built in pistons, washers, springs and whatever else. Then they are used for the race. These shocks are not externally adjustable, but are lighter, and more reliable.
One advantage of having a gas/oil shock is that since gas compresses, you can have a rising rate shock, that gives increased resistance when almost fully compressed.

[NickT]

Judging from your last post Ciro I hope your spark is coming back again

Excellent explinations from Ciro and yzfr7 thanks guys, I for one really appreciate your work.

Ok, I have only just read this thread, seem increasingly short of time these days, but what struck me was how we could make use of the 3rd spring and damper assemblies. Lets take this assembly and mount it vertically between the drivers legs or feet or further forward. Now thanks to Ciro's illustration I don't have to try and describe what I am thinking, because all that would have to happen is for the "Dividing Piston" to aquire some weight around eeerrrrrmmmmm...... 9 kilos Then all you have to do is recalibrate the damper and its "Gas Charge" to cope with the extra weight

What do you think I believe it is all part of existing suspension design and it is simply being repackaged Although it might just get a little difficult squeezing 9 kilos into an existing damper assembly