What the 'Fric' is it?

[abw]

You have the fluid pressure acting on the pipe wall. the wall will expand with pressure, but if you are familar with material properties, we are talking micro strains; very small movements. And these movements will be slow, maybe so slow that once the fluid passes through the orifices for damper purposes, that microscopic expansion hasn't even completed.

Not to dispute any of the other, points I have deleted from the comment above, but you may have a misconception about how quickly a metal responds to strain.

These small strains you describe in the pipe wall would be elastic (reversible), and well approximated as linearly elastic Hooke's Law stuff. Think: atoms in regular 3-D crystalline lattices, connected to one another by springs, and generally vibrating back-and-forth around some equilbrium-separation distance. Stresses not high enough to deform the lattice permanently (plastic strain) will compress or stretch the atoms from their equilibrium separation, neighbors will push/pull on neighbors, next-neighbors will push back, and so on.

If you think about pushing on an outer surface of a huge lattice of atoms thus connected by springs (and it helps me to envision it if I imagine this as a sudden push), it is easy to imagine that the surface displacement would propagate through the lattice similar to how sound propagates through air. (Like pushing on one end of a stretched slinky.)

Anyway, the rate that these waves of elastic deformation propagate through the lattice is the same as the speed of sound in the lattice. And that speed is pretty high (about 6000 m/s). If you still consider that speed slow compared to the flow rate through dampers, then I apologize for the lecture (and I clearly need to learn more about dampers). But in my mind, for this type of problem, I consider it instantaneous--the deformation occurs as soon as there is a force high enough to cause it.

(Note that this is not meant to comment on how quickly a macroscopic spring will react to an applied force. Waves do not propagate from one end to the other of a "macroscopic slinky" at the speed of sound, only the waves that push one atom against the next one to create that overall macroscopic effect do.)

[ringo]

Well i guess in metal you would look on it on a granular level. The grain structure, or grain packaging. There would be an instant response if you look at it in one plane, however along a lenght is a different story.

Any how, this is my idea of how they control the ride height. I feel only the front is controled. Reason being the rear is pull rod.
The bleeding principle works when the pushrod lenght is reduced. This will reduce ride height. A pull rod would have to be increased in lenght to reduce the ride height. This would require fluid to be pumped into the system under pressure.

So it's easier to vary the front by bleeding. Just the weight of the car is needed and a control valve that allows fluid to flow at a desired event.

In this case my control valve is a spool that is connect like a heave spring. It only works under high aero loading, like the end of a back straight. As you can see the spool valve is connected to the bell cranks. A slot on the rod of this valve allows free movement of the rocker and lack of activation until the crank comes to the end of the slot and starts pushing the spool (similar to a heave spring).
Once the spool is activated and valve cracks open, fluid will bleed from the pushrods, and go into a reservoir, which has a bleeder valve to relieve air pressure.
So this will happen at the end of every straight, or at whatever speed the team desires. Fluid will prediodically bleed into this tank at measured amounts, reducing the ride height as the race progresses.

Oh yes, there are two spools ( one behind the other, not shown in the drawing), one per wheel, and they are activated simultaneously.
There are check valves in the lines to prevent back flow. When the spool is closed the hydraulic fluid has no where to go so it acts like a solid part of the push rod.
This system can be adapted to the rear pull rod,but will reuqire fluid under pressure and it will be the reverse of what i have in the drawing. The reservoir will be an accumulator instead, but principle of operation is the same.

[timbo]

How this system would be activated between qualifying and the race?
It looks pretty unreliable though, which may explain Mercedes problems

[Powerslide]

after reading a few pages i think we need to clarify some stuff. pull-rod rear suspension, because recent aerodynamic design changes, double diffuser asked for a higher gearbox so push-rod were still fashionable but after double diffuser were banned Adrian Newey decided to drop the rear or make as much space on the rear for more open area so more air can influence downforce since the lower area now is limited. so they dropped the gearbox to allow more air from the top to come down probably alo allowing some guidance to the exhaust flow. low gearbox also allows for low center of gravity. mechanical design of an F-1 car today is strongly influenced by aerodynamics rather than mechanical advantage.

FRIC, target would be soft suspension over curb yet support anti-dive and squat properties, probably holding vertical loads stronger than merely third spring dependent at the same time offering form of advance anti-roll behaviour with less interruption on the inner wheel load change. inter-linking axles would also result in handling inconsistency because suspension axle load changes would effect the axle that is not effected by load changes. a front suspension that is set up nicely is independent of a rear suspension that is set up nicely. having inter-linking the two would disrupt this. we need to understand that, the two axles represent front and rear which also equates to it representing understeer and oversteer so if your front suspension goes over a rouch surface, it will distrupt loads at the rear even before the rear suspension goes over it, creating oversteer. incedently, mercedes and lotus are both using these systems yet, mercedes seems to qualify well but not race as effectively meanwhile lotus is, arguable, being more successful doing the opposite. between the two, lotus definitely has the system working to its favour

[marcush.]

after reading a few pages i think we need to clarify some stuff. pull-rod rear suspension, because recent aerodynamic design changes, double diffuser asked for a higher gearbox so push-rod were still fashionable but after double diffuser were banned Adrian Newey decided to drop the rear or make as much space on the rear for more open area so more air can influence downforce since the lower area now is limited. so they dropped the gearbox to allow more air from the top to come down probably alo allowing some guidance to the exhaust flow. low gearbox also allows for low center of gravity. mechanical design of an F-1 car today is strongly influenced by aerodynamics rather than mechanical advantage.

FRIC, target would be soft suspension over curb yet support anti-dive and squat properties, probably holding vertical loads stronger than merely third spring dependent at the same time offering form of advance anti-roll behaviour with less interruption on the inner wheel load change. inter-linking axles would also result in handling inconsistency because suspension axle load changes would effect the axle that is not effected by load changes. a front suspension that is set up nicely is independent of a rear suspension that is set up nicely. having inter-linking the two would disrupt this. we need to understand that, the two axles represent front and rear which also equates to it representing understeer and oversteer so if your front suspension goes over a rouch surface, it will distrupt loads at the rear even before the rear suspension goes over it, creating oversteer. incedently, mercedes and lotus are both using these systems yet, mercedes seems to qualify well but not race as effectively meanwhile lotus is, arguable, being more successful doing the opposite. between the two, lotus definitely has the system working to its favour

to think of front and rear being independend of each other just because there is no direct linkage or tubes is a bit of a stretch ,car dynamics is not just 4 quarter cars stuck together loosely ..your workings at the rear will always have an effect on the front and vice versa.
edit-if there was some balance to start with .An extreme understeer car will not realy respond to minute changes at the wrong end of course.

[Tim.Wright]

You might be interested to know that some F1 suspensions for the last few years have achieved a roll/warp stiffness ratios of around 5. Perhaps an interconnected suspension allows similar ratios to be achieved with fewer contraints.

Hi Dave,

Bringing a post back from about a month ago, I'm interested in this point here that you made about the roll to warp stiffness. I'm doing some calculations on vertical stiffness in different modes just for my own research and I've seen that if you don't have a front to rear interconnection, then the roll stiffness is the same as your warp stiffness. I.e. the roll/warp ratio = 1.

In the F1 car you tested, was there a front/rear interconnection? What's your definition of roll and warp stiffness? My definitions are:
roll stiffness = dFz_fl@1mm_roll - dFz_fr@1mm_roll + dFz_rl@1mm_roll - dFz_rr@1mm_roll
warp stiffness = dFz_fl@1mm_roll - dFz_fr@1mm_roll - dFz_rl@1mm_roll + dFz_rr@1mm_roll

Basically I'm summing the change of vertical force at all 4 corners at 1mm of roll (left +1mm right -1mm) and 1mm of warp (fl +1mm, fr -1mm, rl -1mm, rr +1mm)

I can upload my excel sheet with the calcs later when I'm home.

Tim

[flyboy2160]

....In this case my control valve is a spool that is connect like a heave spring. It only works under high aero loading, like the end of a back straight....So this will happen at the end of every straight, or at whatever speed the team desires. Fluid will prediodically bleed into this tank at measured amounts, reducing the ride height as the race progresses.
...

How does your system distinguish aero loads from braking loads and from running-over-curbs loads?

I thought somebody tied something like this years ago but with a mechanical ratchet system.

[gt6racer]

Tim,
From your comments I think you are on the right track.
Take your image of Apr 17th posting and spin it 90 degrees. Now you have an "in in" pitch stiff system still with warp freedom. Then you can bolt on more smarts, such as softening the pitch stiffness in straight ahead ( just add a connection between the two hydraulic circuits ) to let the rear drop under aero at high speed, or even get more clever to switch back to the original Apr 17th connections during turns to get back to a roll stiffness system. This latter point was hinted at in Scarbs's article of Oct 2011. How they switch is still a puzzle to me as I've posted earlier - any ideas ?
Beyond this, the system could be tricked up to add pitch damping, scaled pitch coupling or even ride height change.

[DaveW]

In the F1 car you tested, was there a front/rear interconnection? What's your definition of roll and warp stiffness?

I am reasonably sure that the was no front/rear connection. I suspect that you may have ignored sprung mass motion. Consider the (terminal) case of a stiff front roll stiffness and zero rear roll stiffness (e.g. a "3rd" spring, but no corner sprungs or anti-roll bar). The suspension will have zero warp stiffness because any front roll deflection will, within limits, simply be transferred to the rear suspension by body roll. A roll moment will be supported, however, provided that the chassis can support a roll moment (I think).

[Tim.Wright]

In the F1 car you tested, was there a front/rear interconnection? What's your definition of roll and warp stiffness?

I am reasonably sure that the was no front/rear connection. I suspect that you may have ignored sprung mass motion. Consider the (terminal) case of a stiff front roll stiffness and zero rear roll stiffness (e.g. a "3rd" spring, but no corner sprungs or anti-roll bar). The suspension will have zero warp stiffness because any front roll deflection will, within limits, simply be transferred to the rear suspension by body roll. A roll moment will be supported, however, provided that the chassis can support a roll moment (I think).

Ok, I got you, its a difference of definition. I was imposing a motion of:
+1mm -1mm
-1mm +1mm
and then measuring the resulting forces, but of course this is not realistic for the reasons you mentioned. Thanks for the example, it cleared it up well. My method of calculation is effectively like fixing the body to ground, and moving the wheels. In your method, you are moving the wheels and leaving the body free.

Are you able to disclose, how you define/measure the different modes on the rig? I'd like to setup my spread sheet so that its speaking a language that people are currently working in. I will shoot you a copy once its ok if you are interested.

Tim

[Powerslide]

[quote="marcush."] to think of front and rear being independend of each other just because there is no direct linkage or tubes is a bit of a stretch ,car dynamics is not just 4 quarter cars stuck together loosely ..your workings at the rear will always have an effect on the front and vice versa.
edit-if there was some balance to start with .An extreme understeer car will not realy respond to minute changes at the wrong end of course. [/quote]

yes, the two axles are linked by the chassis. what i was trying to explain was there is under and over steer as there are two axles working. of course both axle sliding would make it a four wheel drift. point is, if one axle is over a rough plane it will disrupt the other axles set up while it is one a smooth surface. a chassis on the other hand has a lot of mass to absorb or ballast off some movement whereas interlinked suspension has direct involvement with each other

[DaveW]

Ok, I got you, its a difference of definition.

I define modal deflections of the wheel pan and CPL in a similar way to you. The rest is down to observation - of a real vehicle on a rig....See another thread...(apologies, I couldn't resist).

[marcush.]

to think of front and rear being independend of each other just because there is no direct linkage or tubes is a bit of a stretch ,car dynamics is not just 4 quarter cars stuck together loosely ..your workings at the rear will always have an effect on the front and vice versa.
edit-if there was some balance to start with .An extreme understeer car will not realy respond to minute changes at the wrong end of course.

yes, the two axles are linked by the chassis. what i was trying to explain was there is under and over steer as there are two axles working. of course both axle sliding would make it a four wheel drift. point is, if one axle is over a rough plane it will disrupt the other axles set up while it is one a smooth surface. a chassis on the other hand has a lot of mass to absorb or ballast off some movement whereas interlinked suspension has direct involvement with each other

just get your head around the fact aero cars do not have significant droop travel ...so you might think making the thing softer at the rear would help rear but you might already lift the diagonal front completely off the track by doing this ...and will this not induce even less grip at the front ? sure you have halfed the load capacity at the front by doing this ..
Maybe not the intended thing dominates your change.

[Powerslide]

i was actually trying to make it a bit basic that interlinking suspension axles are not all positives but you seem to prey on anything. by the way, when an inner front lifts you dont lose half of frontal grip as proven by the delta shaped race car as center of pressure will determine its physics

[Tim.Wright]

Ok, I got you, its a difference of definition.

I define modal deflections of the wheel pan and CPL in a similar way to you. The rest is down to observation - of a real vehicle on a rig....See another thread...(apologies, I couldn't resist).

The difference is that your and my definfition of warp are not the same. In my calculations, I'm assuming a fixed body, and applying a warp displacement at the contact patch. It seems that you leave the body free (body force actuators = 0N) when you apply a warp movement at the contact patch (which to me actually seems more correct, and I will change my calculations to do the same). Is this correct?

I would assume that for a heave, roll and pitch movement, the body is fixed.

Just so I understand a few things;
What do you mean by wheel pan and CPL?
Is your rig a 4 post or 7 post? (its not clear from the company's website)