To learn and share about dampers / shock absorbers

[DaveW]

Belatti: I think that you should be able to improve the characteristics of your damper considerably, although the overall damping will still vary with temperature.

This, for example, is a slightly sanitized plot extracted from a rig test of a vehicle fitted with the same type of damper as yours (I believe), although the reservoirs were close-coupled in this case. I have removed the effect of a 10 KN/mm "series spring". The equivalent series spring estimated from your data was rather less than 1 KN/mm in compression. The two plots are from the same run, one starting at 6.6 Hz, the other starting at 13.4 Hz.

[747heavy]

another example for hysteresis caused by cavitation due to too low reservoir pressue.

courtesty of Ohlins:

[DaveW]

The TT44 is a very good example of the "shimmed" genre (in its 3-way adjustable form), largely because component quality control is/was excellent, & 44 (mm. dia.) is a very good number...

[netoperek]

Why does noone even mention Active or semi-active absorbers? they can be at least as much, probably much more effective, really Unless they are banned where You want to use them
Fill those absorbers mentioned with MR fluid, add tiny electromagnet and wire it to some DSP,with sensor readings, as well. Just simple even proportional control and You have much, much better absorber MR fluids change their density due to the magnetic field present, and those changes can be really significant. Anyways, there's much more science about noise cancelation than some D or 0 shaped figures. In the end all You want from absorber is to dissipate all the energy that is unwanted, nothing more (ie dissipate too much). But anyways, You all already know that Bear in mind You dont want Your absorber to PERFECTLY counteract ALL the vibrations, because Your car wouldn't make it till next corner

[DaveW]

Why does noone even mention Active or semi-active absorbers? they can be at least as much, probably much more effective, really. Unless they are banned where You want to use them.

I believe that suspension units with wires attached to them are permitted in no major race series apart, perhaps, from WRC.

MR fluids change their density due to the magnetic field present, and those changes can be really significant.

Forgive me, but are you sure about that? (Apologies. That was an unfair question. I think that viscosity, rather than density, is the controlled property of an MR fluid.)

Bear in mind You dont want Your absorber to PERFECTLY counteract ALL the vibrations, because Your car wouldn't make it till next corner.

True, in part at any rate.

MR fluid is just one technology that can be used for adaptive damping. Others include controllable ports of various designs & ER (electro-rheological) fluids. The last has been in development for at least 40 years, I believe. BTW, do you know if the flow inside an MR fluid damper is laminar, or turbulent?

[747heavy]

some info about cavitation in dampers with some visualisation in a transparent damper. Interesting !!

http://www.vehicledynamics-expousa.com/ ... _wentz.pdf

some info about temperature effects on dampers and how they show on the dyno ( allowed this is very dependent of the damper design in question, so this is more of an overall assessment from a damper dyno manufacturer)

http://www.roehrigengineering.com/Techn ... 0CURVE.pdf

Investigation of Damper Valve Dynamics Using Parametric Numerical Methods
http://espace.library.uq.edu.au/eserv.p ... _16_07.pdf

some other stuff about dampers (more basic)

http://www.fastfordmag.co.uk/files/2009/09/susp.pdf
http://www.zupin.de/uploads/tx_userzupi ... 412-01.pdf
http://www.theoryinpracticeengineering. ... tuning.pdf

[747heavy]

Advanced Damper Testing for Vehicle Ride Tuning

This article explores the relationship between the damper and its mounting and outlines the objective techniques that would aid product development and benchmarking accuracy.

http://www.vehicledynamics-expo.com/06v ... randon.pdf

[DaveW]

Advanced Damper Testing for Vehicle Ride Tuning

http://www.vehicledynamics-expo.com/06v ... randon.pdf

Interesting presentation, 747. Observably, (& at a less esoteric level, perhaps) much remains to be understood (or even accepted in some quarters) on the influence of power train mounts on suspension performance, and power train dynamics on suspension transmissibility.

BTW, I remain baffled why road car engineers still insist that their vehicles have a negative weight (sorry, that was crudely put - but a negative value for compressive damper force implies that compressive spring force should also be negative in a consistent world....hence negative weight on wheels).

[netoperek]

DaveW,
thanks for spotting such an error EM field changes the alignment of the particles, but surely not their count, i do really have to re-read what i write at least twice
I do not exactly know, which flow do You mean. Isn't that true, that in shock absorbers, fluids are generally being compressed, not pushed through? BUT... If my memory serves me well, in one of the MR dampers i played with some time ago, there were few round holes in piston, so there was actually a flow, but i might be wrong. But i suppose, in that case, flow's character could change depending on viscosity, ie, laminar at high voltage applied and turbulent with low or none voltage, wouldn't it?

Still, i'm no expert on that matters (or at any matters, at my age, to be more precise), i have just been taught the basic concept.

[DaveW]

But i suppose, in that case, flow's character could change depending on viscosity, ie, laminar at high voltage applied and turbulent with low or none voltage, wouldn't it?

I'm unfamiliar with the internal details of an MR damper, but I suspect you are correct about flow conditions. To be pedantic, I think the "variable" element of viscosity is a function of drive current, rather than voltage, & the switching speed (the bandwidth) of the damper will depend upon the drive amplifier "head room" (i.e. its ability to "sink" back emf, just like any audio amplifier).

The suspension of any vehicle is required to control disturbance energy dissipation "efficiently", as you suggested, whilst also controlling vehicle transient response and, for a race application, giving a driver the confidence to drive close to the performance limits of the vehicle. These are mainly concerned with contact patch load control in the presence of both road & driver inputs. The suspension of a road vehicle has the additional requirement of achieving the first two requirements "comfortably" (i.e. minimizing load variations transmitted to the passenger "cell").

The three (or four) requirements "pull" in different directions & so, as a result, an acceptable suspension set-up will be a compromise, dependent upon the intended market, development driver preferences, and the consistency of the hardware. It will also depend (often) upon decisions that have been cast in concrete by the time a development driver starts to weave his magic.

Adaptive dampers for road vehicles are seductive because they offer the possibility of relaxing the compromises imposed by "fixed" dampers. Usually, that means changing damping in response to driver inputs, and adjusting damping as a function of instantaneous damper position & velocity. Without question, however, the performance of the system will be acceptable only if the hardware performs consistently. I think that any novel damping device is likely to have both general and specific problems to be solved in order to achieve a performance that is both reliable, consistent, & has acceptable failure modes. Overall weight would be another potential issue in a racing application...

p.s. I have slightly more than an abstract interest in MR dampers, because they are fitted to my current road vehicle.

[747heavy]

some additions to Belatti´s data base (in no particular order)

racing/rally damper manufacturers

ZF Sachs Race Engineering
http://www.zf.com/corporate/en/products ... rmula.html

Bilstein Motorsport
http://www.motorsport.bilstein.de/Racin ... .html?&L=1

KW competiton
http://www.kw-suspensions.eu/int/kw_competition.php

Proflex
http://www.proflex-shockabsorbers.com/
http://www.proflexuk.com/

Moton
http://www.motonsuspension.com/

TEIN
http://www.tein.com/products/super_racing.html

EXE-TC
http://www.exe-tc.co.uk/

Reiger
http://www.reigersuspension.com/index.p ... tom_lang=3

JRZ Suspension
http://www.jrzusa.net/

SPAX
http://www.spax.co.uk/

JRi Shocks
http://www.jrishocks.com/

Extreme Tech
http://www.extremetech.it/

AFCO
http://www.afabcorp.com/AFCO_Dynatech_U ... ore_Code=A

Intrax Racing
http://intraxracinguk.com/

Quantum
http://www.quantumracing.co.uk/

Nitron Racing Shocks
http://www.nitron.co.uk/

RS&SP Argentina
http://www.rsspsuspension.com.ar/i_index.html

RE suspensions (parts for Öhlins, Penske and others)
http://www.resuspension.com/

damper/shock dyno´s

SPA design
http://www.spa-uk.co.uk/dynamometers/

MTS
http://www.mts.com/
http://www.mts.com/stellent/groups/publ ... 004062.pdf
http://www.mts.com/stellent/groups/publ ... 002242.pdf

[marcush.]

unfortunatelly the project for active motormounts in my workgroup was binned before it even took off .I would have loved it .So no connector or cables on motormounts and one more reason to leave...

[RacingManiac]

MR Damper makes use of a mode of MR fluid usage called "valve" mode. You make a piston with coils built into the piston, while cut in small passages to create flow restriction. As current flow through the coil, the MR fluid around the piston aligns and "closes" the passage on the piston. Depends on the current applied, the hole can be bigger or smaller, thus effectively changes damping force. When the damper speed goes fast enough that the differential pressure force is greater than the shear strength of the aligned MR particle, the fluid effectively shears and the piston can "blow-off". Basic tuning can be made to the size of the fluid passage to determine a base damping curve. Note that this damper essentially fails in soft mode, as no electronic current, all your damping comes from the flow restriction of the passage in the piston.

Compare to a lot of the adaptive damping technology, MR might be the least complicated due to lack of moving parts in the "valving". More tradition design deals with armature controlled spring preload and valving...Although in those type of design they might be able to design in a more favorable fail-safe mode.

[vinuneuro]

Hey guys, it's been a while since I delved deeply into dampers. Here are some questions I hope you might be able to shed some light on:

What temperature do monotube (non-res) dampers typically get to? Is this accounted for in pressure recommendations?

-Is there a logarithmic decaying relationship between natural frequency and damping ratio? Told by the guy who did Ohlins work for Vishnu, has since moved on to race engineering in ALMS.

-Is ARB rate accounted for in both low and high speed damping since most bumps are offset?

-Which natural frequency modes do you valve for? How do you determine natural frequencies of these; datalog, simulation? Typically we only talk about vertical/heave in forums.

-Transmissibility -> transition point on digressive curve. The cross-over point for a given damping ratio is sqrt2*ridefrequency. But how do you correlate that to a velocity? f=v/lambda isn't really useful since both velocity and displacement are variables, and multiple combinations of velocity and displacement can produce the same frequency. So which do you optimize for? Especially tough in applications that see street and track time.

-Is there a minimum rod/piston diameter you need to run a non-preloaded stack?

-With high gas pressure is there a concern for lowered sensitivity over initial displacement?

-How much does tire construction affect valving?

-Dave Williams in an article said that most drivers prefer digressive valving because it offers more feedback and a little more responsive in corner entry, but linear valving gives more grip. But for linear valving the driver must commit to the corner to counteract the loss of driveability. Thoughts on this?

[DaveW]

I hope this won't seem to be too curt. If it does, I apologise.

Hey guys, it's been a while since I delved deeply into dampers. Here are some questions I hope you might be able to shed some light on:

What temperature do monotube (non-res) dampers typically get to? Is this accounted for in pressure recommendations?

All dampers have reservoirs, I believe. They are built in in some cases, "piggy-backed" or separate in others. Temperatures depend on the "work" they do & the environment they operate in. In most (non-test) situations, I suspect that the second has the more influence. Actual temperatures might range up to 180degC (enclosed within the engine cover) - more on occasion (e.g. Lotus last race).

-Is there a logarithmic decaying relationship between natural frequency and damping ratio? Told by the guy who did Ohlins work for Vishnu, has since moved on to race engineering in ALMS.

The question opens a can of worms, which requires a separate response, I think.

-Is ARB rate accounted for in both low and high speed damping since most bumps are offset?

I think I know what is behind your question, but dampers normally yield a velocity (not displacement) in response to an applied force, & what goes up also comes down (hopefully). ARB's add to spring stiffness in roll (but not heave) & it could be legitimate to account for that when setting dampers (but the ARB increment to spring stiffness is often quite small).

-Which natural frequency modes do you valve for? How do you determine natural frequencies of these; datalog, simulation? Typically we only talk about vertical/heave in forums.

Another can of worms, I think. Technically, "natural frequencies" cannot be deduced directly from measurements, although it is sometimes possible to identify model parameters from measurements, & derive estimates of natural frequencies (& damping ratios) from identified parameters. The simplest "bicycle" vehicle model will (usually) have four complex pairs of "roots", each pair can be used to obtain the natural frequency & damping ratio of the "root". It is normal practice to describe the four "roots" (in order of increasing frequency) as heave, pitch, & the two hub modes, although they are often highly cross-coupled when the vehicle is heavily damped.

-Transmissibility -> transition point on digressive curve. The cross-over point for a given damping ratio is sqrt2*ridefrequency. But how do you correlate that to a velocity? f=v/lambda isn't really useful since both velocity and displacement are variables, and multiple combinations of velocity and displacement can produce the same frequency. So which do you optimize for? Especially tough in applications that see street and track time.

Apologies, but I don't agree with the basic premise, although there might, in some circumstances, be an "accidental" correlation, I suppose. It is certainly true that ride vs handling always requires a compromise, because they "pull" set-ups in opposite directions....

-Is there a minimum rod/piston diameter you need to run a non-preloaded stack?

Dampers work best with modest pressure drops across the piston. Otherwise, I can't contribute to that debate (in a racing application, I wouldn't use damper architectures for which that is an issue).

-With high gas pressure is there a concern for lowered sensitivity over initial displacement?

Same comment as above, really.

-How much does tire construction affect valving?

Can be huge... (essentially, mechanical set-up is all about making the vehicle and its tyres work together whilst keeping the driver "on side").

-Dave Williams in an article said that most drivers prefer digressive valving because it offers more feedback and a little more responsive in corner entry, but linear valving gives more grip. But for linear valving the driver must commit to the corner to counteract the loss of driveability. Thoughts on this?

I leave others to comment - but I can't think I would have uttered the last sentence....