Adjustable damping effect 8

[Alfninux]

Hello,

what are the advantages of having an adjustable damping effect?
I mean, in case of semi-passive dampers, it is possible to adjust the damping effect so to work in different conditions. Why is it good to have the possibility to modify the damping effect (the damping force)?

 

[GregLocock]

I guess you are talking about cars. Typically you'd like more damping for control than for comfort. It is complex.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BUGGAR]

You have to modify the damping force because the damping requirements are different. For example, when driving slow, stiff shocks are necessary to prevent wallow over rolling bumps (low energy input). When driving fast, the shocks have to soften when they hit those same bumps at speed without the jarring of the stiff shocks (high energy input). So the shocks are valved to "collapse" at higher speeds (the knee of the shock curve).
Now they are using magnetic hydraulic fluid to electronically control the viscosity of shock absorbers. This is a big chassis tuning thing being used in the new Corvette to capitalize on its yaw responsiveness from its mid-engine polar moment of Inertia. Shocks are cool!

 

[CWB1]

what are the advantages of having an adjustable damping effect?

Simple, it allows you to adjust for unknown or changing conditions.

 

[Alfninux]

I'm talking in general. Not only automotive applications. One of the main requirements of semi-passive dampers is that the damping effect can be activated or de-activated when required. I didn't get why sometimes is required to have a damping value set to zero...which is the advantage?

 

[djhurayt]

One reason could be wear. As other parts in the system (or even the damper itself) wear, friction can increase or decrease and the system may need more or less damping force to account for the change.

Or in the case of a hydraulic system it may require different damping as the oil heats up from initial start up temperatures.

 

[RVAmeche]

For a more general discussion, I think it depends on the harmonics of the system. Sometimes you can add in damping to reduce the force felt or maybe you just want damping above a certain value.

 

[handleman]

Mass changes (full vs empty vehicle)
Performance optimization for conditions/desired response (bicycle rear suspension)

Honestly, this is a pretty incomplete question. If you have some application in mind, perhaps we could tell you why it's desirable for that application. Otherwise, it's kind of like asking why red paint exists. Sometimes, you want to paint something red...

 

[btrueblood]

"I guess you are talking about cars. Typically you'd like more damping for control than for comfort. It is complex." (Greg L)

And involves numbers...complex numbers...

I'll show myself out.

um, wait,

"I didn't get why sometimes is required to have a damping value set to zero...which is the advantage?" (OP)

Damping can affect the system response, i.e. typically adding damping makes the system respond more slowly. So reducing damping can make the system respond faster, though maybe it oscillates more around the target value. So, being able to turn damping off (say during startup or other large changes in operating state) could reduce time to reach a near-normal condition, then the damping is "turned up" to dial-in to a desired steady state condition.

 

[GregLocock]

So here's how it might help. Driver turns steering wheel. Latacc develops. Vehicle starts to roll in response to latacc but can't reach steady state immediately due to roll inertia and damping. So, why not detect the SWA, switch the dampers to zero until you reach the desired SS roll for that latacc, and then zip the dampers up to maximum. It might feel horrible, it would need tuning. This minimises the impact of roll/rollsteer coupling.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Alfninux]

Honestly, this is a pretty incomplete question. If you have some application in mind, perhaps we could tell you why it's desirable for that application. Otherwise, it's kind of like asking why red paint exists. Sometimes, you want to paint something red... (handleman)

A possible application can be washing machines. In some studies I've read, the idea is to develop a semi-passive damper in such a way that, during the washing phase and during the spinning phase, the damping is usually reduced or set to zero, while during the transition from washing to spinning (crossing the resonance frequency) the damping is increased.

My question is: what is the effect of having a high damping force during only spinning, or only washing?
Why during these phases it is suggested to decrease the damping value?

(It's clear the reason why during the transition it must be set to a high value)

 

[BUGGAR]

The question is incomplete but the answers are superb!