active vs. passive damping

[DEGBERT]

I’ve got a little down time here at work, so I thought I would try to start another midvalve (active valve) post. I’m not really asking a question, just sorta thinking about the relationship between the active valve configuration and the passive valve configuration. OK, we know that if have too much midvalve float you might as well have a check valve. I have no idea how you know how much float is to much, but I guess it all depends on oil flow threw the active piston, which depends on the damper rod OD / cartridge ratio (bigger damper more flow).
I would also think that more float, up to a point would be better for the woods and less float would be better for MX, or would you leave the float the same and just lighten up on the active stack?


So does the passive valve configuration have any effect on the active valve damping? Or does the active valve have the same damping regardless of the passive configuration?

Would a passive stack with lots of high and low speed damping cause some kind of back pressure on the active valve, making the shims deflect at different shaft speeds. If the passive stack affects the active stack or vise versa it would seem there would be countless combinations of active and passive stacks.

Anyone have any thoughts on this?

 

[marcusgunby]

[ If the passive stack affects the active stack or vise versa it would seem there would be countless combinations of active and passive stacks.

Anyone have any thoughts on this? [/B]

Thats the way i see it :worship: i have been grapling with the concept of how to adjust a good stack for different riders/conditions and am interested in others opinions. :thumb: as you know i feel we can adjust a stack with just the amount of float(within sensible limits)for different riders.I am not saying i know this ,just that it makes sense to me.A large amount of float i would say is 3mm any more any you have no real midvalve participation.

Jer on this topic i saw a set of SXS forks apart, and it had a midvalve very similar to a std 01 fork but it had even more lift-something like 5mm is this the way they come from KTM so you know?

 

[Jeremy Wilkey]

DE,
The whole purpose of the valves is confused in my estomantion. When we divide the circuits up we can gain in one speed range, and not pay a consequence in another. In other words the two valves contribute to a overall damping coeficent..

Now what is good.. The smaller the volume the lower the float would be for obvious reasons. So lets just generalize about the relationship for now..

I like to break valving down to a couple of concepts..

Fixed orfice, Adjustable fixed orfice, and variable orfice. Any valve stack is really a varibale orfice and there in lies the real purpose or advantage of it.

A mid valve is just a varibale orfice meaning the size of the orfice chnages based on what the force acting on the system is. The advanatage is that the valve can better optomize its flow characteritics to be neither over or under damamped.

More gernaralizations. The tricky part about valving is controling the subtle range of deflections from full open to full closed, one valve opening may work but does that provide the best feel, at lower speeds the restiance, is low, at higher speeds the resitance may be exsessive. The better able the shim, piston configuration is the more subtlely the valve can operate, and the better the feel will be.. Again good feel being in a state that is idealy damped. (Not over or under)

In a midvalve the fluid flow is very large generally, and this means that large deflections would be easy to create. For this reason and to aid in resposiveness some lift, or minium fork speed must be attainde bfore the valve contributes damping. The only problem then becomes that the remaining valving must be stiff and progressive enough to limit the growth of the valves area, with out being over or under, This is inhently becomes harder the greater the float. Also the rider can notice what they precive as inconsistencies, why when I hit that did the fork feel this way but when I hit that it feels much stiffer/softer.. The rider cannot percive the subtle diferences, between loads and inertias so the fork can have a very too face feel to it. This has an anlology to true mutli stage valving, yet for the time being we will stay out of it.

One other important detail is what we call latency, and it has beocme quite the buzz. When a Valve slows and changes direction the check circuit takes a certian amount of time// travel before it closes and seals. This delay can make the fork feel off and inconsistent. The delay can be better controled by runing larger areas, and lower lifts.

IMO the best mid-valve set-up is one that runs as litte lift as posible, and has a soft a stack as posible.(posible is very relative here BTW) This way the float is minimal, and the fork has the most consiotent feel, yet the valves area is best conmtrolled throught the midspeed, yet is soft enough valving wise that it is not over progresive and by the time it controls midspeed it creates to limited growth of area on the high speed IE harsh..

Some banner designs for the midvalve are the new 02-03 KYB 32 mm pistons, the ohlins, and posible the WP... The 03 KX has a very cool post arangment that allows for very small pivots which is ALA WP...

Now for the pressures etc, for a split second the passive and active fit each other in a state of hydraliuc vibrations. When the open cartirgide does not have suficent internal air pressure the active psiton pushes oil and then the actie seeing its normal flow load quadrupled reists with 16 times the resitance... Then the active instantly flows oil.. Once internal pressure rises the system works efeicnetly. The action is inconsistent, and not as predicatribale.. Allso consider that most likely the top of the stroke after the first compresion becomes airiated, and not only do they fight eachother playing catch but allso sudly go bame, as the air is compressed inside the cartidge.. Look at the KYB thread to endevor more into this topic..

I've often sudgested that riders actually leav a small air build up in ther open cartdige forks to promote better feel..

Well I hope this starts things..

 

[DEGBERT]

From what I have seen and tested 3mm is way to much. On my 43WP's it seems anything more than .75mm has no affect. I wonder why the SXS forks have 5mm? Why not just a check valve? Maybe the SXS have a bigger OD damper rod than the stock 01 WP.

 

[Jeremy Wilkey]

Originally posted by DEGBERT
Maybe the SXS have a bigger OD damper rod than the stock 01 WP.

Nope you mean Clyinder... :)

 

[marcusgunby]

The shim stack looked like it was a simple stack with just a load of same sized shims-so essentially it was a check plate.Im not sure the SXS comes this way as i havnt seen any others apart.Do the SXS have a larger piston?

 

[Jeremy Wilkey]

Nope!

 

[DEGBERT]

I meant damper rod, but now that I had a chance to think about it a little more last night I see why the SXS forks have 5mm of float and the 43 have about 3mm. It has nothing to do with the damper rod, it's the bigger clyinder like Jer said. Bigger clyinder=more oil flow thru the active piston=more float in order to achieve same damping. Is this even close?

 

[Jeremy Wilkey]

Guys all valid points however the disapointing fact is that the float is irrelivent on the WP's as the both the SXS and SX and EXC and MXC all run the same cylinder and pistons... Bummer but if it was bigger then by all means it would make sence arcording to my feelings/thoughts on the topic..

BR,
Jer

 

[marcusgunby]

I think this goes back to dogberts original point-the SXS fork i seen has esentially had the midvalve disabled for simplicity and all the work is done by the base valve.

 

[Jeremy Wilkey]

BUMP

 

[svi]

When the open cartirgide does not have suficent internal air pressure the active psiton pushes oil and then the actie seeing its normal flow load quadrupled reists with 16 times the resitance... Then the active instantly flows oil..

This must surely mean then that in the very initial part of the stroke the forks are cavitating?

 

[JTT]

I believe, and I stand to be corrected, that this is one of the benefits of the Twin Chamber Showa design, that effectively removes the air gap, making damper "purely hydraulic" (incompressable oil vs oil with compressable air gap).

...inserting neck into the "stupid guy guillotine" ;)

 

[Jeremy Wilkey]

SVI,
Yeah at the top of the stroke its definetly hapening, after the intial compression. I've learned more from conversations about the CV with Ross Maeda, and the purpose of the valve is primalry a controled leak to make sure the cartridge is allways filled, If you think about it air can bleed out with very little resitance, and oil will be slowed much more dramictaclly. Purpose seems to allso include a modifcation to the compression chararteristic, that includes a reduction to high speed.

I just got back from a few Days Ohlins and some time on the Dyno, John Curea and I tested several diferent arnagements, specifacly set-up to try to isolate the effects and charactertstics of all the valves. Quite simply it verified my postion that a properly confifgured set-up has each aspect contribtuing to a speed range, and that way we find the most efficent overall arangement, without being over or under damped.


As for the effects of rebound, we have a couple of seriois to consider, if you think about it when it comes to rear suspoension we have times when when the bike is on the gas and off, to properly adress these aspects, how do you think this might effect the needs of the motorcycle?

BR,
Jer

 

[svi]

MMMMMM, you need float to prevent cavitation throughout the stroke at low shaft speeds, so how does the face shim control and vary the orifice size when it has actually floated away from the piston, I was under the impression that in general shim stacks lift very little throughout the speed range so if it lifts away from the face before being able to pivot how does it control the flow through the orifice?
As for rebound I have heard of very stiff check systems being used to pin the forks down during mid turn so that the front doesn't instantly react to minor variations in throttle.

 

[Jeremy Wilkey]

Originally posted by svi
MMMMMM, you need float to prevent cavitation throughout the stroke at low shaft speeds, so how does the face shim control and vary the orifice size when it has actually floated away from the piston,

Well lets rethink this toether, no I'm saying flaot has anything to do with cavitation. Flaot is used to allow the forks "midvalve" to be configured in such a way that does not allow it to contrinbute to the low speed compression, beacuse then the fork would be too stiff.. Flaot allows some intial speed to be acheived before the shims provide addtional resistance to valve area/flow requimetns.

In a base-valve defelectins are very low as you asume, however in a active or midvalve deflections are much higher, due to the substantially larger volumes. The deflection is almost too much sometimes and this causes shim ware, and poor manipulation.. The new KYB midvalve psitons are configured in a way to allow less velocity and less deflction, which increases tunablity.

BR,
Jer

Ohlins idea of useing wave washers to control intial opening presure has some merrit, as softer midvalve valing can be used, but the springs linear nature is poor at controlling subsequent valve area growth. We are working on a hybrid approach thats uses a preloaed wave washer for low defelction control and shims for mid and highspeed deflections.

 

[svi]

I've been looking at the HMAS pistons that Honda use to try and understand why they use that arrangement. My thinking being that there is obviously some of the most brilliant engineering minds in the world working for Honda so what can they see that is completely beyond me?

 

[Jeremy Wilkey]

Originally posted by svi
I've been looking at the HMAS pistons that Honda use to try and understand why they use that arrangement. My thinking being that there is obviously some of the most brilliant engineering minds in the world working for Honda so what can they see that is completely beyond me?

SVI,
Dude, while I complety understand and agree with your stance about very talented engineers, its that type of lock step tendency that prevents the mind from doing its job.

Some of the best I deas come from the most obsecure corners of a grarge, and some of the worst come from talented enginners.(nothing against the engineers here, just a point.) For instance we have major oems that don't even understand midvalve technolgy. The Midvalve as we know it. I might go out on a limb, and suggest is owed to Ross Maeda, yet he did not invent it, Showa was the first to use it, but I still don't think they quite know it like KYB.. Certianly Ohlins or WP are not even on the chart, and Marzocchi?

The Honda Idea is solid, yet poorly implamented, they are useing the small ports to create velocity and force, which createw large deflections. The linear valve stacks are stiif, but as deflection increases subsequent high speed is minimal.. Its a fair idea poorly implamented.

BR,
Jer

 

[marcusgunby]

On the wavey washer-the 03 KYB on the KX 125 has one-unfortunatly it also has loads of midvalve lift and just to confuse me even more-it uses a 2 stage midvalve stack that makes no sence when it has lots of lift.I beleive it can be a very good fork once set up-my friend owns one and we are working on it now.

 

[russ17]

The 03 KX 250 and the RMs have what I believe you are calling a wavey washer. I was woundering about that wavey washer I thought that over a period of time that it might lose its tention compared to a check plate spring. Is this wavey washer a good thing as far as durability.I also thought it was kind of intresting on that 2-stage stack also.

 

[russ17]

As for rebound I have heard of very stiff check systems being used to pin the forks down during mid turn so that the front doesn't instantly react to minor variations in throttle

. [/B][/QUOTE]

Sounds intresting please more!