M-100 Message Board
M-100 Message Board
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
Forgot your Password?

 All Forums
 M-100 Message Forum
 General Discussions
 Martin shows us how air valves work
 New Topic  Reply to Topic
 Printer Friendly
Previous Page | Next Page
Author Previous Topic Topic Next Topic
Page: of 4

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  07:34:46  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Hi Chris

Very helpful if you are describing your experience about the ‘rearing’.
It is not that I don’t understand what is happening. I just don’t have this experience ..or should I say I don’t have this to this degree that I noticed it very much? I think the reason it could be differences in percipience of the event...maybe I just don’t notice it the same way you do?

Now can you do me a favor: Let’s play Sherlock…. I want to find out what is happening. Can you describe for me exactly what happened…. How was your driving when this happens (how fast, what roads, topo, how much braking etc.). Does it happen only sometimes, does it happen always? Is it depending on circumstances?
When ‘rearing’ happens…was there always a lot of braking involved right before the stop… when the car is then coming up. I mean more than ‘normal’ braking? (what is normal?... this gets philosophical)

Then describe exactly how you experience how you notice this rearing…. When you stop…how do you notice that the car goes (50mm) up…
because this is hard to notice?
How do you know that it is 50mm? How do you know that the car is going down after the stop (engine on or off?... at a signal? ). Do you feel it going down, do hear the air exhaust? For how long do you hear the exhaust going? I imagine it must been as if you are in 'High' mode and the push the knob?

Sorry for the many questions… I just want to get closer.
I was starting asking around people who drive these cars and 2 out of 2 didn’t agree with the 'rearing' but I will keep asking more.
So this is either a matter of different percipience of the event …or there is technically a different event happening (system is different or the driving is different) .
I just want to try solving the riddle and take the mysterious factor out.

Martin

Edited by - werminghausen on 03/10/2014 10:52:01
Go to Top of Page

Chris Johnson

USA
3751 Posts

Posted - 03/10/2014 :  10:48:25  Show Profile  Reply with Quote
This is no "riddle" here. The only riddle would be what is wrong if a car doesn't display this behavior.

Fact: Some magnitude of braking will cause the front suspension to compress.

Fact: Assuming properly working systems, beyond a certain point of front suspension compression The E (inlet) valve will open.

Fact: So long as the air pressure in the front air chambers is lower than the supply pressure, air WILL flow into the air chambers from the supply. Throttles and pressure differentials will influence HOW MUCH air will flow over a given period of time, but cannot change the fact that air will flow.

Fact: The extra air in the chambers will cause the front of the car to be higher than it was before the admission of the extra air once the transient load on the front is removed.

Fact: If the extra air raised the front of the car enough to open the A (exhaust) with the transient load removed, the extra air can leave the air chamber and the front of the car will drop.

The variables are the pressure differentials and the time which the E valve was open and, within a small range, the throttling of the E valve itself if it is opened enough to barely raise the valve from its seat.

So, there is no riddle here. The system is behaving exactly as could be predicted it would. The real question is why a certain car doesn't display this behavior.

quote:
I was asking around people who drive the car and 2 didn’t agree with the rearing.


So? What's your point? Do you dispute the facts as stated above? In your mind, what qualifies these other two folks to be an authority worth refering to when even simple mechanics and physics clearly indicates that they are wrong? You have a better understanding of what the system is comprised of than most folks, so you know perfectly well that there are no hidden functions of some parts somewhere that might change the basic rules.

When the physics contradicts the empirical evidence then it is appropriate to challenge the emperical evidence, but this can only be done succesfully if you first acknowledge the incontravertible physics. Once done, it is clear that vehicles that do not display this behavior, while perhaps typical now, are not "normal" and are suffering some sort of deficiency in their operation. That is the riddle.


Chris Johnson
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  11:43:23  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Dear Chris, I am not questioning the physics at all and you are right on all accounts …that there will be some airflow during breaking…I think we all agree here.
The only question I have is: How much air can flow during braking a car down ….say from 60mph to zero… Say A) the fastest braking possible vs B) slow braking (that triggers E to open)
What counts for airflow is (as I think we all agree)…
1) time of impact, 2) throttle in E and A bullet, 3) pressure differentials –valve unit 4) weight of car (has some influence on pressure differentials as the work pressure is different)
The null zone adjustment has no influence for opening of E valve (in the scenario when the car height before braking is end of E closing (see my diagram couple days ago).
Let’s assume the car is to specs and 2) and 3) 4) are known .. .and correct (meaning correct valve unit settings, correct throttle and car with 1 man, no other big load)
The two calculation become complex indeed but in principle
Scenario A: 5 seconds
fastest braking possible 60 to zero (for a 109)
Let’s assume 5 seconds

Scenario B : 50 seconds
Braking car as little as possible… but still open E:
In order to fully open E it takes about 1- 1.5mm of axle height differential…meaning (1.1mm/kp coefficient)- 2 wheels- roughly 2-3kp more force on the front wheels you could in theory open the front E valves… yes…with little force as this you could trigger E to open if there is no slack in the mechanics.
let’s assume for the example you are a master of slow braking and have a constant brake force over 50 seconds to get the car to a stop …maybe you could brake slower and still trigger E to open.

So let’s compare A) and B)
1) Time: 5 seconds vs. 50 seconds
2), 4) are identical
3) Pressure Differentials: As the bellow in A) is compressed very much the pressure in the bellow is 9bar close to 10 bar and the pressure differential is 1 bar only
In scenario B the pressure in Bellow is lower, say 6.5 bar and the pressure differential therefore 10- 6.5 = 3.5 bar...meaning factor 3.5 higher than in A)
How much more air in flowing in A) vs. B)?
With all my assumptions (hell knows if these are correct)
Slow braking will have factor 35 times the amount of air flowing compared to fast braking! (10* 3.5)
Well …we know that lifting the car from D to high will take … 30- 60 seconds (I have not tested this to be honest) ?..... it tells me that Chris must be right that it is possible to bring the car up 50mm by slow braking…not by fast braking however.

But I have my doubts that braking in this disciplined and slow manner is normal driving… I have another suspicion:
As there is only little force needed to open E in the front I just wonder if there is not the possibility that aerodynamics will push the front in a way that E opens at a certain constant speed and then if you brake there is an additional air intake by E and the ‘rearing’ happens?

Martin



Edited by - werminghausen on 03/10/2014 14:25:58
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  12:31:52  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Downforce: I never looked into this before but probably we should together in order to find something or not. At least then we know a bit better.
Downforce is a aerodynamic force that comes into play with rising wind speeds.
It is a wind force and as such difficult to handle as we just don't see it (I have some experience around wind generators and the forces that are in play...and ...it is complicated).
Of course the form of the car is important and then also how it sits on the road (car height front and back).
As you put this W109 car into the wind channel...what is happening?
Can the W109 produce downforce under normal conditions?

Martin (fearing that this upsets Chris)





Edited by - werminghausen on 03/10/2014 12:38:14
Go to Top of Page

Chris Johnson

USA
3751 Posts

Posted - 03/10/2014 :  12:37:35  Show Profile  Reply with Quote
But the slow braking (50 seconds, minimal suspension compression) example does not take into account the fact that the system could more than overcome the minor compression in a short period of time, so the last ~48 seconds of that example would be with the front suspension at normal height, not admitting any more air to the chambers. Once no longer braking, the excess air would be discharged and the suspension would return to the normal height.

The effects of air flow over the body of the car are irrelavent as they return to zero as the car is braked to a stop, so long as the system is capable of charging/discharging air at a rate equal to or faster than the rate of change of the effects of air flow. The effects from weight tranfer that compresses the suspension when braking will far exceed any minor effects from air flow over the car as the car comes to a stop. This is emperically evident from the fact that the driver can see the front of the car drop when he hits the brakes under normal circumstances, irrelavent of the car's initial speed whether it be 15 mph or 130 mph.

I used the expression "normal braking". Not tromping on the brake pedal, not just a little drag, but what any typical driver would do coming up to a stop. For the sake of conversation, let's say it is a clear, bright, day with a dry asphalt street. The driver is approaching a stop sign at 35 mph with no other traffic around.




Chris Johnson
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  12:46:33  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Chris...
yes..you are right again. The minimal force braking scenario will work only if the breaking is not constant but progressive in order to always make sure that E is open.... needs to be progressive...good catch.
In order to max total amount of airflow during braking you need to brake progressively so that the front will dip constantly 2mm or more ...this means you hit the breaks constantly harder.. braking progressively in order to push the front constantly down.
Question is: If you do this...how long does it take to get to a stop?
much faster I fear as the progression tell you.

Coming from the other side: how long does it take to raise a car from normal to 50mm (high)? What do people think how long it takes? I don't have access to a car so I can't do this test with a stop watch.
This would be the amount of time needed to pump the airbag up during braking as described by Chris.

Martin


Edited by - werminghausen on 03/10/2014 15:00:04
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  14:53:48  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Another attempt to consider aerodynamics as a force in play: of course the force that pushes the car down will be compensated over time by the air suspension and in theory this could at least be part of what is happening (car rearing after a stop).
Say the downward force during fast driving will be 100kp total on the front ( I know this seems to be a lot- can this be?)
Following this example...the 100kp would push the car down (assuming a spring softness coefficient per wheel for example s= 1.1mm/kp.. makes a total for the front of 0.55 mm/kp) and this will be compensated (as we know).
H= F*s … 100kp * 0.55 mm/kp = 55mm: with this force of 100kp the car would go down by 55mm and thus storing as much energy as Chris is describing to be released after a stop.
If this car comes to a stop by braking none of the stored air will be released…and actually some more air could pump up the front springs depending how long braking takes until the car stops and then after stop the car will be suddenly 55mm+ higher than normal.
This is at least a scenario I can imagine is possible if downforce is an option for the car.
Again we’d need someone who knows about the aerodynamic forces around a W109… I just don’t know if it exists and how much it is.
This is the reason I wanted people to describe exactly how things are happening with their cars (as there are also people who don’t seem to have the same experience and I just want to find out why).
Let’s turn the conversation around and say that there must be a rise in front spring pressure during each braking (which brings your car up) from what threshold on would you typically notice this? In other words there is (and never was) the doubt that this happens but it is the discourse of how much pressure will be stored there or how much the car will go up after the stop and how much will be noticeable for different people (the different perception) .

If I were to rationalize this discussion and had a car I’d propose to add a tank to the air filter port and try to catch the air being exhausted after stops and measure the air volume through the pressure rise… or probably better: to measure the pressure in the front work group… add a pressure gauge and monitor the pressure rise during fast driving and during braking and compare to the pressure after stop… I think the latter would be the best way to test.
But how to add a port for a gauge there? Not an easy task indeed. I'd build a custom air fitting and replace the regular one at B-port. I have an idea. This is an interesting discussion and I might just take this on. It will take a while to accomplish though.
I just bought a nice South Bend 9A lathe and could machine now such toys..
Martin

Edited by - werminghausen on 03/10/2014 14:54:39
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  17:27:34  Show Profile  Visit werminghausen's Homepage  Reply with Quote
I just can't imagine that Mother Benz in her great wisdom could have designed such a flaw. Maybe this is why I can't get my head around this issue... so I am biased. Please forgive me.

Martin

Edited by - werminghausen on 03/10/2014 17:31:00
Go to Top of Page

Chris Johnson

USA
3751 Posts

Posted - 03/10/2014 :  18:04:46  Show Profile  Reply with Quote
And there inlies your problem: considering this to be a flaw. Why would this possibly be considered a "flaw"? It's a suspension, and has range both below and above the neutral point, and it's that way for a reason.

A car with steel springs will do the exact same thing too, though not to quite the same degree. Hold the brake pedal at a consistant pressure until the car comes to a dead stop. The car will take a nose-down attitude all the way through the braking process and then rebound above the normal suspension height as the steel springs extend back out once the car stops.

Any typical vehicle does this. I say "typical" so that I don't have to defend my statements against arguments like "what if the shocks are over-rated?" or "what if I replace the springs with rigid steel beams?".

The factory's air suspension system is a big improvement over even their steel springs suspensions, let alone the suspensions used on most cars at the time. There is no "flaw" in it. You need to go out and drive some properly operating vehicles rather than sit around and ponder unquantifiables.

If the suspension compressed by two inches when at speed, that would be a flaw.




Chris Johnson
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/10/2014 :  19:56:32  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Agreed...I am biased...need to recalibrate.
Regardless I am pondering.
Yes I agree with Chris and the assumption a 100kp aerodynamic load on the front of the car would be a flaw....(where are the engineers knowing this here?). I was just making this up to get all possibilities covered.... in my despair.
If Chris is right and the car goes up 50mm 'any time' you have used the brakes in a certain pattern (well not driving just around the corner to CVS hopefully!) and it is supposed to be that way..a tolerable event let's say....
then my personal perception was just a bit off... or my car didn't do it right. But I can't think of a reason then that my car didn't do it as all was per specs.
My perception (filtered thru my bias) leads me to not believing in the 50mm (see how strong a belief is? You know what is funny about a belief? There is nothing funny about a belief...)I'd rather think it were much less than 50mm..But to my excuse there was also no one telling their stories so far except for the two Chris's and some others) For my sake then(and in absence of test driving a car right now) I decided to go the longer scientific way and will research the pressures in the work group during driving and braking. This research will however take a while... How does this sound to you Chris and others?
And we can continue a fruitful discussion at a later time?

There is one thing left and this was about the valve timing...where we started the discourse: the null zone and keeping this zone to a small amount, say 2mm of axle movement.
Question is: What difference does it make if this null zone is bigger...say 4mm? I mean what advantage and disadvantages would be considered one vs the other?

Martin
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/14/2014 :  13:54:09  Show Profile  Visit werminghausen's Homepage  Reply with Quote
quote:
Originally posted by werminghausen

If I were to rationalize this discussion and had a car I’d propose to add a tank to the air filter port and try to catch the air being exhausted after stops and measure the air volume through the pressure rise… or probably better: to measure the pressure in the front work group… add a pressure gauge and monitor the pressure rise during fast driving and during braking and compare to the pressure after stop… I think the latter would be the best way to test.






Lazy as I am I found an online calculator and tried to get close to the condition what is happening in our cars...
I used parameters like 4mm airline and 0.63mm orifice and a flow coefficient of 0.5 (as we have not an orifice[0.7]
but a more complicated set-up with higher resistance, 3.5 bar pressure differential and calculated the air flow at 0.115 liters/sec...= 6.9 l/min
A second set of parameters (as the pressure differential drops as the car pumps up with 3 bars and 0.4 coefficient ends up at approx 5 l/minute.

So if my assumptions are not completely off I'd say that the car gets pumped up 50mm in the front in about 30 seconds. This is probably also my guess without having this tested in real time.
I just wanted to do my part here to get things logical.
It would be better to do a real flow test but I fear I should have the test been done on the real car with everything set up...not a bench test only.
I am having trouble to upload the online calcs. Sorry, will try later again.
Martin









Edited by - werminghausen on 03/15/2014 17:09:53
Go to Top of Page

Ian Keers

United Kingdom
407 Posts

Posted - 03/15/2014 :  15:45:51  Show Profile  Reply with Quote
I am not an engineer, merely a 6.3 owner with much (bitter) experience of air suspension issues, albeit now with a happy car. Your discussion is academically fascinating and I salute both Martin and Chris on their impressively knowledgeable posts which I try to follow. My only observation is this: both your academic points of view are based on the performance of new systems. In the real world, we all run cars that are 45 years old (in my case at least). Things have changed over the years, (probably for the worst).

Ian Keers
United Kingdom
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 03/15/2014 :  22:07:21  Show Profile  Visit werminghausen's Homepage  Reply with Quote
quote:
Originally posted by Ian Keers

I am not an engineer, merely a 6.3 owner with much (bitter) experience of air suspension issues, albeit now with a happy car. Your discussion is academically fascinating and I salute both Martin and Chris on their impressively knowledgeable posts which I try to follow. My only observation is this: both your academic points of view are based on the performance of new systems. In the real world, we all run cars that are 45 years old (in my case at least). Things have changed over the years, (probably for the worst).

Ian Keers
United Kingdom



Hi Ian,
thanks so much. You know what the fun part is with 45 year old cars like these?
They can still be performing as designed or very close to that if they are maintained and repaired. Pretty fascinating and a pleasure to drive. The air suspension I often compare with a Swiss watch ...and it actually is if all the parts work together as they are designed.
Of course we drift more on the extreme side in our discussion...I know.
Martin
Go to Top of Page

Ruud

Netherlands
65 Posts

Posted - 09/09/2014 :  16:02:55  Show Profile  Reply with Quote
After reading most of the posts here, and watching Mr. Werminghausen on youtube, I thought it would be safe to send my air suspension valves to Mr Werminghausen. The old ones were not bad, but when the drain valve of my airtank was leaking (took me some time to figure that out), the front of my car would sink - most probably a leaking E-valve. I must say, Mr.Werminghausen sent me a set perfectly overhauled air valves. They look like new, but more importantly, there is no leak anymored, and consequently no sinking. Also - at first I thought it was a matter of misperception - the steering and cornering of the car feels better. The difference is not big of course, but the car feels a bit more agile, and even a little bit more comfortable. Finally, communication was great, event hough he lives in the US and I in Europe. Sending and receiving the parts was simple and on schedule. I know that there are more addresses for this, and probably good ones, but from my own experience I can highly recommend Mr Werminghausen. (And I didn't get a discount for writing this :-)
Go to Top of Page

werminghausen

USA
760 Posts

Posted - 01/12/2015 :  12:59:05  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Thanks Ruud for your nice note.

Allow me to resume some ideas about better understanding the 'behavior' issues of the air suspension cars which Chris came up with...cars pumping up during driving/braking.

I'd suggest that 109, 100 and 112 drivers could help doing some research with a simple test and report here in order to understand what is going on in our cars. I'd expect the car suspension coming up during this test because it cannot go down. The question is how much will the cars come up in front and back.

Testing procedure:

1)Drive the car a bit in N (normal driving mode) in order to get the car to normal height
2)Then get out of the car on a horizontal surface/garage and measure height of the car (e.g. clearance of the wheel well edge from garage floor)

3)TPut the knob inside in S for 'locked' which closes the exhaust and no air escapes. This means the car will only go up but not down if your suspension is to specs.

4) You are driving in S- mode for a while, say 5 or 10 miles, come back to exactly the same place you measured before.

5) Then you measure again the height of the 4 wheels and note the differences in height.

6) I'd be interested on the amount of increase in car height. Note also how many miles you drove, how fast, flat or hills. lost of braking etc. AS braking seems to be one of the issues I'd be happy seeing people braking a lot!

My 109 is under a pile of snow unfortunately and I cannot drive but maybe there are cars in warmer areas of the planet driving for the test?

Note also how for how many miles you drove, how fast, flat or hills etc.

Don't drive like crazy...drive just as you normally do.

Best Martin

Go to Top of Page
Page: of 4 Previous Topic Topic Next Topic  
Previous Page | Next Page
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
M-100 Message Board © 2002-2015 International M-100 Group, Inc. Go To Top Of Page
This page was generated in 0.45 seconds. Powered By: Snitz Forums 2000 Version 3.4.06