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werminghausen

USA
760 Posts

Posted - 03/05/2014 :  08:58:56  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Interesting.

Overpressure and underpressure in the air springs (mostly concerning the front axles) was the issue MB was working on when they introduced the air suspension as this is obviously a potential flaw in the system if not addressed. This is during braking and curves.
So let us say you love to drive in continuous circles at constant speed for a while (until you can't bear it any more).. and do this fast. What happens is: The front of the outside wheel will be down (make the pressure in the work group increase-car goes up) the other side, the inside wheel, will go up (thus the pressure in the work group will be released, exhaust opens- car goes down). If you reach then the equilibrium in the system if you drive the curve in a constant speed for instance you axles will both be at neutral after some loops when the LCV have corrected the height.
If you then stop the car...of course... the axles will be out of balance. This is probably what Chris is describing..in principle (car going up or down by external forces...braking, turning, high speed- aerodynamic force).
During the forces are at work the car will be too high or too low.. and the LCVs will correct this after the stop.

Of course this happens if the Null Zone is to specs...which I am adjusting to 2mm axle movement. This means if the axle is moving 2mm the LCV will correct height.

So now I need to get my head around Chris's braking issue.
Other than in a constant curve ...during braking a) both wheels are affected (looking at front wheels...though this is true for the rear but in a different way) and b) the decelerating forces are limited in the timeline and need to be followed by the opposite force in order to keep the car going- acceleration...bringing the front up...unless you drive downhill and have a more constant brake force.
Let us say you drive on a highway horizontally ...fast... you accelerate and you brake...and in average you drive at one speed... In this scenario I'd say you front suspension should not go up or down much in average from braking... I can't believe the 2".
What happens during sudden braking (and this is only for a second or less. The car goes deep down in front and the pressure in the springs rise probably close to the support pressure (10bar) and there is not much pressure differential at all in order to pump it up..
Chris, can it be that the car was (is) pushed down in the front due to aerodynamic forces during fast driving? I have never considered this and never experienced this on my W109 but this would be my only explanation...you'd need a constant force to push the car down in order to make the LCV act this way.

I mean I was not driving slowly in Oman with a 'tight' air suspension (well Arabs don't go slow at all)but I honestly have not experienced 2" even after hardest driving. I just wonder Chris how you explain this happen. Was the pressure holding valve adjusted at a higher level like 4 bar and the exhaust didn't work during 'not braking'? Or was it 'bad' aerodynamics?


The other note of yours is interesting indeed.
When I have some time I'll test different harnesses of Buna rings. It is mostly the E valve that I will be testing on... I wanted to machine bullets that have a screw connection so that I can change the o-ring in the same bullet and test avoid the flanging.
In theory with a harder ring the 'travel' is less for opening and closing the valve but this probably compromises the proper seal.
This is on my list for sure...to test.
Anyhow with a standard Buna ring the Null Zone can be kept at roughly 2mm axle movement. Well this is only true if there is no play in any of the mechanical parts from the axle to the control piston. With no play I mean in total less than 0.04mm relative to the control piston movement- the greatest play I experience between toggle ends and boring of the spring package and control piston. Greatest play I 'saw' between STk and piston was 0.1mm once and then I need to correct this play in order to get to the foreseen Null Zone adjustment.

Martin

Edited by - werminghausen on 03/07/2014 20:04:33
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Ron B

Australia
11488 Posts

Posted - 03/05/2014 :  15:59:38  Show Profile  Visit Ron B's Homepage  Reply with Quote
A guy in italy, Pagadino, has done a lot to sort out this cornering pressure build up effect . It turned out to be very simple. He suggests replacing the rear caliper hold down bolt rubber bushes with nolathane or similar and shortening the tubes on the front sway bar bolts by 5 mm. I have done the former and the result is dramatic. The car sits dead level under hard braking even though my shocks are getting very tired. I do notice the feeling of height jacking at high speed through sweeping turns though and i may bring the rear down to give the car more negative rear camber.


quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
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Orange County Section
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werminghausen

USA
760 Posts

Posted - 03/06/2014 :  19:20:17  Show Profile  Visit werminghausen's Homepage  Reply with Quote


Hi Ron,
good topic...we are getting somewhere. Let's pause for a moment
what exactly is the guy in Italy achieving..technically (not the method by which he achieved it)?
It seem he is stiffening the rear brake rotational movement be replacing the soft rubber by something stiffer..so the movement at the caliper hold down was less? And what did the shortening of the sway bar bolts do?
And what effect does this have on the air suspension?

Chris did not respond yet to the theory it might be rather some constant force (constant turns or aerodynamic push down force at high speed)at work that build up higher work group pressures which once released at a stop bring the car high up.... I mean 2" is the high position after all.

Back to the opening and closing of the E and A valves... here is the schematic diagram













Edited by - werminghausen on 03/06/2014 19:21:31
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Chris Johnson

USA
3751 Posts

Posted - 03/06/2014 :  19:58:23  Show Profile  Reply with Quote
Hello Martin and all,

My apologies for being late. I have to ration out how much writing I do.

First, I would say the guy in Italy has accomplished nothing, other than replacing some worn out rubber parts in the rear. You could completely remove those rubber parts and not gain anything, though things would certainly be noisier when you hit the brakes. The stiffness of the rubber will determine how far the caliper rotates on the axle when the brakes are applied, but has virtually zero effect on the amount of downward force on the body of the car. That is not, in any way, determined by how soft some noise-reducing rubber bushing is.

And changing the length of the front sway bar connecting bolt effective length by 5 mm? Give me a break! Let me see what the sine change on one degree is. Hmm. You would have to change the sway bar angle downward (or upward) by eight degrees to get a one percent change in effective stiffness of the sway bar. Any difference he saw in this change was probably due to changing the rubber bushings at the same time, and that WILL make a noticeable difference.

Back to the original topic.

There is no black magic at work here. Please correct me if I am wrong, but I rather got the impression that you felt that the front of the car didn't drop much under normal braking. It is the act of braking that is the cause of the effect, nothing else.

So, that would lead me to believe that your car is no different than a number of these cars in that the front suspension is too stiff. Granted, I understand (I think) that you don't have access to the car to do a test. At this particualr moment, I don't either, but a casual lean on the front fender should result in the fender dropping away a good inch. Putting my body weight on the front fender (applied quickly) should drop the fender a minimum of three inches and then return to normal as you ride the working air suspension system back to normal height.

I will certainly admit that even having any idea what is normal on one of these cars is a difficult task for most folks. I can offer some idea solely because I've worked on and owned so many of these cars. I can also say that returning a suspension to its proper working condition can be a real bastard in some cases. Replacing all the wearing parts is a necessary and appropriate first step, but rarely the last one.

Anyway, proceed with my original statements about how the front suspension behaves after normal braking. I don't generally specifically say it, but any description of any sort of behavior I offer should be interpretted to also include "in proper working condition".

Chris Johnson
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paul-NL

Netherlands
4167 Posts

Posted - 03/06/2014 :  21:33:39  Show Profile  Reply with Quote
About the sway bar it is imho only effective when you increase the thickniss of the bar. The way of connection has no influence ....
The antiroll component from the sway bar is gotten by it stiffnes of the bar between each side ...... no more no less. So imho shortening those mentioned connection has no impact at all.

Second, I would point to the fact that the CONUS which dives in the airchaimber has the effect, that the pressure not goes up linear but progressive .... So the further the cone dives in, the higher the pressure and the less your car goes down ....

That also supports the working of the SWAYBAR-function. Because the suspension dives in in the outer cornerside airchaimber and retracts from the innerside of the corner it supports the swaybar also PROGRESSIVLY (in compare to a steel suspension) .......

just to understand the differences between air- and steel suspension
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paul-NL

Netherlands
4167 Posts

Posted - 03/06/2014 :  21:50:00  Show Profile  Reply with Quote
I have to add :

when you increase the "stiffnes" of the swaybar by using a thicker one, you will risk that the innerwheel will lift from the road and loose roadcontact !!!!

So those components have to be choosen carefully to act together in a safe way.
It is not usefull to experiment with those factory choosen parts individualy ..... They have to match with each other ....




Edited by - paul-NL on 03/07/2014 12:50:01
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Ron B

Australia
11488 Posts

Posted - 03/07/2014 :  16:32:43  Show Profile  Visit Ron B's Homepage  Reply with Quote
pagadino is well known for his various different projects but his experience with this comes from Racing a 300SE with AMG pistons, Schrick cam and enlarged throttle body. It also has the 5 speed trans. He has installed the anti dive components into a W111 Coupe with steel springs and the W112 rear bar.
With a stiff rear bar the car will understeer before lifting the inside rear wheel as happened with the earlier high center pivot axles.
Stiffening the Front causes the rear to break free too quickly (oversteer) .
I don't think there is any reason to enlarge the sway bar as the variable nature of the air springs takes this into account.

quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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werminghausen

USA
760 Posts

Posted - 03/07/2014 :  19:57:12  Show Profile  Visit werminghausen's Homepage  Reply with Quote
quote:
Originally posted by Chris Johnson

Hello Martin and all,

My apologies for being late. I have to ration out how much writing I do.

First, I would say the guy in Italy has accomplished nothing, other than replacing some worn out rubber parts in the rear. You could completely remove those rubber parts and not gain anything, though things would certainly be noisier when you hit the brakes. The stiffness of the rubber will determine how far the caliper rotates on the axle when the brakes are applied, but has virtually zero effect on the amount of downward force on the body of the car. That is not, in any way, determined by how soft some noise-reducing rubber bushing is.

And changing the length of the front sway bar connecting bolt effective length by 5 mm? Give me a break! Let me see what the sine change on one degree is. Hmm. You would have to change the sway bar angle downward (or upward) by eight degrees to get a one percent change in effective stiffness of the sway bar. Any difference he saw in this change was probably due to changing the rubber bushings at the same time, and that WILL make a noticeable difference.

Back to the original topic.

There is no black magic at work here. Please correct me if I am wrong, but I rather got the impression that you felt that the front of the car didn't drop much under normal braking. It is the act of braking that is the cause of the effect, nothing else.

So, that would lead me to believe that your car is no different than a number of these cars in that the front suspension is too stiff. Granted, I understand (I think) that you don't have access to the car to do a test. At this particualr moment, I don't either, but a casual lean on the front fender should result in the fender dropping away a good inch. Putting my body weight on the front fender (applied quickly) should drop the fender a minimum of three inches and then return to normal as you ride the working air suspension system back to normal height.

I will certainly admit that even having any idea what is normal on one of these cars is a difficult task for most folks. I can offer some idea solely because I've worked on and owned so many of these cars. I can also say that returning a suspension to its proper working condition can be a real bastard in some cases. Replacing all the wearing parts is a necessary and appropriate first step, but rarely the last one.

Anyway, proceed with my original statements about how the front suspension behaves after normal braking. I don't generally specifically say it, but any description of any sort of behavior I offer should be interpretted to also include "in proper working condition".

Chris Johnson





Hi Chris and all

I want to find out about the mechanism that takes place inside your car…no judgment of anything. There is only the ‘consciousness’ of the air suspension, let’s say the front level control valve.
So let’s make a journey to the inside of the air suspension while you are driving, fast and furious.
In the process the lever is moving up and down whenever the dynamic forces create a shift: wind, hill, uneven roads, curves, braking and accelerating and of course a combination of all.
Whenever the axle is moving [driven by these forces] out of the null zone [2mm axle movement!] one of the valves, E or A-valve will open and the opposite valve will stay closed. Outside a zone of maybe 4mm axle movement the valve will be fully open (and the opposite will be closed). For simplicity let’s consider for a moment that the valve is always fully open when the lever moves beyond the 4mm zone.
Now it does not matter if the lever moves less or more beyond the 4mm zone there will be not more open area for airflow in or out. In other words beyond the 4mm zone if the force is low or high will not make any difference in air flow.
The equation of airflow in and out of the work group (air spring volume) will have only 2 linear parameters which are:
1) Time
2) Pressure differential between support group and work group.
There is also a factor involved we have not talked much about: this is the throttle or the limiting opening the air needs to pass through. This is defined in the E and A valves…but this factor is always the same once in place. With these 3 the amount of air moving is defined.
Lets walk through a couple scenarios:
A) Normal braking:
The car is going down, Lever will go up E opens and by the time impact and pressure differential a certain amount of air will flow into the air spring and raise the car by the increase air volume and pressure increase in the spring.
After braking (you cannot brake for a long time) the LCV will sense a high position and open the Exhaust valve (E) and the car will go down to null zone.
B) Normal curve:
Let’s pretend you are driving a curve…a circle in the extreme and you do this for a short time…say 90degrees to the right: Car will go down on the outside wheel (left) and go up on the inside wheel.
Left LCV will open E for the time the forces are active and the pressure differential (and throttle) will define the amount of air moving this side will finally going up. After the event the ‘brain’ senses that the axle height is too high and will release air ..back to null.

C) Extreme braking:
If the car will experience an extreme force (like harsh braking) the lever will go up extremely but this will not open the valve any more and therefore the same rules apply as for A). Rather less air will move relative to A as the time will be shorter and the pressure differential will less and therefore the mount of air moving will be minimal defined by the known parameters and factor.
D) Extreme curves:
If the car is driven in circle for a long time…. The LCV sees the same thing as for B) but for a longer time and therefore the amount of air will be more. Let’s say B) will be 3 seconds and D) 30 seconds …with same speed (pushing and pulling force) then in D ) there will be several times more air flow than in B) It might pump the axle up back to the neutral zone and release the other side in order to get the lever back to null.

Conclusion: The amount of time and the pressure differentials are the only variables in the system and will define the air flow in and from the air spring.
If Chris is experiencing a 50mm axle rise after stop the air in the spring was compressed and has stored energy by this push/pull force and was released after the stop. The 50mm are the high position of the car and if you put the valve unit into High you hear and feel the car moving… this is the stored energy in the air tank that gets moved to the air spring. This takes time defined by the factors we discussed (force- lift of car and throttle and pressure differential) . Now the in Chris’s case the energy is already in the spring and therefore the car goes up or is already up…and Chris will hear the sound of air release after he gets out of the car right after the stop.

As I said I have not experienced this extreme and I wonder what this force was that pushed the car down for a long time in order to store that much energy.
Sorry for the long story…

Martin

Edited by - werminghausen on 03/07/2014 20:08:04
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Chris Johnson

USA
3751 Posts

Posted - 03/07/2014 :  20:37:49  Show Profile  Reply with Quote
quote:
Now the in Chris’s case the energy is already in the spring and therefore the car goes up or is already up…and Chris will hear the sound of air release after he gets out of the car right after the stop.

As I said I have not experienced this extreme and I wonder what this force was that pushed the car down for a long time in order to store that much energy.
Sorry for the long story…

Martin


What? Perhaps I'm not reading this properly, but getting out of the car is a completely separate and unrelated event. The front of the car drops from the over-pressure once the car comes to a stop after normal braking.

This is not an exceptional or unusual event, nor is it a behavior unique to my cars, nor is known only to me.

Have we moved on to another aspect and I'm just stuck thinking we are still talking about the original one?

Chris Johnson

Edited by - Chris Johnson on 03/07/2014 20:38:46
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werminghausen

USA
760 Posts

Posted - 03/07/2014 :  23:38:13  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Chris, sorry and no offense and I just want to understand and clarify
I fear my lines are misleading.
I meant if your car is 50mm too high (relative to null) at a stop after hard braking it will open the A valve no matter what and you car will release pressure and go down to null...following the logic.
But typically you won't hear the air escaping noise at the air filter unless the engine is off and you are getting out of the car. Of course getting out of the car is unrelated to main cause and the A-valve opening in your case (and you'd be right). The driver leaving the car will release just some additional gravitational force..car goes slightly higher and add some air to be exhausted on top of the great amount of air that accumulated in the air spring (during braking) and wants to get out now. It is complex enough.

In order to get closer to a solution: How strong were you braking in these events and for how long? I guess you hit the brake until you came to a stop and thus pumping up the air spring to the extreme?

Best, Martin

*This is for information:
On the front of the 1965 300SE (as an example)the air springs have 2.8liter volume each and with driver only the spring has about 6.2bar (@null).... with hard braking pressure rises to 8.2bar max = 2 bar differential and car will go down 120mm! before the axle hits the rubber stop. This force will be there only for seconds until braking is over. The fully loaded car (max live load) will need a spring pressure of 7.2 bar (@ null)...this pressure goes then up to 9.5bar if you hit the brake..and the car again 120mm down.
With driver only.. if the car goes down by 50mm a down pushing force of 55kp is needed (per front wheel).
Putting 45kp on each front wheel (=90kp) will bring the entire front down by ca. 50mm and a pressure of roughly 7bar is needed to bring it back to null... meaning that a volume of 2.24 liter air needs to be added to each front spring and the pressure in this event differential will be 10bar - 7 bar= 3bar for the support pressure. The throttle will be less than 0.4sqmm. The air tank needs to pump 2x 2.24 liter through 2x 0.4sqmm of free area with 3 bar (pressure differential). That is what is happening roughly in numbers if the air suspension is built per spec....if I am not mistaken.
The dynamic spring softness coefficient of the front axle for the 300SE is roughly 1.1mm/kp. This means if you put just your weight on one front wheel as Chris described...depending on you own weight... this side goes down quite a bit roughly 50 kg = 55mm



** I'll look for the paper from the MB engineer who was writing about the air suspension and braking and curve driving engineering solution. It is unfortunately in German. Article was in magazine ATZ 1965 Heft 2, Februar 1963, Weller and Neuschaefer, Daimler-Benz- Luftfederung, page 38



Edited by - werminghausen on 03/09/2014 15:07:07
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Ron B

Australia
11488 Posts

Posted - 03/08/2014 :  18:48:56  Show Profile  Visit Ron B's Homepage  Reply with Quote
120MM !,No wonder they changed the valve design.
I can put a slightly different slant on this. I always thought my 6.3 was acting correctly when pulling up to traffic lights etc the nose would dip,around 50-80 mm (judging by sight guesstimation on the car in front ).I replaced the bags after Christmas,as the ones on the car were getting a bit too cracked and dated 1983.
Well,the immediate difference was that the suspension felt firmer the nose ceased diving so much under braking (normal braking,not hard ) and the car sits flatter in tight fast turns.
It is now my belief that the bags ,over time become a lot more flexible .
Now,the rear sway bushes on mine need replacing this year (around 10 years old )and one of the fundamental things is that the bar is moving up and down 2-4mm . Rather than being held firmly in the bushes and twisting as designed.
This has to be affecting the action of the rear valve.
To make the rear valve work exactly as intended I would say that all six sway bushes Must be in good condition. The ball ends for the actuating rod must also be perfect.

Now to Martins point. If the rear bar and it's bushes are correct,that 2mm differential is essential . It would be around 4mm rotation at the bar?
If the bar is twisting the amount, movement at the valve spindle is negligible ,especially if the bar is twisting at each end at the leverage point of the bushes.
The speed of the twisting would be in fractions of a second as a generalisation so if the valve was made to work faster,that is,to get rid of most of the "dead" area of movement, there could be consequences in the form of rapid valve wear as the air pressure was directed from side to side of the filling ports.
To put it simply ,the valve is designed to keep the rear at a set consistant height as the bar is turned,as opposed to twisting .
It is not designed to fill either side bag to compensate for lean into turns. That is the job of the two separate bags in front.

If this was a desired effect,the cones could be made bigger so that the air pressure rises higher as the bag rolls down the cone ,without having to add more air.
As it does already.
I am going to experiment this year with Heim joints on the rear bar ,to make the twisting of the torsion bar transmission to the chassis more positive as an exercise .


quote:
12-14-2004, 11:49 PM #8
Tom Hanson
MBCA Member

What the heck, try to stuff a MB 6.9 liter V8 in it. What a machine that would be..
__________________
Tom Hanson
Orange County Section
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werminghausen

USA
760 Posts

Posted - 03/09/2014 :  15:02:27  Show Profile  Visit werminghausen's Homepage  Reply with Quote

Hi Ron

I think you are right. In order to function correctly all component of the air suspension should be per specification and these include all of this : compressor, tank and tank valves, antifreeze incl air filter (often neglected) valve unit incl pressure settings, LCVs (all specs incl. valve timing and throttle), airbags and all the mechanical linkage (no play)and bushes (no play) in order to operate the LCVs without much mechanical play.
And yes the spring coefficient will change of course if the air bag is softer for whatever reason...it would inflate like a balloon (and not to spec) and it will throw off your suspension fundamentally.

Any of the components not to spec will change the equation.
And by the way this is my suspicion with Chris's car that acts weird in my mind (still does until I understand).
I think at this point without knowing greater details about the car that does this (being 50mm higher than normal after braking)... it must be an air suspension not entirely to specs.
It could be the valve unit providing pressure higher than 10bar and pressure holding less than 3bar and/or it could be the bullet throttle that is not to specs (the front bullets have a tighter throttle for exactly this reason..some rebuilders don't know this.
In fact in Chris's case the null zone adjustment in the LCV is only secondary (in my mind). As I pointed out earlier the valve is either open or close (if we neglect the opening movement of the valves)and thus it doesn't matter beyond the opening point how strong the forces are... for the air flow velocity into the airbag (or out)will be not affected if there is more force..only time does. During harsh braking actually the airflow velocity is smaller than during moderate braking as the pressure differentials are very low and with less pressure differential (during hard braking) there is less airflow velocity compared to moderate braking. The other explanation could be: it is something else and not the braking (or not braking only)..aerodynamic forces or any other force that push the car down during faster driving? (Here is a question: Who knows about aerodynamics on a W109?)

Ron's question about the sway bar bushes and sway bar movements.
It is correct that any play in the bushes and ball joints are adding to the slack in the suspension . This outer play would then add to the internal null zone in the LCV and reduce the ability of the suspension to correct height. Now the gear that translates the movements from the axle to the LCV is different in front and back and these movements are rather complicated and not necessarily linear.
The twist of the sway bar in the rear does have an effect on
LCV valve timing only if it turns the sway bar in the center location where the lever for the LCV is fixed. If the rear axle on one side goes up and the other side goes down the same amount there is no movement in the LCV lever. If one wheel stays and another moves the twist will move the lever..of course and the height will be corrected. The LCV senses only the medium rear axle height... it doesn't know where left and right rear axles are....it just can't.

Martin

Edited by - werminghausen on 03/09/2014 15:03:38
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paul-NL

Netherlands
4167 Posts

Posted - 03/09/2014 :  15:28:17  Show Profile  Reply with Quote
Martin,

On an unequal ground you have ALWAYS to adjust one table leg to hit the ground. Therefore use a "three-legs" table .... => all three legs will hit the ground and therefore create a stabile table.

So does the airsuspension if there are three valves instead of four (for each wheel one valve). Four airvalves would continiously be acting to get the right level for each wheel, which is not possible on an unequal ground. imho NEIGHTER on an equal floor, because it is simply practically NOT possibble "to adjust them/that"
[Imagine one left rearwheel would stop on a 10 cm brick and the other three wheels are standing on a flat garagefloor. Now the valve on the left rear "higher" wheel starts acting and pumping that bellow (because the valvearm is lifted. Because the floor is unequal, the left rear is pushed up , the rigfht front will be pushed in and the left front and right rear is also (some (because the right front will also start pumping the bellow up) lifting, so the complete system will get false informations from the unequal floor, because the system cant recognize that there is an unequal floor ....... The car will never get/be "stable" .......)

Because the rear has one valve, and both airchambres are connected, they act as one leg from the "threelegs" table ....
That has the effect, that the rear always "follow" the level from the frontsuspension and THEN (in that internal circuit) compensate the differences for the rearwheels between those connected rear airchaimbers ....




Edited by - paul-NL on 03/09/2014 16:09:14
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werminghausen

USA
760 Posts

Posted - 03/09/2014 :  16:44:19  Show Profile  Visit werminghausen's Homepage  Reply with Quote
Hi Paul, I think we are saying the same thing here. The precise equation what potential height differences on the ground do to the axle height...is rather complicated.
The picture of the tripod is good. Let's say the tripod has 'air suspension (this would be an invention...would it?) If we were able to measure the vertical force in each leg and how this force would change when the ground plain where the tripod stands is shifting (and change relative elevation of single legs) then we had an indicator...if the air suspension is adjusting or not. Of course it would change weights and at a certain point (if valves are outside the null zone)air suspension would respond...and Paul is right.

Martin
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ctmaher

USA
640 Posts

Posted - 03/09/2014 :  22:26:52  Show Profile  Reply with Quote
Martin, this is the other Chris, but I think what Chris was referring to is normal behavior for all the air suspension and hydropneumatic suspension vehicles. When you brake, there is a weight shift to the front of the car, this causes the front end to drop. This drop is compensated for by the system filling the front bags (or struts in a hydro system). After the car comes to a complete stop, the weight shifts back off the nose and it now rises because of the extra pressure. The system does not react instantly, and is not expected to. The front valves (or valve in hydro) dump the excess pressure and the nose drops back to normal height. This is exactly what I thought Chris described in his post. My 300SEL 3.5 did it, my 6.9 does it, I've driven a few 500SEL's with hydro suspension, and they did it as well as a 600 that belongs to a friend. It's just one of those quirks of the system. I don't know if there was a misunderstanding of what was being described but this is my experience with air ride cars.

Chris in AZ
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