SNAIL

Pimslet · Posted: Thu Nov 22, 2007 5:36 pm Post subject: Hydraulic

Hello,

Just make some hydropneumatics.

I'm stuying the questions, have all the parameter of the citroen 2cv suspension, have the law which gives the stiffness of the suspension. I need the diameter of the piston of a suspension cylinder and the rate it can move in the cylinder.
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Kustombart · Posted: Thu Nov 22, 2007 9:22 pm Post subject:

Hey Acalex, great combination. If you plan on fitting a new body, might as well channel it.

Hey Pimslet. Hydraulic cilinders are several sizes. I would choose BX or Xantia rear cilinders. They are horizontal and you can even use the brackets and weld them to the 2CV suspension arms.

You can vary the pressure in the spheres from 35 to 75 bar, varying from hard suspension to comfortable. Cilinder diameter is about 4cm, travel will be about 8 or 9cms. If you want I can find out exactly.
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Pimslet · Posted: Thu Nov 22, 2007 11:27 pm Post subject:

Thanks Kustombart,

Have you got the exact diameter and the exact travel. Or i'll have to go to Citroen?

When you talk about the cylinders, you talk about the volume 400 or 500cm3.

The system i prepare is a new one, different from M35.

I know that you can change the pressure, that the parameter you change to adjust the frequency of the suspension. I'h choosen 1Hz front and 1.15Hz rear. A stock 2cv is 0.75Hz front and 0.9Hz rear. Geoff race cars are 1.3Hz front and 1.56Hz rear if you calulate it with stock weight.

I also have a whole study of the 2cv suspension that has been made in my school.

I think that i'll put the road high at 150mm, with an horizontal frame.
The low stop at 40 mm and the maximun at 300mm.

I think that i'll be soon studied. After i'll have to make the high corrector command.
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Always trying to gets more power on my AZLP, fortunately the fuel has been cheaper for one month.

Kustombart · Posted: Fri Nov 23, 2007 10:41 am Post subject:

Hey Pim,

I don't know about those frequencies, I was comparing the weight of a BX on the rear wheels as compared to the weight on 2CV front wheels. I think that's about the same.

I used to work at a citroen parts company. We dismantled old cars and sold the parts and had them restored by a hydraulics-specialist who also supplies citroen itself. The company is caled Lizarte, they are in Spain. If you need any hydraulics made, they are the ones to contact.

We had a filling machine for the spheres and we would regularly experiment with different spheres and pressures on our own cars. They are easy to change. Even the "dampers" are easy to play with.

My ex boss used to race DS's and he had a setup in the car where he could change pressure in the spheres with a nitrogen tank and some valves, pipes leading straight into the top of the spheres! He raced against Camaro's, Mustangs and BMW's and despite being underpowered, the DS would win on gravel and sand every time.

Hydraulics pumps are the same for almost all types of hydraulic citroens. Only the pipes, connections and pulleys are different depending on engine layout and engine RPM. You should be able to work out at what speed the pump is rotating and then work out the size of the pulley you need on a 2CV to get the same pump rpm. Pulleys are pressed onto the axle of the pump and new pumps are available with a wide range of pulleys or without a pulley, so you can fit your own.

Also, the safety valves are the same. Only difference is in 4 or 5 hydraulic connections. Same story for the Pressure regulator.

The vehicle height correction valves are also all the same, only the connection to the stabiliser bars is different. But they are easy to change, and easy to adapt for different ride-heights.

Without any calculations, I would say take the whole system from a BX, make new pipes, make a bracket to fit the pump to the engine (or fit an electric motor) and use rear cilinders at the front and the rear. Start off with that, drive it and play with pressure to get the best result.
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Jasu · Dropped Joined: 30 Sep 2007 Posts: 211 Location: Finland

Kustombart told many details You gonna need to know. "Short lesson" from basic Citroen-hydraulics...

Bx rear cylinder is 35mm diameter, in break/estate it is 37mm. I'm designing hydraulic suspension, "copying" M-35, and using Bx 35mm rear cylinders in every wheel. So, if front cylinder is too small, I put this 37mm version there... More ideas are coming all the way, maybe using Xm Hydractive system to get adjustabe stifness when running, or Xantia Activa's "active roll-bar"..? Maybe something happens in some year.

Maybe it's reasonable to use electric motor to pump, or Gs engine. Or good idle speed correcting (easy with Megasquirt) when pressure regulator asks for more pressure, controlled by pressure switch between pump and regulator..? Pump takes so much power that idle speed with Bx16GTi engine falls several hundred revs... Even in Xm's 2,1 turbodiesel idle falls little, how it happens with 0,6 engine..? Maybe I need to test that in garage in some day... Rolling Eyes

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Pimslet · Posted: Sat Nov 24, 2007 12:40 pm Post subject:

Thanks for the dimensions.

My made calculations with the dimensions of the stock 2cv suspension.

Length from wheel axle to arm axe 405,8mm
Length from arm axle to suspension knife 108,6mm

If i want a frequency of 1,2Hz front, which make a good sport car, but smoother than racing cup, by using a direct system i have to inflate the spheres at 6,6bars which is very low.

Then when the car is put on the ground the pressure will be 46bars, and the volume nitrogen will be reduced at 0,055liters.

I made the calculations with a road high of 150mm.

But i used 40mm diameter for cylinders. So with 35mm, i will recalculate it.

Pimslet · Posted: Sun Nov 25, 2007 1:46 pm Post subject:

hello,

I'have understood why the pressure was very low, that is because the frequency of the static car is very low, lower than a stock 2cv.

For a BX GTI, it is 0,6hz, while it is given for 1hz.

So, i'have made some general calculations, and now i'am able to give you the pressure you have to inflate your sphère with the weight of your car and the frequency you want.

If, you use directly some BX spheres, even rear ones, it will never work, because the pressure given by the weight of the car would be lower, than the inflate pressure of the sphère. You will have to delate then to a maximun pressure which correspond to the pressure given by the weight of the car.

So under a certain acceleration, the suspension will be totaly rigid because the membrane will stay on the metal of the sphere.

For the spheres, there are: 0.4, 0?45 and 0.5 liters.
For the cylinders: 35, 37, 40 mm

ratio of 2cv suspension: front 3,74
rear 2,85

And to this you have to had the problem of the damper, which caracteristic is the size of the hole.

If you want smoother suspension, you have to inflate.
If you want harder suspensions, you have to deflate.
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Always trying to gets more power on my AZLP, fortunately the fuel has been cheaper for one month.

Kustombart · Posted: Sun Nov 25, 2007 6:15 pm Post subject:

I don't know how you calculate these frequencies, please explain.

I made a small drawing of the system. With A being the distance between wheelbearing centre and the pivot point of the suspension arm. B is the distance between pivot point and the rod coming out of the cilinder.

The force acting on the cilinder multiplied by B should equal the weight resting on the wheel multipiled by distance A.

So, for the BX rear wheel, a BX is 900 kg, 35% on the rear wheels equals 157.5kg on 1 rear wheel. That's 1.544N. With distance A being 0.35m (I am just guessing these numbers) and B=0.10m, the force on the cilinder would be 5.403N.

If you know what distance is the wheelarm on a 2CV (.4058m) and what weight there is on that wheel (a guess: 650kg x 35/100 divided by two =114kg ( you can measure exactly by putting a weight scale under each wheel)), you can just change distance B on your 2CV wheelarm to get the same force on the cilinder with less weight on the wheel.

So in this exampe, B should be 114kg x9.8m/s2 * 0.4058m / 5.403N=0.0084m (or 8.4cm)s.

This way you just change distance B (a little cutting and welding) and keep the rest stock BX.

Or am I thinking too simple now?
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Pimslet · Posted: Mon Nov 26, 2007 10:45 am Post subject:

Hello?

To calculate the frequency, it is a bit special, because, the frequency of the suspension is not linear, but increases while the volume of nitrogen decreases.

There is something wonderful on this suspension, it is that the pression you have to inflate the sphere, when it is off from the cylinders, do not depend of the geometry of the suspension.

It only depend of the suspended weight of the wheel, the volume of the sphere and the frequency you want.
DS, ultra comfortable: 0.3Hz
Xantia hydratice, sport mode 0.7Hz
My project 0.75Hz

I'll write it on a pièce of paper, and i'll scan it.

My choise is rear 2cv arm modificated to be put on front and rear.
xantia spheres with their dampers.
Bx estate cylinders.

I've carred to my calculation, and everything is right.

But, it gives great debate of the piston, it is due to the fact that for big mouvement of the wheel you have to had the fact, that the hight corrector is opened and fill the sphere, what increases the pressure in the sphere and contribue to increase the frequency more rapidly, than if you had no corrector.

If there was no corrector, all the car with hydraulics will slam.
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Always trying to gets more power on my AZLP, fortunately the fuel has been cheaper for one month.

Kustombart · Posted: Mon Nov 26, 2007 11:01 am Post subject:

I'm very curious to see this calculation. I had to learn it in school but it was an early morning class and I was sleepy most of the time. They even took 2 hours to explain 2CV suspension and why it was so special but I missed that class.

It's a miracle I got a diploma after 5 years.
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Pimslet · Posted: Wed Nov 28, 2007 10:53 am Post subject:

Hello,

Hope, that you'll read and understand me.

Ask, if you need more explanations.

http://www.servimg.com/image_preview.php?i=15&u=11385271

http://www.servimg.com/image_preview.php?i=16&u=11385271

http://www.servimg.com/image_preview.php?i=17&u=11385271

http://www.servimg.com/image_preview.php?i=19&u=11385271
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Always trying to gets more power on my AZLP, fortunately the fuel has been cheaper for one month.

Kustombart · Posted: Sat Dec 01, 2007 4:37 pm Post subject:

OK, this was a long time ago. It takes a while to get my head wrapped around it. I'll get back to you on this.
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Etienne · Hoodrider Joined: 25 May 2007 Posts: 2829

I guess we could do the same on a 2CV, no??

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Olli · Posted: Sun Feb 10, 2008 8:01 pm Post subject:

Looks great! I really prefer clean Air bags than dirty LHM systems..

-Olli
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Etienne · Hoodrider Joined: 25 May 2007 Posts: 2829