damper mounting

[mach11]

hi all,

If we mount the damper upside down... Will it cause problems for roll stability for the chassis...

And... Will it cause oscillation to the vehicle...

[mach11]

the mono schock that i was trying to use for my final yeah thesis... Cannot be mounted into a stock wheel upright assembly...

The only solution that i can find is to mount the mono spring and damper arrrangement has to be mounted upside down...

The arrangement is a double wishbone arrangement...

This is a race car of fsae rule book for my final year thesis...

1. The disadvantage of mounting it upside down would only actuate the spring... And the damper would become inactive...

2. Though the spring supports the weight of the vehicle... It will provide traction while on the race track by keeping the wheel to the ground ( the spring compresses on loading and retains its state while the load is removed)...

this is my understanding... Pl do correct me if i am wrong....

[marcush.]

if your damper is not capable of upside down mounting it is what ? a twin tube design without gas pressure? ...How much travel does a damper like this need to build up force? i don´t think this is a useful part for your vehicle.
You could as well delete it completely and just run on bump rubbers .I bet there would be NO difference in performance.

[DaveW]

I suspect there is a context here that is hidden from me. To answer the question, damper designs in which the gas reservoir is physically separated from the fluid (e.g. by a reservoir piston) can be mounted in any orientation. Designs where that is not the case can't - at least they can't if they are required to work in a predictable way.

[mep]

Heeeee?
Why can't you mount your damper in any position you like?
As far as I know is a damper not affected by gravity at all so I don't see the problem here. Ok there should not be lots of air in the damper but that’s anyway a bad thing.

[DaveW]

mep: I think you confuse function with implementation. Logically, dampers are unaffected by gravity, as you suggest. That is not the case when air can mix with the damper fluid internally. All dampers contain air to accommodate changes in internal volume as the damper is moved & changes in fluid volume with temperature.

[mep]

Yea Dave that’s why I said there should not be air in the damper because it can mix with the fluid. However as far as I know this is prevented by some kind of membrane (or some other smart design) if you don’t use the cheapest and simplest damper. So the problem of air mixing with oil is solved because it doesn’t come into direct contact and therefore the damper is completely independent of gravity and can be mounted in every position you like.

That’s just my line of thinking I would be happy if you (Dave) can explain why its not the case.

[DaveW]

This post contains a good illustration of a damper that works happily as shown, but not inverted because there is no physical barrier between the fluid & the gas. Commercial "twin tube" dampers are often like this for cost reasons.

[Belatti]

For a twin tube damper I completely agree with Dave.

A monotube pressurized damper can work in any orientation. However when you mount it in a double wishbone arrangement between, for example, the chassis and lower wishbone or upright there might be a little difference: you have to take into account the innertia of the mass thats moving so maybe the mass of the damper you consider suspended vs un-suspended.

In the example I gave, I tend to attach the tube to the chasis and the rod to the wishbone/upright
However I just noted that I never compared the weight of a damper rod+piston vs. the weight of the tube and the parts fixed to it.

[Belatti]

Sorry, to better answer mach11 original question, I cant understand what he states here:

1. The disadvantage of mounting it upside down would only actuate the spring... And the damper would become inactive...

2. Though the spring supports the weight of the vehicle... It will provide traction while on the race track by keeping the wheel to the ground ( the spring compresses on loading and retains its state while the load is removed)...

this is my understanding... Pl do correct me if i am wrong....

I guess there is no difference on how a coilover spring - monotube damper arrangement works in general principle, whatever the orientation. You probably can discard the thing I wrote in the post above for that type of car...

[marcush.]

Ohlins TTX40 is actually 2 tube and still can be used upside down-so it is not restricted to monotube designs . the gas volume must be physically separated from the fluid by a seal.You could even put a gasbag into the damper .

The main point is only to avoid air getting into fluid paths or air mixing with hydraulic fluids.
btw under suction loads(low pressure) hydraulic fluids can start to produce gas bubbles giving the same effects-no or reduced damping damping and severe damage to the piston flow passages.