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remote suspension using hydraulics

Jesus-Ninja - 12/1/08 at 11:07 AM

We are, I'm sure, familiar of the concept of mounting shock/spring on the body, and linking using push / pull rods and bell cranks, to reduce unsprung weight, and to assist with packaging.

Is anyone aware of what the issues might be of replacing the rods and cranks with hydraulics?

Seems to me this would be an excellent way of putting the mass of the coil/spring exactly where you want it, and not being restricted by the availabilty of points to which cranks can be mounted, or the "line of sight" required for a rod.

I surely cannot be the first mind to conceive this, but I've not seen it implemented anywhere, so there must be a reason it's not used.

How "reactive" would a hydraulic system be? Would it introduce latency? Not forgeting that a damper is itself a hydraulic unit.

[Edited on 12/1/08 by Jesus-Ninja]

[Edited on 12/1/08 by Jesus-Ninja]

nitram38 - 12/1/08 at 11:20 AM

I am using these from arnott industries in cape canaveral.
Air is used to pump them up from a small compressor and a dual pressure gauge/switch set up.
I can vary the ride height from 3-6" for those speed bumps and lower the car to the ground.
In order to do that, I have to use a cam ratio of 2:1 as the shocks move 3" and I need a 6" range on the lifting.

Description

[Edited on 12/1/2008 by nitram38]

Jesus-Ninja - 12/1/08 at 11:24 AM

Yes, but they will be linked to the suspension via a mechanical system, yes?

I am proposing to mount a shock / spring on the vehicle, and then link this to the suspension via a pair of cylinders connected pipes and filled with hydraulic fluid.

britishtrident - 12/1/08 at 11:44 AM

No saving in unsprung MASS over a conventional setup --- in fact it will increase because of the two hydraulic cylinders and fluid.

And while the hydraulic system will act as an additional damper you have no easy control over the ammount of damping.

Forget weight it is the mass of all the parts that are moving with the suspension that is important.

[Edited on 12/1/08 by britishtrident]

llionellis - 12/1/08 at 11:44 AM

Hi
Would you not need slave cylinders mounted in similar locations to normal suspension units? Must be possible hydrolastic sort of did it.

Jesus-Ninja - 12/1/08 at 12:07 PM

quote:
Forget weight it is the mass of all the parts that are moving with the suspension that is important.

Apologies! School boy error. I should know better!

And yes, now that I think about it, the fact that the portion of the shock "below" the spring in the system is mounted remotely does not remove it from unsprung mass - it's still acting on the suspension, just, well, remotely!

OK, but from a packaging perspective- which is another of my issues, the bottom line is "will it work, and if so, how well"

Yes, there is additional damping introduced from the hydraulic linkage, although this I would have thought can be mimiised by using appropriately gauged pipework and cylinders. Also, adjustable shocks coul compensate for this, provided the hydraulic systems introduce the same level of damping across systems an axle.

nitram38 - 12/1/08 at 12:41 PM

Your idea of changing the push rod to hydraulic will probaly work.....for a while.
You cylinders will get a pounding. I thought about trying all of these set ups, but think about the air ride for a minute.
Air will replace the spring so you already have removed some weight from the shock, although you will still have the weight of a small compressor on board.
You will be able to vary the ride height, front and rear, at the flick of a switch and the pushrods will also be adjustable to set up your corner weights/height adjustments.
I have made "solid" shocks to put in place of the shocks to set up my suspension. Remember it is an air spring.
I'll let you know how it all works out when I have it working!
If the worst comes to the worst, all I will do is change the shocks to coil overs.

caber - 12/1/08 at 12:51 PM

How about looking at Citroen suspension? this is hydraulic with the springs being spheres with rubber diaphram and pressurised gas. This system has hydraulic links front to back and side to side and control the flow between the spheres too adjust pitch and roll, these days you have a computer to do this originally it was inertia controlled valves.

Caber

MikeRJ - 12/1/08 at 03:28 PM

Nitram,

I have been pondering a few points on air suspension you may be able to help with:

Corner weighting; The shocks you show don't appear to have any facility for mechanically adjusting length to set corner weights, so I guess this has to be done by setting the air pressure individually in each shock? How can you keep this consistent when raising/lowering car?

Also, as the air heats up from both the action of the suspension and ambient temperature, will the ride height not change somewhat? e.g. low in winter, higher in summer?

nitram38 - 13/1/08 at 06:11 AM

quote:
Originally posted by MikeRJ
Nitram,

I have been pondering a few points on air suspension you may be able to help with:

Corner weighting; The shocks you show don't appear to have any facility for mechanically adjusting length to set corner weights, so I guess this has to be done by setting the air pressure individually in each shock? How can you keep this consistent when raising/lowering car?

Also, as the air heats up from both the action of the suspension and ambient temperature, will the ride height not change somewhat? e.g. low in winter, higher in summer?

If you read what I wrote before, I have solid replacement shocks (all same length solid rods) that will be used to set up the suspension while the shocks are removed. Inboard suspension means that the corner weights will be set up using the pushrods which have a LH and RH rod end.
The shocks work in pairs. One pair front and one pair at the rear and are both controlled via two switches and a dual pointer pressure gauge. This also means that that each pair will recieve the same pressure and therefore equal.
It will take a bit of practise and setting up, but by adjusting the height on the switches and marking points on the gauge, I will have some infinitely adjustable ride height.
As to any ride height in winter/summer, I will be able to adjust my settings on the move, unlike a standard coilover.
I have also designed my wishbones and mounts in such a way that camber change is not excessive over the 3" to 6" running height.

[Edited on 13/1/2008 by nitram38]