Remote third spring

[mep]

Don't think it matters mep, you can't use hydraulics for pulling, that's all there is to it really.

I still believe the image is a single acting cylinder with means to adjust the hydraulic volume and thus the front ride-height.

It is never pulling. In the case where it would be pulling the second oil circuit (not drawn by scarbs) is working in compression thus preventing that the first oil circuit increases its volume. Front and rear heave pistons are completely restrained in oil circuits (dual acting cylinders, equal piston surfaces).

Possible is that the device in the picture is just there to maintain a certain pressure in the system. Basically working as accumulator. Interesting to notice is the relative high diameter of the cylinder and the geometry of the spring. The interlinked suspension cylinders I have seen so far are tinny compared to that.

[DaveW]

Those I have seen are not badly damped, Tim, but if it is required to maintain a pressure drop across the piston, then a leakage path across it is not a good idea.

I can't fault X's logic, but I think he is probably taking Scarb's sketch too literally. We don't know exactly how the connections to the suspension are mechanised. If it is possible to ensure that the pressure in the feeder pipes is always positive (and it is in one I have played with) then I guess he would be content.

In any case, I think the problems he describes are encountered in conventional dampers (e.g. Penske) and they can be arranged not to cavitate. Long feeder pipes wouldn't help, however.

edit: Sorry mep, I missed your post...

[marcush.]

if you separate the compression and rebound action hydraulically and mount the pistons accordingly in a ways you are compressing the fluid on both actions plus give it a free path to flow back I´d say it will work .it´s quite elaborate plumbing and a few pistons more but it´s possible.

[DaveW]

It is never pulling....

Sadly, I have yet to find an image of the lower hydraulic connections to the device. If it is turns out that there are two feeder pipes connected, then it would suggest, perhaps, that Caterham have implemented mep's solution.

By the way, I think that the "remote third spring" is mainly a way of changing the effective front/rear area ratio of the system. That would be useful to tailor the system response to aero properties, modify the rake (by preload), and would (I suppose) be relatively easy to engineer non-linear characteristics (the adjustable bump rubber).

[xpensive]

I think we can agree that scarb's xplanation, as drawn, would perhaps not really work as intended, while I don't think there are any hydraulic connections to the other end of the cylinder/spring-unit shown on the Caterham anyway?

http://i.imgur.com/5mwomXm.jpg

[scarbs]

I can see two hydraulic connections to the cylinder, one wrapped in silver sleeve goes off the front (left), the other passes in similar sleeving to the rear (right), with a T&P sensor inbetween. It would at first suggest both are connected to the same point on the top of the cylinder, unless there's a drilling feeding one down to the bottom of the cylinder.

[xpensive]

It's really difficult to tell, there's a third or fourth something at the top, but it seems disconnected?

[Blanchimont]

http://cdn.jalopnik.com.br/wp-content/u ... nter-7.jpg

This picture shows the left side from behind and at the top of the spring below the connectors there seems to be a black round something attached. From this black and round something there seems to extend another something (a cable??) backwards.

[RickRick]

my guess, though probably badly explained would be it's one hydraulic line going from front heave to rear heave. the tricky part would be making the piston that's connected in the pic (via a tee) try to contract when pressure increases, i'm sure this can be done with some clever engineering, probably lifting the lower spring platform, which might explain the cutaways in the body to reduce friction. that would mean the spring is resisting oil flowing into the piston, therefore supporting the weight/heave action

[DaveW]

http://cdn.jalopnik.com.br/wp-content/u ... nter-7.jpg

Thanks for the image. I had seen it, but concluded that it didn't add much to the image posted by Brian (different car, race, or state of development?).

I can see two hydraulic connections to the cylinder, one wrapped in silver sleeve goes off the front (left), the other passes in similar sleeving to the rear (right), with a T&P sensor inbetween. It would at first suggest both are connected to the same point on the top of the cylinder, unless there's a drilling feeding one down to the bottom of the cylinder.

I agree, pretty much, but the drilling idea seems complicated (why do it that way).

my guess, though probably badly explained would be it's one hydraulic line going from front heave to rear heave. the tricky part would be making the piston that's connected in the pic (via a tee) try to contract when pressure increases, i'm sure this can be done with some clever engineering, probably lifting the lower spring platform, which might explain the cutaways in the body to reduce friction. that would mean the spring is resisting oil flowing into the piston, therefore supporting the weight/heave action

You could be right, except that it would then be reservoir (as suggested by X, I think). I con't help thinking that if it is a reservoir, I wouldn't want to do it that way .... It think the cutaways allow the preload to be torqued up easily. The spring might (possibly) affect heave stiffness if it is a reservoir, but not pitch stiffness, I think. Again if it is a reservoir, then the actuator could well incorporate damping controls.

I would still like a see an image of the bottom spring retainer. Sorry X.

[xpensive]

If this is what I think it is, a single-acting hydraulic cylinder compressing a coil-spring to act as a remotely located heave spring, it would need no fixing to anything at its lower end. The xtra line at the top would be to adjust the incompressible volume between the hydraulic cylinder seen in the images and the actuators at the front rockers, all in order to adjust ride-height.

This way the front ride-height could be adjusted remotely by means of an electrical stepper-motor, if that would be legal?

[DaveW]

If this is what I think it is, a single-acting hydraulic cylinder compressing a coil-spring to act as a remotely located heave spring...

Would this be a schematic representing your thoughts? I used Scarbs format to show the hydraulic coupling, & adapted the Penske remotely coupled 3rd spring shown by marsush. Front & rear springs would be required to make it viable (as shown in Marcus' image), I think, so what is the function of the spring shown?

[mep]

That is more or less what I think it is.
It basically allows to have a certain compressibility of the link. That is the practical solution to what I had in my equations for the interlinked suspension.
Only that I would connect the rearward link to the other side of the cylinder but we have already figured that there are different concepts available.

[DaveW]

That is more or less what I think it is....

It would be interesting to compare this with the concept devised by RideRate (if he could be persuaded to generate a diagram).

[xpensive]

If this is what I think it is, a single-acting hydraulic cylinder compressing a coil-spring to act as a remotely located heave spring...

Would this be a schematic representing your thoughts? I used Scarbs format to show the hydraulic coupling, & adapted the Penske remotely coupled 3rd spring shown by marsush. Front & rear springs would be required to make it viable (as shown in Marcus' image), I think, so what is the function of the spring shown?

Pretty much so Dave, though I would add a line to adjust the amount of fluid, which would control the front ride-height.