Benefit of Pilette suspension design

[hardingfv32]

The is a 1994 Pilette F3 car with a very unique suspension design (same front and rear). What are the possible benefits of this design? All I can come up with is packaging. No rockers or coil overs on the chassis.

http://www.race-cars.com/carsales/other ... 4046ss.htm

Brian

[DaveW]

Interesting, if not successful, idea:

http://www.f3history.co.uk/Manufacturer ... ilette.htm

Assuming they exist, I suppose the dampers are mounted outboard. They only similar layout I have seen had so much friction that dampers were not really needed.

[hardingfv32]

I assume the shocks are part of the upright. I would say a strut type of shock system. The upper control arm mounting does not look like it provides freedom for steering rotation, so the upright would pivot around the strut. The strut could be designing to operate with low friction or this just too small a base for the strut bearings?

What do you think were the design goals?

Brian

[strad]

I think if it were worth a damn we would see it in common use.

[DaveW]

I wouldn't presume to comment on the design goals.

The suspension layout appears to require the damper to transmit maneuvering loads in bending, with very small moment arms. Hence very high bearing loads & associated high friction, I think.

[hardingfv32]

Do you think there is anything unusual with say the camber curve?

Would better aero from slimmer packaging with fewer mechanisms mounted to the chassis be worth the mechanical compromises? Does aero hold that strong a position?

Brian

[bill shoe]

Interesting design. Dave's link shows they were 8 seconds off the pace. Non-spec racers may be good/bad/ugly but they will always be interesting.

It took me a while to (partially) understand it. The front and rear ends look the same. For each end--

It looks like the upper wishbone and pullrod are fixed to the main structure. The inboard end of the pullrod is rigidly attached to the structure (more on this later). Therefore the upper wishbone and pullrod are really part of the main structure rather than the suspension. The static ride height and corner weights would be adjusted with the pullrod length.

The main suspension mechanism at each corner appears to be the mini-strut contained within the wheel. I don't see a damper on the mini-strut, but there might be one. Damper or not, there must be bending loads on the strut mechanism as Dave mentioned.

OK, so it's just a strut suspension where the strut-top is structurally supported by a three-arm truss that consists of an upper wishbone and a pullrod.

The pushrods appear to actuate relatively conventional anti-roll devices, and there is no separate damping for roll.

I don't understand the logic of the overall suspension. One possibility is that the inboard end of each pullrod is NOT rigidly attached to the car and therefore ride height can somehow be controlled or adjusted on the fly by actuating the inboard end of these pullrods. There is no good picture of the inboard pullrod mount. Perhaps it is some mechanism that attempted to keep ride height constant under changing downforce loads. This seems vaguely logical since the designer was involved with the twin-chassis Lotus.

[thisisatest]

if the pullrods were rigidly mounted on the inboard side, there would be little need for the ball joints on the inside of the upper wishbones (besides for ride height adjustment, but if that were it, i'd have looked for another way of accommodating that).
so my belief is that:
the inboard end of the pullrods are attached to each other with a sliding device, essentially making a "pro roll" bar, allowing more roll than heave,
or they are connected to the steering rack, allowing for a slight lean-in attitude.
none of that really explains the pushrods, though, which seem to be an anti-roll bar...
are parts missing?

[DaveW]

...the inboard end of the pullrods are attached to each other with a sliding device....

Makes some sense, I think, for camber control. My only question is that the outboard end of the pull rods appears to have two length adjusters (internal springs perhaps). Either way, control over the dynamic motion would appear to be lacking.

[thisisatest]

if my theory is correct, then it's a strut suspension in bump, and a combination of strut and double wishbone suspension in roll. the lower arm slopes down to the wheels, suggesting some negative camber gain (is that camber loss?) in bump but with relatively high jacking in a corner. BUT, with the majority of roll being handled by the upper wishbone and pull rods, in a double wishbone format, it would be able to roll easier, with less jacking forces in a corner.
it would be possible to have a net roll of the body in a corner, but with the outer strut EXTENDED?
in the other photos in the car-sales site, there were extra springs, the large ones clearly for the strut part. there were also much smaller, much-higher-rate ones in there too, and i'm not sure they would fit along with the strut, where would it go? i would assume the strut shaft would need to be larger in diameter than the I.D. of the small springs... so they could go along with the pull rods, allowing a mechanism to slide..

[Jersey Tom]

Not sure I'd want anything to do with that.

[Tim.Wright]

Considering the top arm is fixed by the looks, and the spring/damper would be in bending under braking forces, I think it could be best descibed as a Mcpherson strut with a push rod actuated anti-roll bar.

Still struggling to find out why you would go to so much trouble to move the springs outboard like that. Would be a tremendous increase in unsprung mass not to mention a packaging nightmare for the hub.

Tim

[DaveW]

Considering the top arm is fixed by the looks, and the spring/damper would be in bending under braking forces, I think it could be best descibed as a Mcpherson strut with a push rod actuated anti-roll bar.

Still struggling to find out why you would go to so much trouble to move the springs outboard like that. Would be a tremendous increase in unsprung mass not to mention a packaging nightmare for the hub.

Good description, except that I don't think that the unsprung mass would be increased, necessarily - although the sprung mass roll inertia would definitely be increased. Why go the trouble? To provide a movable top mount, I guess.

[scarbs]

I cant work out the function of the long torsion bar fitted ahead of the steerign rack and above the gearbox. perhaps the pull rod is linked to that providing heave stiffness or by allowing the top wishbone to move it allows camber recovery?

[DaveW]

scarbs, They appear to be solid, with no connections. The front bar is centered using jubilee clips, apparently. I guess they could be rigging bars.