40 replies to this topic

[Powersteer]

I drew this (in Corel Draw, wow?) and the red lines are another version of an anti-roll bar. It should have some packaging and weight issues. Generally this idea should stabilize roll with less interuption between the left and right wheel which are narrower than the wheelbase of the car. Has this been done before. Debate? I wonder if such an idea would be worth while testing on a road going car.

[Greg Locock]

I think you've just drawn a pro-pitch bar!

Moulton was always very interested in cross car coupling, and insisted that BL did it all wrong on the Metro.

[Powersteer]

Pro-pitch or neautral pitch?

I did a search on the name Moulton and found The Bible

[Greg Locock]

Well, as the front suspension pushes up, it'll push down on the rear suspension.

so, Pro-pitch


Oh, and that version of the bible is full of mistakes and fantasy (aren't they all). The entry for the Ford Control blade IRS has so many errors that it is laughable. Nice picture tho.

[Powersteer]

Come to think of it, this actually keeps the ground clearance more controlled and actually becomes an active spring. But it does not help rear or front pitch at all and could behave like a seesaw Ironicly adding front and rear 'Z' or 'N' bars that connect the left and right wheels might help this but then, send things back to the beginning? Although interconnecting the wide wheels will get the third spring system.

[Stoatspeed]

SO, we have a cunning device to transfer vertical loads from one end of the car to the other while cornering ......
errrr ... I'll defer to Greg and a quick ADAMS model on this one, but sounds like a recipe for exploring the surrounding scenery rather sharply to me ....
but then, I rllied Triumph Heralds and hillclimbed a Vitesse once, so what do I know about imperfect suspension?

Dave

[Fat Boy]

Originally posted by Stoatspeed
SO, we have a cunning device to transfer vertical loads from one end of the car to the other while cornering ......

sounds like a recipe for exploring the surrounding scenery rather sharply to me ....


Dave

I'll drink to that!

[Powersteer]

Originally posted by Stoatspeed
SO, we have a cunning device to transfer vertical loads from one end of the car to the other while cornering ......
errrr ... I'll defer to Greg and a quick ADAMS model on this one, but sounds like a recipe for exploring the surrounding scenery rather sharply to me ....
but then, I rllied Triumph Heralds and hillclimbed a Vitesse once, so what do I know about imperfect suspension?

Dave

Then add a 4WD system so you won't get stuck. I remember Luc Pellerin said he his wanted his reactive system to linked to all four wheels. More scenery you think?

[Stoatspeed]

Originally posted by Powersteer


Then add a 4WD system so you won't get stuck. I remember Luc Pellerin said he his wanted his reactive system to linked to all four wheels. More scenery you think?

Perhaps if wejust add a fully active AWD system with traction and stability management .... oh, wait, let's just go back to an old fashioned side to side ARB ... I think we all understand how they work, however imperfect they may be!
Reminds me a little of the ultimate vehicle dynamics experimental test bed, Lotus's SID. If you don't know about SID, go look it up here .. an amazing technology demonstrator that took the meaning of "fully active" to incredible heights in the early 90's ....
While I was at Lotus in 1994, there was an attempt to revive SID for some project or other, but after weeks of fettling and adjusting (and a few laps of the track!) it was decreed that the whole control/sensor/connector system had already decayed to the point where the car was simply too risky to drive, being liable to "glitches" which could catastrophically upset the stability of the car, even running in a straight line ... so SID was retired to the museum!

[Powersteer]

I think we are all aware of the various technologies out there. Still, as you said, people stick to the good old right to left ARB. I think it is exciting explore once in a while as it also make us learn. I mean, the 747 would be piston powered if we adopted to fixed attitude and joke about it. Think active suspension is a fantastic technology. It was exciting to find out it can be made to control camber as well with the suspension travel probably in a similar fashion that Gordon Murray prefered not to have an anti-roll bar on the rear suspension of his cars. But for a simple modification to play around with its too expensive.

Well, you claim you were at Lotus, you claim you had raced so why not share your experience to why it would end up as part of the scenery with this device.

[bobqzzi]

Originally posted by Stoatspeed



....
While I was at Lotus in 1994, there was an attempt to revive SID for some project or other, but after weeks of fettling and adjusting (and a few laps of the track!) it was decreed that the whole control/sensor/connector system had already decayed to the point where the car was simply too risky to drive, being liable to "glitches" which could catastrophically upset the stability of the car, even running in a straight line ...

reminds me of my old Europa!

[Stoatspeed]

Originally posted by Powersteer
Well, you claim you were at Lotus, you claim you had raced so why not share your experience to why it would end up as part of the scenery with this device.

I'm not quite sure what the "you claim" is about .. I can refer you to witnesses of my tenure as Chief Engineer in Vehicle Engineering if you want .. but I'll treat the post as a genuine question, not a statement of doubt ... sorry if the following is blindingly obvious to many on this thread .. and sorry the post in unfashionably long ..

In order to deliver maximum cornering performance, designers strive to make the chassis apply loads to the tyres so as to make full use of the available grip. To corner in a stable manner, it is nice to have each end of the car do simialr work, so the yaw moments about the centre of gravity is low .... the car does not want to spin. In steady state each axle contributes an amount of lateral force from the inner and outer tyre .... it is the sum of these forces which keeps the car stable, so if there is some transfer of load from one wheel to the other on the same axle, the total lateral force stays about constant .... within limits, given tyres are highly non-linear, and if one tyre is already at its limit of grip, trying to get more lat force will make it slip ...
However, if the roll control device has the effect of changing the forces from one axle to the other (as Greg described it "pro-pitch") then the yaw stability will be disturbed, with the likely effect of the car wanting to swop ends ... hence my original casual comment about exploring the scenery.

This type of undesireable weight transfer was the reason SID was declared too dangerous .... the control system was only as reliable as the sensors, and there was a distinct risk that the fully active suspension (and also active rear steer in this case) might decide to share the wheel load in a different manner than the one allowing the car to be stable ....

You may remember Mika's scary accident at Hockenheim when the rear wing flew off .... the car spun really fast (in part) because the rear axle suddenly lost downforce but the front did not ... hence yaw instability ..

Hope this helps ... by the way, I am not at all opposed to experiments to make progress, and I quite agree that we should debate. However there are some concepts that do not stand close examination long before you bolt them to a car and drive them... IMHO, this type of interconnection is one of those, sorry!

Hope that was the kind of "sharing" you wanted, Powersteer?

[Powersteer]

Stoatspeed. You said the system would end up as scenery which is nice to know, only now. Yes it is quite funny. Just liked to know why. Anyway, I had always thought it best to keep credentials away and let the subject do the talking since this is a "technical" forum and not a place to flaunt our credentials without giving much credit, if you know what i mean. I really appreciated the responce by the way. Thank you.



Anyway, I thought to apply such system from the third spring concept but instead connecting front and rear suspension. As stoatspeed explained, the front and rear spring loads from the axles difference in weight distribution has two different chracteristics. Probably an adjustment to the torsion bar leverage between the front and rear could fix this.

[Supercar]

Well, aside from the pro-pitch feature, in roll this system works similar to the diagonal ARB. So if you do not brake or accelerate, I would say the car will be driveable.

[jo-briggs]

On the Austin/Morris 1,100 & 1,300 the front and back wheels on the same side were coupled hydraulically; the theory being that when the front wheels rose over a bump the rear ride height increased thereby keeping the car level. Its secondary effect was to stiffen the car in roll so that it cornered very flat. It was not noticably unstable in pitch, didn't dive excessively under braking, barely understeered, and cornered as flat as a pancake seeing off most 1960s sportscars with the exception of various Loti and other specialists sportscars. Mgs, TRs, Alfas and the like were blown into the weeds; I still think it the one of the best balanced cars I've ever driven; I spent many happy hours rorting round the lanes of the Bishops Stortford area in my Father's company car.

I believe the "Hydragas" suspension on the 1,100/1,300s had a restrictor valve that slowed its action in dive, but allowed a substantial degree of squat - you could sit at traffic lights with the handbrake on and rock the car like your Granny's favourite chair.

I personally that the Metro had too short a wheelbase to use the system effectively.

[Supercar]

I suppose if the car also has a lot of anti-dive and anti-squat, then these pro-pitch bars will rarely be adding any pitch or squat.

Although I remember someone, maybe Carroll Smith, saying: "Cars are like all other creatures, they must squat to go".

[Powersteer]

Originally posted by Supercar
So if you do not brake or accelerate, I would say the car will be driveable.

You mean, it won't be part of a painting?

During pitch possibly other methods of anti-dive can be used.

On a front wheel drive car with 60front/40rear weight distribution. The torque would literary split and would apply the same strength as would the wheel from the opposite right/left side of the car.

[Powersteer]

Originally posted by Supercar
diagonal ARB.

This system would most definately be scenery A non critical traction wheel can disrupt a critical wheel on a corner.

[imaginesix]

Powersteer,

There is a limited number of ways to interconnect suspensions, and they have all been thought of before. Racecar Engineering Vol.7, Nos.7 and 8 contained a brilliant piece on the subject that explains it to the layperson quite well. I found it inspirational myself.

I came across a website that posts the first of the articles. Click here to have a look.

[jo-briggs]

Originally posted by Supercar
I suppose if the car also has a lot of anti-dive and anti-squat, then these pro-pitch bars will rarely be adding any pitch or squat.

Although I remember someone, maybe Carroll Smith, saying: "Cars are like all other creatures, they must squat to go".

Charming, but incorrect, the car may wish to squat, but by aligning the pick up points on a double wishbone system so that a line drawn through them passes through the centre of gravity ( it's a bit more problematical on other suspension systems), dive and squat can be eliminated. Chapman tried it on various Loti, but the drivers complained about lack of "Feel". Indeed, by aligning the suspension above the C of G, a car can be made to squat under braking & vice versa. Ditto with roll. A car cornering like a powerboat, leaning into the corner, is most disconcerting.

[Powersteer]

Originally posted by imaginesix
Powersteer,

There is a limited number of ways to interconnect suspensions, and they have all been thought of before. Racecar Engineering Vol.7, Nos.7 and 8 contained a brilliant piece on the subject that explains it to the layperson quite well. I found it inspirational myself.

I came across a website that posts the first of the articles. Click here to have a look.

Thanks imaginesix, it really bites to know there is an extention of this article. However, it did mension this though

Beam axle chassis really do have inherent disadvantages. They produce too much lateral tyre scrub when the front or rear wheel pair moves oppositionally. Their unsprung mass inertia is too great, especially in synchronous motion at the rear. Warp-softness is their only major advantage over present-day independent suspension. The fact that beam-axle cars can run as well as they do suggests how significant this one advantage is, and logically leads us to wonder what we might achieve with a comparably warp-soft independent suspension.

I need to read more on people who have experience with such a set up and ditched it. For now, still intruiged which is possibly swallowing the wrong pill so now I want to know what it does to me.

[Greg Locock]

Amazing. There are at least two people on this thread with experience with a tunable warp car. Yet you ignore or disparage their comments. Pretty funny really.

To answer a point you raised much earlier, no, obviously, changing the linkage ratios cannot make it antipitch. As drawn it will always push down on the rear supsension, when the front suspension is pushed up. To make it antipitch, make it look like a longitudinal sta bar ie U shaped, not Z shaped. Admittedly this won't help the roll stiffness at all.

I'm not saying that pro-pitch is the end of the world, but it is not something that I've ever been asked to supply. If your cg was incredibly low then it might make some sense I suppose. But generally I'd just reduce antidive and antisquat, which has the advantage of cleaning up the kinematics, rather than using a bar.

[imaginesix]

I'm with you Powersteer, I believe there is potential for outstanding improvements in ride/handling using interconnected suspension. However, there would have to be some missing 'key' to it's success as way it has being researched and applied to date has not yielded all of the advantages that it appears to promise.

[Greg Locock]

Um, there's no secret. Kinetik's interconnected suspensions have wiped the floor in two racing series for a coupel fo years, and have now been banned.

[imaginesix]

They haven't been banned on road cars, but what has happened to the cars that tried more than just anti-roll bars? They don't exist anymore, that's what.

Interesting about Kinetik, didn't know that.

[Powersteer]

Originally posted by Greg Locock
Amazing. There are at least two people on this thread with experience with a tunable warp car. Yet you ignore or disparage their comments. Pretty funny really.

To answer a point you raised much earlier, no, obviously, changing the linkage ratios cannot make it antipitch. As drawn it will always push down on the rear supsension, when the front suspension is pushed up. To make it antipitch, make it look like a longitudinal sta bar ie U shaped, not Z shaped. Admittedly this won't help the roll stiffness at all.

I'm not saying that pro-pitch is the end of the world, but it is not something that I've ever been asked to supply. If your cg was incredibly low then it might make some sense I suppose. But generally I'd just reduce antidive and antisquat, which has the advantage of cleaning up the kinematics, rather than using a bar.

I think stoatspeed, after pushing him to the cliff exposed his credentials He said that undisturbed axle should remain the axis of yaw while the disturbed axle negotioate itself. Fantastic really.

So the reason why I continue is, I believe it is tunable and I am willing to check out the scenery for this. If a car is disturbed at the front, most possiblly it will go out of its line and understeer while the rear is completely planted. If we disrupt the rear with interconnection then the whole car would be unsettle. Then you understeer and then oversteer. But if we can tune this disruption and make it less and less evident then maybe the rear would slightly be 'offended' by the front but enough so tackle it.

I remember a thread here where some were contemplating (think it was desmo, think) traction control can be tuned so well that it might offer control oversteer to help any understeer. Maybe this effect can be tailored into this system. If a car front gets disrupted maybe the rear has some part to play in straightening it, not neccessarily take full control of either end. When an axle is disrupted, it is in a state far worse than the axle that is planted. Just curious if we can tune this or not.

Also the reason for the difference in leverage that on the picture is to level off any weight distribution issues that might really disrupt the concept. On a Porsche 911's light weight front (especially if the driver is one a diet) and heavy rear (engineguy's V8 911 ;) just kidding), movement from the rear connection to the front that has the same rates would make drastic irregularities to the front.

[Stoatspeed]

Originally posted by Powersteer


I think stoatspeed, after pushing him to the cliff exposed his credentials He said that undisturbed axle should remain the axis of yaw while the disturbed axle negotioate itself. Fantastic really.

I said WHAT? .... I think I've lost the entire point of this thread , so you'll need to sort it out among yourselves

[jo-briggs]

"A tunable warp car"

Was that in the "Trouble with Tribbles" episode of Star Trek?

[Powersteer]

Originally posted by jo-briggs
"A tunable warp car"

It would get us to warp speed Think the typical anti-roll bar is argueably a tuneable warp device?

[jo-briggs]

It may be a tunable torsional device.........

[Powersteer]

Here is another one Seems like what they use in racing of a third spring device. I am just tripping on a sort of Caterham like sport car actually. Anyway unlike the racing cars this one does not have a load spring (imaginesix, guess I did not learn from the URL you sent me) like a torsion device or coil spring. It lives purely from the center spring and a tough anti-roll bar that also acts to load up the center spring. (think it has been used by radio control cars) What I though would be interesting is an anti-roll bar that when the car pitches, it changes leverage a lot making it a lot more sensitive so stability won't be too disturbed by the center of pressure moving forward.

[Supercar]

I am not quite sure how this mechanism works, but to increase the front roll stiffness when the car pitches you can use progressive rate springs, dual rate springs, bump stops or packers.

[Greg Locock]

As the car pitches due to braking the stabilinks rotate to a more vertical orientation, and so are more effective at exciting the sta bar, so increasing the roll rate under braking (not actually a smart move in the real world).

That's the theory.

In practice a competent draughtsman or (even) engineering student could demonstrate that with the geometry shown the effect is very small, in less time than it takes to write a post.

Having said that, yes, we do mess about with stabilink orientation, for all sorts of reasons. It is very useful to be able to decouple roll effects from pitch/bounce.

[LMP900]

Isn't the Kinetik principle a diagonal "U" sta bar? That offers anti-roll and anti-pitch, and is something I've been trying to implement on a single-seater racing car for a while. But a simple, tunable, economical system is difficult to package.

[Powersteer]

Originally posted by Greg Locock
As the car pitches due to braking the stabilinks rotate to a more vertical orientation, and so are more effective at exciting the sta bar, so increasing the roll rate under braking (not actually a smart move in the real world).

It increases the roll rate? Why,Help? Are other methods other than those mentioned by Supercar out there in the sense that it changes leverage? A leverage booster perhaps? However I like the simplicity of that set-up. I was trying to design a suspension where it would be dynamic yet simple. Applying the central monoshock and use an anti-roll device to tackle problems directly without adding extras like a normal spring or torsion bar. That is why there is no bellcrank boosters or push-rod (not that they are a bad thing).

[Greg Locock]

Powesteer - look at the geometry. Move the arms up. Look at the geometry again. Work out the motion ratio for the sta bar in the two positions. Depending on how you set it up, the motion ratio should improve as the nagle between the link and the arm changes (it is possible to screw it up and get the opposite effect). Either way, for 'reasonable' values, the effect is slight. "reasonable' being a weasel word of course.

LMP9000 - Kinetic (sorry I spelled it wrong) have about 3 generations of complexity. Their simplest is cross linked shocks across the axle, using double acting pistons in monotubes instead of the normal shock absorber pistons. That replaces a mechanical sta bar. They then extended the concept, up to and including a low bandwidth active system, with remote mounted reservoirs, needle valves, and cross linking between all the shocks on both axles. If I were trying to homebrew such a system I'd start by having a good look at Fox externally valved shock absorbers (used for off-road buggies).

http://www.racerimpo...ex.php?page=fox

Kinetic's variable sta bar system uses a hydraulic cylinder to activate and deactivate a reasonably conventional sta bar. To be honest IMO, although the 4wd crowd like it, it is not as elegant as their other more purely hydraulic systems. The demo is impressive, either way.

http://www.kinetic.au.com/techno.html

The semi active sta bar is in their RFS, on the left hand side

[imaginesix]

I can't imagine what came over the FIA to ban interconnected suspensions, unless they are active system.
Are they dangerous? Quite the opposite. Are they prohibitively expensive? No more than any other good suspension kit. Are they fast? Of course, isn't that the whole friggin point of racing!?!

[Powersteer]

Originally posted by imaginesix
I can't imagine what came over the FIA to ban interconnected suspensions, unless they are active system.
Are they dangerous? Quite the opposite. Are they prohibitively expensive? No more than any other good suspension kit. Are they fast? Of course, isn't that the whole friggin point of racing!?!

I am for you but some might argue against you. Is it banned in all race series? I'd like to see light and the end of the tunnel.

[Powersteer]

Originally posted by Greg Locock
http://www.kinetic.au.com/techno.html

The semi active sta bar is in their RFS, on the left hand side

Does it put the car into the scenery or has this thing beenmaking waves?

[Stoatspeed]

This thread put me in mond of the active/adaptive roll control device invented by Michael Mumford 20(?) years ago - IIRC, the patent was taken on by one of the major chassis systems companies (maybe Delphi or TRW), but I tried Googling and couldn't find it. Memory says it was a self-powered device of some sort, and very effective for off-road vehicles. One of my good friends from years ago worked for Mumford for a while on some Group A race car work, and I think has knowledge ... I'll try to track him down ...

[jo-briggs]

Originally posted by imaginesix
I can't imagine what came over the FIA to ban interconnected suspensions, unless they are active system.
Are they dangerous? Quite the opposite. Are they prohibitively expensive? No more than any other good suspension kit. Are they fast? Of course, isn't that the whole friggin point of racing!?!

No - The whole point of racing is to generate cash for those that put on the show, generate tourist income for the area in which the race takes place, and give a leg up the political ladder to those organising what used to be a sport.