there are suspension springs , they load up
In the kinetic system, yes. But the SAE paper desmo referred to describes a car with a mode decoupled system (with no warp stiffness) which replaces corner springs entirely.
Posted 06 March 2012 - 20:17
there are suspension springs , they load up
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Posted 06 March 2012 - 23:39
An interesting & seductive read. I confess that I don't know quite how respond, except to say that I was closely involved with a variety of active vehicles from road cars to F1 all of which simulated modal suspensions & I didn't reach the same conclusions. I think that the gist of Mr. Zapletal's argument has merit, but his conclusions fail to recognize the complexity of suspension problem.Interesting read. A few interesting concepts and opinions.
Edited by DaveW, 06 March 2012 - 23:41.
Posted 07 March 2012 - 02:28
Apart from the obvious advantage of even tyre loadings on a "warped" section of road, the lack of warp stiffness results in a reduced stiffness in single wheel bump for a given roll and pitch stiffness.Interesting read, that SAE paper. Why not decouple the modes? Do we need warp/twist mode stiffness at all?
Posted 07 March 2012 - 09:53
Quite right, but that is not the whole story.Apart from the obvious advantage of even tyre loadings on a "warped" section of road, the lack of warp stiffness results in a reduced stiffness in single wheel bump for a given roll and pitch stiffness.
Edited by DaveW, 07 March 2012 - 11:04.
Posted 07 March 2012 - 12:29
Am I missing something? Wouldn't low warp stiffness improve the single wheel kerb strike by increasing the load of the 2 nearest wheels? Is this the opposite of what you are saying?The initial input at the front wheels of a kerb strike is not a pure roll input, it is the combination of a roll & a heave input (I neglect warp for now). With a stiff heave spring, a soft roll spring will reduce the load change at the loaded wheel as you suggest, but it will also increase the load reduction at the unloaded wheel.
Posted 07 March 2012 - 23:02
...If the input is big enough, then (in this condition) the stiff heave spring will cause the unloaded wheel to become airborne...
Posted 09 March 2012 - 19:46
Posted 09 March 2012 - 23:56
I was talking about the initial hit (before the rear wheel encounters the kerb).... Logically, a soft roll/warp stiffness will not move the sprung mass to alleviate the hit the unloaded wheel will take when kerbing with a high heave stiffness. It is difficult to describe, but a modal suspension does always work in a obvious way - I am trying to compile a simple model in an attempt to explain & intend to post when I am happy that it works. Pugfan, please be patient.Am I missing something? Wouldn't low warp stiffness improve the single wheel kerb strike by increasing the load of the 2 nearest wheels? Is this the opposite of what you are saying?
If heave is H*[1,1,1,1], pitch is P*[1,1,-1,-1], roll is R*[1,-1,1,-1] & warp is W*[1,-1,-1,1], then I think you are looking for values for P & R that will equilibrate [W, -W, -W, W] with [P+R, P-R, -P+R, -P-R]. Try it & see....I may be even more confused. How is warp not a linear superposition of pitch and roll?
Edited by DaveW, 10 March 2012 - 00:00.
Posted 10 March 2012 - 06:14
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Posted 10 March 2012 - 06:20
Let me re-phrase Dave's answer in layman's terms (the kind I need in order to understand these things). Any combination of pitch and roll will still end up with the four contact patches "in plane" ie a flat road. To warp a suspension requires a warped road or a wheel lift.I may be even more confused. How is warp not a linear superposition of pitch and roll?
Posted 20 March 2012 - 10:51
Here is my long-delayed reply.Am I missing something? Wouldn't low warp stiffness improve the single wheel kerb strike by increasing the load of the 2 nearest wheels? Is this the opposite of what you are saying?
Posted 20 March 2012 - 12:38
Posted 20 March 2012 - 20:36
Thanks, but it was not too onerous. I used the opportunity to become more familiar with SciLab. I admitted defeat for a while, becoming convinced that my distant knowledge of Matlab was not helping. Finally I tried SciLab version 5.4 (pre-release) & it came together fairly quickly. My kerb input was obtained by adding together different generator elements, & two peaks was more interesting than one (I thought)...Very interesting Dave and thanks for the considerable effort you must have put in. I don't understand your outputs 100%, for example Graphic #1 - is this two bumps/kerbs?
Perhaps I was being too simplistic, although I have tested an F1 vehicle which had a front roll stiffness (& I too mean roll) rather less than 10 percent of the heave stiffness, courtesy of a stiff "heave" spring & rather notional "corner" springs & bar. Interestingly, the heave stiffness was also around 3 times the tyre stiffness. Such a set-up is extreme and, in the limit, it does require the sprung mass to be moved around to maintain continuous tyre contact.Are you sure your zero front roll stiffness is equivalent to zero warp stiffness (ZWS)? The lack of any roll response in Graphic 3 doesn't fit with my (intuitive only) view of how a ZWS system with normal levels of roll, pitch and heave stiffness would respond. A single wheel kerb strike should produce pitch and roll responses via the lateral and longitudinal "Z bar" or equivalent couplings.
Posted 24 March 2012 - 19:17
..one has run the Kinetic system in track racing, and can say very effective, with immense possibilities. Our system had installation problems (never really worked out the bugs in the hydraulics and mechanical bits, our problem, not Kinetics...), more due to a competitive championship...when we got the edge with a conventional car, dropped the Kinetic H2O system as lacked development. Have discussed it with the people who ran it in rally cars, and they were pretty happy with it. Suspect our small suspension movement and mega aero car did not get as much gain from it as a rally car on gravel and flying...GL-Having seen one of these Kinetic systems up close and personal I am not going to write them off.
Posted 27 March 2012 - 04:29
Edited by gruntguru, 27 March 2012 - 04:43.
Posted 27 March 2012 - 08:51
Posted 27 March 2012 - 19:30
Forgive me, Johan, but are you sure. It seems to me that changing roll resistance distribution will, in a turn, introduce a warp displacement of the suspension. Zero warp resistance implies that the displacement will not generate a warp load, so it follows that changing the roll resistance distribution will change the "average" roll resistance, coupled with some warp deflection in a turn, but no change in "balance".Roll resistance distribution front/rear can be changed by adjusting the leverage ratios of the rockers
Posted 28 March 2012 - 08:12
Well I was, kind of, but now...... but are you sure.
I think I understand what you mean: If the rockers are the same geometry front and rear the axles can be moved in warp without roll movement of the chassis, and vice-versa. If the geometry of one of the rockers is changed, moving the axles in warp will also give roll movement of the chassis, and vice-versa. I can also see that the average roll resistance changes.It seems to me that changing roll resistance distribution will, in a turn, introduce a warp displacement of the suspension. Zero warp resistance implies that the displacement will not generate a warp load, so it follows that changing the roll resistance distribution will change the "average" roll resistance, coupled with some warp deflection in a turn, but no change in "balance".
Posted 07 January 2013 - 00:27
The key here is that regardless of the ERMD setting, the suspension can be "warped" without displacing any of the springs. The fact that the chassis may simultaneously roll a little, depending on the ERMD setting is not relevent.Well I was, kind of, but now...
Edited by gruntguru, 07 January 2013 - 00:31.
Posted 07 January 2013 - 18:44
I've been thinking along these lines:Johan. Not sure if I asked this question earlier, but what are your thoughts on the complete lack of warp mode damping?
Posted 07 January 2013 - 23:17
UWA 2012 photos courtesy of Rex Chan - University of Melbourne.Do you have any pictures of or links to the UWA system? Would be interesting to check it out!
Posted 09 October 2014 - 23:43
Bump. John - how is your project car going? There is a new thread here about torsionally soft chassis, which is relevant to your soft-twist suspension setup.
Posted 11 October 2014 - 19:37
Edited by imaginesix, 11 October 2014 - 19:43.
Posted 12 October 2014 - 19:24
Bump. John - how is your project car going? There is a new thread here about torsionally soft chassis, which is relevant to your soft-twist suspension setup.
It's moving on slowly. Nothing new on the suspension.
The big job left is to finish the bodywork. Then it's electrics and paint.
(Not fully developed aluminum shaping skills set a minimum safe viewing distance of 5 m )
I've read the thread on fsae.com on beam axles (http://www.fsae.com/...or-both./page15), and there is some interesting stuff. For example the distinction between warp-soft and twist-soft
Posted 12 October 2014 - 23:01
Johan that looks awesome. I guess I am more than 5m away.
Posted 15 October 2014 - 09:07
I've read the thread on fsae.com on beam axles (http://www.fsae.com/...or-both./page15), and there is some interesting stuff. For example the distinction between warp-soft and twist-soft
When I first encountered an F1 vehicle (many moons ago) two levers were fitted in the cockpit to the right of the driver. They controlled the stiffness of the front and rear arb's and were used to control the overall roll stiffness and the mechanical lateral balance of the vehicle. Balance issues were almost never discussed. They are now banned in all race series, except IRL I think. Why?
On topic, I believe that the longitudinal position of the centre pivot of Zapletal's suspension sets the lateral balance of the vehicle. If so, then the distinction between "warp-soft" and "twist-soft" is a little blurred, at least in a race vehicle. Ideally, the position should be adjustable, depending on tyre wear, temperature and pressure (for example). Alternatively, an additional arb might work.
Zapletal almost never mentions the tyres, which is a pity, because the suspension (a conventional one at any rate) is required to damp the unsprung modes. It is hard to see how that can be achieved without warp damping.
Posted 15 October 2014 - 14:35
When I first encountered an F1 vehicle (many moons ago) two levers were fitted in the cockpit to the right of the driver. They controlled the stiffness of the front and rear arb's and were used to control the overall roll stiffness and the mechanical lateral balance of the vehicle. Balance issues were almost never discussed. They are now banned in all race series, except IRL I think. Why?
Posted 15 October 2014 - 16:44
Thank you for bringing this up. I've wondered the same for ages and I've never heard anything approaching a remotely logical explanation. Why not let the drivers adjust wing angles and maybe spring preload by corner as well? Are race engineers afraid they'll be put out of a job listening to the drivers incessantly bitching about over/understeer?
The first thing I did to the car I worked on this year was put an adjustable FARB in it. It's a tool, but it's not a panacea. Do you really think that having the ability to change bar settings eliminates the job of an engineer? C'mon.
Posted 15 October 2014 - 16:46
When I first encountered an F1 vehicle (many moons ago) two levers were fitted in the cockpit to the right of the driver. They controlled the stiffness of the front and rear arb's and were used to control the overall roll stiffness and the mechanical lateral balance of the vehicle. Balance issues were almost never discussed. They are now banned in all race series, except IRL I think. Why?
Ummm, going to have to check rules packages, Dave. They're very common. The only series I know of that doesn't allow it is World Challenge.
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Posted 15 October 2014 - 17:45
The first thing I did to the car I worked on this year was put an adjustable FARB in it. It's a tool, but it's not a panacea. Do you really think that having the ability to change bar settings eliminates the job of an engineer? C'mon.
Posted 15 October 2014 - 18:26
It never gets any easier, you just go faster. - Greg Lemond
Posted 15 October 2014 - 22:09
A quote to remember FB....
So far as I am aware, no European open wheel series use them (although F1 has its own impressively expensive solution), & I don't recall FAtlantic using them. Touring Cars used to, but not any more. I'm not sure about DP.
Posted 15 October 2014 - 23:00
On topic, I believe that the longitudinal position of the centre pivot of Zapletal's suspension sets the lateral balance of the vehicle. If so, then the distinction between "warp-soft" and "twist-soft" is a little blurred, at least in a race vehicle. Ideally, the position should be adjustable, depending on tyre wear, temperature and pressure (for example). Alternatively, an additional arb might work.
Zapletal almost never mentions the tyres, which is a pity, because the suspension (a conventional one at any rate) is required to damp the unsprung modes. It is hard to see how that can be achieved without warp damping.
I don't think an additional ARB will help - the twist mode and roll moment distribution won't change. (RMD is as you say defined by the position of the centre pivot.
Single wheel disturbances will excite roll, pitch and heave modes as well, so single wheel damping will remain significant.
Location of the dampers is an interesting point I have wondered about in the past. In Johan's design above, the dampers are located with the springs (at the four pivot points) providing roll, pitch and heave damping but zero warp damping. OTOH the UWA car located the dampers conventionally - one at each wheel.
Posted 16 October 2014 - 08:41
I don't think an additional ARB will help - the twist mode and roll moment distribution won't change. (RMD is as you say defined by the position of the centre pivot.
Would that be a reason for rejecting the "Balanced Suspension", unless a neat way can be found to control the position of the centre point?
Posted 16 October 2014 - 16:59
A quote to remember FB....
So far as I am aware, no European open wheel series use them (although F1 has its own impressively expensive solution), & I don't recall FAtlantic using them. Touring Cars used to, but not any more. I'm not sure about DP.
I really don't know about Euro series, so I can't comment there.
All of the older Atlantics had adjustable bars. The last one (Swift 016) only had the front adjustable because it was built to a cost cap and the adjustable rear bar added a couple hundred bucks they didn't want to spend. The teams would have put one one unquestioned, it wasn't allowed.
Indycars have them, as do Lights cars (old on the front and new...both). The Pro Mazda and F2000 both adjust the front. The rear would be adjustable, but again, they're not allowed to by the rules. DP cars have both front and rear adjustable. GT cars can/do have adjustable bars in the TUDOR series. They're not allowed in World Challenge...again, a rules thing.
I don't believe GT3 cars in Europe run adjustable bars, I don't really know why that is. My experience with the Euro mindset of chassis tuning/development is fundamentally different than the American approach. We spend a lot more time developing what we have in an almost analog progession. They are more likely to race what they have for 'X' amount of time and spend thier development time to introduce the next model as a quantum jump forward. I'm not saying that one is better than the other, but what I'm saying is that an American is more likely to want to have more knobs to spin and the Euro is more likely to leave each model as it is.
Again, this isn't some sort of grand law, just tendencies based on my observations.
Posted 17 October 2014 - 06:27
Would that be a reason for rejecting the "Balanced Suspension", unless a neat way can be found to control the position of the centre point?
It could be viewed as a drawback although I would think the opposite. Shifting the ERMD is as simple as moving a link end forward or backward although that may be tricky to implement in a "driver-adjustable" form. The UWA version had only an ARB connected to the centre point.
Posted 20 October 2014 - 18:27
There are some test results and driver feedback on a comparison between conventional suspension and Creuat's implementation of a "mode separated" suspension system on a GT Viper and an LMP1:
http://www.creuat.co...Viper ORECA.pdf
http://www.creuat.com/rfh.html
Interesting comments in the Viper doc regarding the low(er) warp stiffness:
"...b) Lack of steering feedback in fast corners...
...The lack of feedback we believe is due to the change the suspension
makes in the contribution of chassis torsion. Drivers are used to some
chassis deflection that creates a particular feedback over surface
bumps. Chassis is like a spring with no damping, and this has a
particular effect on response to different frequency inputs.
The fact our suspension has a low axle-crossing stiffness eliminates
the role of the chassis torsion. This means that frequency response of
the suspension changes and drivers perceive this as a lack of
feedback.
We are of the thinking that this should be a positive factor and that
drivers could take advantage of it with a proper training."
Could this be a common characteristic for all twist-soft suspensions?
Posted 21 October 2014 - 07:15
Fascinating...
I recall Senna saying something similar about the Lotus active suspension*, on the other hand he did tell a fellow driver that he no longer had to tape up his hands (no power steering)....
The quoted settings on the Viper would suggest to me a fairly dramatic turn-in under-steer, washing out as the dampers catch up. I need to think about the other modes, but I suspect the the roll mode was too stiff (assuming that I have read the units correctly - tyre rates would have been around 600 N/mm). I wonder if they ran a self-leveling strategy?
* I think the comment went something like "I know how a normal car will behave in a corner without turning the steering wheel, but I have to believe this car will react predictably to a steering input."
Edited by DaveW, 21 October 2014 - 08:01.
Posted 23 October 2014 - 23:15
Assuming that I have interpreted Creuat's nomenclature correctly, their Viper set-up of 30 Sept 2004 was not modally decoupled. The modal stiffness array was:
30 20 0 0
10 170 0 0
0 0 420 2.5
0 0 75 27.5
Incidentally, their "axle crossing" mode was what I like to call the "warp" mode (rather than Zapletal's "twist" mode).
A unit warp displacement (1, -1, -1, 1) mm generated axle loads of (30, -30, -25, 25) Newtons, whilst a unit roll displacement (1, -1, 1, -1) mm generated axle loads of (495, -495, 345, -345) Newtons.
Posted 24 October 2014 - 15:55
I guess the Creuat Viper set-up was not fully mode decoupled because they needed to adjust the elastic roll moment distribution
...The first mode configures an isostatic weight distribution. In this mode, the axle crossing is completely free, and the scales would also measure 50%/50% diagonal weights. The second mode includes a slight stiffness of the axle crossing, which is used to change also the front/rear roll stiffness, and therefore the understeer rate...
I think with modes decoupled (in heave, pitch, roll, warp) the only way to change ERMD is to move from pure warp (1, -1, -1, 1) to "twist" (ie not pure warp) and thereby couple roll and warp.
Posted 12 November 2014 - 04:44
I have a vehicle with KDSS - a Toyota. Like the Lexus GX, but instead of a 4.6 petrol V8, its got a turbo 3 litre diesel. its also got cameras for viewing things off road, and its got off road condition selection modes, which you manually select. Its also got off road cruise control, and you can adjust the speed by buttons off road. This avoids when hitting bumps, your foot hitting the throttle unevenly. It gives very good control, and you don't have to worry the power issues. It also figures out the slippage and gets the vehicle out of bad conditions, such as sand, a bit like smart ABS but in reverse, and acting on each wheel. It takes some time, but then the car moves out. All very clever. Nonetheless, and idiot will think that the car can do anything and hence it likely is of little help most of the time!!!
It does improve the highway ride too, and off bitumen, quite a bit.
The suspension can also be raised quite cheaply too (I have not done so yet).
By the way, the un-coupling of the roll bars is not the way I imagined. Before buying my vehicle (call a Toyota Prado Kakadu) I had one raised and walked underneath, to check out the KDSS. Up front, I recall there was what looked like an air bag against the front anti roll bar, in the middle of it I recall. I think that what happens is that air pressure (or maybe its hydraulic) releases its pressure against the roll bar, and hence the roll bar looses its tension, hence its un coupled. That was how it looked to work to me.
I asked the Toyota mechanics there, and they did not have a clue even what it was!!
I could crawl under and take a photo if people want.
there are lots of videos on the system, but I have to find them and post the links. I have not even read this thread - I looked at a few posts and realised their were engineers here who know their stuff. I entered to find information about Honda's new F1 motor but so far I haven't found anything.
Also my vehicle has a locking rear differential which is a neat extra. It adds to the standard centre locking diff which means 50% of slip is guaranteed to both front and rear diffs. With the rear locker, you can be sure you'll get at least 25% power then, due to the presumption of one wheel at the back having grip.
These things also have a low range, and there is only one off road mode that operates in normal high gear. Hence the electronics part is orientated for crawling speeds.
The big Landcruiser 200's upper models get KDSS standard, and the FJCruisers in the USA can get KDSS, which makes a great off road vehicle IMO.
The worst thing about KDSS in Australia, is that if you want to increase your towing capacity to 3,000kg from 2,500kg, there aren't any auto engineers that have had a system developed for KDSS equipped vehicles here in Australia. The 3 tonnne tow upgrade is only available to non KDSS equipped cars, via a private non factory tow upgrade.
Posted 12 November 2014 - 08:02
Some links to real world example of KDSS:
This is primarilly a craw control example, but the 200 series would have KDSS, being a Saudi one, I think they get all the options. Except for the diesel that is!!
Overall video demo of KDSS on Toyota:
Note the system was invented by an Australian from Western Australia, but the he sold the company to the US group that is the largest world producer of shock absorbers, amongst other businesses, owns Monroe Shockers. I'm not sure if it was bought before or after Toyota bought the system. Toyota had their off road R&D area in Australia. Western Australian would have been a place they'd have gone to, although I suspect the Flinders rangers in South Australia has always been popular for testing, but perhaps these days its so public that the West might offer more secret areas to go testing. I imagine that's where they found KDSS, but I am only guessing.
Posted 13 November 2014 - 01:11
Kinetik was sold to Tenneco years ago.I'm pretty sure the roll bar coupler will be hydraulic, basically a dog clutch would do if it is just on-off, although you could do something fancier.
Posted 13 November 2014 - 13:16
Kinetik was sold to Tenneco years ago.I'm pretty sure the roll bar coupler will be hydraulic, basically a dog clutch would do if it is just on-off, although you could do something fancier.
I think the roll bars are always attached to the both sides. My impression (and the mechanics had no idea) was that the device, being central, when it moved, it removed tension from the roll bar. I'm not an engineer, but wanted to look underneath one before buying.
My version also had different off road modes. On road, you have three different modes too - which must change the valving on the KDSS, hence giving soft ride, normal, and sport. On a used 2009 version, that control didn't seem to work. On my later one, it works very well.
I also trialled a standard suspension and found on a section of road at 100KMH, that the ride was very jiggly and poor. The KDSS really does remove such behaviour. I haven't tried mine on corrugations. These are a big deal in Australian dirt roads. Maybe it will provide a good ride.
The fear for me is that the "truck" is engineered for ride, and not for off road toughness. But on severe bad roads, the system is said to provide a lot more reach for the wheels. Landrover use decoupling of anti roll bars, but the Toyota KDSS system appears much simpler and hence reliable. However as far as my version, I am not sure about that.
Posted 11 August 2019 - 07:42
a piece on tenneco's kinetic hydraulic anti-roll solution and how linking all fours improve compliance
Posted 13 August 2019 - 18:06
Just been reading the SAE paper below, has anyone read it before? If so, what do you think of it?
Erik Zapletal, Balanced Suspension - http://www.scribd.co...nced-suspension
Opinions? Particularly on the part that says how side-pair-models meet the requirements of racing suspension the most, and how Zapletal is surprised the racing community hasn't picked up more on this 50 year old technology..
Old thread, but whatever.
Zapletal approached racing with the hubris of someone who would never actually compete.
Posted 14 August 2019 - 22:45
There have been some highly successful examples eg UWA FSAE around 20006 - 2009 ranked #1 or 2 in the world at the time.
Posted 29 August 2019 - 17:00
There have been some highly successful examples eg UWA FSAE around 20006 - 2009 ranked #1 or 2 in the world at the time.
Don't mistake FSAE success for racing success. The two are mutually exclusive.
Posted 29 August 2019 - 22:26
A portion of FSAE is in fact "racing" and UWA were one of the fastest - ie "racing success".
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Posted 30 August 2019 - 02:42