So what happens next?
Fri, 15/06/2012 - 15:26
#62
Re: So what happens next?
Jag, very interesting that. Is that why pressurised shocks (gas charged) work better? Does it give the oil, in effect, a positive head?
Fri, 15/06/2012 - 22:34
#63
Re: So what happens next?
Dean15, thanks for links. Seen the car bibles one. Here's what someone said on the other link.
"short answer : Duolever allows the suspension designers to very precisely tailor the change in rake and trail of a bike as it's suspension compresses/extends to suit the intended role of the bike. Telelever gives an the engineers much less choice in how rake and trail are changed by suspension stroke"
I think he might have a good point. As there are 2 wishbones, by varying the lengths of each one, and where the pivots are placed with respect to each other, in principle you could generate a wheel spindle locus more tailored to what you would like. In practice however, on a bike, there are considerable constraints which will limit both the wishbone lengths and their respective positions.
With Telelever, you can play around, to a point with wishbone length and pivot location, but as there is no second wishbone to play around with this would limit wheel travel path somewhat.
Looking at it another way, perhaps duo lever may allow a locus more arc like thus generating anti dive properties (and suspension) with a non linear rate. If, say, wheel travel was in an arc curving backwards, that should give less anti dive as the suspension compressed, but soften up the feel of the suspension over bumps. And so on. I need to get the graph paper out!
Fri, 15/06/2012 - 16:41
#64
Re: So what happens next?
Can't find any graph paper. Haven't got a drawing board. Haven't got a cad program. But playing around with a pen and rule I think things are now clearer. It's pretty much as I said above. In theory the double wishbone set up SHOULD offer more scope for tailoring wheel travel but IN PRACTICE it doesn't. What has the biggest effect is wishbone length, especially the lower one (the only one in the case of Telelever).
It seems obvious when you stop to think, but a longer (lower) wishbone equates to longer manageable wheel travel. I think the reason the two different systems are used is a case of horses for courses. The bikes which have Telelever tend to need longer travel and coincidentally have an engine format whiich accepts a longer wishbone fairly easily. The bikes with duo lever don't have the room to easily fit a long wishbone, but don't have the need for such long travel suspension. There will be a host of other pros/cons involved but these may be the main ones. Engineering is compromises.
I can see how the compact nature of the duo lever wishbones may take higher forces generated from braking at the speeds the k bikes are capable of. Both system give pretty much vertical wheel travel as the various pivots fall most easily into place. I think the double wishbone set up lends itself a bit more to altering wheel path slightly more. The main thing which readily affects wheel spindle path (locus) is how horizontal the lower wishbone sits with the bike unloaded.but other factors do too.
Fri, 15/06/2012 - 23:27
#65
Re: So what happens next?
If anyone has mentioned this before, then apologies. But check out "suspension smith" girder equipped R1. He has some great on board footage showing the girders really working on track
Dean15, in essence, this is very much more like the girdraulic you mentioned above.
Check out this appraisal of Laurie smith's girder R1.
By Rennie Scaybrooks, "Can this Crazy Front End Really Replace Forks?"
Sat, 16/06/2012 - 01:19
#66
Re: So what happens next?
I was having a think, on the train, on the way back home from the smoke today. And I thought about a couple of flies in the ointment with semi-active electronic suspension.
Firstly, what if you're riding very hard on very tight roads, yet not topping 50 mph say and the bike thinks (because you're going slow) that you want a soft a mushy ride, which you don't?
And secondly, with semi or fully, if the manufacturer has worked out the optimum settings (which will alter per ride weight accordingly), which is after all the whole reason for having it, what if you think they've got the settings wrong? Ducati's rear preload on the Diavel is a full 20 turns wrong IMHO! But if it's all manufacturer set, do you have to see an engineer with a plug in kit to change the settings or will it all be DES style?
"I wonder if Telelever is more suitable for longer travel? What I mean is, a longer wishbone surely must accommodate long travel better"
... could be? Maybe the wishbone is longer purely because the forks are more kicked out on R's than K's? I'd like to see how both perform on a short wheelbase bike, but BMW don't make one. Well, not without conventional forks fitted!
Imploding bubbles of hydrocarbon? I should coco! I'm sure you're right Jag. Erm, probably! :-D
I've got some graph paper Pitts. It's languishing unloved in my home office!
Sat, 16/06/2012 - 01:56
#67
Re: So what happens next?
Suspension and TIRES or TYRES
Why do you Brits always spell it wrong?
I am surprised no one has mentioned the importance of TIRES in regards to bike handling.
C/S wrote:
"Firstly, what if you're riding very hard on very tight roads, yet not topping 50 mph say and the bike thinks (because you're going slow) that you want a soft a mushy ride, which you don't?"
Why don't you want a mushy ride? As long as it's controlled with little or no spring rebound or bouncing and does not top or bottom out and the sprung weight remains at a constant level, what's the problem?
Is not one of the major goals of a suspension system to keep the sprung weight at a constant level so the wheels always remain in contact with and follow the road surface?
Now you can let me have it real proper.
I think I can see bubbles on my screen. They are very, very small but they are there.
Regards,
JAG
Sat, 16/06/2012 - 12:23
#68
Re: So what happens next?
Very basic hydo/pneumatic suspension system
I have attached a simple schematic of how one way such a system might work.
I did it in paint so it looks pretty primative.
Regards,
JAG
Sat, 16/06/2012 - 12:32
#69
Re: So what happens next?
Few questions re circuit.
The two tanks shown on the pump side of the piston. Are they the same tank?
On the rod side of the piston. Are we just moving air?
Is the needle valve on the rod side to act as a damper? If so, the answer to question 2 can't be yes!
If the answer to question 2 is no, then I'm guessing all three tanks are actually the same tank?
Cheers Jag.
Sat, 16/06/2012 - 13:26
#70
Re: So what happens next?
Hi pittsy,
One tank.
The system is completely full with oil except for the accumulator bladder with is charged with nitrogen.
No spring.
The pump flow (output) is pushing against the small adjustable orifice. If the orifice size remains the same, the higher the pump flow, the greater the pressure between the orifice and the pump's outlet will be.
The greater the pressure the more the extension force on the telescopic fork tube will be.
In a sense the bike's sprung weight is now floating in oil.
The piston has no seals. In fact it would have holes drilled through it so the oil can circulate freely.
Regards,
JAG
Sat, 16/06/2012 - 13:49
#71
Re: So what happens next?
Cheers Jag.
Could you put seals in the piston and pump oil into both ends of the cylinder? Use a large diameter rod to create reasonable pressure differential.
The accumulator is the spring, but how do you control suspension damping?
Sat, 16/06/2012 - 15:07
#72
Re: So what happens next?
Hi pittsy,
See new schematic. I hope it answers some of your questions.
Force pushing or extending the tube is pressure PSI X area of the rod or tube.
Regards,
JAG
Sat, 16/06/2012 - 19:01
#73
Re: So what happens next?
Hi jag.
It's probably my i pad, but there are no pictures this end. Just a couple of little blue question marks!
Sat, 16/06/2012 - 19:55
#74
Re: So what happens next?
"Why do you Brits always spell it wrong?"
... because the word tire is only used to describe how Brits feel about the ways in which foreign people decimate the language they invented! What do you mean you don't got that? Must be your bad! ;-D
"Why don't you want a mushy ride?"
... I take it you've never scrapped a knee slide Jag! ;-D When saying one doesn't want a mushy ride, that doesn't equate to a default meaning that a rock hard one is required. A well composed yet compliant ride is what is sort for sporty riding.
"what's the problem?"
... the problem is that excessive movement through a bend alters the composure of the bike, detracting from handling and reducing rider confidence to maintain good speed. It's a bit like when racing you must get your body movements over well and truly before you enter the bend, because if you start messing around with the c of g mid bend you'll not go around it the fastest or most composed. The rider themselves is just as important as the unsprung lightweight, high grip tyres in terms of the impact upon the suspension to do it's job properly.
"Is not one of the major goals of a suspension system to keep the sprung weight at a constant level so the wheels always remain in contact with and follow the road surface?"
... it's a goal. Or one goal. But it isn't that simple. Having greater weight transfer to the front tyre helps the bike both stop and then turn quicker. Something not lost on BMW when they chose USD forks for their SRR, in preference to the two other variants they had at their OTS disposal. Weight transfer does again not mean that both wheels do not remain in contact with or follow the road surface by default, it's just affecting performance. Weight transfer is often a good thing in terms of both braking and turning tighter, but also in being able to lay down power when weight is transferred backwards too. In some ways telelever ape's a traditional BMW saloon (sorry sedan!), by separating the steering, suspension and drive forces. Each have pros and cons, which is what makes 'what happens next' less than straightforwards and subjective in many ways.
"Now you can let me have it real proper."
... as if! ;-D
I was going to ask all the same questions as Pitts :-D
Sat, 16/06/2012 - 22:36
#75
Re: So what happens next?
Hi pittsy,
I don't think it is your pad.
I think I did something wrong.
Let's try it again.
Tired it again but smaller.
Still no luck.
Sorry
JAG
Sat, 16/06/2012 - 22:49
#76
Re: So what happens next?
Thanks for responding Captain Scarlet,
I am getting tired looking at my front tired tire.
Does look stupid !
You are right.
From now on I am going to spell the rubber thing on a wheel rim a TYRE.
If there is one thing I have learned from you comments and others is that the suspension on a motorcycle is a very complicated thing. Much more than on a car I fear.
Also that good braking and turning techniques require a very high skill level to do well.
Thanks again,
JAG
Sun, 17/06/2012 - 00:07
#77
Re: So what happens next?
Hi pittsy and Captain Scarlet,
How does a hydro/pneumatic system dampen road shock.
Good question.
I’ll try show how I see it by focusing on only one of the front forks of a telescope suspension.
Suppose the total sprung weight of the bike and rider is 600 lbs. (not counting unsprung weight)
Suppose half the sprung weight is on the rear suspension and the other half is on the front.
The one fork of the front suspension has to suspend about 150 lbs.
Suppose the one front fork has a 43 mm tube and has 6 inches of total travel from bottom to top.
Suppose the normal riding height is at about ½ of the total travel or 3 inches.
With a 43 mm tube the system pressure would be about 65 to 70 PSI. This riding height is maintained and controlled by the DC motor and small gear pump.
Suppose the front TYRE hits a bump on the road traveling at speed.
The front fork tube retracts ½ inch in 5/1000 of a second.
In that 5/1000 of a second the tube displaces 1.125 cubic inches of oil. That displaced oil has to go somewhere.
If that tube was a pump it would be pumping about 58 GPM. That is a big pump. There is no safe way you can pump 58 gallons per minute through a small 1 mm (0.040”) orifice or partially opened needle valve.
There is also no way our small 2 GPM pump could keep up.
That is the job of the accumulator. The bladder simply and quickly decreases (compressed) in volume about 1.125 cubic inches. As the bladder volume decreases its internal pressure increases.
System pressure will also go up during this time. How much it goes up depends on the accumulator pre-charge, its volume and how fast the tube moves and how much it moves.
Of course some of the extra displaced oil does bleed through the small orifice. The higher the system pressure the more it will bleed. This takes extra energy which turns into heat. It is this increased bleeding that that increases the dampening effect.
So the higher the pressure, the greater the flow through the small orifice and the greater the dampening effect.
JAG.
Sun, 17/06/2012 - 12:11
#78
Re: So what happens next?
Schematic
Road shock:
When the fork tube is extending and retracting as a result of road shock.
In a sense, when the fork tube is retracting, the tube is acting like a hydraulic pump and compressing the accumulator.
When the tube is extending it is acting like a hydraulic motor and is being driven by the expanding accumulator.
NOTE: The accumulator and tube don't actually come into physical contact
JAG
Sun, 17/06/2012 - 12:51
#79
Re: So what happens next?
Road feel and hydro/pneumatic suspension
I have read of many comments on good suspension systems where the rider can actually feel the road. They feel very connected to what the road conditions are like. They like this feature.
How could a hydro/pneumatic system achieve this?
On our single front fork telescope example there is only one dynamic seal (except for the pump's shaft seal). That is the seal at the fork tube where it connects at the fork housing. In hydraulics we call it a gland seal.
The seal will have some stickion (resistance to tube movement). The greater the pressure, the greater the stickion. I suspect it it this stiction that will transmit to the rider directly what is going on at the road surface and help him or her feel connected.
Regards,
JAG
Mon, 18/06/2012 - 08:54
#80
Re: So what happens next?
Jag, I can see how, even with holes in the piston, the rod would extend and retract by raising and lowering the pressure, but wouldn't the system perform better by having a solid piston and pumping oil to both sides (Ok, leave the seals out)? By doing that the surface area is increased, lowering system pressure and increasing response to hitting a bump.
I can't see how you have any effective spring damping?
Would the self levelling and suspension aspects be better dealt with separately?
By having the accumulator inside the cylinder, it feels system pressure. As system pressure varies, so will spring rate. No?
Mon, 18/06/2012 - 11:55
#81
Re: So what happens next?
Hi pittsy,
Pittsy wrote:
Jag, I can see how, even with holes in the piston, the rod would extend and retract by raising and lowering the pressure, but wouldn't the system perform better by having a solid piston and pumping oil to both sides (Ok, leave the seals out)? By doing that the surface area is increased, lowering system pressure and increasing response to hitting a bump.
No.
If you had a piston with seals and applied the same pressure to both sides of the piston both sides of the piston would be exposed to the same pressure. The difference between the sides of the piston is that one side has a piston rod attached to it. So the side with the piston rod attached has less effective surface area then the other.
Example:
3 inch diameter piston with a 1 inch diameter piston rod.
Apply 100 PSI pressure to both sides of the piston.
Piston area = 7.065 square inches
Piston rod area = 0.785 square inches
Effective piston area of the piston with the rod attached is 7.065 – 0.785 = 6.28 square inches.
Top of piston = 7.065 x 100 = 706.5 lbs of force trying to extend the rod out.
Rod end of the piston = 6.28 x 100 = 628 lbs of force trying to retract the rod.
The two forces acting on the piston are not the same even though the pressure is the same.
There is more force (706.5 – 628= 78.5) lbs of force more trying to extend the piston than retract it. Therefore the piston will extend.
The difference in force is only the area of the piston rod. The area of the piston has no effect.
JAG
Mon, 18/06/2012 - 17:02
#82
Re: So what happens next?
Sorry jag, I obviously didn't explain myself very well. I already understand the different surface area thing.
I think I'll stick to Telelever. : )
Tue, 19/06/2012 - 02:00
#83
Re: So what happens next?
Hey, pittsy,
I think the problem is with me.
I didn't answer your second question.
"How will the hydro/pneumatic suspension system dampen."
I needed some time to try to think it through in my head. To see a picture of how it might work.
I suspect all this is getting pretty boring to most members.
Here goes, hope it works.
Back to basics.
What does a normal shock in a spring and shock system actually do?
A shock changes kinetic energy (spring movement) into heat energy.
In OUR (see I am already very skillfully spreading the blame if it all goes bad) hydro/pneumatic suspension system at the variable orifice (needle valve) we are changing hydraulic pressure change (pressure drop through the orifice) into heat energy.
In our basic simple system example to maintain correct sprung height we are pumping 2 GPM through the system at about 70 PSI pressure. All this flow normally goes through the needle valve.
The pressure drop through the needle valve is 70 PSI.
The flow through the valve is 2 GPM.
We can calculate the HP required for the pump to push the oil throught the needle valve of the front fork when the bike is running on a smooth road at a constant height.
Hyd HP = (GPM)(PSI)
----------
1714
Hyd HP = (2x70) = 0.08168 HP
-----
1714
0.08168 HP = 61 watts of heat energy lost going through the needle valve to maintain that constant road height.
Suppose you momentarily double the pressure to 140 PSI (going over that 1/2 inch bump), the flow through the needle valve will peak to double to 4 GPM during that time.
If you double the pressure drop through the needle valve, the flow also doubles through the needle valve.
Hyd HP = 4 GPM x 140 PSI
----------------
1714
Hyd HP = 0.32672 HP
1 HP = 746 watts
0.32672 HP = 243.7 watts of heat energy lost going through the needle valve.
If the pressure spike was 240 PSI the heat energy loss would peak at 835.7 watts through the needle valve.
That is how a very basic hydro/pneumatic suspension system dampens road shock.
The greater the movement of the front fork as a result of road shock, the greater the pressure spikes will be, so therefore the greater the dampening effect will be.
Regards,
JAG
P.S. Another reason it took so long to answer your good question regarding damping is that, in this very simple example of a hydro/pneumatic suspension system, we have a potential challenge.
Can you spot it?
Tue, 19/06/2012 - 02:47
#84
Re: So what happens next?
I guess if I was ambitious, I would try to jerry rig something up at work and try it on the test bench and see what happens. Kind of a proto-type of a proto-type.
Use some left over stuff from my goody bin.
The guys developing the pro-active suspension system may not be too happy.
JAG
Tue, 19/06/2012 - 08:51
#85
Re: So what happens next?
I still go back to the holy piston. It worries me.
If there are no seals and the piston is full of holes, how will an increase in effective mass (the vehicle encountering a large bump) create a pressure rise? The rod will certainly move but no oil will be displaced in either direction. Unless the accumulator bladder is actually supporting the piston? If not, the bike will not be supported beyond its static weight.
If the bladder is supporting the piston, then fair enough, it will act like a spring and I suppose, like a pump. In that case you are relying on the bladder to pump enough oil through the orifice. The piston itself won't. But, on encountering a bump, the bladder would actually contract, causing, if anything, a pressure drop in the oil.
I'd hesitate before scooting off down the road.
Tue, 19/06/2012 - 11:41
#86
Re: So what happens next?
Good morning pittsy,
You are right. Moving the piston up or down in our model does not do anything. It certainly doesn't effect pressure.
It's the rod that causes an increase in pressure as it retracts (goes in) and pressure to drop as it extends (goes out). Moving the rod in and out displaces oil in the cylinder or changes the volume of oil in the oil filled cylinder.
When you retract the rod that displaced oil has to go somewhere as the rod goes in. A little bit of the displaced oil bleeds through the orifice but most of it compresses the pre-charged accumulator bladder.
How much the increase in pressure would be would largely depend on the pre-charge pressure of the accumulaor.
If you did not have an accumulator you would probably have a hydraulic lock situation (very,very high pressure) as the rod tried to moved into the cylinder. If you were lucky, you would only blow the rod seal all apart.
JAG
Tue, 19/06/2012 - 11:42
#87
Re: So what happens next?
Good morning Jag,
I think, for now, I'll stick with my Telelever. Bog standard. No gadgets.
If I happen to encounter cavitation, I'll stop for a cuppa while it goes away : D
Cheers!
Thu, 21/06/2012 - 02:31
#88
Re: So what happens next?
Sorry, dropped off the Disk World for a while - blahdy work!
"If there is one thing I have learned from your comments and others is that the suspension on a motorcycle is a very complicated thing. Much more than on a car I fear. Also that good braking and turning techniques require a very high skill level to do well."
... very true. It's definitely an interesting and almost infinite topic. And the harder we are able (or wish) to push our bikes suspension performance, based on preference, the larger the impact of the design and importance of the number crunching becomes. I don't know if it's a shallow sounding thing to suggest. But I genuinely believe that the 'next big thing' could be (still) born in a forum of often technical threads such as this site spawns. Collectively we could and perhaps even can, create and make great things that will make a genuine difference. And when I accept the Noble peace prize, I'd like to thank my parents, my cat shampoo'er...
Erm, your comment no.77/78/79 precisely justifies my comment immediately above. Just without the cat and peace prize connotations! ;-D
"stickion"
... I think the term is 'stiction' hence nitride coatings.
"I suspect it it this stiction"
... the speed at which your knowledge ramps up, outweighs my ability to reply! ;-D
Thanks Pitts, I haven't a hope in hell of challenging JAG technically! However, whilst telelever, duo-lever and UJM USD forks, not to mention ESA, DES and TTX style rear shocks technically work well for most to enjoy acceptable control and ride quality, I can't help thinking that suspension, despite it's legacy and longevity is but still in it's embryonic state in terms of it's actual potential. It's going to take cleverer blokes than I, like you and JAG, to invoke that next big realization, but that is the direct reason for this thread. Maybe, not necessarily, to create and drive a solution, but perhaps more to surmise what the future state might be, in a pragmatic, rather than hover-boards type way. So the bottom line is, keep thinking and suggesting what will come to pass! :-D
Thu, 21/06/2012 - 09:59
#89
Re: So what happens next?
Captain scarlet, thanks for your comments. But please don't over estimate my abilities! My knowledge of hydraulics is limited. But as this is "just" a forum, and as we're not sending anyone to the moon based on our comments, it's fair game to comment, as I see it.
The need for self levelling is not there for my riding as I'm out without pillion most of the time. The occasional need to manually adjust ride height, damping (and tyre pressures) is not a problem, because it is occasional.
However, I can see some merit in having a system where these things are adjusted automatically if your riding frequently involves adding a pillion and/or luggage.
The following to be taken with a generous smattering of "IMPO". : )
There already is a pretty good solution available in the ESA2, although it is still not quite there. But then that does allow them scope to always leave you wanting more, and charging for the privilege.
I would break the problem down into 4 chunks:
How to maintain the desired static ride height and geometry, according to payload.
How to adjust damping and spring rate according to payload.
How to adjust damping and spring rate according to payload and ANTICIPATED terrain/ ANTICIPATED riding style.
How to automatically adjust damping and spring rate according to payload and ACTUAL terrain/ACTUAL riding style.
Not coincidentally, this is the order in which I see the gadgets addressing those issues coming onto the market. They are in order of marketable value, market acceptance and technical difficulty.
If I've understood the implications properly, then the first three are a passive suspension, whilst the fourth is active suspension.
ESA2 already addresses the first two pretty well and the third in a limited, simplistic way.
I'm not sure how accurate the changing of ride height is on ESA2? The method of adjustment is good, but I don't know if there is a sensor in there, to tell the system when to stop? Or is it simply number of revs of a servo motor? I don't know how they are presently doing it.
I think the idea of having to tell the system the payload weight is probably the best way.
Next level of sophistication is to tell it what type of payload as well as weight. eg: rider 80kg, pillion 70kg, pannier payload 15kg, etc. Then the damping and spring rate for front and rear could be worked out (and tyre pressure advice on screen too).
Another, more advanced way, would be to load up the machine with all persons and luggage and let the the thing self level to a sensor. This method is theoretically the best, and is not complicated, but falls apart because it would require everyone to sit still for 30 seconds! Anyone bouncing up and down or fidgeting would have the poor thing confused and just plain wrong!
Next up is to tell it what what terrain you are anticipating, additionally your anticipated riding style over that terrain. This should be able to be adjusted on the move, although there will be safety concerns.
Next level is active suspension.....
Thu, 21/06/2012 - 10:08
#90
Re: So what happens next?
I think the idea of temporarily lowering the suspension has merit, as suggested by someone earlier on this thread, to allow for those of shorter leg, or just simply better static balance. For this system I would change the method of ride height adjustment. It is already hydraulic but is not rapid enough. Something akin to what jag has suggested, but definitely with a solid piston, with seals! Also, I would keep the suspension element separate from the height adjustment. I think I would lock in the hydraulic pressure once ride height is achieved, and release it, under power, to lower the machine. Sensors would detect the predetermined ride height and quickly hydraulically lock the system, dumping excess pump pressure to tank. The pump could be started (in anticipation) and stopped automatically at a certain road speed, say 5 mph, but the raise/lower facility only activated manually. Again, safety issues would be a worry, not technical issues. Although hydraulic failure once locked in and on the move is a real worry! There is something to be said for mechanical things after all!
None of this bothers me. I'm a Luddite!
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Well, I can't think of anything smart to say, but here are some interesting links.
http://www.advrider.com/forums/showthread.php?t=120042
http://www.carbibles.com/suspension_bible_bikes.html
This has made me realise that Telelever is really Macpherson strut; whereas Duolever is double-wishbone. Sort of.