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PostPosted: Tue Dec 05, 2017 10:24 pm 
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Some interesting but not directly Hydrolastic info here on the closely related Moulton Hydragas suspension system and the benefits of interconnection......

While reading about the development of the R6 K-Series Rover Metro/100 on AROnline recently I came across this extract below explaining how Alex Moulton's research greatly improved the performance of the later 1990's Rover Metro/100 Hydragas suspension over the original Austin Metro Hydragas setup by reverting to installing front to rear interconnection pipes, as were used on his earlier BMC/BL designs.....but were omitted from the 1980's Austin Metro range as a cost saving exercise.

Metromorphosis - R6 (Rover Metro/100)
With the question of engine and gearbox choice answered, the only real headache that the R6 posed was what suspension system would be needed. When launched in 1980, the Metro’s Hydragas system gave it class competitive ride quality and handling – as well as a degree of “chuckability” that endeared it to its buyers. But times had moved on: the Peugeot 205 especially, had shown that smaller cars had grown, but also that small car ride and handling had become significantly more sophisticated. Because of these huge leaps and bounds made by the opposition, there were still unanswered questions on what was the preferable system to use in the R6: on one hand, work was completed on adapting the conventional set-up used in the AR6 for the R6, but as the Metro’s floorpan would require expensive (and extensive) re-engineering to accomodate the AR6 system, this was not an ideal solution. With this in mind, work also continued in-house on refining the existing car’s Hydragas set-up.

Swiftly, the configuration of the R6 was set: K-series engine, PSA gearbox, and a slight increase in wheel track, front and rear – only the suspension layout was yet to be settled. That is, until the homemade efforts of Doctor Alex Moulton were brought to the attention of Rover.

As the inventor of Hydragas (and Hydrolastic before it), Moulton was keen to demonstrate the benefits of his system: the suspension units were more compact, and therefore easier to package. Besides, Rover knew that in order to use a conventional system in the R6, a degree of re-engineering in the floorpan would be needed. As explained briefly in the Metro story, Moulton had modified his own W-registered Metro to accept front/rear interconnected Hydragas suspension.

Why front/rear interconnection as opposed to the vestigial side to side as it was on the existing car (“vestigial” meaning a small pipe interconnecting the two rear displacers, eliminating the “three legged stool” effect of zero-interconnected Hydragas – a decision taken out of safety consideration)? When the front wheel encounters a bump and rises, the suspension fluid will rush from the front suspension unit to the rear. The rear wheel will resultantly lower, lifting the tail of the car and allowing a level ride. Citroëns demonstrate this trait perfectly when encountering a “sleeping policeman” – the whole car rises in unison and suspension “see-sawing” encountered in conventional cars (and the original Metro) is eliminated.

Why this ideal arrangement was omitted from the original Metro can be best summed up by Moulton himself, “I was struggling to show how an interconnected Hydragas Mini, for all its diminutive size could give better results than a VW Polo. But BL’s Spen King, a very strong-minded and knowledgeable automotive engineer, didn’t like it. He preferred absolutely conventional cars. Yet I was persistently and consistently offering something superior in Hydragas.” In fact, the original Metro was so compromised by its non-interconnected Hydragas arrangement, that Moulton felt that at best, the solution would only produce a car that was average.

“All they’re doing is substituting the conventional spring and damper with a Hydragas unit” and that because of the compromise engineering in making this system work, needless complexity was designed in anyway, “Anyone coming in from outside would take one look, pronounce it burdened with nasty costs to no advantage and get rid of it.” Of course the real reason that Spen King adopted non-interconnected Hydragas for the original Metro was that the extra piping of the system employed on the Allegro and Princess would have cost extra money. So it was dropped – and it has to be said that the decision to do so was a rather questionable one. King himself recalled recently that, “we all had guns to our heads…”, which would go some way towards explaining the immense pressure he was under as the company’s Technical Director.

Doctor Moulton invited CAR magazine to drive his modified Metro, which they did… and they were stunned at the difference that interconnection made to the package. How Rover’s own engineers heard about the car is an interesting tale in itself: during July 1987, Moulton had received Sir Michael Edwardes as a guest at his house, and during the meeting, Moulton invited Edwardes to drive his interconnected Metro… like CAR magazine, Edwardes was very impressed, and he telephoned Graham Day up to tell him that they, “should incorporate the system and charge £100 extra for it!” Duly alerted about the existence of the Moulton solution, and allied with the painful decisions that the company had made over the AR6 and with question of the what the configuration of the R6 needed to be still to be unanswered, a viewing of Moulton’s solution would prove irresistible for Rover.

And so it was. Rover took the car away to Canley and engineers thrashed it around, before rapidly deciding that Hydagas did indeed have a great deal of life left in it and that following the example set by Moulton, with careful development, the system could be developed into a class-leading package. The decision was easily made: the R6 would be launched with Moulton’s interconnected version of Hydragas – and in taking that decision, Rover demonstrated that lateral thinking sometimes produced results far in excess of corporate compromise…

If the press were disappointed at the styling of the new car – oh, so familiar inside and out, they found the driving experience something of a revelation.
An example of this was the verdict reported by What Car? magazine, who after testing the Rover Metro 1.1L against such luminaries as the Peugeot 205, FIAT Uno and their then Car of The Year, the Ford Fiesta pronounced an easy victor.

“The New Metro is a quantum leap, and on several accounts. For a start it’s light years ahead of its predecessor, far more so than its obvious family resemblance would suggest. But, more important still, it sets new standards of quality, ride and refinement for the class… In its chassis dynamics – ride and handling – it takes on the acknowledged masters of the art, the French, and beats them. It’s probably the quietest, smoothest, most refined car this side of £10,000 or even a bit higher.”
The Full Story here:-
https://www.aronline.co.uk/cars/rover/r ... t-history/


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PostPosted: Fri Dec 08, 2017 12:38 pm 
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I'm not sure why we are comparing displaced to field guns and earthmoving equipment?

the best thing functionally to compare with is a shock absorber.

You need two components, a spring and a damper.

Or the rubber spring and the valve.

These two components contribute to three features of any suspension

Spring Rate, compression and rebound.

Springrate is a determined by the spring shape and material

compression and rebound are controlled by the valve, exactly as in a coil over.

The front back interconnect will play some role in this, but someone please do the calculations on the outlet diameter on the displacer and the actual flow rate when a simulated log appears at an agreed speed. Inertia probably has more to do with keeping the car level. It's no use imaging suspension dynamics in a Tesco carpark, unless that's where you do all your driving.

As I was saying before, there's no use burying your head in the sand and believing the rubber will last forever. It won't, don't kid yourself. Rubber bands dry out, so will displacers from the outside in.

A valve on the interconnect won't work for two reasons, it doesn't affect the dampening inside the displacer. If you treat it as fluid transfer then you are missing the point of suspension. You want different rates for bound and rebound because it's important for the suspension to be able to react quickly, transferring energy into the spring and to release that energy slowly, so the car doesn't bounce like a lowrider. You can't control compression and rebound with a common valve.


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PostPosted: Fri Dec 08, 2017 3:54 pm 
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While I don't want to labour or argue the point but the point of someone makes of using JCB's as a point and me the field gun analogy is purely illustrative, where you can actually SEE hydraulics at work....... Hydra...., hydrolastic..... see it now! And you cannot see hydrolastic in isolation. It is two connected units like I said...., otherwise you've got a 70's era bloody space hopper toy!!!!!!! You're stating the what my mum used to call '....the bleedin obvious' 69K. We all KNOW that rubber won't last for ever, that's why a) the units are failing and b), everyone is trying hard to find an answer. Forgive me for being a bit harsh, but it must be said. There's been a LOT of input on this 13 page thread and it has to be said equally, a LOT of background/behind the scenes burning the midnight oil and PM'ing by the main contributors. Let me see now..... you've made three contributions so far. You've come over as a defeatist when there WILL be an answer somewhere and hopefully the optimists will crack it.


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PostPosted: Mon Dec 11, 2017 2:54 am 
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Location: Eugene, Oregon USA
There's a lot of really helpful information in this string of posts. I'm still rebuilding some of these things, but thanks to some of these entries, I may have been able to avoid some errors. Particularly the one about degradation of the rubber spring. I think it was Peter who made this note. I was not at first sure that it was valid because all of the displacers I opened looked and felt about the same. However, thanks to the post, I went about measuring the spring rate and the hardness of the spring rubber and by golly there is a substantial difference. I also can now see the displaced set (flattening) on some of the units. I measured hardness from 68 to 80 Shore A scale, spring rate from 2747 to 5730 lbs/inch and displacement from what I believe to be original position of up to .20". I'm glad I checked.
The good news is that I've got 4 that appear to be usable. I think the hardness that will work is about 70 A, and the spring rate is about 2800 lbs/inch. The worst case was 80 A and rate of 5700 lbs/inch. The 4 parts I can use do not appear to have any flattening (the spring cannot move any further down). Also there are 2 at 2750 lbs/inch and 2 at 2875 lbs /inch so I can use the stiffer units forward and the softer rear and will have good side to side symmetry.
The bad news is that not all of the old units will be candidates for rebuild. Too bad. Be calm and carry on.
I'll switch to the use of the best candidates, the valve apertures are are being machined, most of the plating is complete (except for the alternate spring units) the aluminum clamping assembly is ready so I'm getting close. We'll see how it goes.

Oh. Yes, my end game for now is to rebuild, but based on that experience it may be possible to recreate. We now know that the springs will need to be recreated, and that includes the upper housing. That may be pretty easy with two component compounds available now as opposed to the whole vulcanizing bit. The diaphram and sealing membrane is another matter. I'm working on disassembling one of these now to see if it can be done with the components intact. The paper someone noted above gets pretty detailed on the geometry of the housing and the intent (the whole variable area for the diaphragm bit). Really helpful. I can envision an machined aluminum unit that bolts together and duplicates all the features of the original, perhaps even with adjustable valving like an adjustable shock. But vision is easier than implementation. And my bottle of Scotch may empty before that happens........


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PostPosted: Mon Dec 11, 2017 9:03 am 
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Niles, it was me that have mentioned originaly that old displacers that were under pressure for a good number of years have their rubber spring permanently deformed.
Interresting that you have found such big differents in the spring rates between the displacers. It certainly ties up with the difference in comfort between a car with tired displacers, and another with new(ish) ones.
If we can open and close again the displacer like you did, i believe that it would not be that difficult to remove the old rubber from the upper part, and cast in the original housing a new spring from suitable rubber.


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PostPosted: Tue Dec 12, 2017 2:59 am 
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Location: Eugene, Oregon USA
Sorry Glacier. I didn't bother to re-read the whole string. So much information.

I agree, the upper could be replaced. To open the device it is the upper shell cut to remove the crimp. I'm no so sure about the ease of removing the rubber. It is pretty well bonded to the shell and the inner cone. However it is probably the easiest part to remake and attach to the lower diaphragm assembly. A replacement could redesigned with a more elegant coupling mechanism that I was able using the original welded and formed tube.

I may start looking into replacement materials. We use 2 component silicone materials all the time in the composite shop, but they have a rather low durometer. I'm not sure anything is available at 60-70. And then I've really got no way of determining the reliability of these materials in this application. I read the article by Moulton above and apparently a significant effort was involved in getting the compound right for the rate and longevity. But we work with what we have.


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PostPosted: Tue Dec 12, 2017 7:38 am 
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Very interesting, I'm a press operator and with rubber rollers it's everyday use. I know very well that a plastic is never the same, aging is a VITAL factor.
I follow the discussion with interest. :D


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