The future of Hydrolastic suspension

[Peter Laidler]

Nines, you are a total genius par excellence........... I just wish you were one of my tutors at Uni while I was struggling to get the hang of fluid transmission, valves and Boyles law* as it sort-of related to all this hydro and air pressure stuff............... I still don't understand the fluid part of hydrolastic - but I will do after your lessons. The mechanicals are simple - that why mechanical engineers are simpletons (that's what the Chemical Engineers call us!)!
*fluid transmission, it's not Boyles law but the principles are similar!

Niles....., why don't you write up a sort of uni thesis/dissertation about this subject. To be honest, you've made the HYDRO part of this thread so easy-readable in much the same way as Spider has made the LASTIC part of it the same

[rich@minispares.com]

I'm not sure of the reason for the bypass, perhaps simply to let the fluid move unimpeded for small motions.

would it not be to help any air find its way up through the displacer and out the pipe when first filling them maybe?

[nileseh]

I'm not sure of the reason for the bypass, perhaps simply to let the fluid move unimpeded for small motions.

would it not be to help any air find its way up through the displacer and out the pipe when first filling them maybe?

Perhaps, but that would not explain the diameter difference. Also the hydrolastic service machine is intended to evacuate the system prior to filling it with fluid. The book says pull at least 27 inHg which is about 13.3 psi vacuum. 14.7 psi is full vacuum at sea level so that's pretty much all the air.

(I always think it's odd to speak of vacuum in terms of pounds per square inch. 14.7 psi is atmospheric pressure at sea level, so if all the air is out of a sealed vessel, there will be 14.7 psi force applied over its outer surface)

[Peter Laidler]

NIles and Spider........ On the subject of valves and valving, in practice, anything that restricts the free flow of fluid during normal transmission (of the fluid) is a valve so on that basis, at it's simplest, if the valve mechanism inside a hydro unit has failed totally* you COULD easily have an external valve (and a restrictor is a valve by definition don't forget) in the fluid line. It was said, and I don't know how true it is/was, that comps cars had a specially made 'valve' in the form of a secondary restrictor in each of the specially made ADAPTOR, 21A-1524, This is the hex nut on the front bulkhead that allows the F to R hydro pipes to attach to the hydro unit hose and attach to the bulkhead. So, thinking on my feet and back to my physics teacher days this two way valve - equal both ways of course - is what is needed

*If the internal valve is rusted solid or has jammed in anything but the totally OPEN position, there could be a problem. But whether this internal valve is open/partially-open/closed can easily be established by timing the total evacuation of a filled dodgy unit against a known serviceable unit.

The idea of an external valve/restrictor SEEMS to be the perfect solution to Niles methodology. That of machining open the hydro units and ring clamping together. If the valve and diaphragms are OK....., all well and good, If the valve is knackered, just scrap the valve part and return the re-assembled unit(s) with a new modified ADAPTOR 21A 1524. And while we're there, incorporate a secondary (or main) evacuate/refill valve on the adaptor too!

It's a rainy Sunday morning and I'm deep in thought about this. And thinking that if I were a zillionaire, I'd get all those technically interested parties together at Niles workshop for a week. We'd have this cracked in a few days and the rest of the time we could all have a holiday!

[Spider]

Peter - only a week? Oh for god's sake man, it would take us more than a week to get through a few boxes of beer,,,,,,,,

Niles - I tend to think in absolute pressures, where a 'vacuum' of 30 inches is 0 PSI and Air is at 14.7 PSI, so in the case of the Hydro Service Unit, when the system is evacuated, it's at 1.5 PSI absolute - give or take.

Peter, the restrictor you mention was most like used. I'm not aware of them, however, I am aware that the Comps Dept did get up to a few hidden things, to get around some of the various comp rules so quite likely borne from that.

In regards to your suggestion of external valving, that's something similar to what I tried a few years back. I fitted a T piece at the font displacer. On each side of that, non-return valves in opposing directions, so that flow in would go via one and the reverse flow would go out the other. On to these, I fitted Needle Valves, which are a 'throttable' valve, these were then plumped back together via a Tee and connected to the Pipe running to the rear. It was a little bulky.

With the Needle Valves, I was then able to adjust the Bump characteristics for the fronts, which was the rebound on the Rears, and independently adjust the rebound for the Front, (which was the Bump on the Rear). It was an experiment initially to restore the lost damping but then to play around with the tuning of the system. Interesting exercise, but as the front and rear were interconnected, it was difficult to arrive at that 'sweet spot'. Now I better see where the original damping restrictors are in the system, external valving, while will work, won't quite work the same and this was what I found. Not rubbish by any means, just different.

I'd suggest though, that a simple 'one size fits all' restrictor fitting, as you've suggested would be a very practical option here and it would all look 'right'.

[Peter Laidler]

Ok then Spider, if Niles agrees we'll make it two weeks. In that time we'll have cracked the hydrolastic - less the hydro part conversion PLUS have the wet to dry (and vice-verca) swinging arm nonsense sorted out too Plus time for a few tinnies and....... and.......

[mab01uk]

Looking at these photos of the unique modified Moulton Moke (auctioned in 2013) which was used for Hydrolastic suspension research by Alex Moulton has anyone any ideas as to what mods he was trying out?

"This Moke was one of the first produced (at Longbridge, where all UK Mokes were built) following the model's introduction in August 1964. The first owner was Morris Motors Limited of Cowley, Oxford. On 23rd August 1965 the vehicle was transferred to The Austin Motor Co Ltd, Longbridge, Birmingham. At the suggestion of Alec Issigonis, Alex Moulton (through Moulton Developments Ltd) acquired the Moke from BMC in January 1966 for the purposes of suspension research, and it was delivered to Bradford-on-Avon where work immediately commenced to fit Hydrolastic suspension. Subsequently it was used for several years as a test-bed for further Hydrolastic system development.
This is an extremely rare UK-specification Mini Moke dating from the first few weeks of production. The fitting of Hydrolastic suspension by the system's inventor makes this vehicle unique and, although it will require some restoration and re-commissioning, it is a very important piece of the historical jigsaw relating to BMC/BL/Rover Group's widespread use of Moulton's suspension systems."
https://www.bonhams.com/auctions/21274/lot/349/

[minimans]

We had permanent external resisters in the ADO16 grass track racer back in the day............Smack pipe with hammer and close it up a bit....................

[Peter Laidler]

I worked with Moultons Chief (?) Engineer, Joe Xxxxxxx at Warminster. I also found myself the owner of one of his early 60's Moulton bike. Seems that he was a bit of a one-trick-pony in that everything he did was opposite to the engineering rule of thumb - K.I.S.S.. Like Hydro suspension......, just try getting spare parts for one of his bikes! I could be wrong of course

[rich@minispares.com]

my dad has a Moulton bike, one of the normal ones, not the really fancy ones

he discovered the flaw with the small wheels is that when you are 'giving it some' down a hill the front wheel starts to 'flap' as it goes faster and faster - in the end it will spit you off, as my old man found out.

he has never ridden it since

[nileseh]

Hmm. Much to consider.

External valving occured to me as well. Theoretically removal of internal restrictions and the addition of external would deal with dampening. To match the factory performance, there would have to be two paths, inflow and outflow, because measurements suggest there is a difference between bounce and rebound dampening. I haven't quite reasoned out the impact of full fluid flow on the spring. I think we tend to discuss the "hydro" element of the system more that the "lastic" bit. The springing on the car is flexure of the rubber donut just as in the dry cars. The donut is deflected in response to suspension travel operating thru the in-compressible fluid. The valving is a restriction to flow that provides dampening (as in shock absorber). External valving should do the same, its just a matter of where the flow is restricted. It would require a fair amount of plumbing to get the same action as provided by the rather simple internal valves.

One could perhaps achieve the same end by removing the internal valving and adding telescoping shock absorbers as in the dry cars. Make them adjustable (are they available with bounce and rebound adjustments separate?). If the fluid flow is impeded by dampening the motion of the suspension, it seems that the same effect is achieved as impeding fluid flow thru an aperture. But, as I think I noted previously, what's the fun in that?

The test car is interesting. The controls appear to be push-pull cables attached to rotary valves in the line from the front displacers and presumably elsewhere. There are three rows of controls, 2 in each row with one cable at the bottom. I think the 1st and 3rd rows are ganged together to be operated simultaneously, and placarding as I make it out is "front springs" and "rear springs". The left control in the 2nd row is placarded "fore-aft OUT". Can't make out the other side. Can't make out the bottom control either. The yellow tape on the side marks the un-laden and laden "CofG" (center of gravity). Another thing I find of interest is what appears to be a yellow pressure vessel under the front right wing. Do you suppose it's possible that this is a test bed for the development of "hydrogas" suspension rather than "hydrolastic"? Recall that the methods are similar, with the rubber donut replaced by compressible nitrogen to support the car. Ganging the front and rear controls could have been to level the car fore-aft with adjustable ride height afforded by gas suspensions, and the front-rear fluid transfer is the same.

Anyone know where this car is now?

[Glacier white]

I have been through the whole thread, and was surspised to see that the role of internal valves is not really understood. Only nileseh in his last message seems to address the problem that an external in-line valve will only damp the front-rear interconnection, but not the direct bump-rebound action of each wheel.
The placement of the valves in the port plate before the rubber spring, manages to damp the action of the spring. An equivalent valve after the spring, will allow the spring to deflect without control, so would be unsuitable.

By the way, has anyone's car failed the MOT or any equivalent roadworthiness test due to deteriorated displacer damping valves?

[Peter Laidler]

Mmmmmmmmm...... Glacier, you haven't given me/us (Spider, Nilseh, Mab) enough to get to the point but it seems that you're thinking of the hydro system as being too complicated. I/we seem to think that it's made to be AND sound complicated when really, it's just fluid moving between two inflatable bags. And you DO want to control the front to rear connection - that's the whole idea! I'll come back after giving a bit of thought but like all things on the forum, it's all our own opinions of course. Some based on mechanical and hydraulic facts, others based on fuzzy logic. But of itself, the hydro/liquid system is simple. It's the internal mechanicals that complicate things and it's these internal mechanicals that cause the problems...... apart from leaky bags of course which are another matter entirely.

Need to sit down with a glass of Scotch after Sunday lunch. Join me for a tot Spider and Niles?

[nileseh]

Hmmmmm indeed.

I think I agree with Glacier on the placement of the valve on the suspension side of the rubber spring. In this location the velocity of the fluid is mitigated before the spring, or parallel to the spring as is the case with a shock absorber and the total fluid flow to the opposite displacer is also regulated.. On the other hand, since the fluid is non-compressible, it theoretically makes no difference where the flow is impeded. I don't know, it makes my head hurt. I'll just stick with Mr. Moulton's configuration.

I am making headway. The aluminum bits for resealing via a circumferential clamp are fabricated and out for anodize. I designed a valve body of plastic, and printed (3D printer, FDM process from ABS) a trial. I think it will work fine. I'll reuse the rubber valve bits, as well as steel valve restricter bridge. Unfortunately I was unable to get any useful dimensions off the rusted out displacer I was sent so I'll have to extrapolate the valve dimensions from what I have. I have to seal the large diameter standard relief holes and drill the smaller diameter Cooper S holes then I'll have the displacer bodys cadmium plated for corrosion resistance. I (I tested it on an unrecoverable unit and the plating process does not affect the rubber). I have a new hose material and I can crimp the connection to the chassis tubing, but I'll have to use hose clamps on the displacer nipple because I cant get a crimp tool in the cavity. So in a few weeks I should be able to assemble 4 of these things and start pressure testing. When I tested the prototype I took it to 300 psi with the factory service unit and left it connected for 4-5 days without any loss in pressure. Seem to work fine.

Once they are assembled I'll try to post a picture.

Then move on the the Scotch.........

[Spider]

Wonderful work once again there Niles. Let's see how it all goes.

Need to sit down with a glass of Scotch after Sunday lunch. Join me for a tot Spider and Niles?

Yr on buddy

[Peter Laidler]

Welcome to the discussion Glacier and thanks for your thought provoking input. Join Me, Spider and Niles with a large glass of scotch while I try to take the matter on a bit further along the simplicity route. I'm not a familiar with fluid transfer situations beyond large field gun recoil and recuperation systems which, believe it or not, are quite similar to Mr Moultons practice. What is different is that in field guns, we want the recoil to he short and well buffered but the recuperation (or run-out) has got to be a lot more gentle. Look at it in slow time next time you see an anti-tank gun or 25 pounder in action. That's the only system I can think of where it's necessary to have UNequal flow/transfer of fluid (there'll be others but I can't think of any because....., anyway). That's all I'm going to say.

In the mini system, has to be the same BOTH ways...... the transfer of fluid front to rear and rear to front MUST be the same. Here's an example why. Take the EMER or workshop manual, Chapter H, page 9, illustrative figures 10 and 11. When the front wheels ascent the hump in the road, the fluid transfers from the front and lifts the rear of the car via the hydro unit bags, struts and radius arms, keeping it level. To achieve all this and at the same time, the rear radius or swinging arm rotates downwards, stretching the helper spring. We've already got TWO facts of physics that we can't defeat.
a) you can't compress a liquid - it's moved from front bag to back bag (and yes, it's stretched the bags a bit too......)
b) a spring is simply a means of storing energy - and in this case, it's a strong spring storing a lot of energy.

Car moves along a bit, so what do you think is going to happen? Yes, the helpers immediately reassert themselves and pull the radius arms upwards. Yep....., immediately transferring the fluid forwards. Once again leveling the car out. Ready for the REAR wheels to repeat the same process, but in reverse........ The REAR wheels are going to lift and transfer the fluid FORWARDS to repeat the process

Just think of the mayhem if the IN-flow and OUT-flow of the valves were different. In this simple Fig H10 situation the front wheels would descent the bump and instead of the immediate transfer of fluid back to the front, it'd transfer slower. To achieve what?
Or think about it in the opposite direction, where it transferred SLOWLY to the rear and FASTER to the front. Nope, wouldn't work that way either.

The fact that both front and rear hydro units are identical just emphasises this point. I believe that the transfer of fluid to achieve the same effect can be achieved by in-line restrictors. The car is held level by the strength of the helper springs and the shock absorbing is the restricted flow of the fluid through the valves or restrictors (which in fluid applications are just valves).

Now where did I put that almost empty glass of Scotch. Want a top-up Spider? What about you Niles? Top-up Glacier.....? Cheers

[Dr S]

Do the helper springs not also act to counter the difference in leverage ration from the front to the rear of the car? If not then a bump on the front would have an excessive reaction at the rear?

[smithyrc30]

I thought on a hydro car the lever ratios front to rear were the same at 5:1.

As far as I can see all the helper springs do is prevent the front pulling down because most of the cars unladen weight is on the front units.

I don't see why the valving cannot be different front to rear, there is a big rubber 'spring' in there and while fluid is incompressible, the rubber is not. So and equalising of the bounce and jounce would be done in the rubber, with the fluid catching up a little later.

[Peter Laidler]

Well, in my opinion until I think about it a bit and try to make my wooden classroom model a tad more realistic, I'd say no, they don't because all things being equal, such as rear weight = front weight, i'd say you could do without the helpers as the car would naturally sit level. But that's just speaking/thinking on my feet. The helpers pull the rear DOWN to help balance the car or equate the weight artificially - if that's the right word. I had both my helpers unhooked a few weeks ago and it just wallowed front down like a stuck pig of course. It's thought provoking Doc........ Come back with your thoughts because between us I think that we've got this pretty well cracked. Another Scotch on the verandah Niles, Spider?

You're right Smithy, but don't forget that once again, the rubber diaphragm is just another 'spring' in another form that will reassert itself PDQ

[Spider]

Another Scotch on the verandah Niles, Spider?

Respectfully, can we end this thread?

It's turning me in to an alcoholic