Idée Fixe [3]

In this final part, Steve Randle concludes his proposal for a latterday successor to the seminal Citroën DS. 

Image: citroenvie

Previously, we explored styling, power unit and drivetrain. Today, Steve Randle outlines his thoughts on body structure and vehicle dynamics.

Structure:  “Aluminium and magnesium would dominate the vehicle. The recycling problem with composites – particularly thermosets – are a concern. While both Aluminium and magnesium alloys are expensive in the first instance, they are easy to recycle.”

Driven To Write: Given the problems inherent with using aluminium for the upper structure of the vehicle – the necessity for much stronger and thicker pillars/smaller openings – how would you see this being resolved? What areas of the structure would the use of magnesium benefit from?

Steve Randle:  “Magnesium is good for seat frames, dash beams and so forth. With modern jointing techniques, a mixture of materials is no problem. Steel for door beams and pillars is a good solution. Castings are helpful where section nodes and hardpoints are required.”

Chassis:  “I would retain the gas hydraulic approach for both practical and cultural reasons. The system should be configured to eliminate warp stiffness – this idea was successfully introduced in the McLaren 12C, though steel road springs were retained. Use of a completely gas hydraulic system would provide further ride benefits, as would pitch interconnection. The high speed damping valves now available would be useful in optimising ride composure. There is still an issue with any gas or air suspension in that the spring becomes stiffer with suspension velocity (the adiabatic / isothermal issue), but we would be running lower ride frequencies which will help.”

Image: thecarhobby

“We also have a few ideas we could apply to further improve matters here. I would also introduce more longitudinal compliance into the suspensions – having the frequency below wheel hop gives significant benefits. We’ve developed multi-link suspension systems that can deliver this while still giving the necessary elasto-kinematic properties. Finally, I would like to see a return to higher profile tyres. 17” wheels were declared some years back by Michelin to be the point beyond which there was little point in proceeding unless you need huge brakes or styling demanded it. I don’t believe anything has changed since then. We’ve also been involved with some interesting research work into adaptive camber controlled suspensions – this allows a narrower, lower drag tyre to be run without loss of grip. I’d like to investigate this further.”

DTW: Can you elaborate upon ‘warp stiffness’ and how it manifests itself?

SR:  “Warp is when each axle is in roll, but they are in opposition. (like jacking up front right and rear left). A fully interconnected system where the four degrees of freedom are warp, heave (all wheels in phase), pitch (front & rear out of phase), and roll (left & right out of phase) would be an interesting approach.”

DTW: With wheel diameter limited to 17″, what about tyre aspect ratio? Would you advocate a taller sidewall than the 60-series which appears to be the most generous nowadays.

SR:  “I think 60 profile tyres are a reasonable compromise. I’d seek to work with Michelin on this.”

DTW: Regarding Oleopneumatics, would you advocate a totally analogue system, the electronics-assisted version used in the latter-day cars, or a full electronically governed system?

SR:  “Electronic control offers a greater range of possibilities and performance.”

DTW: I would assume braking would be handled by this oleopneumatic ‘ringmain’ as well. Is there any benefit to the driver in the original ‘solid’ brake, or would you apply an artificial travel as Citroën did latterly?

SR:  “The road car brake pedal is an interesting combination of displacement and force control. Clearly, even the original Citroën brakes had a small amount of displacement. Racing drivers rely pretty much exclusively on force. I think a firm pedal with an appreciable amount of motion is preferable. Enough to remind you it’s a Citroën.”

DTW: Given that light weight is likely to be a key element of this vehicle, are there any merits in revisiting the idea of composite wheels – a la SM?

SR:  “Carbon has its place, but I’m not sure it’s in a road wheel. I’ve seen some good looking solutions, but they’re not spectacularly light. They are however spectacularly expensive. Aluminium alloy wheels are typically design driven and are usually heavier than a steel wheel. Magnesium has been unfairly overlooked of late I think, as the corrosion issues have now been addressed.”

Steering:  “We are developing an electric steering system which will provide manual steering levels of feedback with the potential for adaptive vehicle dynamic tuning. I’d like to see this in the car.”

DTW: What is your position on the subject of four-wheel steering?

SR:  “There’s a lot we can achieve with front steer intervention, and with adaptive camber control. With both of those, rear steer becomes superfluous I feel.”

DTW: Have you reached a conclusion about the autonomy question?

SR:  “Autonomy is coming, but I think it’s a yes or no answer. I have grave concerns about partial autonomy (throttle and brake only for instance), or expecting the driver to step in if things get tricky. I really feel that is asking for trouble. I believe that something needs to change significantly in the cockpit if the car has selectable driver and autonomy modes (steering wheel folded away, seat turned around or similar). You can’t risk the driver forgetting who is in control. If you’ve got used to an automatic, it’s easy to forget to dip the clutch of a manual as you come to a halt. That’s not a life-threatening oversight though.”

DTW: Given that the turbine idea has so much merit (and appears such an elegant solution), why is everyone blindly piling into batteries? Is it the path of least resistance?

SR:  “Batteries are the bandwagon right now. They have their place as part of the solution – demand smoothing in particular. Energy density is still poor, as are their whole life cost and environmental impact. I would sooner carry as few as reasonably possible.”

As we draw our ruminations to a close, I ask Randle to reflect on such a vehicle’s likely reception with the motoring public.  “Having successfully put off 90% of luxury car buyers, I intend that this car will be the firm favourite of those that remain. Far better that than everyone’s third or fourth favourite.”

We began this piece with LJK Setright so it’s appropriate we conclude with that great iconoclast, wordsmith, aesthete, critic and commentator, who summed up the original, the only Déesse in inimitable fashion. His words apply equally here I feel.

Image: fotki

 “No car had ever been cleverer. No car was ever braver. The DS should have inspired the world to embark on a new course of motor engineering, to accept and advance the new standards that Citroën had set. All it did was gratify the desires of 1.3 million people, to stimulate a lot of arguments, to expose a great deal of ignorance and to stand as a lasting reproach to the rest of the industry whenever we compared what they were making with what, on the evidence of the DS, they should have been making. If it achieved no more than that, it was not the fault of Citroën, it was the fault of everyone else.”

©Driven to Write. All rights reserved.

Author: Eóin Doyle

Founding Editor. Content Provider.

22 thoughts on “Idée Fixe [3]”

  1. Interesting. I’ve always been bothered with the high roll angle on the DS, and wished for them to have interconnectedness left and right and not only front and back. As I understand it, the old oleopneumatic non electronic system required one sphere per wheel plus one for the brakes, five spheres in total. And that one sphere ccould only be interconnected to one other, thus giving a choice to dampen either pitch or roll. And that the Hydractive system was just adding another complete set of spheres giving ten in total or so. In addition to the four connected front and back, another four connected left and right.

    It seems for solving every problem, they just doubled up on complexity. So, why couldn’t the four wheels be connected to one large and central sphere, thus evening out any unbalance on any wheel with the mass of all the others? It seems to me the only way to dampen warp, heave, pitch, and roll at the same time would be to have all the wheels interconnected with all the others at all times. But yes, this is a re-active system that depends on actual physical action/reaction to function, to have a pro-active system that thinks ahead one must control all the factors independently. I can only see that with sensors that can see the road ahead and take action before it happens.

    Concerning the engine, the DS experience has never been about the engine, mostly because the only engine they had was a modernised Tracta unit with a crossflow top and five bearing main. A part from that possibly antediluvian in origin. I’ve spent hours contemplating other engines in counter factual thought experiments, and I’ve always wondered what would’ve happened if they had bought their engines from GM, I’m thinking the boxer 6 from the Chevrolet Corvair. Then they could’ve had their aircooled boxer six and the top of the line would’ve been called DS24 and DS27.

    My point is, for an experiment like this, they not buy the entire engine and drive train package from another car maker? I’ve always wanted to retrofit a restored DS with the drive train from a Toyota Prius. And why not? Why not have a hybrid drive train? They always said about the DS that one could run the entire car from the pressure generator. Why not turn it around and have the generator run the entire car? Switch the generator to an industrial grade electric engine and have the ICE unit only feed the batteries. Citroen just didn’t think that far ahead sixty years ago. The point is, the choice of engine really doesn’t matter, as long as it is adequate enough. Why not think out of the box on that one?

    1. Ingvar: Better technical minds than mine may be able to clarify, but my reading on the hydractive version of the oleopneumatic system simply added one additional suspension sphere to the original compliment – certainly as fitted to the original XM. Hydractive 3 may have been a different matter however.

  2. These are very interesting thoughts on the suspension, although the information is still a bit sparse for me to grasp it all. I like how new, unorthodox thinking comes in, and still the Citroën tradition can be respected. And thank you for opting for real tyres instead of rubber plated metal billets. The challenge here is to incorporate this in a way that doesn’t make the car look old-fashioned.

  3. What an excellent piece! Thanks for taking the time, Eoin. I remember seeing a Randle rear suspension photo in the previous interviews on Jaguar, and it’s pretty obvious that he is a suspension nut. Couldn’t be a better person to have a think about a new big Citroen design on that front.

    It seems to me that for the oleo, oil hydraulic part of the suspension that a central control block could be designed, where the oil displacements from the suspension units could be combined by a series of valves to be routed in certain ways from one unit to any other. Electronically connecting these valves and fed with sensor information as to cornering, braking, steering, and bump forces, then oil could be sent wherever it’s needed. Side-to-side and front to back and diagonally, all at the same time.

    The control strategy might be complicated or it might turn out to only need to be relatively simple. The Tenneco system used on earlier McLarens sort of does his, but doesn’t use air/nitrogen as the springing medium. Using air springs allows one to “weigh” the car and occupants by monitoring static pressure after the car rolls a few feet from rest to shake out rubber suspension bush friction forces. Then you can tailor the spring rates to the load for a comfortable ride under all conditions. The oil rushing about through the dampers and through the control valve block can be used as a substitute for anti-roll bars, tailor warp resonse, front to rear response. Think of that ridiculous new Audi A8 mechanical nightmare suspension we looked at last week, and think how much simpler this would be. Two oil lines from each suspension unit, above and below the oil piston, connected to a central control block fed from a main reservoir and held at a given pressure by a hydraulic pump.

    Fore and aft suspension compliance at the level of the control arms and bushes to the body is a bit of a black art, since sideways compliance ideally should not be affected. Geometrically unlikely multi-link suspensions have been the solution to that problem for 25 years, torturing rubber bushes in the process, but the quality of results depend on acual configuration and tuning.

    Both Audi and Ford (who churn out a million alloy bodied F150 pickup trucks a year) don’t seem to have run into JLR’s problem with requiring massive structural cross sections and consequently small door openings, so alloy seems to have a bright future in vehicle bodies. In addition, Honda has developed methods for welding steel and aluminum together to avoid galvanic corrosion problems, so door openings, etc could be made stronger and lighter by judicious choice of materials. Many vehicles already have magnesium beams in the dash tieing the A-pillars together.

    Excellent series of articles. Unfortunately PSA is likely to do nothing so daring as the ideas discussed. A pity.

    1. Thanks for posting that comment, Bill. I am not well-enough versed in suspension design to be able to comment incisively. What is it that so repels engineers from the kind of solution you propose? Another question is why we hear so little about McLaren’s suspension (the magazines didn’t say a lot)?
      The first thing a good suspension system has to do is evenly balance the ride-handling problem. I would love to hear why Citroen felt that the pattery low-speed ride of later large Citroens was justified by marginal gains in handling. I think engineering design in general needs to rank compromises (other things being equal) in order of their occurrence. A 5% reduction in capability used 1% of the time (apart from safety) is worth it if it gains 5% improvement in some capability used all the time.

  4. Extruding oil quickly up and down pipes to/from a central block is going to bring unexpected and likely unwanted dynamic effects. Try modelling up the old interconnected hydragas units and you’ll soon find all sorts of interesting effects, not many of them welcome. This is going to be the same. Hydraulic interconnected systems do not behave quite like promoters seem to expect. Citroen got away with it because they made SLOW additions and subtractions of oil from their circuit in operation.

    There is really only the one option for a Citroen and that is going to be full active suspension just as Lotus F-1 developed years ago, but further developed, servo-valves and all. A nice touch about fast high pressure hydraulics is that you can run active camber and toe control on all four wheels independently in real time. Once you have full active, you have the power supply nailed. There is your answer. It will grip, handle and be safe beyond anything around these times. Yes, in effect it will have four wheel steer. So what? If you really want to go all out and get the road-holding & ride really good you’ll need to look into harmonic dampers as well.

    Forget about driverless. For a start such systems are not about autonomy, they are dependency systems. They rely one way or another on outside and centralised control by software, a manufacturer, a master traffic centre, the security services and the authorities etc. Such cars are not autonomous. Autonomous cars are what we have now. The driver is the autonomous decision maker, not some disconnected authoritarian digital stranger. Anyway, driverless is not Citroen. Citroen is about elevating the driving experience not doing away with it.

    I am not confident in the idea of “welding” steel to aluminium or magnesium or aluminium or whatever. Such things are batteries and the result is inevitable. Build the damn thing to last indefinitely. This is the second most expensive asset most people will ever pay for (largest in the case of those who don’t own their own residence). Build it not as a throw away, but as something to hand on to the progeny.

    As far as magnesium is concerned- never as a structural element such as a wheel. I do not care which alloy you reckon you got. The stuff propagates cracks really, really well. Those can be devastatingly difficult to detect. There is no warning. It’s all lovely and OK until BANG! Now it isn’t lovely and OK any more. Too bad if it pitches you into a lorry going the other way or worse onto the footpath and into someone’s stroller. Magnesium also suffers from creep. Same deal. It’s OK until it aint and very few people are going to spot the looming failure until BANG! By the way, have any of you tried working the stuff or worse welding it?

    There is nothing wrong with steel if it is used intelligently. There is nothing wrong with natural organics either. Design for goodness sake. Stop seeking the latest trendy materials. You do not need them. Do good design.

    By the way, for a series which started out identifying that the right questions have to be asked to get to the good answers, well, where were those questions disclosed? Reason I ask is that a lot of this work seems derivative. It is a bit like thinking that since Citroen used to have certain features then those are the features it must have. While there is nothing wrong with tradition and nothing wrong with selecting traditional Citroen solutions, that approach can only work if those solutions answer the questions- you know the right questions which we were going to be asking… So, an interesting series but one with many assertions and indications of answers, yet still absent the questions themselves. So what we have here has been, in the main, not directed towards answering at all….

    Ratu

    1. The whole “autonomous” driving thing needs close examination. A priori it is true that every increase in the efficiency of the driverless network means a reduction in control for the passenger. Have you noticed trains run to schedules? Run to its logical conclusion the driverless car will make you wait before moving off because it knows the state of the system.
      I will come back to this as it deserves its own thread.

    2. Ratu: as you say, the first part in design is identifying the problem. However, despite decades of writing on the matter, no-one has anchored the design process to an objective reference. Anyone who claims to have an entirely objective design solution is denying or is unaware of he fact that they made a value judgement to prioritise the laws of physics.
      Industrial design differs from engineering design in that it is grounded in values and aimed at human users. Thus it’s legitimate to set up discretionary, value-based criteria for a new design. In this case those criteria are “make it a Citroen” and allowing for the designer to choose what they create is necessary. That’s a fundamental basis of freely-chosen but directed creativity.

  5. Hello Richard

    Quoting, “it is true that every increase in the efficiency of the driverless network means a reduction in control for the passenger”. This surely is correct. The passengers do not control anything much, potentially not even the destination.

    Trains run to schedules and make you wait, just as an ultimate expression of the driverless network would also make you wait. That’s because both are public transport with all the issues of loss of privacy, dignity, convenience and utility that necessarily implies. As a dependent user, the individual comes in dead last. There are far more important interests to be satisfied first!

    The reason I identified the answering of the right questions as an issue is not due to believing that design is objective etc. The reason was that the series started off by discussing the asking of the right questions in order to get to the expression of what a new Citroen could be like. I was led into expecting to see some of those questions identified and stated.

    Revisiting some of the traditional features is fine but it is not enough. Those features have to have a reason for being selected apart from the notion that there were there last time around (and didn’t Jaguar get hammered several times with that lesson). When the DS was being created the designers and developers were not looking back. They were not just repeating features that had been seen traditionally on Citroens. Many of the great features they introduced (as opposed to repeated) were to attend to the issues they identified as needing to be addressed. So they were asking the right questions. And that is the point where we started off.

    I think that Citroen could be a very great marque again. It would occupy a modest sized niche, but they would be the only ones in it and so they’d get 100% of it. While they would annoy and frighten many people, the remainder would be attracted, convert, then become very loyal and attached. No SUV or pick-up necessary.

    BTW I am most suspicious of the turbine idea. It doesn’t seem to make all that much sense if efficiency and economy (including purchase price) are what is sought.

    Cheers!

    1. Dealing with only the public
      transport part, I have to disagree with the assertion
      it’s undignified. I use it all the time in many European countries and enjoy the system. I think the indignity is a function in the UK and US of a political system opposed to the concept and managed accordingly.
      I find car breakdowns, traffic jams, car accidents and mechanics undignified. Unless I have a heart attack, I’ll never die on a train trip.

    2. Had Citroen’s blood supply not been cut off in the PSA era, the oleopneumatic system would likely have been developed well beyond what was actually produced. They would probably have gravitated towards active ride, but it’s worth asking why no motor manufacturer got over the transom and actually put such a system into production. Yes, GM and Volvo were said to be working with Lotus on developing it during the late 1980’s but when the likes of Mercedes-Benz who clearly had the financial resources to do so, never to my knowledge seriously considered it, opting instead for their ‘magic ride’ gubbins, one does have to wonder.

      Flawed as it was, oleopneumatic gave an excellent ride and very safe handling. I found the CX’s and BX’s I drove extensively to drive very well indeed and were eminently suited to the awful roads that still predominate in Ireland – and these days to an ever-increasing degree in the UK. Yes, the system could be caught out under certain conditions, but never in a manner which would do anything but cause mild (and brief) discomfort. Given that very little had changed from the system developed in the 1950’s, the scope for improvement should have been quite broad. So to the assertion of ‘why oleopneumatic’, I would reply, ‘why not?’

      Regarding the turbine idea. I’m not an engineer, so am not qualified to debate its merits, but it has been espoused (separately) by two very eminent practitioners whose conclusions I’m minded to concur with.

    3. Had Citroen’s blood supply not been cut off in the PSA era, the oleopneumatic system would likely have been developed well beyond what was actually produced. They would probably have gravitated towards active ride, but it’s worth asking why no motor manufacturer got over the transom and actually put such a system into production. Yes, GM and Volvo were said to be working with Lotus on developing it during the late 1980’s but when the likes of Mercedes-Benz who clearly had the financial resources to do so, never to my knowledge seriously considered it, opting instead for their ‘magic ride’ gubbins, one does have to wonder.

      Flawed as it was, oleopneumatic gave an excellent ride and very safe handling. I found the CX’s and BX’s I drove extensively to drive very well indeed and were eminently suited to the awful roads that still predominate in Ireland – and these days to an ever-increasing degree in the UK. Yes, the system could be caught out under certain conditions, but never in a manner which would do anything but cause mild (and brief) discomfort. Given that very little had changed from the system developed in the 1950’s, the scope for improvement should have been quite broad. So to the assertion of ‘why oleopneumatic’, I would reply, ‘why not?’

      Regarding the turbine idea. I’m not an engineer, so am not qualified to debate its merits, but it has been espoused (separately) by two very eminent practitioners whose conclusions I’m minded to concur with.

  6. Hi Richard

    A train ride in Europe across the continent from city to city can be excellent. Local commuter rail is a very, very different matter. They do derail and they have crashes from time to time. Falls between the platform and carriages are not as uncommon as may be imagined. Fights and muggings are common enough. Delays and service cancellations occur routinely. You are forced into close contact with persons you’d rather not even have to have the misfortune to look at let alone have to deal with. The interiors are unhygienic. People are treated as cattle. Mass transit indeed. Undignified it most certainly is.

    My home is near a station and my usual place of work is likewise near a station. Most days I take one of the cars. Mine are clean, convenient, private and safe. As one of my colleagues says, “We have the miracle of internal combustion at our direct service.”

    What’s wrong with mechanics? Some of my friends are mechanics. They are decent and kind, hard working guys (OK, two of them are girls). Hard to find a reason not to get on with them. Hardly undignified to be around.

    Ratu

    1. Interesting.
      For the US deaths per passenger billion miles showed driving at the top of
      the league and trains at the bottom. In 2008: 14500 dead in cars and 24 in trains.

    2. What other than cattle are we in a car, standing in a traffic jam in a city? That’s certainly not driving pleasure. And sitting in a car in that situation probably isn’t as undignified as some situations in public transport, but what about the people living in the clogged streets? What about their dignity?
      As much as I love cars, urban commuting is not a place I think they belong in.

    3. I am in agreement. While I find cars fascinating they are also a fascinating problem. Truth be told, if I was hanging around Karl Benz in the 1880s I´d tell him to think about how to improve trains.

  7. Simonstahel

    Last I noticed cattle are not found in cars, even while stationary. It would appear that the conventional means in which such are transported from farm to abattoir is in mobile pens, with numerous cows all huddled inside together. The cows are crowded in there, contained within a common space. They have not got control. They can’t get out, even if something goes wrong. They are taken as cargo to where it is someone else has decided they are to be delivered. That has a lot more in common with the public transit experience than that of a private car.

    I would enquire on this though. What is anyone doing spending their life in a city with traffic jams that annoy them to the point of considering themselves to be undignified by the experience? If such a thing irks so much then why are they even there? There is no need to be suffering a place that does not need to be suffered.

    Anyway cars are fine for urban commuting. Much better than transit.

    Ratu

    1. Yes, the car gives you the illusion of control and free choice. However, it does not deliver on its promise, not in the setting I have described. Of course, you can choose to drive whatever way you like, provided you make it to the next intersection. But you will end up on the next clogged street or turn in a direction that leads you away from your destination.

  8. Hi Richard

    There is a reason Karl did not direct most of his attention towards trains. That is that there was not much he could have done for the train. The characteristics and shortcomings it had in 1880 it retains now. To eliminate those shortcomings means getting rid of its form altogether and having something else entirely. Then what you’d have would not be a train. It would approximate the car.

    In that regard PRT and GRT are a somewhat interesting effort. Check them out. Beware that they have drawbacks also (one being congestion, driverless vehicle networks do not avoid that problem at all despite what the shills like to pretend).

    The trouble for trains is that what makes them efficient and reasonable for hauling bulk freight, makes them much less desirable at hauling multiple small high value payloads and people point to point. For the vast majority of places they are unsuitable and just far too expensive to be afforded. Time to move on. Sad but true.

    Ratu

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